Article

Change in soil organic carbon between 1981 and 2011 in croplands of Heilongjiang Province, northeast China

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Abstract

BACKGROUND Soil organic carbon (SOC) is fundamental for mitigating climate change as well as improving soil fertility. Databases of SOC obtained from soil surveys in 1981 and 2011 were used to assess SOC change (0–20 cm) in croplands of Heilongjiang Province in northeast China. Three counties (Lindian, Hailun and Baoqing) were selected as typical croplands representing major soil types and land use types in the region. RESULTS The changes in SOC density (SOCD) between 1981 and 2001 were −6.6, −14.7 and 5.7 Mg C ha−1 in Lindian, Hailun and Baoqing Counties respectively. The total SOC storage (SOCS) changes were estimated to be −11.3, −19.1 and 16.5% of those in 1981 in the respective counties. The results showed 22–550% increases in SOCS in rice (Oryza sativa L.) paddies in the three counties, but 28–33% decreases in dry cropland in Lindian and Hailun Counties. In addition, an increase of 11.4 Mg C ha−1 in SOCD was observed in state-owned farms (P < 0.05), whereas no significant change was observed in family-owned farms. CONCLUSION Soil C:N ratio and initial SOCD related to soil groups were important determinants of SOCD changes. Land use and residue returning greatly affected SOC changes in the study region. To increase the topsoil SOCD, the results suggