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Overgrazing decreases soil organic carbon stocks the most under dry climates and low soil pH: A meta-analysis shows
Abstract
Grasslands occupy about 40% of the world’s land surface and store approximately 10% of the global soil organic carbon (SOC) stock. This SOC pool, in which a larger proportion is held in the topsoil (0–0.3 m), is strongly influenced by grassland management. Despite this, it is not yet fully understood how grassland SOC stocks respond to degradation, particularly for the different environmental conditions found globally. The objective of this review was to elucidate the impact of grassland degradation on changes in SOC stocks and the main environmental controls, worldwide, as a prerequisite for rehabilitation. A comprehensive meta-analysis was conducted using 55 studies with 628 soil profiles under temperate, humid, sub-humid, tropical and semi-arid conditions, to compare SOC stocks in the topsoil of non-degraded and degraded grassland soils. Grassland degradation significantly reduced SOC stocks by 16% in dry climates (<600 mm) compared to 8% in wet climates (>1000 mm) and Asia was the most affected continent (−23.7%). Moreover, the depletion of SOC stock induced by degradation was more pronounced in sandy (<20% clay) soils with a high SOC depletion of 10% compared to 1% in clayey (≥32% clay) soils. Furthermore, grassland degradation significantly reduced SOC by 14% in acidic soils (pH ≤ 5), while SOC changes were negligible for higher pH. Assuming that 30% of grasslands worldwide are degraded, the amount of SOC likely to be lost would be 4.05 Gt C, with a 95% confidence between 1.8 and 6.3 Gt C (i.e. from 1.2 to 4.2% of the whole grassland soil stock). These results by pointing to greater SOC losses from grasslands under dry climates and sandy acidic soils allow identification of grassland soils for which SOC stocks are the most vulnerable, while also informing on rehabilitation measures.
... Grasslands occupy about 40% of the world's land surface, exclusive of Antarctica and Greenland, supporting the livelihoods and food security of almost a billion people (Kemp et al., 2013;Dlamini et al., 2016). However, many of these grasslands suffer degradation because of overused and mismanaged, especially in developing countries (Suttie et al., 2005;Schönbach et al., 2011;Han et al., 2018). ...
... And soil is hard to recover once degraded (Langmaack et al., 2002). Grazing affects soil physicochemical properties through biomass removal and trampling (Dlamini et al., 2016). Reasonable grazing can improve accumulation quantity of plant litter and nutrient cycling (Bardgett et al., 1998). ...
... Reasonable grazing can improve accumulation quantity of plant litter and nutrient cycling (Bardgett et al., 1998). Unreasonable grazing would increase soil bulk density, reduce permeability and aeration, thereby affecting grassland nutrient cycles, causing grassland degradation and losses of soil organic carbon (Dlamini et al., 2016;Yang et al., 2018). These results suggest that the effects of grazing pressure on aboveground and belowground ecosystems are more complex than imagination (Zolda, 2006). ...
Grazing is a main land use of natural grasslands in the world, which has both positive and negative impact on plant community structure and ecosystem functioning. However, the effects of long-term grazing management on the plant–soil system, in particular above- and belowground community characteristics, are still not well understood in alpine meadow community. In this study, we investigated the vegetation, roots, and soil properties under three management types (16 years of fencing since 2004-2020, moderate grazing and heavy grazing managements) in an alpine meadow on the Tibetan Plateau. The results showed that, compared with moderate grazing meadows, long-term fencing increased plant community cover, above- and belowground biomass, proportion of grass and litter but reduced forbs and soil bulk density, which caused the increases in soil organic carbon, total nitrogen and water content and the decreases in soil pH. However, heavy grazing led to opposite changes in proportion of grass, community biomass and soil physicochemical properties. The maximum of species richness and plant density appeared in moderate grazing meadows, supporting the intermediate disturbance hypothesis, and it can maintain above- and belowground biomass and soil physicochemical properties at medium level. Grazing increased the root: shoot ratio and caused root system shallow, which is consistent with the optimal partitioning hypothesis. Overall, our study suggested that moderate grazing is a more reasonable grazing management for sustainable development in alpine meadows of Tibetan Plateau, fencing could be an effective management strategy for vegetation restoration as well as for nutrient sequestration in degraded grasslands, but long-term fencing dose not benefit for biodiversity maintenance.
... These goals encompass crucial targets like ensuring food security (SDG 2: Zero Hunger), mitigating climate change (SDG 13: Climate Action), and promoting healthy ecosystems (SDG 15: Life on Land) (Veenstra et al., 2024). Soil pH and organic carbon content are pivotal indicators of soil health, influencing plant growth, nutrient availability, and overall ecosystem function-ing (Dlamini et al., 2016). Soil pH regulates nutrient availability and microbial activity, ensuring that plants can access essential nutrients while maintaining a healthy microbial ecosystem (Guo et al., 2022). ...
... This balance is crucial for optimal plant growth and nutrient cycling. Soil organic carbon (SOC), on the other hand, improves soil structure, enhancing water retention and aeration, which supports robust root development and plant health (Dlamini et al., 2016;Odebiri et al., 2021). Both significantly influence soil quality, agricultural sustainability, and environmental health (Maurya et al., 2020). ...
Accurate soil pH and soil organic carbon (SOC) estimations are vital for sustainable agriculture, as pH affects nutrient availability, and SOC is crucial for soil health and fertility. Hyperspectral imaging provides a faster, non-destructive, and economical alternative to standard soil testing. The study utilizes imaging spectroscopic data from the Africa Soil Information Service (AfSIS) and Land Use and Coverage Area Frame Survey (LUCAS-2009) hyperspectral datasets, capturing spatially distributed spectral information. Machine learning (ML) approaches using high-dimensional spectral bands can be computationally expensive, while those using spectral indices are typically limited to multispectral data. This study addresses these challenges by comparing soil pH and SOC prediction using ML models, with both existing spectral indices and individual hyperspectral bands as input features. Results demonstrate that hyperspectral bands outperform existing indices in predictive accuracy, with R values ranging from 0.8 to 0.94 for both soil pH and SOC. To further enhance prediction performance, this study proposes novel spectral indices-soil pH index (SPI) and soil organic carbon index (SOCI)-specifically designed for hyperspectral data using principal component analysis (PCA) and artificial neural networks (ANN). The proposed SPI and SOCI indices address multicollinearity issues and high dimensionality in raw spectral bands, significantly improving predictive accuracy. The SPI and SOCI indices achieve R values of 0.86 for AfSIS soil pH, 0.945 for LUCAS-2009 soil pH, 0.952 for AfSIS SOC, and 0.963 for LUCAS-2009 SOC. These results show that the proposed spectral indices provide a practical solution for precision agriculture, enhancing soil pH and SOC estimations.
... Livestock grazing is a common strategy to manage grasslands and exerts notable effects on SOC (Abdalla et al. 2018;Bork et al. 2023;Dlamini et al. 2016). Grazing can stimulate shallow and fine roots in C 4 species, leading to an SOC increase (Derner et al. 2006). ...
... In steppe grasslands, although soil EC significantly affected SOC, the influence of soil pH was considerably greater (Table 3; Fig. 4b). Soil pH directly contributes to the decomposition of soil organic matter (Dlamini et al. 2016). Furthermore, species richness of vascular plant communities often exhibits a positive correlation with soil pH (Pärtel 2002). ...
Background and aims
Soil organic carbon (SOC) content dominates the organic carbon pools in grasslands. Thus, factors that influence and regulate SOC content must be clarified when addressing global climate change.
Methods
We investigated SOC in the top 10 cm of the soil layer from 109 plots of the Mongolian Plateau, including both desert-steppe and steppe landscapes. We then examined the association between SOC with grazing intensity, climatic factors, soil properties, and vegetation diversity indices.
Results
Desert-steppe samples had lower mean SOC than steppe samples (0.3% versus 1.5%). Desert-steppe SOC did not vary with grazing intensity, but steppe SOC did. Instead, desert-steppe SOC decreased and increased, respectively, with higher growing season temperature and soil electrical conductivity; these two variables were the major factors influencing SOC in this grassland type. Besides grazing, outside growing season precipitation and soil pH were the major environmental factors that correlated positively with steppe SOC.
Conclusion
The SOC of steppe grasslands was more sensitive to grazing than SOC of desert-steppe grasslands. Additionally, while climate, grazing, soil, and vegetation all regulated SOC, the most influential variables differed between the two grassland types. These findings enhance our understanding of SOC regulatory mechanisms in different grasslands on the Mongolian Plateau. Such knowledge is crucial for predicting the consequences of environmental change on carbon sequestration.
... Moreover, due to the strong global demand for dairy products (i.e., meat, milk and cheese), the number of dairy farms in New Zealand has significantly increased during the past two decades. In addition, intense animal farming for the dairy industry has been shown to deplete the terrestrial carbon pool (Dlamini et al., 2016), causing soil degradation and contamination because of the urea in the urine of animals and their entry into the soil and the increased risk of increasing nitrates in the soil (Di and Cameron, 2018;Van Der Weerden et al., 2016). Consequently, it has led to an intensification of lands use in agriculture/grassland/animal farming, with its associated losses of soil carbon and increased nutrient and microbial contaminant emissions to waterways (Foote et al., 2015). ...
... Agricultural pollution can be defined as "a global environmental concern" and it is overwhelmingly induced by the "application of farming inputs" such as overgrazing (Dlamini et al., 2016) and excessive amounts of fertilizers (Zhu et al., 2016) and pesticides (Chen et al., 2015). Agricultural pollutants generally include toxic inorganic (e.g., heavy metals), and organic compounds (e.g., herbicides and pesticides) as well as can be excessive amounts of essential plant nutrients (e.g., nitrate (NO 3 − ) and phosphate (PO 4 3− )) (Dymond et al., 2013). ...
Due to increasing intensive agricultural activities, the importance of water quality for drinking is increasing over time. Especially, high concentrations of nitrate (NO3–) can cause severe health problems such as cyanosis in infants. This article reviewed the general plant biochemical responses to NO3– contamination and examined case studies currently used for NO3– removal and phytoremediation of most common tree species and confirmed whether conifer tree species have been conducted for nitrogen pollution research and compiled currently available 117 publications in forest tree species in phytoremediation study. It was explored how intensive agricultural activity can cause nitrate pollution and documented that 89% of the New Zealand’s plantation forests are Pinus radiata species, consisting of 1.63 million hectares and the N uptake potential by P. radiata ranged from 3 to 109 kg ha−1 y−1 based on literature review. Also, it was discussed that if it is necessary to pay attention to the role of Pinus radiata in farmlands and streams to develop novel ideas that can positively affect New Zealand’s environmental policy in the post-Paris Agreement era. I propose to consider choosing and exploiting Pinus radiata for several reasons: (1) to foster Pinus radiata research in nitrogen pollution research, finding new biological functions including the benefits of NO3– removal with conifer tree species; (2) to attract the attention to conduct the study of NO3– toxicity to plants and (3) to improve the attention of agroecosystem resilience based on fast-growing conifer trees’ regulating services. This article aims to re-evaluate our understanding of whether New Zealand’s Pinus radiata can deal with environmental stress conditions similar to more commonly studied fast-growing broad-leaved tree species.
... However, some of the arable land has been converted to building land during the urbanization process, offsetting the potential growth of the arable land area and making the increase of the arable land area slow (Deng et al., 2015a;Yansui Liu et al., 2014). In addition, the decrease in grassland area is mainly attributed to overgrazing and irrational land use, resulting in grassland degradation and conversion of part of the grassland into bare land or desert; at the same time, part of the grassland has been reclaimed as farmland to meet the increasing demand for food, which further exacerbates the shrinkage of grassland area (Ma et al., 2023;Dlamini et al., 2016). These land use changes not only reflect China's efforts to balance economic development and ecological protection, but also reveal the complex challenges facing sustainable land management in the future. ...
Under the context of climate change, the energy exchange mechanisms between terrestrial ecosystems and the atmosphere are highly complex. This study investigates the impact of land cover changes on solar radiation using China's land cover data and surface solar radiation absorption data. We analyze the data changes over two adjacent periods and integrate additional factors to explore the impacts of surface cover changes on solar radiation. The results indicate that: (1) Although grassland and bare land are the land categories with the largest area share, their radiation absorption capacity is significantly lower than that of water body and forests. (2) During 2001 –2020, 84.94% of land remains unchanged, but the expansion of the forested land and the reduction of the bare land in the changed areas have a significant impact on the radiation absorption, which suggests that the policy should focus on the restoration of the forested land of the arid area, bare land on the edge of the city, and greening, so as to minimize the intervention cost and maximize the benefits of climate moderation. This study provides a key theoretical basis for constructing a comprehensive evaluation model of "land-climate-ecology" synergy by revealing the multi-process coupling mechanism and cascading response relationship of solar radiation absorption by land cover change.
... The decline in regeneration in Socotra is driven by anthropogenic pressures, particularly overgrazing by goats, which have intensified due to the abandonment of traditional grazing practices. Overgrazing remains a significant threat to vegetation and soil health across various arid environments globally (Hempson et al. 2015;Dlamini et al. 2016). For example, in the Xinjiang Uygur Autonomous Region (China), long-term overgrazing has significantly reduced vegetation cover, negatively impacting ecosystem services like carbon sequestration and water regulation (Tai et al. 2021). ...
Question
Plant–plant facilitation is a critical ecological mechanism in arid environments, influencing biodiversity and ecosystem resilience globally. Shrubs often serve as nurse species, enhancing tree regeneration and sheltering plant communities, particularly in overgrazed or degraded habitats. In this study, we examine the role of shrubs as nurse species in the Socotra Archipelago (Yemen), a biodiversity hotspot in which several endemic tree species, including the iconic frankincense ( Boswellia spp.), myrrh ( Commiphora spp.), and Socotran dragon's blood ( Dracaena cinnabari ) trees, are threatened. This is largely due to a lack of natural regeneration caused by the combined effects of overgrazing by goats, sheep, and climatic events such as extreme droughts and cyclones. To aid conservation of threatened trees in arid regions, nature‐based solutions are urgently needed to help tree regeneration. Effective nurse plants have this potential, particularly in arid environments. We therefore examined the role of thorny, poisonous, and/or unpalatable shrubs as nurse plants in sheltering threatened plant communities, with a focus on woody species in an arid insular context.
Study Area
The Socotra Archipelago (Yemen) situated in the western Indian Ocean, east of the Horn of Africa. It is a biodiversity sanctuary and a UNESCO Natural World Heritage Site.
Methods
Vegetation surveys were conducted in 144 paired plots under six common shrub species and adjacent open areas. Community data, environmental variables, and functional traits were analysed using RLQ and fourth‐corner analyses, while Linear Mixed Models (LMMs) evaluated the effects of environmental variables and nurse species on key functional traits based on Community Weighted Means (CWMs). Facilitation effects were quantified using the Relative Interaction Index (RII).
Results
Our analysis revealed significant variations in species composition and functional traits between under‐canopy and open‐area plots. Certain shrubs, such as Cebatha balfourii , facilitated significantly higher species richness under its canopy compared to open areas. Elevation and grazing pressure influenced these interactions, with notable effects on functional traits like the occurrence of legumes and tree growth forms. Buxus hildebrandtii was less effective in supporting species richness, while C. balfourii, Lycium sokotranum , and two Cissus species exhibited significant positive facilitation. The LMMs confirmed the importance of environmental variables and nurse shrub characteristics in shaping plant community dynamics.
Conclusions
The results highlight differences in the facilitative potential of the studied species, with some showing a stronger ability to act as nurse shelters through microhabitat amelioration and protection from herbivory. The presence of tree species under shrubs is confirmed, and the role of these nurse species in supporting diverse plant communities provides critical insights for conservation strategies, supporting biodiversity resilience and sustainable management in degraded landscapes like Socotra Island and other arid environments. Future efforts should focus on leveraging nurse shrubs to mitigate environmental pressures and enhance ecological restoration, in particular to help conserve range‐restricted and threatened plant species.
... SOC accumulation and STN have been reported to decrease with continuous intensive grazing (Wright et al., 2004). Another alternative is that overgrazing on dry fields with low pH and low clay content is more likely to result in SOC loss than other activities, according to data from previous studies conducted globally across various climate zones (Dlamini et al., 2016). Reduction in SOC and soil fertility was reported due to heavy grazing in forage lands and nutrient stratification because of manure decomposition (Sarkar et al., 2020). ...
Accurately accounting for soil organic carbon stocks is crucial in assessing the sequestration potential of arid and semi-arid rangelands. This study, conducted in the rangelands near Loving, southeastern New Mexico, aims to evaluate soil organic carbon stocks, assess the potential for soil organic carbon sequestration, and identify both biotic and abiotic factors influencing this process. To achieve these goals, soil samples were collected and subjected to analysis for soil particle size, bulk density, soil characteristic curve, as well as soil total carbon and inorganic carbon. Soil total carbon stock (STCS), soil organic carbon stock (SOCS), soil inorganic carbon stock (SICS), and soil total nitrogen stock (STNS) were determined. Soil depth, vegetation types, and coverages on each ranch were identified. Additionally, soil ion concentrations, soil cation exchange capacity (CEC), and soil sodium adsorption ratio (SAR) were assessed. The soil CEC ranged from 6 to 20 meq/100 g soil, and SAR from 0.02 to 0.58 cmol/kg^0.5. The concentrations of Na and Cl were 42 and 13 mg/l, at a depth of 0–20 cm, increasing to 74 and 34 mg/l at 20–32 cm depth, respectively. In October 2021, STCS measured 39 Mg/ha at 0–20 cm and 11 Mg/ha at 20–32 cm soil depth. SOCS ranged from 18 Mg/ha at 0–20 cm to 6 Mg/ha at 20–32 cm soil depth, while SICS ranged from 20 to 1 Mg/ha at 0–20 cm and 20–32 cm soil depth, respectively. STNS varied from 1 Mg/ha at 0–20 cm to 3.8 Mg/ha at 20–32 cm soil depth. In the 20 cm sandy loam soil depth, ranches 1, 7, 8, 9, and 11 exhibited the highest SOCS, increased with increasing clay content, particularly where honey mesquite was the dominant species. These findings emphasize the importance of exploring soil carbon storage fluctuations in southern New Mexico. The differences in SOCS among ranches under different vegetation underscore the considerable potential for storing soil organic carbon in the semi-arid rangelands of this region.
... This could be especially pertinent in California, where loss of perennial grasses has contributed to degradation of rangeland soils (Koteen et al., 2011). It is generally accepted that this has been exacerbated by heavy continuous grazing (Burcham, 1957;Dlamini et al., 2016). However, management strategies to re-establish perennial grass dominance on California rangelands remain notoriously elusive, and studies have shown promising but highly variable perennial response following improved grazing (Bartolome et al., 2004;Carey, Gravuer, et al., 2020;Davy et al., 2017;Heady, 1961;Henneman et al., 2014;Stahlheber & D'Antonio, 2013). ...
Adaptive multi-paddock (AMP) grazing is gaining attention for its potential to increase soil organic carbon (SOC), yet its efficacy on arid and semi-arid rangelands remains debated. Given the adaptive nature of AMP, on-ranch studies are essential for measuring its applied outcomes. To assess AMP’s impact on Mediterranean California rangelands, we collected 1,440 soil samples from four paired AMP and conventional (CONV) grazing sites across northern California. Three AMP ranches had significantly greater SOC stocks in surface soils (17% greater SOC at 0–10 cm), and two had greater SOC stocks to 100 cm (32% greater), compared to CONV ranches. The largest SOC differences occurred in the mineral-associated organic matter fraction, suggesting longer-term SOC storage. While plant community composition did not differ significantly, AMP ranches, on average, had slightly less bare ground, greater live plant cover, and two sites had 82% greater perennial grass cover. These factors may have contributed to SOC differences. Further research is needed to understand site-specific constraints, underlying mechanisms, and SOC changes over time under AMP grazing.
... For instance, Samuelson et al. (2008) showed a little effect of irrigation of plant biomass and growth in temperate plantation. Other studies disclosed that besides environmental variables, edaphic factors like soil texture, soil pH, topography can also play a major role in increasing SOC-S (Dlamini et al., 2016;Mao et al., 2015;Tavakkoli et al., 2015). Also, SOC depends mostly on carbon input and output balance, plant productivity, decomposition process, and litter chemistry. ...
Soil carbon sequestration and its monitoring is important to improve climate resilience and mitigate global warming. According to the European Environment Agency (EEA), soils in Europe are losing carbon that could hamper achieving the EU climate targets. Hence, it is necessary to explore the dynamics of soil organic carbon (SOC) storage in different ecosystems so that the EU policymakers can observe the progress towards achieving EU Green Deal objectives. The aim of this research was to quantify the ΔSOC-S in woodland and shrubland in the last decade (2009–2018) and to study the ΔSOC-S due to the land use conversion. In this regard, revisited sampling points between 2009 and 2018 from the topsoil (0–20 cm) of woodland and shrubland of the EU + UK soil database named Land Use/Land Cover Area Frame Survey (LUCAS) was used. The analysis revealed that broadleaved-woodland to coniferous- or mixed-woodland conversion in 2018, and shrubland to woodland conversion in 2015 increased SOC-S. Overall, we found a net accumulation of SOC-S in woodland (2184.08 ton ha−1) and shrubland (302.78 ton ha−1) soil with 7.78% increment in woodland and 12.56% in shrubland between 2009/12 and 2018. Also, in central Europe, mean annual temperature (MAT) increased and precipitation (MAP) decreased between the study periods. The relationship between precipitation and temperature showed that precipitation and SOC-S in woodland had no relationship, but with the rising temperature, SOC-S in both land types significantly decreased revealing warming can significantly affect SOC-S.
... The 16 variables were divided into 16 categories, each was further classified to three to five subgroups (Table 1). Food and Agriculture Organization guidelines for agricultural climate zoning were used (Fischer et al., 2001) along with previous meta-analyses (Dlamini et al., 2016;Li et al., 2021) as well as characteristics of the collected data. ...
... The growth of roots enhances the conservation of carbon . However, the effects of grazing on SOC remain controversial, with studies indicating that grazing can increase (Hewins et al., 2018;Shen et al., 2023), decrease (Zhao et al., 2009;Dlamini et al., 2016;Ren et al., 2024) or leave SOC unchanged (Derner et al., 2019). This controversy may arise from differences in the climatic zones studied and the negative impact of climate change on livestock production (Ghahramani et al., 2019;Li et al., 2022). ...
Overgrazing leads to steppe degradation and soil structure deterioration, which is common in desert steppes. Restricted grazing is a sustainable practice, but the mechanisms by which soil structure responds to restricted grazing have received little attention. This study examined the effects of two different grazing management strategies, namely, restricted grazing and free grazing (CK), on soil structure indicators in the desert steppe. The restricted grazing further included grazing exclusion (GE) and seasonal grazing (SG). Additionally, a preliminary exploration was conducted to identify the main factors affecting the soil aggregate stability. Our results demonstrated that GE significantly increased clay (<0.002 mm) and silt (0.002–0.02 mm) in the 0–10 cm and 10–20 cm layers by an average of 71.27% and 70.64%, respectively. Additionally, SG significantly increased clay (<0.002 mm), silt (0.002–0.02 mm), and macroaggregates (>0.25 mm) in the 0–10 cm layer. GE significantly increased soil organic carbon in the 0–10 cm and 10–20 cm layers by 7.02 g/kg and 7.45 g/kg, respectively. In addition, SG had no significant effect on soil organic carbon. The findings obtained from the computations using the boosted regression tree (BRT) demonstrated that, within the study period, soil porosity significantly affects soil aggregate stability compared to other factors. Moreover, it possessed an average explanatory power that surpassed 45%. Overall, the soil structure is better under GE than under SG, and GE is the key to improving the soil structure of desert steppe. The research will contribute to a more profound comprehension of the impact of grazing on soil structure. Therefore, it is recommended that grazing closures be prioritized in desert grasslands to promote coordination between grassland restoration and livestock development.
... Soil pH controls a variety of soil characteristics and plays a vital role in supplying soil nutrients in agroecosystems [53,42] . SOC and TSN pool degradation was greater under slightly acidic conditions, as previously shown by Dlamini et al. in their meta-analysis of SOC in semiarid soils [54] . Tu et al. confirmed that the pH of the soil increases SOC and TSN. ...
Soil is a crucial nonrenewable resource for agriculture and has a direct impact on food security. However, the decline in crop yield post-Green Revolution suggested soil health deterioration due to soil degradation through harmful chemicals and anthropogenic activities. Therefore, restoring the health of the land and the environment is very important. In the last ten years, there has been a large increase in interest in soil health around the world. Many government, nongovernmental, and private sector groups are working on developing monitoring and assessment techniques. The concept of soil health is defined as the continuous capacity of soil to function as a vital ecosystem service supporting plants, animals, and humans. Biofertilizers, vermicompost, farmyard and green manure, and biopesticides are natural fertilizers that can be used instead of chemical fertilizers. This can help crops grow well while also being good for the land and climate. This brief study focused on soil health indicators such as soil biological, chemical, and physical properties and the urgent need for soil health restoration through the adoption of regenerative agriculture management practices.
... Overgrazing can lead to SOC losses. In overgrazed grasslands, the resulting limited energy reserves for biomass regeneration (in roots) affect the regrowth of pastures, leading to reduced soil cover and increased soil erosion and SOC loss (Abdalla et al., 2022;Dlamini et al., 2016). Furthermore, changes in soil compaction associated with the presence of herbivores in grassland ecosystems reduce the volume of air-filled pore space, thereby reducing mineralization processes and, consequently, SOC accumulation rates (Drewry et al., 2017;Schrama et al., 2013). ...
Background
There is limited knowledge on how to increase soil organic carbon (SOC) stocks under tropical conditions. This study investigates SOC changes after converting land from native savanna (NS) to improved pasture (IP) land use.
Methods
Two acidic soil conversion sites were examined: (i) a poorly drained slope with medium‐texture soil (Casanare [CAS]1) and (ii) flat terrain with fine‐texture soil (CAS2). Another flat site was evaluated (Atlántico [ATL]), with fine‐textured to moderately textured neutral soil. Soil samples were collected and analyzed. SOC stocks (0–60 cm soil depth) were estimated, with a complex analysis of variance analyzing pasture type and soil depth.
Results
NS to IP conversion resulted in significant SOC accumulation in two regions, with losses in one (CAS2). ATL showed higher SOC accumulation than CAS. IP adoption led to SOC accumulation at depth (0–60 cm) after 10 years in CAS1. Elevated clay content in CAS2 favored SOC storage, while poorly drained areas hindered accumulation in CAS1. Cultivating rice before IP at CAS2 likely depleted SOC (0–20 cm), with 4 years of IP not restoring initial levels.
Conclusions
Adopting IP over NS can increase SOC. Grassland type, soil properties, and land‐use change all influence SOC accumulation. These data inform sustainable land management for low‐emission livestock production.
... Grassland covers approximately 40% of the world's land and stores 30% of the world's soil carbon (Raich et al. 2002;Dlamini et al. 2016). The massive soil carbon storage plays an important role in regulating carbon exchange between the atmosphere and the earth's surface (Raich et al. 1992;Carey et al. 2016;Mou et al. 2024). ...
Bcakground
Soil respiration (Rs), as the second largest CO 2 emissions of terrestrial ecosystems, is sensitive to disturbance and consequent environmental changes. Mowing is strategically implemented as an management approach and has the potential to influence carbon cycling in meadow steppes. However, it remains unclear how and why Rs and its heterotrophic (Rh) and autotrophic (Ra) components respond to consecutive mowing and associated ecological consequences. Here, we conducted a field mowing experiment in a meadow steppe in 2018 and monitored Rs, Rh, and Ra from 2019 to 2022.
Results
We observed a significant reduction in Rs by 4.8% across four years, primarily attributed to a decrease in Rh. This decline in Rs intensified over time, indicating an accumulative effect of mowing. In addition, mowing induced an generally increasing Ra/Rs ratio over the experimental years with a simultaneous increase in the ratio of belowground to aboveground biomass (BGB/AGB). Furthermore, structural equation modeling results revealed that the decline in Rs was largely ascribed to reduced microbial biomass carbon (MBC) under mowing, while the increased Ra/Rs was primarily explained by the enhanced BGB/AGB. Partial regression analysis suggested that the biotic factor of microbial biomass dominated changes in soil respiration induced by mowing rather than abiotic soil temperature.
Conclusions
Our findings showed that consecutive mowing decreased Rs and raised Ra/Rs in meadow steppe by decreasing plant biomass and altering the proportion of biomass allocation. This observed decline in Rs would help to reduce CO 2 concentration in atmosphere as well as alleviate global warming. However, considering the concurrent lower microbial biomass, the potential positive impacts of mowing on climate and ecosystem function should be reevaluated in future grassland management practices.
... As an ecological and productive complex, grasslands have been significantly impacted by human activities. Extensive grazing on grasslands has led to a reduction in plant cover and aboveground biomass [2,3], causing significant changes in plant community composition and structure and a decline in the regenerative capacity of the grasslands [4], ultimately leading to grassland degradation [5]. Additionally, trampling by livestock also causes soil compaction, reducing the infiltration capacity of grassland soils [6]. ...
Fenced enclosures, a proven strategy for restoring degraded grassland, have been widely implemented. However, recent climate trends of warming and drying, accompanied by increased extreme rainfall, have heightened soil erosion risks. It is crucial to assess the long-term effectiveness of fenced enclosures on grassland restoration and their impact on soil physicochemical properties and water infiltration capacity. This study investigated the effects of enclosure duration on soil organic matter, aggregate composition and stability, and infiltration capacity in Yunwu Mountain Grassland Nature Reserve, comparing grasslands with enclosure durations of 2, 14, 30, and 39 years. Results showed that grasslands enclosed for 14, 30, and 39 years had infiltration rates increased by 20.66%, 152.03%, and 61.19%, respectively, compared to those enclosed for only 2 years. After 30 years of enclosure, soil quality reached its optimum, with the highest root biomass, soil organic matter, aggregate stability, and a notably superior infiltration rate. The findings suggest that long-term fenced enclosures facilitate grassland vegetation restoration and enhance soil infiltration capacity, with the most significant improvement observed at the 30-year enclosure milestone, followed by a gradual decline in this effect.
... In the Southern grasslands, for example, the number of animals to be grazing should be appropriate to the availability of forage and the maintenance of a heterogeneous grassland physiognomy, with more and less intensively grazed patches, dominated by prostrate and erect plants, respectively (Carvalho et al., 2009;Caram et al., 2023). This is important because overgrazing can cause the degradation of natural pastures due to the loss of vegetation cover (Nabinger et al., 2009;Dlamini et al., 2016). Therefore, controlling grazing intensity is a central point to maintain the dynamics of the native vegetation and the floristic richness and diversity of these areas (Nabinger et al., 2009). ...
Abstract-Legal reserve areas (LRAs) are a fundamental part of the Brazilian conservation strategy, together with permanent preservation areas. The LRAs are intended to maintain biodiversity and can be managed sustainably. When these areas are home to ecosystems that depend on fire and grazing, such as native grasslands and savannas, management practices that are suitable for their conservation and for dealing with the effects of global climate change should be adopted. However, this subject is still poorly discussed in Brazil, and public policies are not clear on this matter. This review article describes the grassland and savanna ecosystems in Brazil, the legal aspects related to the management of LRAs, the current and future climate scenarios, and the relationship between climate and fire risk. It also presents a review about the use of fire and grazing in grassland and savanna ecosystems, the legal challenges related to their application in LRAs, and the use of geotechnologies to monitor these practices. The conclusion is that grazing and fire, as management tools, are adequate for LRA functions, as long as they are practiced in accordance with legal and scientifically based standards to avoid the negative effects of their incorrect use.
... SOC acts as a nutrient reservoir for pasture, enhancing water-holding capacity, microbial activity, and nutrient availability (Gerke, 2022;Lal, 2016;Rajakaruna and Boyd, 2008). However, SOC can be regulated by a number of other factors such as soil texture, pH and different cropping practices (Dlamini et al., 2016;Xie et al., 2017). Although soil organic matter generally enhances soil quality, organic matter can absorb heavy metals, which can be toxic to plants or cause soil contamination, thereby reducing soil quality (Fageria, 2012). ...
... Grazing exclusion is not conducive to the recovery of soil nutrients in areas with mountain grassland but improves the stability of soil fungi in temperate steppe grassland. Therefore, the type of Introduction Grazing is a major grassland utilization strategy that comes with certain economic effects and environmental consequences (Yin et al., 2021), such as grassland degradation due to interactions with changing climatic conditions, slowing vegetation growth (Dlamini et al., 2016), altering the soil structure, and significantly affecting ecosystem services such as grassland windbreaks and sand stabilization, water retention, and carbon sequestration functions (Zhao et al., 2020). Grassland degradation has become an important ecological problem worldwide and has received increasing attention from ecologists (Bardgett et al., 2021;Wang et al., 2022c). ...
Overgrazing and climate change are the main causes of grassland degradation, and grazing exclusion is one of the most common measures for restoring degraded grasslands worldwide. Soil fungi can respond rapidly to environmental stresses, but the response of different grassland types to grazing control has not been uniformly determined. Three grassland types (temperate desert, temperate steppe grassland, and mountain meadow) that were closed for grazing exclusion for 9 years were used to study the effects of grazing exclusion on soil nutrients as well as fungal community structure in the three grassland types. The results showed that (1) in the 0–5 cm soil layer, grazing exclusion significantly affected the soil water content of the three grassland types (P < 0.05), and the pH, total phosphorous (TP), and nitrogen-to-phosphorous ratio (N/P) changed significantly in all three grassland types (P < 0.05). Significant changes in soil nutrients in the 5–10 cm soil layer after grazing exclusion occurred in the mountain meadow grasslands (P < 0.05), but not in the temperate desert and temperate steppe grasslands. (2) For the different grassland types, Archaeorhizomycetes was most abundant in the montane meadows, and Dothideomycetes was most abundant in the temperate desert grasslands and was significantly more abundant than in the remaining two grassland types (P < 0.05). Grazing exclusion led to insignificant changes in the dominant soil fungal phyla and α diversity, but significant changes in the β diversity of soil fungi (P < 0.05). (3) Grazing exclusion areas have higher mean clustering coefficients and modularity classes than grazing areas. In particular, the highest modularity class is found in temperate steppe grassland grazing exclusion areas. (4) We also found that pH is the main driving factor affecting soil fungal community structure, that plant coverage is a key environmental factor affecting soil community composition, and that grazing exclusion indirectly affects soil fungal communities by affecting soil nutrients. The above results suggest that grazing exclusion may regulate microbial ecological processes by changing the soil fungal β diversity in the three grassland types. Grazing exclusion is not conducive to the recovery of soil nutrients in areas with mountain grassland but improves the stability of soil fungi in temperate steppe grassland. Therefore, the type of degraded grassland should be considered when formulating suitable restoration programmes when grazing exclusion measures are implemented. The results of this study provide new insights into the response of soil fungal communities to grazing exclusion, providing a theoretical basis for the management of degraded grassland restoration.
... Generally, light or moderate grazing can improve grassland diversity and productivity, while heavy grazing leads to serious grassland degradation (Kemp et al., 2013;McNaughton, 1979). Degradation of grasslands due to overgrazing has emerged as a significant global ecological issue (Dlamini et al., 2016;van de Koppel et al., 1997;Yang et al., 2023). Long-term grazing caused a variety of adaptive evolutionary mechanisms in individual plant growth and morphological characteristics such as plant height , abundance (Ridding et al., 2021), and biomass (Hao and He, 2019). ...
Stipa breviflora is a dominant species in the desert steppe of Northern China. Grazing is the main land use pattern of grassland, which could cause a variety of adaptive evolutionary mechanisms in plant community composition as well as individual plant growth and morphological characteristics. However, very little is known about the morphological structure and transcriptional regulation response to different grazing intensities in S. breviflora. In this study, transcriptome and anatomical analyses of S. breviflora under different grazing intensities, including no grazing, moderate grazing, and heavy grazing, were performed. The anatomical analysis results showed that epidermis cells and xylems significantly thicken with grazing intensity, suggesting that grazing results in increasing lignification. Furthermore, the components of cell walls such as lignin, cellulose, hemicellulose, and pectin were all increased dramatically and significantly under both moderate and heavy grazing. Transcriptome analysis showed that the differentially expressed genes related to different grazing intensities were also engaged in plant cell wall formation and in photosynthesis and respiration. In addition, the activities of ATP synthase and Rubisco-activating enzyme increased significantly with enhanced grazing intensity and differed significantly between moderate and heavy grazing intensities. The trends in transcriptome and plant phenotype changes are consistent. Taken together, these results indicated that S. breviflora has evolved a grazing tolerance strategy under long-term grazing conditions, influencing photosynthesis and respiration in terms of its own structure and enzyme activities in the body, to maintain normal life activities under different grazing conditions.
... Meta-analysis was conducted for each categorical sub group such as mean annual precipitation (dry <400 mm; normal, 400-600 mm and wet >600 mm), temperature regions (frigid <8 • C; mesic, 8-15 • C and thermic > 15 • C), and soil texture (fine, medium and coarse) (Dlamini et al., 2016). Soil sampling depth was categorized into topsoil (0-150 mm) and subsoil (150-400 mm), which made up to 68% and 32% of the data groups used in this study, respectively. ...
Global climate change stress has greatly influenced agricultural crop production which leads to the global problems such as food security. To cope with global climate change, nature based solutions (NBS) are desirable because these lead to improve our environment. Environmental stresses such as drought and salinity are big soil problems and can be eradicated by increasing soil organic matter which is directly related to soil organic carbon (SOC). SOC is one of the key components of the worldwide carbon (C) cycle. Different types of land use patterns have shown significant impacts on SOC stocks. However, their effects on the various SOC fractions are not well-understood at the global level which make it difficult to predict how SOC changes over time. We aim to investigate changes in various SOC fractions, including mineral associated organic carbon (MAOC), mineral associated organic matter (MAOM), soil organic carbon (SOC), easily oxidized organic carbon (EOC), microbial biomass carbon (MBC) and particulate organic carbon (POC) under various types of land use patterns (NBS), including cropping pattern, residue management, conservation tillages such as no tillage (NT) and reduced tillage (RT) using data from 97 studies on a global scale. The results showed that NT overall increased MAOC, MAOM, SOC, MBC, EOC and POC by 16.2%, 26.8%, 24.1%, 16.2%, 27.9% and 33.2% (P < 0.05) compared to CT. No tillage with residue retention (NTR) increased MAOC, MAOM, SOC, MBC, EOC and POC by 38.0%, 29.9%, 47.5%, 33.1%, 35.7% and 49.0%, respectively, compared to CT (P < 0.05). RT overall increased MAOC, MAOM, SOC, MBC, EOC and POC by 36.8%, 14.1%, 25.8%, 25.9, 18.7% and 16.6% (P < 0.05) compared to CT. Reduced tillage with residue retention (RTR) increased MAOM, SOC and POC by 14.2%, 36.2% and 30.7%, respectively, compared to CT (P < 0.05). Multiple cropping increased MAOC, MBC and EOC by 14.1%, 39.8% and 21.5%, respectively, compared to mono cropping (P < 0.05). The response ratios of SOC fractions (MAOC, MAOM, SOC, MBC, EOC and POC) under NT and RT were mostly influenced by NBS such as residue management, cropping pattern along with soil depth, mean annual precipitation, mean annual temperature and soil texture. Our findings imply that when assessing the effects of conservation tillage methods on SOC sequestration, SOC fractions especially those taking part in driving soil biological activities, should be taken into account rather than total SOC. We conclude that conservation tillages under multiple cropping systems and with retention of crop residues enhance soil carbon sequestration as compared to CT in varying edaphic and climatic conditions of the world.
... Soil is a significant carbon storage and contains about 1505 Pg C in the topsoil, which is about twice as much as in the atmosphere or three times as much as in terrestrial vegetation (Dlamini et al., 2016). Soil organic carbon (SOC) constitutes the majority of the terrestrial soil carbon pool (accounting for almost 62% of soil carbon) and plays an important role in the global carbon cycle and balance (Piao et al., 2020). ...
Soil organic carbon comprises the majority of the terrestrial soil carbon pool and plays an important role in the global carbon cycle and balance. Even minor changes in soil organic carbon (SOC) can have a significant impact, not only on climate but also on ecosystem stability, due to its key role in soil-atmosphere carbon exchange, plant growth, and food production. In order to assess the feedbacks between the terrestrial carbon cycle and climate change, and to maintain ecosystem functions, it is crucial to understand the spatial and temporal changes in SOC and the drivers of these changes. The role of soil as a source or sink of atmospheric CO2 is primarily influenced by changes in climate and soil water content. Climate change, particularly global warming, can have a direct or indirect impact on the decomposition of organic matter by regulating soil microbes and fauna, enzyme activity, and soil respiration. A warming climate may increase the loss of soil carbon to the atmosphere because warming has a stronger effect on respiration than on photosynthesis, resulting in a positive soil carbon-climate feedback. Climate warming can significantly affect soil organic matter stocks, with the magnitude of the effect largely dependent on the initial organic matter stock size. Soil carbon content is a crucial aspect of terrestrial ecosystems that affects their functional properties and the climate. Conversely, climate also has an impact on soil organic carbon content. The spatial variability of soil organic carbon content and the predictions made for the west-central European region are also important considerations. The study identified the spatial variation of soil organic carbon throughout Europe and forecast its dynamics in the next 50–70 years, considering global climate change. Digital soil mapping enables a more precise representation of soil properties in space, including the spatial quantification of prediction errors. The accuracy of these predictions increases as more local observations, such as soil profiles, are available to construct the prediction model. Digital soil mapping allows flexible spatial development of soil property maps. Soil properties, such as nutrient concentration and stocks, carbon, heavy metals, pH, cation exchange capacity, and physical properties like particle size and bulk density, can be modelled at different depths and spatial resolutions depending on the project's objectives and available input data. The r GSOCmap project used a 1 km grid to model soil organic matter content. In Europe, the range of soil organic carbon content is from 0 to 750 t/ha, with a mean of 78.1 t/ha and a standard deviation of 50.1 t/ha. Climatic factors were found to account for 29% of the variation in soil organic carbon based on regression analysis. The study revealed that an increase in air temperature leads to a decrease in soil organic carbon content, while an increase in precipitation results in an increase in this indicator. Additionally, the content of soil organic matter is negatively impacted by an increase in the seasonality of precipitation. According to the forecast, global climate change will cause an increase of 1.0–1.1 t/ha in the organic carbon content of 3.6% of the continent's area over the next 70 years. On 7.6% of the area, the changes will be insignificant. The soil organic carbon content is expected to decrease on 88.9% of the area. Of this, 35.1% will experience a slight decrease in carbon content by 0–1 t/ha, 28.4% will experience a moderate decrease in soil organic carbon content by 1.0–1.1 t/ha, and 25.3% will experience a significant decrease by 1.1–1.3 t/ha. The Baltic countries, Belarus, and the Black Earth zone of Russia are at the highest risk. The risk of Russia becoming highly dependent on food imports is increased by this fact. The prospects for Ukraine are quite optimistic. Even in the northern Azov region, we can expect an intensification of humus accumulation processes in the near future, mainly due to increased precipitation. Precipitation in southern Ukraine is a limiting factor that significantly affects agricultural productivity. Increased precipitation and organic matter growth in the soil present positive prospects for agriculture in southern Ukraine, including the northern Azov, Black Sea, and Crimea. It is possible that the occupation of these territories, which are promising for agricultural production, is one of the goals of Russian armed aggression against Ukraine.
... Soil organic carbon (SOC) is a crucial component of the terrestrial soil carbon pool, accounting for approximately two-thirds of the carbon stocks in terrestrial ecosystems, surpassing the combined carbon stock in the global atmosphere and vegetation [1][2][3]. Maintaining and increasing SOC content is crucial for enhancing ecosystem productivity, mitigating climate change, and other related aspects [4,5]. However, the dynamics and stability of SOC are changed due to continuous alterations in climate, vegetation conditions, and land-use changes [6][7][8]. ...
Soil carbon content and stability are primarily influenced by the stabilization of particulate organic matter (POM) and mineral-associated organic matter (MAOM). Despite extensive research on the stabilization processes of POM and MAOM carbon components under various land-use types, the investigation into stabilization processes of soil carbon remains limited in saline–alkali soils. Therefore, we collected soil samples from different positions of saline–alkali drainage ditches at four reclamation times (the first, seventh, fifteenth, and thirtieth year) to determine their carbon content and physicochemical properties. Moreover, POM and MAOM fractions were separated from soil samples, and Fourier transform infrared spectra (FTIR) were used to investigate changes in their chemical composition. The results showed that with increasing reclamation time, the soil total carbon and soil organic carbon (SOC) contents significantly increased from 14 to 15 and 2.9 to 5.5 g kg⁻¹, respectively. In contrast, soil inorganic carbon content significantly decreased from 11 to 9.6 g kg⁻¹. Notably, the changes in soil carbon components following the increasing reclamation time were primarily observed in the furrow sole at a depth of 20–40 cm. While the SOC content of the POM fraction (SOCPOM) decreased significantly, the SOC content of the MAOM fraction (SOCMAOM) increased significantly. These alterations were largely dominated by drainage processes after reclamation instead of a possible conversion from SOCPOM to SOCMAOM. FTIR results revealed that MAOM was greatly influenced by the reclamation time more than POM was, but the change in both POM and MAOM contributed to an increase in soil carbon stability. Our findings will deepen the comprehension of soil carbon stabilization processes in saline–alkali drainage ditches after reclamation and offer a research framework to investigate the stability processes of soil carbon components via alterations in POM and MAOM fractions.
... The negative impact of grazing has been attributed primarily to soil compaction through animal trampling and reduced structural pore space, as indicated by higher soil bulk density values in more heavily grazed areas (Dudley et al., 2002;Lai & Kumar, 2020;Lulandala et al., 2022). In addition, heavy grazing can lead to reductions in plant cover and biomass, and SOC (Dlamini et al., 2016;Eldridge et al., 2016;Kikoti et al., 2015;Lai & Kumar, 2020;Lulandala et al., 2022;Savadogo et al., 2007), which can also contribute to decreasing infiltration capacity. Heavy livestock grazing and other anthropogenic activities can dilute or override the positive impacts of woody vegetation on K fs (Ghimire et al., 2013(Ghimire et al., , 2014Lulandala et al., 2022). ...
Soil infiltration is critical for water security and related ecosystem services. This infiltration, the ability of soils to absorb water at their surface, is controlled by the soil hydraulic conductivity. Despite recent efforts in assembling measurements of soil hydraulic conductivity, global databases and derived pedotransfer functions lack coverage in the tropics. Here, we present soil infiltration measurements and other indicators of soil and land health collected systematically in 3,573 plots from 83 100 km² sites across 19 countries in sub‐Saharan Africa. We use these data to (a) determine field‐saturated hydraulic conductivity (Kfs) and (b) explore which variables best predict variation in Kfs. Our results show that sand content, soil organic carbon (SOC), and woody cover had a positive relationship with Kfs, whereas grazing intensity and soil pH had a negative relationship. Our findings highlight that, despite soil texture being important, structure also plays a critical role. These results indicate considerable potential to improve soil hydrological functioning through management and restoration practices that target soil structure. Enhancing SOC content, limiting animal stocking, promoting trees, shrubs, and other vegetation cover, and preventing soil erosion can increase Kfs and improve water security. This data set can contribute to improving Earth system and land surface models for applications in Africa.
... Soil organic matter is the largest organic carbon reservoir of near-surface terrestrial ecosystems (Dlamini et al., 2016). Even subtle acceleration in soil organic carbon (SOC) decomposition will result in large CO 2 emissions (Davidson and Janssens, 2006). ...
Nitrogen (N) and warming effects on ecosystem carbon (C) budgets and stabilization are critical to understand as C sequestration is considered as a mechanism to offset anthropogenic CO2 emissions, which is important for accurately predicting ecosystem C sequestration and/or potential C loss, remaining controversial though. However, the relevant information, especially for the intervention of environmental controls on grassland soil, is limited in Tibetan Plateau (TP) regions. Here we used a 9-year two-way factorial experiment involving warming with open top chambers (+1.80 ∘C in the daytime and +0.77 ∘C in the nighttime at the soil surface) and multilevel nitrogen (N) enrichment treatments (0, 5, 10, and 15 gm-2yr-1) in the TP to investigate the changes in soil organic carbon (SOC) pool size and chemical structure. Nine-year warming treatment significantly decreased SOC stock in the Tibetan grassland. We observed decreasing SOC concentrations which may be related to changes in the C-degrading enzymes. Surprisingly, the SOC molecular structure remained unchanged in all N-enrichment and warmed plots, suggesting that both treatments had affected all forms of SOC, from simple and complex polymeric in a similar way. Our results suggest that long-term warming stimulates soil C loss but no preference in SOC loss with different chemical structures.
... Therefore, small uctuations in SOC pools show a remarkable tendency to disturb atmospheric carbon concentrations (Zhou et As a common strategy of grassland management, livestock grazing has been shown to have differential effects on soil organic carbon (SOC). Numerous studies have been devoted to investigating the sequestration and depletion of SOC resulting from grazing (Abdalla et al. 2018; Bork et al. 2023; Dlamini et al. 2016). It is widely recognized that inappropriate grazing in grassland ecosystems can result in the loss of SOC (Wang et al. 2011), whereas, grazing exclusion measurements can contribute to the enhancement of SOC ). ...
Purpose
Soil organic carbon (SOC) predominates organic carbon pools in grassland. To address global climate change, it is essential to explore the soil organic carbon influencing factors and mechanisms.
Method
s We investigated the soil organic carbon (SOC) in 109 plots along the Mongolian Plateau grassland, which covers the desert-steppe and steppe. Specifically, we analyzed the SOC in the top 10 cm soil layer and its relationships with grazing intensity, climatic factors, soil properties, and vegetation diversity index.
Results
The average SOC of the desert-steppe (0.3%) was lower than that of the steppe (1.5%). In the desert-steppe, SOC did not vary with grazing intensity. In the steppe, SOC varied significantly with grazing pressure. Significant negative relationships were found between the SOC and growing season temperature (GST) and growing season aridity index (GSR) in the two regions. The responses of SOC to mean annual precipitation (MAP), growing season precipitation (GSP), and outside growing season precipitation (OGSP) in two types of grasslands were different. GST and soil EC were respectively identified as the major positive and negative factors influencing the SOC in the desert-steppe; the OGSP and soil PH were the major positive factors influencing the SOC in the steppe.
Conclusion
Out results proposed that soils of steppe grasslands have a large carbon sink potential but are more susceptible to grazing. These findings enhance our understanding of the different mechanisms of SOC in different grasslands along the Mongolian Plateau, which are crucial for predicting the effects and consequences of environmental change on carbon sequestration.
... Details are presented in the supplement (Tables S2 and S3). The SOC and N tot stocks (kg m −2 ) to 15 cm soil depth were calculated according to Dlamini et al. (2016) using the measured soil bulk densities of 1.41 g cm −3 for short patches and 1.40 g cm −3 for tall patches (Tables S2, S3, and below). ...
Background
Selective grazing creates stable patches of contrasting sward height, thereby providing different growth conditions for the grass sward above and below ground and potentially affecting soil organic carbon (SOC) stocks. We hypothesized that the presence of patches leads to greater spatial variability in belowground biomass (BGB) and SOC stocks than occurs between pastures managed under different stocking intensities.
Methods
A long‐term grazing experiment consisting of three stocking intensities was used for this study. We studied BGB, SOC, and soil total nitrogen (N tot ) stocks in the 0–15 cm soil depth. Shannon diversity of plant species, soil bulk density, soil phosphorus, potassium, and magnesium contents were considered.
Results
There were no significant effects of patch or stocking intensity on BGB, SOC, and N tot stocks. Short patches had a greater Shannon diversity than tall patches ( p < 0.05) and plant‐available nutrients in soil correlated positively with sward height ( p < 0.05).
Conclusions
We conclude from the current results and previous studies that higher plant species diversity with lower soil nutrient contents in short‐patch areas and higher nutrient contents together with light competition in tall‐patch areas might balance each other out with respect to BGB and SOC stocks.
... We further categorized the independent variables to aid in data interpretation (Table 1). These categories were based on polymer type [14], microplastics type [47], exposure time [48], plant presence [48], soil texture [49], initial soil pH [50], initial SOC [51], and initial soil TN [52]. We effectively categorized the concentration and size of microplastics and experimental temperature based on the range and characteristics of the data presented in the studies included in our meta-analysis (Table 1). ...
... cultural activities and industrial activities.Abdalla et al. (2018) studied the effects of grazing on SOC stocks based on meta-analysis and revealed that grazing could significantly decrease the SOC stocks (taken as a grand mean).Yu, Li, et al. (2019) found that decreased grazing can reduce soil erosion and increase SOC stocks in the Loess Plateau.Dlamini et al. (2016) used a meta-analysis to indicated that grassland degradation in arid climates by overgrazing significantly reduced SOC stocks by 16% at a global scale. Furthermore, studied the impacts of grazing on the typical steppe of Inner Mongolia, and pointed out that heavy grazing would affect vegetation conditions, reduce SOC content by 4.3%, an ...
Soil organic carbon (SOC) in grasslands not only plays an important role in carbon cycle but also largely affects soil function and thus determines grasslands' productivity. However, the influence mechanism of different factors on SOC storage in grasslands of northern China remains unclear. Based on an extensive field investigation and multiple statistical approaches, we mapped SOC of the grassland in northern China, and explored their correlations with climatic factors, biological factors, human activity intensity (HAI), and soil physicochemical factors. The effects of these factors on SOC were also analyzed by structural equation model. The results showed that the SOC varied across the regions and was strongly correlated with soil chemical factors (i.e., soil total nitrogen [TN], amorphous Al, and amorphous Fe) and soil physical factors (i.e., clay, silt, and sand). HAI, which was mainly influenced by grazing, had a significant but negative impact on SOC. Different from previous studies, we found that climatic factors such as temperature and precipitation indirectly affected SOC by influencing biological factors such as vegetation coverage, vegetation height, Shannon–Weiner index, and species richness. The soil physicochemical properties and HAI were the dominant influencing factors for controlling SOC distribution in the grasslands of northern China. Our findings will further increase the understanding of the carbon cycle in grassland ecosystems, while providing important scientific references for temperate grassland ecosystem management.
Grassland soil carbon stocks contain substantial amounts of organic carbon and play a crucial role in the global carbon cycle. Grazing is one of the most primary land use types in grasslands. However, few studies have focused on the impact of three grazing behaviors (mowing (M), trampling (T), and dung and urine addition (D)) on the soil organic carbon (SOC) of mountain meadows. In this experiment, we simulated three grazing behaviors to explore the impacts of grazing behaviors on plant characteristics with plant growth, soil physicochemical properties, soil aggregate, and analyzed the main factors influencing the changes in SOC. After six years of treatment, the experimental results showed that M significantly decreased plant height, density, and aboveground biomass and significantly decreased soil organic carbon (SOC) (no M vs. M, −3.64%). T significantly increased soil bulk density, the proportion of macroaggregates, the organic carbon of microaggregates, and silt and clay aggregates and significantly increasing SOC (no T vs. T, +3.17%). D significantly increased plant density, soil total nitrogen and the organic carbon of macroaggregates, significantly increasing SOC (no D vs. D, +9.74%). Correlation and principal component analyses indicated that SOC was significantly negatively correlated with soil bulk density and plant coverage and significantly positively correlated with soil total nitrogen, soil C/N, microaggregate proportion, and the organic carbon of macroaggregates. Redundancy analysis indicated that the proportion of microaggregates and the organic carbon of macroaggregates were the main factors influencing SOC. The following conclusions were drawn: SOC responds differently to three types of grazing behaviors, D primarily increases the organic carbon in macroaggregates, while T mainly enhances the organic carbon in microaggregates and silt and clay aggregates, thereby affecting the SOC in mountain meadows.
Based on a growing understanding of the role of wild megafauna in the functioning of natural ecosystems, trophic
rewilding by large herbivores is increasingly used as a nature-based solution to mitigate biodiversity loss and
climate change in Europe and beyond. Despite the growing interest in implementing nature-based approaches to
restore key non-productive ecosystem services, there is relatively little data available to assess the benefits and
risks of rewilding projects. We therefore investigated the effects of year-round grazing by large ungulates on
plant biomass characteristics and their relationship with soil properties at seven trophic rewilding sites in the
Czech Republic. We found that trophic rewilding systematicaly reduced aboveground biomass, but improved
plant nitrogen supply through enhanced nitrogen recycling, resulting in higher water and nitrogen content in the
aboveground plant biomass and providing high-quality forage for grazing ungulates. Belowground biomass
remained unchanged, indicating that the current grazing intensity allowed sufficient plant regeneration and
organic matter input into the soil, increasing soil organic matter sequestration and water retention capacity.
Rewilding further altered plant-soil interactions and strengthened the relationship between vegetation and soil
microbial processes, which improved root growth and phosphorus uptake. These newly emerged herbivorevegetation-
soil interactions are of critical importance, as phosphorus and water availability have been identified
as important edaphic factors controlling plant productivity and forage quality of rewilded sites. We propose
that close herbivore-plant-soil relationships may promote the dynamics and self-regulatory capacity of rewilded ecosystems and facilitate their ability to promptly respond and adapt to changing biospheric and climatic
conditions.
The foundation of sustainable agriculture rests on integrating ecological principles into farming systems. This includes conserving biodiversity through practices like crop rotations, intercropping, agroforestry, and habitat preservation, which sustain key ecosystem services. Sustainable methods emphasize soil health via practices like cover cropping and reduced tillage, while efficient nutrient cycling minimizes reliance on synthetic fertilizers. Water management techniques such as precision irrigation are crucial, and integrated pest management reduces pesticide use by focusing on prevention and monitoring. Conservation agriculture and agroecology complement each other, enhancing farming resilience and sustainability by maintaining soil health and integrating ecological elements into agricultural systems.
As áreas de reserva legal (ARLs) são parte fundamental da estratégia
brasileira de conservação, juntamente com as áreas de preservação permanente.
As ARLs são destinadas à manutenção da biodiversidade e podem ser manejadas
de forma sustentável. Quando essas áreas abrigam ecossistemas dependentes
de fogo e pastejo, como os campos nativos e as savanas, devem ser adotadas
práticas de manejo adequadas à sua conservação e ao enfrentamento dos efeitos
das mudanças climáticas globais. No entanto, esse assunto ainda é pouco
discutido no Brasil, e as políticas públicas não são claras a esse respeito. Este
artigo de revisão descreve os ecossistemas campestres e savânicos no Brasil, os
aspectos legais relacionados com o manejo das ARLs, os cenários climáticos
atuais e futuros, e a relação entre clima e risco de incêndios. Também apresenta
uma revisão sobre o uso do fogo e do pastejo em ecossistemas campestres e
savânicos, os desafios legais relativos à sua aplicação nas ARLs e o uso de
geotecnologias no monitoramento destas práticas. Conclui-se que o pastejo e
o fogo, como instrumentos de manejo, são adequados às funções das ARLs,
desde que praticados segundo normas legais e cientificamente embasadas para
evitar os efeitos negativos do seu uso equivocado.
Background and aims
Grazing drives carbon (C) and nitrogen (N) dynamics of grasslands through livestock trampling, defoliation, and excretion. Still, the responses of N uptake by plant species and simultaneous C allocation into the soil to grazing intensity remain unclear.
Methods
In-situ 15NH4⁺ / ¹⁵NO3⁻ and ¹³C-CO2 labeling experiment was conducted in Inner Mongolia grasslands under 5 years of grazing with no, light (4 sheep 1.33 ha⁻¹) and heavy (12 sheep 1.33 ha⁻¹) intensity to reveal the contribution of plant-derived C into the soil and the fate of N on day one and three after ¹³C-labeling. Experiment had a completely randomized design (n = 3), and every plot included Leymus chinensis, Carex korshinskyi, Cleistogenes squarrosa, and Stipa grandis.
Results
Grazing increased plants’ total N uptake compared to control (no grazing); higher NO3⁻ uptake was found compared to NH4⁺ (aboveground: 0.40–20.78 vs. 0.32–6.58 µg N m⁻²; belowground: 0.04–9.92 vs. 0.01–0.49 µg N m⁻²), irrespective of grazing intensity. C. korshinskyi showed the highest N uptake (3–21 µg N m⁻²) under the three grazing intensities. ¹³C-CO2 assimilation was the lowest under heavy grazing (aboveground: 1.06–10.67 mg C m⁻²; belowground: 0.25–1.53 mg C m⁻²) regardless of plant species. ¹³C-CO2 assimilation by L. chinensis and C. squarrosa decreased 3–5 times with grazing intensity. Grazing increased ¹³C-SOC irrespective to soil depth compared to no grazing.
Conclusions
Grazing patterns affected the plants’ total assimilation C capacity and N uptake and the response varies among plant species, as well as the allocation of plant-C transfer into the soil.
Among options for atmospheric CO 2 removal, sequestering soil organic carbon (SOC) via improved grazing management is a rare opportunity because it is scalable across millions of globally grazed acres, low cost, and has high technical potential. Decades of scientific research on grazing and SOC has failed to form a cohesive understanding of how grazing management affects SOC stocks and their distribution between particulate (POM) and mineral‐associated organic matter (MAOM)—characterized by different formation and stabilization pathways—across different climatic contexts. As we increasingly look to grazing management for SOC sequestration on grazinglands to bolster our climate change mitigation efforts, we need a clear and collective understanding of grazing management's impact on pathways of SOC change to inform on‐the‐ground management decisions. We set out to review the effects of grazing management on SOC through a unified plant ecophysiology and soil biogeochemistry conceptual framework, where elements such as productivity, input quality, soil mineral capacity, and climate variables such as aridity co‐govern SOC accumulation and distribution into POM and MAOM. To maximize applicability to grazingland managers, we discuss how common management levers that drive overall grazing pattern, including timing, intensity, duration, and frequency can be used to optimize mechanistic pathways of SOC sequestration. We discuss important research needs and measurement challenges, and highlight how our conceptual framework can inform more robust research with greater applicability for maximizing the use of grazing management to sequester SOC.
Grazing is one of the most important forms of terrestrial use, and the soil microbial community plays an important role in nutrient cycling and biodiversity maintenance of grazing grassland, but the response of soil bacterial and fungal communities α‐diversity to grazing and the potential mechanisms of grazing‐induced soil microbial change have not been well synthesized. We conducted a meta‐analysis of 87 pairs of globally distributed observations from 35 published papers to investigate the response of the soil microbial community to grazing and the underlying mechanisms. Our results showed that light grazing increased the soil bacterial community Shannon index by 2.4%, but the soil fungal Shannon index decreased by 21.4%. Yak ( Bos grunniens ) grazing significantly increased the soil bacterial and fungal Shannon index by 1.5% and 11.3%, respectively. Grazing duration of 5–10 years increased the soil bacterial Chao1 index by 9.1% and fungal Chao1 and evenness indexes by 11.3% and 30.4%, respectively. In areas with <400 mm of precipitation, grazing decreased the soil bacterial Simpson index, and in areas of ≥400 mm, grazing also reduced the soil bacterial Simpson and increased the fungal richness and evenness. A linear analysis between soil microbial α‐diversity indexes and other related variables showed that soil bacterial and fungal communities α‐diversity and abundance under grazing conditions were significantly and positively correlated with grassland vegetation, soil pH, soil water content (SWC), total nitrogen (TN), total phosphorus (TP), organic carbon (SOC), and nitrate nitrogen (NO 3 ⁻ ‐N), suggesting that changes in microbial communities were the combined result of grazing‐induced vegetation and soil changes. Our results revealed the effects of grazing on soil bacterial and fungal α‐diversity and their underlying mechanisms, which provide a basis for advocating moderate grazing and studying grassland management practices.
Purpose
Soil organic carbon (SOC) storage in paddy profiles plays an important role in regulating terrestrial carbon cycling and global climatic change. The changes in groundwater level may influence the accumulation characteristics of SOC fractions in paddy soil profiles. However, the characteristics of organic carbon storage in paddy profiles under different groundwater levels are not well recognized.
Materials and methods
In this work, effects of groundwater levels (high and low groundwater levels at 20 and 80 cm depths, respectively) on the distribution of SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) in red paddy profiles (0–20, 20–40, and 40–60 cm depths) with 40 years of chemical fertilization (CF) and organic fertilization (OF) were investigated.
Results and discussion
The results showed that compared to a low groundwater level, a high groundwater level resulted in an increase in SOC, POC, and MAOC contents in the profiles. SOC and POC increased by 9.00 ~ 9.11% and 22.89 ~ 26.95% at 0–20 cm depth and increased by 24.02 ~ 52.42% and 36.69 ~ 76.94% at 20–40 cm depth, respectively. MAOC increased by 18.18 ~ 38.28% at 20–40 cm depth. No obvious changes were observed in SOC, POC, and MAOC at 40–60 cm depth between the two groundwater levels. At high groundwater level, the contents of aliphatic and aromatic carbon in soil profiles were higher, but the δ¹³C values were less than those at low groundwater level. MAOC constitutes main fraction of SOC in all soil profiles, and the values of MAOC/SOC increased obviously with depth. Moreover, the MAOC/SOC values in all soil layers were higher under low groundwater level than under high groundwater level. Correlation analysis showed that SOC, POC, and MAOC were positively correlated with Feo and significantly negatively correlated with Fed-Feo (P < 0.01) under two groundwater levels.
Conclusions
Overall, distributions of SOC, POC, and MAOC were strongly influenced by groundwater levels, with higher levels leading to increased storage of these fractions in paddy soil profiles, particularly in 20–40 cm soil layer. MAOC is the main component of SOC in the paddy profiles, and higher groundwater levels are available for POC accumulation, especially for OF treatments. The δ¹³C value of SOC decreased with increasing groundwater level. These results suggested that groundwater level is a potential strategy to improve carbon sequestration in paddy soils, which offers new insights for understanding the influence of groundwater levels in distribution of SOC fractions in paddy profiles.
Soil carbon (C) is the largest C pool in terrestrial biosphere and includes both inorganic and organic components. Studying patterns and controls of soil C help us to understand and estimate potential responses of soil C to global change in the future. Here we analyzed topsoil data of 81 sites obtained from a regional survey across grasslands in the Inner Mongolia and on the Tibetan Plateau during 2006–2007, attempting to find the patterns and controls of soil inorganic carbon (SIC) and soil organic carbon (SOC). The average of SIC and SOC in the topsoil (0–20 cm) across the study region were 0.38% and 3.63%, ranging between 0.00–2.92% and 0.32–26.17%, respectively. Both SIC and SOC in the topsoil of the Tibetan grasslands (0.51% and 5.24%, respectively) were higher than those of the Inner Mongolian grasslands (0.21% and 1.61%). Regression tree analyses showed that the spatial pattern of SIC and SOC were controlled by different factors. Chemical and physical processes of soil formation drive the spatial pattern of SIC, while biotic processes drive the spatial pattern of SOC. SIC was controlled by soil acidification and other processes depending on soil pH. Vegetation type is the most important variable driving the spatial pattern of SOC. According to our models, given the acidification rate in Chinese grassland soils in the future is the same as that in Chinese cropland soils during the past two decades: 0.27 and 0.48 units per 20 yr in the Inner Mongolian grasslands and the Tibetan grasslands, respectively, it will lead to 30% and 53% decrease in SIC in the Inner Mongolian grasslands and the Tibetan grasslands, respectively. However, negative relationship between soil pH and SOC suggests that acidification will inhibit decomposition of SOC, thus will not lead to a significant general loss of carbon from soils in these regions.
The aim of this study was to determine the effect of land-use and forest cover depletion on the distribution of soil organic carbon (SOC) within particle-size fractions in a volcanic soil. Emphasis was given to the thermal properties of soils. Six representative sites in Mexico were selected in an area dominated by Andosols: a grassland site, four forested sites with different levels of degradation and an agricultural site. Soils were fractionated using ultrasonic energy until complete dispersion was achieved. The particle-size fractions were coarse sand, fine sand, silt, clay and particulate organic matter from the coarse sand sized fraction (POM-CS) and fine sand (POM-FS). Soil organic carbon decreased by 70% after forest conversion to cropland and long-term cultivation; forest cover loss resulted in a decrease in SOC of up to 60%. The grassland soil contained 45% more SOC than the cropland one. Soil organic carbon was mainly associated with the silt-size fraction; the most sensitive fractions to land-use change and forest cover depletion were POM followed by SOC associated with the silt and clay-sized fractions. Particulate organic matter can be used as an early indicator of SOC loss. The C lost from the clay and silt-sized fractions was thermally labile; therefore, the SOC stored in the more degraded forest soils was more recalcitrant (thermally resistant). Only the transformation of forest to agricultural land produced a similar loss of thermally stable C associated with the silt-sized fraction.
Stocking rate (SR) effects on soil organic carbon (OC) and nitrogen content resulting from 10 year continuous management were determined. Treatments were rotational grazing with four SR levels: light, moderate, heavy and non grazed. Two soils, a Durant loam (Udertic Argiustolls) and a Teller silt loam (Udic Argiustolls) located within common paddocks were sampled. Total OC mass in the surface 60 cm of the Durant soil, averaged across treatments, was 95.7 t ha-1 compared to 56.7 t ha-1 in the Teller soil. In the Durant soil, OC decreased as SR increased, with the non grazed exclosure having the greatest amount of soil OC. In contrast, the Teller soil had similar amounts of OC in the soil profile with all grazing treatments, but less without grazing. Total soil nitrogen followed similar trends as the soil OC. Soil properties should be considered to accurately assess the potential of grazing lands to sequester carbon.
The soil is important in sequestering atmospheric CO2 and in emitting trace gases (e.g. CO2, CH4 and N2O) that are radiatively active and enhance the ‘greenhouse’ effect. Land use changes and predicted global warming, through their effects on net primary productivity, the plant community and soil conditions, may have important effects on the size of the organic matter pool in the soil and directly affect the atmospheric concentration of these trace gases.
A discrepancy of approximately 350 × 1015 g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo-referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project. This database holds 4353 soil profiles distributed globally which are considered to represent the soil units shown on a 1/2° latitude by 1/2° longitude version of the corrected and digitized 1:5 M FAO–UNESCO Soil Map of the World.
Total soil carbon pools for the entire land area of the world, excluding carbon held in the litter layer and charcoal, amounts to 2157–2293 Pg of C in the upper 100 cm. Soil organic carbon is estimated to be 684–724 Pg of C in the upper 30 cm, 1462–1548 Pg of C in the upper 100 cm, and 2376–2456 Pg of C in the upper 200 cm. Although deforestation, changes in land use and predicted climate change can alter the amount of organic carbon held in the superficial soil layers rapidly, this is less so for the soil carbonate carbon. An estimated 695–748 Pg of carbonate-C is held in the upper 100 cm of the world's soils. Mean C: N ratios of soil organic matter range from 9.9 for arid Yermosols to 25.8 for Histosols. Global amounts of soil nitrogen are estimated to be 133–140 Pg of N for the upper 100 cm. Possible changes in soil organic carbon and nitrogen dynamics caused by increased concentrations of atmospheric CO2 and the predicted associated rise in temperature are discussed.
Carbon (C) storage in biomass and soils is a function of climate, vegetation type, soil type and land management. Carbon storage was examined in intact indigenous vegetation and under different land uses in thicket (250–400 mm mean annual precipitation), xeric shrubland (350 mm), karoo (250 mm), and grassland (900–1200 mm). Carbon storage was as follows: (i) mean soil C (0–50 cm): thicket (T) = grassland (G) > xeric shrubland on Dwyka sediments (XS) > xeric shrubland on dolerite (XSD) > karoo (K) (168, 164, 65, 34 & 26 t ha−1, respectively); (ii) mean root C: T > G > XS = XSD (25.4, 11.4, 7.2 & 7.1 t ha−1); (iii) mean above-ground C including leaf litter: T>XS>G>K> XSD (51.6, 12.9, 2.0, 1.7 & 1.51 ha−1). Carbon stocks in intact indigenous vegetation were related more to woodiness of vegetation and frequency of fire than to climate. Biomass C was greatest in woody thicket and soil C stocks were greatest in thicket and grassland. Total C storage of 245 t ha−9 in thicket is exceptionally high for a semi-arid region and is comparable with mesic forests. Soil C dominated ecosystem C storage in grassland and was influenced more by soil parent material than land use. The semi-arid sites (xeric shrubland and thicket) were more sensitive to effects of land use on C storage than the grassland site. Effects of land use on C stocks were site- and land use-specific and defied prediction in many instances. The results suggest that modelling of national C stocks would benefit from further research on the interactions between C storage, land use, and soil properties.
Land use/cover changes in the temperate east Asia region has been a major factor in grassland ecosystem changes for a long period of time. Agricultural and livestock developments have been recorded for millennia in this region. These grasslands are composed of varying proportions of C3 and C4 plant species. This study was undertaken to quantify the C3 and C4 composition of the major grassland ecosystems of temperate east Asia. July wind speed (positive), June precipitation (negative), and the ratio of June-July evapo-transpiration potential to precipitation (positive) were the best predictors for soil carbon isotopes in these grasslands. Thus, C4 plant species were more favorable in water deficient conditions than C3 species. Recent change in land use practices, becoming more sedentary and increasing grazing intensity especially near settlements and water sources, was a main factor impacting on C4 plant cover in grasslands temperate east Asia.
Land degradation is recognized as a main environmental problem that adversely depletes soil organic carbon (SOC) and nitrogen (SON) stocks, which in turn directly affects soils, their fertility, productivity and overall quality. While it is expanding worldwide at rapid pace, quantitative information on the impact of land degradation on the depletion of SOC and SON stocks remains largely unavailable, limiting the ability to predict the impacts of land management on the C losses to the atmosphere and associated global warming. The main objective of this study was to evaluate the consequences of a decrease in grass aerial cover on SOC and SON stocks. A degraded grassland showing an aerial cover gradient from 100% (Cov100, corresponding to a non-degraded grassland) to 50–75% (Cov75), 25–50% (Cov50) and 0–5% (Cov5, corresponding to a heavily degraded grassland), was selected in South Africa. Soil samples were collected in the 0.05 m soil layer at 48 locations along the aerial cover gradient and were subsequently separated into the clay + silt (2–20 μm) and sand (20–2000 μm) fractions, prior to total C and N analysis (n = 288). The decline in grass aerial cover from 100% to 0–5% had a significant (P < 0.05) impact on SOC and SON stocks, with losses by as much as 1.25 kg m− 2 for SOC and 0.074 kg m− 2 for SON, which corresponded to depletion rates of 89 and 76%, respectively. Furthermore, both the C:N ratio and the proportion of SOC and SON in the silt + clay fraction declined with grass aerial cover, which was indicative of a preferential loss of easily decomposable organic matter. The staggering decline in SOC and SON stocks raises concerns about the ability of these acidic sandy loam soils to sustain their main ecosystem functions. The associated decrease in chemical elements (e.g., Ca by a maximum of 67%; Mn, 77%; Cu, 66%; and Zn, 82%) was finally used to discuss the mechanisms at stake in land degradation and the associated stock depletion of SOC and SON stocks, a prerequisite to land rehabilitation and stock replenishment.
We examined the distribution of soil organic carbon (SOC) fractions and roots with depth to improve our understanding of belowground carbon dynamics in the shortgrass steppe of northern Colorado. Weaver and others (1935) found that the surface 15 cm of soil contained over 70% of the total roots found in a tallgrass prairie soil profile, while only accounting for 40% of the profile soil organic matter. We asked whether the relationship between roots and SOC that Weaver and others (1935) found in the tallgrass prairie was also found in the shortgrass steppe. Weaver and others (1935) suggested that the dissimilarity between belowground biomass and SOC with depth is the result of variability in decomposition rates. In an effort to determine whether patterns of SOC are the result of short-term plant input patterns or decomposition, we measured the
14C content of potentially mineralizable C and particulate organic matter (POM) C ten years after pulse labeling shortgrass steppe vegetation. We also estimated the mass specific decomposition rate constant (kPOM) for POM C through a shortgrass steppe soil profile. We found that the distribution of roots and SOM in the shortgrass steppe were similar to those observed in tallgrass prairie (Weaver and others 1935), with a higher proportion of total root biomass in the surface soils than total soil organic matter. Fifty-seven percent of root biomass was found in the surface 15-cm, while this same soil layer contained 23 percent of profile soil organic C. We measured the highest accumulation of 14C at the soil surface (12.0 ng 14C·m-2·cm-1 depth), with the least accumulation from 75-100 cm (0.724 ng 14C·m-2·cm-1 depth). The highest values of potentially mineralizable C were at the soil surface, with no significant differences in total mineralizable C among the 10-100 cm soil depths. The contribution of POM C to total C reached a profile minimum at the 15-20 cm depth increment, with profile maxima in the surface 5 cm and from 75-100 cm. We estimated that the proportion of particulate organic matter lost annually (kPOM) reached a profile maximum of 0.097 yr-1 within the 10-15 cm depth increment. The 75-100 cm depth increment had the lowest kPOM value at 0.058 yr-1. Thus, within the same physical fraction of SOC, decomposition rates vary with depth by nearly twofold. This pattern of high decomposition rates from 10-15 cm with lower decomposition rates at the soil surface and deeper in the soil profile may be the result of higher water availability in sub-surface soils in the shortgrass steppe.
Soil carbon, a major component of the global carbon inventory, has significant potential for change with changing climate and human land use. We applied the Century ecosystem model to a series of forest and grassland sites distributed globally to examine largescale controls over soil carbon. Key site-specific parameters influencing soil carbon dynamics are soil texture and foliar lignin content; accordingly, we perturbed these variables at each site to establish a range of carbon concentrations and turnover times. We examined the simulated soil carbon stores, turnover times, and C:N ratios for correlations with patterns of independent variables. Results showed that soil carbon is related linearly to soil texture, increasing as clay content increases, that soil carbon stores and turnover time are related to mean annual temperature by negative exponential functions. The Century-predicted effect of temperature on carbon storage is modified by as much as 100% by the N cycle feedback. Century results further suggest that if climate change results in drying of organic soils (peats), soil carbon loss rates can be high. -from Authors
Worldwide concerns with global change and its effects on our future environment require an improved understanding of the impact of land cover changes on the global C cycle. Overgrazing causes a reduction in plant cover with accepted consequences on soil infiltration and soil erosion, yet the impact on the loss of soil organic carbon (SOC) and its associated processes remain unaccounted for. In this study performed in South Africa, our main objective was to evaluate the impact of plant cover reduction on (i) SOC erosion by water in both particulate (POC) and dissolved (DOC) forms, and (ii) soil CO2 emissions to the atmosphere. The study performed under sandy-loam Acrisols investigated three proportions of soil surface coverage by plants (Cov), from 100% (Cov100) for the “non-degraded” treatment to 25–50% (Cov50) and 0–5% (Cov5). POC and DOC losses were evaluated using an artificial rainfall of 30 mm h− 1 applied for a period of 30 min on bounded 1 × 1 m² microplots (n = 3 per treatment). CO2 emissions from undisturbed soil samples (n = 9) were evaluated continuously at the laboratory over a 6-month period. At the “non-degraded” treatment of Cov100, plant-C inputs to the soil profile were 1950 ± 180 gC m− 2 y− 1 and SOC stocks in the 0–0.02 m layer were 300.6 ± 16.2 gC m− 2. While soil-C inputs by plants significantly (P < 0.05 level) decreased by 38.5 ± 3.5% at Cov50 and by 75.4 ± 6.9% at Cov5, SOC, the losses by water erosion of 0.75 gC m− 2 at Cov100 increased from 66% at Cov50 (i.e. 3.76 ± 1.8 gC m− 2) to a staggering 213% at Cov5 (i.e. 7.08 ± 2.9 gC m− 2). These losses were for the most part in particulate form (from 88.0% for Cov100 to 98.7% for Cov5). Plant cover reduction significantly decreased both the cumulative C–CO2 emissions (by 68% at Cov50 and 69% at Cov5) and the mineralization rate of the soil organic matter (from 0.039 gC–CO2 gC− 1 at Cov100 to 0.031 gC–CO2 gC− 1 at Cov5). These results are expected to increase our understanding of the impact of land degradation on the global C cycle. Further in-situ research studies, however, need to investigate whether or not grassland degradation induces net C-emissions to the atmosphere.
Soil carbon, a major component of the global carbon inventory, has significant potential for change with changing climate and human land use. We applied the Century ecosystem model to a series of forest and grassland sites distributed globally to examine large-scale controls over soil carbon. Key site-specific parameters influencing soil carbon dynamics are soil texture and foliar lignin content; accordingly, we perturbed these variables at each site to establish a range of carbon concentrations and turnover times. We examined the simulated soil carbon stores, turnover times, and C:N ratios for correlations with patterns of independent variables. Results showed that soil carbon is related linearly to soil texture, increasing as clay content increases, that soil carbon stores and turnover time are related to mean annual temperature by negative exponential functions, and that heterotrophic respiration originates from recent detritus (~50%), microbial turnover (~30%), and soil organic matter (~20%) with modest variations between forest and grassland ecosystems. The effect of changing temperature on soil organic carbon (SOC) estimated by Century is dSOC/dT=183e-0.034T.Global extrapolation of this relationship leads to an estimated sensitivity of soil C storage to a temperature of -11.1 Pg°C-1, excluding extreme arid and organic soils.In Century, net primary production (NPP) and soil carbon are closely coupled through the N cycle, so that as temperatures increase, accelerated N release first results in fertilization response, increasing C inputs. The Century-predicted effect of temperature on carbon storage is modified by as much as 100% by the N cycle feedback. Century-estimated soil C sensitivity (-11.1 Pg°C-1) is similar to losses predicted with a simple data-based calculation (-14.1 Pg°C-1). Inclusion of the N cycle is important for even first-order predictions of terrestrial carbon balance. If the NPP-SOC feedback is disrupted by land use or other disturbances, then SOC sensitivity can greatly exceed that estimated in our simulations. Century results further suggest that if climate change results in drying of organic soils (peats), soil carbon loss rates can be high.
Stocks of soil C to a depth of 50 cm in untransformed, indigenous veld ranged from 21 t ha-1 in karoo to 168 t ha-1 in thicket and stocks of N ranged from 3.41 ha-1 in karoo to 12.8 t ha-1 in grassland. Mean soil C in thicket (5.6%, 0–10 cm) was approximately five times greater than expected for a semi-arid region. Removal of vegetation due to cultivation, grazing or burning reduced soil C and N at all sites. Soil C under intact thicket was greater than at sites degraded by goats (71 vs 40 t ha-1, 0–10 cm). Restoration of thicket could potentially sequester -40 t C ha-1. The sale of this sequestered carbon to the international market may make restoration of thousands of hectares of degraded thicket financially feasible. Soil C under plant cover was greater than In exposed soil in renosterveld (28 vs 15 t ha-1) and in karoo (7 vs 5 t ha-1). Parent material was also related to soil C content. In grassland, soil C was greater in dolerite-derived than sandstone-derived soils (54 vs 271 ha-1); and in bushveld it was greater in basalt-derived than granite-derived soils (28 vs 14 t ha-1 in unburnt plots). Annual burning in bushveld reduced soil C, particularly at the surface. Soil C in the 0–1 cm layer of unburnt plots was 2 to 3 times greater than in burnt plots.
Growing interest in the potential for soils to provide a sink for atmospheric C has prompted studies of effects of management on the amount and nature of soil organic C (SOC). In this study, we evaluated effects of different grazing management regimes (light grazing [LG], heavy grazing [HG], and non-grazed exclosures [EX]) on amount and composition of SOC at the USDA-ARS High Plains Grasslands Research Station (HPGRS), Cheyenne, WY. Soils (0-5 cm) from each treatment were analyzed for total C and N contents and lignin composition. Soil organic C and N contents were significantly greater in LG (SOC-13.8 Mg ha(-1); total N-1.22 Mg ha(-1)) than HG (SOC-10.9 Mg ha(-1); total N-0.94 Mg ha(-1)) or EX (SOC-10.8 Mg ha(-1); total N-0.94 Mg ha(-1)). From CuO oxidation studies, significantly greater (P < 0.05) total lignin (Vanillyl [V] + Syringyl [S] + Cinnamyl [C] compounds) contents were noted in EX (21 g kg(-1) SOC) than LG (12 g kg(-1) SOC) and HG (15 g kg(-1) SOC) soils. The lignin composition of humic (HA) and fulvic (FA) acids indicated that HA under LG contained significantly greater V and S than HG or EX. Fulvic acids contained S-depleted lignin compared with HAs and FAs from HG, which contained significantly greater V and C than FAs extracted from LG and EX. Nuclear magnetic resonance (NMR) spectra of HA and FA, however, did not vary significantly among the three grazing treatments. Results from CuO oxidation and NMR spectroscopy emphasized the familiar problem that determining the nature of soil organic matter (SOM) is a difficult task and sometimes different analytical techniques provide different information about the nature of SOM. Nonetheless, results of this study indicate that LG is the most sustainable grazing management system for northern mixed-grass prairies.
Soil organic matter is a major component of biogeochemical cycles and is important in maintaining soil quality. We investigated relationships between soil organic C and various soil and site properties that may influence long-term soil C accumulation across a range of soil orders in New Zealand. We used pedon and climatic data for 167 pedons under permanent grass, and carried out regression analysis between soil C (0–200 mm) contents (t/ha) or concentrations (g/kg) and climatic and soil properties, namely, precipitation, temperature, and contents or concentrations of sand, silt, clay, pyrophosphate- extractable Alpy, Fe oxide, and allophane. Soil clay content or concentration explained little of the variation in soil C across all soils (R2 0.05) and within each soil type. Likewise, mean annual precipitation and temperature explained little variation in soil C content or concentration (R2 0.15 for precipitation, R2 0.04 for temperature). Allophane content or concentration was unrelated to soil C in the soils of volcanic origin; Alpy, however, correlated strongly with both soil C content and soil C concentration across all soil types (R2 0.55 and 0.60 respectively). When all factors were combined in a multiple regression analysis, the combination of Alpy and allophane contents explained the greatest amount of variation in soil C content (R2 0.57), whereas the combination of Al , Fe oxide, allophane, and clay concentrations explained the greatest amount of variation in soil C concentration (R2 0.67). Our results suggest that in New Zealand soils, chemical stabilization of organic matter is the key process controlling soil C accumulation, and that clay content relates poorly to long-term soil organic C accumulation.
Soil carbon (C) is the largest C pool in the ter-restrial biosphere and includes both inorganic and organic components. Studying patterns and controls of soil C help us to understand and estimate potential responses of soil C to global change in the future. Here we analyzed topsoil data of 81 sites obtained from a regional survey across grasslands in the Inner Mongolia and on the Tibetan Plateau during 2006– 2007, attempting to find the patterns and controls of soil inor-ganic carbon (SIC) and soil organic carbon (SOC). The aver-ages of inorganic and organic carbon in the topsoil (0–20 cm) across the study region were 0.38 % and 3.63 %, ranging be-tween 0.00–2.92 % and 0.32–26.17 % respectively. Both SIC and SOC in the Tibetan grasslands (0.51 % and 5.24 % re-spectively) were higher than those in the Inner Mongolian grasslands (0.21 % and 1.61 %). Regression tree analyses showed that the spatial pattern of SIC and SOC were con-trolled by different factors. Chemical and physical processes of soil formation drive the spatial pattern of SIC, while bi-otic processes drive the spatial pattern of SOC. SIC was con-trolled by soil acidification and other processes depending on soil pH. Vegetation type is the most important variable driving the spatial pattern of SOC. According to our mod-els, given the acidification rate in Chinese grassland soils in the future is the same as that in Chinese cropland soils dur-ing the past two decades: 0.27 and 0.48 units per 20 yr in the Inner Mongolian grasslands and the Tibetan grasslands re-spectively, it will lead to a 30 % and 53 % decrease in SIC in the Inner Mongolian grasslands and the Tibetan grasslands respectively. However, negative relationship between soil pH and SOC suggests that acidification will inhibit decomposi-tion of SOC, thus will not lead to a significant general loss of carbon from soils in these regions.
The distribution of vegetational organic matter above- and below-ground and its productivity was analyzed in an alpine area along a climosequence ranging from subalpine to alpine climates. Emphasis is placed on the quantification of carbon (C) and nitrogen (N) fixed in the above-ground and below-ground vegetation and its annual input. Annual C-input ranged from 17.9 to 60.2 g m—2 year—1 and the N-input from 0.74 to 2.48 g m—2 year—1. Above-ground phytomass and the annual production rate of organic matter showed a distinct correlation with the altitude and, thus, the climate. However, the measurement of the above-ground phytomass is bound to methodological problems: the commonly used harvesting method seems to underestimate the real situation. The harvesting method yielded in its average 100 to 300 g m—2 phytomass which was 35—83% of the values obtained by the soil core method. Thus, the calculation of turnover times of above-ground vegetation greatly depends on the method used. Calculated turnover times based on the harvesting method did not correlate with the climate while a clear tendency of lower turnover times with increasing altitude could be observed using the soil core method. The amount of below-ground phytomass was in the range of 1880 to 2469 g m—2 and the corresponding annual C-input (fixation in the roots) between 91.1 and 162 g m—2 year—1 and the N-input between 2.68 and 4.99 g m—2 year—1. The below-ground phytomass and its production rate in high alpine zones are of greater importance and exceed the above-ground ones. With increasing altitude, furthermore, the importance of the below-ground phytomass increases with respect to the biomass and to the C- and N-input. For high alpine areas, the phytomass is concentrated in the uppermost soil horizons. About 88.7 to 94.5% of the below-ground phytomass was found in the soil compartment 0-20 cm. The below-ground production rate of phytomass in alpine grassland is fundamental in order to calculate any C or N budgets and potential inputs to SOM: its neglection would introduce most significant errors in modeling any C or N cycles.
Pastures at the High Plains Grasslands Research Station near Cheyenne, Wyoming, grazed for the past 11 yr at a heavy stocking rate (67 steer-d/ha) under three management systems, were compared to continuous light grazing (22 steer-d/ha) and to livestock exclosures. Carbon and nitrogen dynamics were greatest in the surface 30 cm where more than three-fourths of the plant root biomass exists. Grazing strategies and stocking ranges imposed for the past 11 yr on this mixed grass prairie did not detrimentally affect soil organic carbon and nitrogen levels. The data, in fact, suggest that responsible grazing enhanced the overall soil quality as assessed by these parameters. -from Authors
At Manyberries and Stavely, Alberta, Mixed prairie and Fescue Grassland ranges were grazed at various intensities for 19 and 22 years, respectively. In 1973, 13 chemical characteristics were determined on the organic matter developed in the soils of the ungrazed and heavy grazed treatments at the two locations. Samples were taken in spring, summer, autumn, and winter. Organic matter characteristics at both locations were closely associated with seasonal fluctuations and grazing-induced pressures; therefore, the time of sampling and the type of management before sampling soils should be defined in range studies. The results further emphasize the fragility of the equilibrium under which the organic matter of the soil of heavily grazed Mixed prairie at Manyberries forms and exists.
Alpine grassland and the soil on which it is growing in the Qinghai-Tibetan Plateau (QTP) of China is being degraded in an attempt to increase food and feed production for an increasing global population. Our objective was to use soil quality assessment to quantify changes in soil chemical and physical properties at three depth increments (0 to 4, 4 to 10, and 10 to 20 cm) and thus determine the linkages between soil and vegetation changes, the soil element(s) limiting grassland restoration in alpine region, and the ability to restore soil fertility by reestablishing grasslands. The soil and vegetation were sampled in the different types of degraded grasslands, that is, moderately degraded grassland (MDG), heavily degraded grassland (HDG) and severely degraded grassland (SDG) as well as in the reestablished grasslands at different ages, that is, 5-yr restored grassland (5yRG), 7-yr restored grassland (7yRG), and 9-yr restored grassland (9yRG) for comparative study. The results show: (i) decreased water holding capacity and increased soil hardness as vegetative cover declined, (ii) decreased soil organic carbon (OC) and total nitrogen (TN) and increased total soil potassium, (TK) (iii) the establishment of artificial grassland did not restore soil quality or nutrient stocks within degraded grassland soils, and (iv) yearly variations in soil properties at different depths were significant along the degree of grassland degradation. Significant variations of soil physical and chemical parameters might be attributed to loss of the top soil and changes of vegetation composition and soil and textures. Soil quality can be used to assess grassland degradation and restoration in the alpine region. In conclusion, better soil management is needed for restoring the degraded alpine grasslands on the QTP.
The effects of grazing on Stipa-Bouteloua prairie soils in Alberta were evaluated after 19 years of continuous summer use by sheep at three stocking intensities. Analysis of the soils under the heavy grazing treatment showed lower values for pH and percent spring moisture but higher values for total carbon (C), alcohol/benzene-extractable C, alkaline-soluble C, polysaccharides, and belowground plant material than the soil under light or no grazing. The results were attributed to changes in amounts and kinds of roots due to species changes caused by grazing and to increased amounts of manure deposited by sheep on fields grazed at a higher intensity. Shallow-rooted species replaced the deeper-rooted ones on the drier environment induced by heavy grazing.
Very heavy grazing of fescue grassland range at Stavely, Alberta, compared to light grazing, changed the color of the Ah horizon from black to dark brown and the pH from 5.7 to 6.2, reduced the percent organic matter, reduced percent total P but increased NaHCO3-soluble P, and increased soil temperature but decreased percent soil moisture. Trends indicated that soil of the very heavily grazed field was being transformed to a soil characteristic of a drier microclimate.
Measurements of carbon, nitrogen, and phosphorus content were carried out in the soils of a hillslope of shortgrass steppe. Plant biomass, soil morphology, and soil physical properties were also measured. Soil morphology indicated that the site had undergone several cycles of rapid erosion and deposition. Total mass of C, N, and P increased downslope, following a trend in soil depth, but the summit A horizon had higher C, N, and organic P concentrations than the backslope, reflecting a higher clay content. Laboratory and field incubations showed that N availability increased downslope, while relative N mineralization (N mineralized: total N) decreased. Organic matter content and mineralization rate were closely coupled to physical properties of the soil, which reflect the geomorphic history of the site.
As the largest pool of terrestrial organic carbon, soils interact strongly with atmospheric composition, climate, and land cover change. Our capacity to predict and ameliorate the consequences of global change depends in part on a better understanding of the distributions and controls of soil organic carbon (SOC) and how vegetation change may affect SOC distributions with depth. The goals of this paper are (1) to examine the association of SOC content with climate and soil texture at different soil depths; (2) to test the hypothesis that vegetation type, through patterns of allocation, is a dominant control on the vertical distribution of SOC; and (3) to estimate global SOC storage to 3 m, including an analysis of the potential effects of vegetation change on soil carbon storage. We based our analysis on >2700 soil profiles in three global databases supplemented with data for climate, vegetation, and land use. The analysis focused on mineral soil layers. Plant functional types significantly affected the v...
The influence of cattle grazing on selected vegetation and soil parameters were evaluated on a clay flat range site with shrub zonal, midgrass, and shortgrass communities in the Rolling Plains near Throckmorton, Texas. Measurements were made on one pasture of each treatment during 1977 following 4 to 20 years of grazing treatments. Heavy, continuous cattle grazing had more area occupied by the shortgrass community than midgrass community. Heavily grazed pastures were generally dominated by the shortgrass community, with midgrasses, depending on the degree of utilization, restricted to the shrub zonal community. Conversely, cattle exclosures had no shortgrass community, and deferred-rotation and moderately stocked continuously grazed systems had much midgrass community with the shortgrass community occupying only 30% of the area, thus increasing range productivity. Vegetation and soil parameters within the high intensity, low frequency and heavily stocked, continuously grazed pastures tended to be similar for the midgrass and shortgrass communities, but the shrub zonal community was generally different. Vegetation and soil parameters in the midgrass community of the moderately stocked, continuously grazed treatment were generally similar to shrub zonal and different from shortgrass communities. Vegetation and soil variables in the exclosures and deferred-rotation treatments were generally similar among the midgrass and shrub zonal communities; however, they differed from the shortgrass communities.
Impacts of long-term cattle grazing on litter and soil organic matter were assessed in mixed prairie, parkland fescue, and foot-hills fescue grasslands of Alberta, Canada. Grazing regimes were of light to very heavy intensities, grazed early, late, and continuously during the growing season. Litter and soil organic matter were sampled in O.l-rnz quadrats and removed as live vegetation, stand-ing Utter, fallen litter, and soil organic matter. Litter and organic matter samples were air dried and sorted by size using sieves and an automatic sieve shaker. Organic carbon content was determined by thermal oxidation. Ground cover was determined using point frames, and heights of standing litter and fallen litter were measured. Heavy intensity and/or early season grazing had greater nep-tive impacts on litter and soil organic matter than did light intensity and/or late season grazing. Under the former regimes there were significant reductions in heights of standing and fallen litter, decreases in live vegetative cover and organic matter mass, and increases in bare ground. More large particle-sized organic matter, particularly standing litter, occurred in controls than in grazed treatments since it would not be removed or trampled by grazing animals. More medium and small particle-sized organic matter occurred in grazed treatments than in ungrazed controls since vegetation likely decomposed more rapidly when it was trampled and broken down as animals grazed.
Three mixed prairie sites at Mandan, N.D. were grazed heavily (0.9 ha steer-1, moderately (2.6 ha steer-1), or left ungrazed (exclosure) since 1916. The increase in blue grama, a species with dense shallow root systems, in the heavily grazed pasture probably accounted for maintenance of soil carbon at levels equal to the exclosure. Changes in species composition from a mixed prairie to predominantly blue grama compensated for soil carbon losses that may result from grazing native grasslands. -from Authors
Management of soil organic matter (SOM) is esential to sustaining the quality and productivity of soils around the globe. This appears to be particularly true in the tropics where there is a greater proportion of nutrient poor, highly weathered soils that are more susceptible to losses of SOM. Developing management practices that promote the maintenance and storage of SOM in the tropics depends on understanding the factors that control SOM dynamics. This paper describes the role that soil physical properties (mineralogy, texture, and structure) play in regulating the accumulation and loss of SOM in tropical soils. Two different approaches are presented here. The first approach explores relationships between total SOM and soil physical properties in the tropics. These include effects of climate and mineralogy on latitudinal gradients in SOM, interactions between texture and mineralogy as determinants of SOM storage and relationships between SOM and the structural stability of soils. The second approach describes characteristics of SOM associated with different physical constituents of the soil, with particular attention to particle-size fractions and aggregated particles of different sizes. In each case we summarise findings on the distribution of SOM among fractions and characterise its biochemical composition, bioavailability and turnover. Evidence for and against the physical protection of organic matter from microbial attack in tropical soils is also given. Wherever possible, we compare and contrast the findings for tropical soils with those of temperate soils. The influence of landuse management on physical control of SOM dynamics is discussed as an overriding factor with each aproach.
Despite the importance of Arctic and boreal regions in the present carbon cycle, estimates of annual high-latitude carbon fluxes vary in sign and magnitude. Without accurate estimates of current carbon fluxes from Arctic and boreal ecosystems, predicting the response of these systems to global change is daunting. A number of factors control carbon turnover in high-latitude soils, but because they are unique to northern systems, they are mostly ignored by biogeochemical models used to predict the response of these systems to global change. Here, we review those factors. First, many northern systems are dominated by mosses, whose extremely slow decomposition is not predicted by commonly used indices of litter quality. Second, cold temperature, permafrost, waterlogging, and substrate quality interact to stabilize soil organic matter, but the relative importance of these factors, and how they respond to climate change, is unknown. Third, recent evidence suggests that biological activity occurring over winter can contribute significantly to annual soil carbon fluxes. However, the controls over this winter activity remain poorly understood. Finally, processes at the landscape scale, such as fire, permafrost dynamics, and drainage, control regional carbon fluxes, complicating the extrapolation of site-level measurements to regional scales.
We evaluated the impact of 7 years of grazing exclusion on vegetation and belowground properties related to soil carbon (C) and nitrogen (N) cycling in grazed, upland grassland in northern England. For this, we compared a landscape-level, moorland restoration project (grazing exclusion) with adjacent continuously grazed acidic grasslands to test whether changes in vegetation composition after restoration impacted on soil properties including soil C storage. Grazing exclusion significantly increased the proportion of dwarf-shrubs at the expense of graminoids. Despite high seasonal variability, this change in vegetation was associated with increased plant litter mass, soil moisture content and the ratio of dissolved organic to inorganic N, and reductions in rates of ammonium mineralisation, soil microbial activity, and microbial biomass N. Our observations suggest that grazing-exclusion as a restoration tool for upland habitats results in a slowing down of rates of C and N cycling. However, as yet, this has had no detectable impact on total C and N stocks in surface soil. Whereas increases in soil C and N stocks might be expected in the longer term, our results suggest that a certain level of grazing is compatible with the provision of ecosystem services such as soil C storage under traditional upland farming practices.
Stock farming plays an important role in the agriculture of alpine regions although deleterious effects on the soils are most pronounced here. We investigated the effects of cattle trampling on soil physical, chemical and microbial properties in a Swiss sub-alpine pasture. About 10% of the study site was bare of vegetation as a result of repeated cattle trampling and the bulk density of these bare steps was 20% higher than of the soils unaffected by trampling. In the upper 25 cm, soil organic carbon (SOC) concentrations and total SOC stocks were 35% and 20% respectively lower than on the vegetated slope. As compared with the vegetated slope, topsoils of the bare steps featured narrower C:N-ratios and were more enriched in the 15N isotope, with typical values of deeper soil layers. This indicates that bare soils primarily evolved by erosion and not by a compaction, which might, together with the reduced litter input, explain the lower SOC contents. The abundances of soil microbes, estimated by the concentrations of phospholipid fatty acid (PLFA), were 30% smaller in the bare soils than in the vegetated areas. This depletion was most pronounced for fungi as expressed in the lower concentrations of the fatty acid 18:2ω6.9 (45%) and ergosterol (50%). The lower fungal abundance very likely has negative consequences for the stability of the bare soils, since fungi play an important role in the formation of soil aggregates. In summary, our results show that cattle trampling decreases soil carbon storage and alters soil microbial community structure.
Changes in agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO 2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long-term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no-till (NT) can sequester 57 ± 14 g C m -2 yr -1 , excluding wheat (Triticum aestivum L.)-fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 ± 12 g C m -2 yr -1 , excluding a change from continuous corn (Zea mays L.) to corn-soybean (Glycine max L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.
Soil organic C and total N contents of grazed virgin grasslands have been used as the comparison standard to assess the change in soil organic matter (OM) generated by cultivation in the Northern Great Plains. The assumption has been that grassland soil properties were not altered by livestock grazing and therefore reflect the native grassland condition at the time man began cultivating for crop production. In this study, soil properties of grazed and nongrazed (relict) virgin grasslands are compared to assess the effect of grazing. Four sites each of moderately coarse‐, medium‐, and fine‐textured soils under grazed and under relict management were sampled at 0‐ to 0.076‐, 0.076‐ to 0.152‐, 0.152‐ to 0.305‐, and 0.305‐ to 0.457‐m depths. Analyses were made to compare organic C, total N, total P, organic P, and inorganic P contents, and bulk density between the management systems. Nutrient contents differed between the two management systems.
The largest content was not exclusively associated with either system; neither was the difference the same among textural groups or sampling depth. When averaged over all soil textures and depths, organic C and total P contents showed opposite trends from total N. Organic C and total P contents to 0.457 m were larger in relict grasslands by about 1.27 and 0.029 kg m ⁻² , respectively, while the total N content was larger in grazed grasslands by about 0.163 kg m ⁻² . Since the fencing of grasslands for livestock control about 75‐yr ago, differences between the two systems have developed at an average annual rate of about 165 kg C, 20 kg N, and 4 kg P ha ⁻¹ . Bulk densities were highest in grazed grassland in the uppermost 0.076 m. Based upon the organic C and total N contents in relict grasslands, reported losses of OM resulting from cultivation have been either over‐ or under‐estimated, depending on whether organic C or total N content in grazed grasslands has been used as the comparison standard.
The soil texture triangle used by the US Department of Agriculture is converted into a new texture diagram which contains all information in the original triangle, but additionally, gives mean particle size and particle size standard deviation of soil samples. Thus, mechanical analysis information on percents of clay, silt, and sand together with particle-size limits for clay, silt, and sand are found in a single unified system. The new diagram provides greater resolution in detecting classified soil samples within a texture region.-from Authors Soil textural classification oil texture triangle eometric mean particle size eometric mean tandard deviation echanical analysis article size.
On a sequence of soils developed under similar vegetation, temperature, and precipitation conditions, but with variations in mineralogical properties, we use organic carbon and 14C inventories to examine mineral protection of soil organic carbon. In these soils, 14C data indicate that the creation of slow-cycling carbon can be modeled as occurring through reaction of organic ligands with Al3+ and Fe3+ cations in the upper horizons, followed by sorption to amorphous inorganic Al compounds at depth. Only one of these processes, the chelation of Al3+ and Fe3+ by organic ligands, is linked to large carbon stocks. Organic ligands stabilized by this process traverse the soil column as dissolved organic carbon (both from surface horizons and root exudates). At our moist grassland site, this chelation and transport process is very strongly correlated with the storage and long-term stabilization of soil organic carbon. Our 14C results show that the mechanisms of organic carbon transport and storage at this site follow a classic model previously believed to only be significant in a single soil order (Spodosols), and closely related to the presence of forests. The presence of this process in the grassland Alfisol, Inceptisol, and Mollisol soils of this chronosequence suggests that this process is a more significant control on organic carbon storage than previously thought.
Acidic soil pH may affect decomposition of added organic materials in humid tropical forest soils. Our objective was to determine the effects of soil pH on decomposition of added organic materials to tropical forest soils of different soil texture and clay mineralogy. Release of 14CO2 and microbial biomass 14C were measured during a 270-d incubation at 25°C after either [14C]glucose or 14C-labeled blue grama grass (Bouteloua gracilis) material had been added to 13 tropical forest smectitic, kaolinitic, oxidic or allophanic mineralogies. Initial soil pH ranged from 3.9 to 6.7. An additional investigation examined 14CO2 release from kaolinitic or oxidic forest soils to which either Ca(OH)2 or CaSO4 had been previously applied to obtain 5 soil pH values. Initial soil pH and cumulative 14CO2 release in glucose-amended soils were positively related only after 1 and 4 d. In contrast, plant-residue-amended soils had positive relationships between initial soil pH and cumulative 14CO2 release after 7 d and continued with that relationship up to 270 d. Microbial biomass 14C was reduced at lower pH values in both glucose-and plant-residue-amended soils after 270 d. Water-extractable 14C was also higher at pH > 5.5 in plant-residue-amended soils after 58 d. Differences in soil texture and clay mineralogy had no apparent effect on the relationship between soil pH and decomposition. Simulated results of the experiment using the CENTURY Soil Organic Matter Model diverged from observed results for soils with pH < 6.5. Further research is required to determine the effects of acidic soil pH on decomposition rates of stable C pools and to develop functions for simulation models to account for the short- and long-term effects of soil acidity on decomposition.
The nature of organic carbon in the < 2, 2–20, 20–53, 53–200, and 200–2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS). Analyses were repeated after high energy ultraviolet photo-oxidation was performed on the three finest fractions. All four soils, studied contained appreciable amounts of physically protected carbon while three of the soils contained even higher amounts of charcoal. It was not possible to measure the charcoal content of soils directly, however, after photo-oxidation, charcoal remained and was identified by its wood-like morphology revealed by scanning electron microscopy (SEM) together with a highly aromatic chemistry determined by solid state 13C n.m.r. Charcoal appears to be the major contributor to the 130 ppm band seen in the n.m.r. spectra of many Australian soils. By using the aromatic region in the n.m.r. spectra, an approximate assessment of the charcoal distribution through the size fractions demonstrated that more than 88% of the charcoal present in two of the soils occurred in the < 53 µm fractions. These soils contained up to 0.8 g C as charcoal per 100 g of soil and up to 30% of the soil carbon as charcoal. Humic acid extractions performed on soil fractions before and after photo-oxidation suggest that charcoal or charcoal-derived material may also contribute significantly to the aromatic signals found in the n.m.r. spectra of humic acids. Finely divided charcoal appears to be a major constituent of many Australian soils and probably contributes significantly to the inert or passive organic carbon pool recognised in carbon turnover models.
The Tibetan Plateau is an essential area to study potential feedback effects of soils to climate change due to the rapid rise of air temperature in the past several decades as well as the large amounts of organic carbon (Corg) stored in soils, particularly in permafrost-affected areas. In order to predict the impact of environmental change on ecosystem functioning, it is of great importance to understand how Corg and soil nitrogen (N) stocks are controlled under changing climate conditions in extreme environments. We therefore investigated the main parameters influencing Corg and N at 47 sites along a 1,200 km transect across the high-altitude and low-latitude permafrost region of the central-eastern Tibetan Plateau. Sites with continuous or discontinuous permafrost as well as areas without or heavily degraded permafrost were studied for comparison of soil dynamics under various environmental settings. Due to the high number of samples and the large-scale transect concept, sophisticated statistical analyses showing significant relationships between pedological parameters as well as Corg and N contents were carried out. The aim of the presented research was to evaluate consequences of permafrost degradation for C and N stocks and hence nutrient supply for plants. The landscape along the investigated transect is a patchwork of geochemically very diverse micro-ecosystems showing variations in organic matter, nutrient stocks, plant communities and productivity. These differences are closely related to topographic position, hydrological regimes and consequently permafrost distribution. The main controlling mechanisms of this heterogeneity on the Tibetan Plateau are related to different soil drainage classes. Ecosystem ecology has traditionally focused on temperature and modeled soils mostly as an ecosystem feature whose attributes vary strongly by thermodynamic principles. However, the general linear regression model (GLM) suggests soil moisture as the most important parameter explaining 64% of Corg and 60% of N variation. The explanatory power of the GLM for C and N concentrations is significantly improved by adding two parameters for pedogenesis to the model, i.e. CaCO3 and soil texture. The extent of the effect of soil moisture is determined by permafrost, current aeolian sedimentation occurring mostly on sites with permafrost degradation, and pedogenesis. We conclude that degradation of permafrost and corresponding changes in soil hydrology combined with a shift from mature stages of pedogenesis to initial stages, have severe impact on soil carbon and importantly on plant available N. Our study shows that other factors than temperature are more important between years and sites at regional and continental scales. Temperature dependence may rather be relevant for ecosystems when soil moisture or other factors are not limiting or altering the relationship between temperature and soil processes. Soil respiration data demonstrate that biomass and particularly belowground biomass as well as soil water content are determinant of spatial variation of soil respiration across the plateau. In summary, both stocks (Corg and N) are coupled with complex feedback mechanisms between permafrost, aeolian processes and the stage of pedogenesis. The latter can be described by acidity, carbonate content and grain size distribution.
In many cases, ecosystems in the puna or grasslands in the Andean plateaus are degraded as a consequence of anthropogenic activities. The Apolobamba Integrated Management National Area is located in the Northwest of La Paz (Bolivia). This grassland ecosystem, with a high biodiversity, is a natural habitat of camelid populations, such as vicuna (Vicugna vicugna), a wild endangered species, and alpaca, a domestic camelid. There is not much information related to carbon reservoirs and camelid influence in these ecosystems. The objectives of this study were to (i) quantify total SOC contents as well as its quality by applying 13C CP/MAS-Nuclear magnetic resonance spectroscopy, and (ii) determine the degree in soil exhaustion in selected zones on the basis of the degradation of SOM, related to vicuna and alpaca populations in Apolobamba. The vicuna densities were considered to select the studied zones as well as other characteristics. The goals of this research were achieved through the analyses of soil organic carbon quantity in soil profiles and in sampling plots. Likewise the 13C CP/MAS-Nuclear magnetic resonance technique was used to gain information about soil carbon quality. Based on Total Organic Carbon contents and functional carbon groups we classified the area into three groups: 1) High, with O-Alkyl-C (50–112ppm) contents between 44% and 41% (zones 8, 4, 5, 7, 2 and 6), 2) Medium, 39% (zone 1), and 3) Low, 36% (zone 3). These results and the Alkyl-C/O-alkyl-C ratios (above 0.7) indicated Soil Organic Matter with a low stabilization. Overall Nuclear Magnetic Resonance spectra pointed out that the degradation of Soil Organic Matter was higher in zones 1 and 3 than in other studied areas in connection with high alpaca concentration. Although, results showed that some studied zones could be excellent carbon reservoirs we suggest that these three zones should be specifically protected from camelid overexploitation to avoid the soil exhaustion and preserve high grassland ecosystems and its biodiversity in the Apolobamba area.
Changes in land use and vegetation cover affect various soil properties, including the soil organic carbon (SOC) pool and the transfer of atmospheric CO2 to terrestrial landscapes. In natural or quasi-natural conditions a reduction in biomass increases the risk of erosion, and can reduce the stored soil organic matter content. This can cause (i) consolidation of low levels of organic carbon stored in the soil; (ii) reduction in the levels of organic carbon because of the onset of erosion processes; and (iii) differing rates of recovery of the soil in response to environmental factors including precipitation, which is a principal agent of indirect recharge of soil organic matter.Few comparable studies have analyzed the reduction of SOC because of erosion, and assessed how this contributes to the loss of soil as vegetation cover decreases. This is particularly the case in semiarid Mediterranean environments, where erosion is one of the main causes of soil degradation.This study presents the results of an experiment carried out along a pluviometric gradient from humid to semiarid Mediterranean conditions, in southern Spain. The study involved two soil depths at five field sites having similar lithology, slope and aspect, but differ in vegetation cover and composition related to their location along the gradient. We used soil cation exchange capacity (CEC) as an indicator of soil degradation.The results showed that: a) SOC decreased with decreasing rainfall; b) SOC is greater at the soil surface than at depth; c) CEC is a good indicator of the degradation of soil surface formations, as it is directly related to the SOC storage capacity; and d) the so-called “Mediterranean mountain” landscape, with sparse and mixed vegetation composed of scrubland and woodland species, is a good organic carbon sink with direct implications in relation to climate change.
Used a model of soil organic matter (SOM) quantity and composition to simulate steady-state organic matter levels for 24 grassland locations. The model was able to simulate the effects of climatic gradients on SOM and productivity. Soil texture was also a major control over organic matter dynamics. Regional trends in SOM can be predicted using temperature, moisture, soil texture, and plant lignin content. Nitrogen inputs must also be known. Grazing intensity during soil development is also a significant control over steady-state levels of SOM. -from Authors
Understanding how terrestrial ecosystems function requires a combined aboveground-belowground approach, because of the importance of feedbacks that occur between herbivores, producers, and the decomposer subsystem. In this paper, we identify several mechanisms by which herbivores can indirectly affect decomposer organisms and soil processes through altering the quantity and quality of resources entering the soil. We show that these mechanisms are broadly similar in nature for both foliar and root herbivory, regardless of whether they operate in the short term as a result of physiological responses of individual plants to herbivore attack or long-term following alteration of plant community structure by herbivores and subsequent changes in the quality of litter inputs to soil. We propose that a variety of possible mechanisms is responsible for the idiosyncratic nature of herbivore effects on soil biota and ecosystem function; positive, negative, or neutral effects of herbivory are possible depending upon the balance of these different mechanisms. However, we predict that positive effects of herbivory on soil biota and soil processes are most common in ecosystems of high soil fertility and high consumption rates, whereas negative effects are most common in unproductive ecosystems with low consumption rates. The significance of multiple-species herbivore communities is also emphasized, and we propose that if resource use complementarity among herbivore species or functional groups leads to greater total consumption of phytomass, and thus greater net herbivory, then both positive and negative consequences of increasing herbivore diversity for belowground prop- erties and processes are theoretically possible. Research priorities are highlighted and in- clude a need for comparative studies of herbivore impacts on above- and belowground processes across ecosystems of varying productivity, as well as a need for experimental testing of the influence of antiherbivore defense compounds on complex multitrophic in- teractions in the rhizosphere and the significance of multiple herbivore species communities on these plant-soil interactions.
Interactions between polyacrylamides (PAMs) and clay minerals are the primary reactions in most applications of the water-soluble polymers. Our main objectives were to study (i) the effects of charge of PAM on the flocculation/dispersion of clay suspensions and on the adsorption of the polymers on clays, and (ii) the surface properties of PAM-clay complexes. Three PAMs—an anionic PAM 836A, a nonionic PAM 903N, and a cationic PAM 494C—were used to react with three common clay minerals—smectite, kaolinite, and illite. In the polymer concentration range tested (0-1.2 g L 21 ), the anionic PAM 836A increased the dispersion of the clay suspensions but the cationic PAM 494C promoted the flocculation. The strong flocculation func- tion of cationic PAM 494C made trapped clay particles inaccessible for adsorption despite its highest affinity for clay surfaces. The adsorption of the polymers was irreversible. Nonionic PAM 903N and cationic PAM 494C intercalated smectite but anionic PAM 836A did not. The adsorbed polymer moderately altered the charge properties: the cation exchange capacity (CEC) and the abilities to remove heavy metal Cu and Cr had the following order: anionic PAM 836A-clay . nonionic PAM 903N-clay » clay . cationic PAM 494C-clay. The PAM-clay complexes did not showdistinct adsorption for hydrophobic chlorophenols, indicating that the adsorbed polymers did not increase the hydrophobicity of the clay surfaces.
Grassland soils in Northern China are being seriously degraded under cultivation and grazing. This study investigated the impacts of land use on soil erosion and soil fertility in alpine grassland of China. Land uses included three levels of pasture degradation, lightly (LDP), moderately (MDP), and heavily degraded pasture (HDP) classified based on vegetation cover, and cultivated fields ranging from 1 to 50 yr of cultivation. Soil samples were collected from 18 sites at seven locations in Chernozemic soils between elevations of 2600 to 3000 m. Soil erosion was estimated by 137Cs radioactivity. When pasture was heavily degraded, 137Cs activity was significantly reduced, and organic C (OC), total N, and cation-exchange capacity declined by 33, 28, and 18% respectively. Cultivation of grassland worsened soil erosion, and after 8-, 16-, and 41-yr cultivation soil OC decreased by 25, 39, and 55%, respectively. Regionally, 59% of OC was lost within 30 to 50 yr of cultivation. There were concomitant losses of total N and exchange capacity. On cultivated soils, soil erosion and mineralization were equally responsible for organic C losses. Pasture degradation and cultivation also caused changes in soil P. Mineralization of organic P, incorporation of subsoil by tillage following erosion, and fertilization increased levels of Ca-P in cultivated fields. This study indicated that grassland degradation and cultivation caused not only severe soil erosion, but also fertility decline and chemical changes of P dynamics.
We measured 14C/12C in density fractions from soils collected before and after atmospheric thermonuclear weapons testing to examine soil organic matter (SOM) dynamics along a 3 million year California soil chronosequence. The mineral-free particulate organic matter (FPOM; 2.2 g cm−3) consists of relatively OM-free sand and OM-rich clays. Three indicators of decomposition (C:N, δ13C, and δ15N) all suggest increasing SOM decomposition with increasing fraction density. The Δ14C-derived SOM turnover rates suggest that ≥90% of FPOM turns over in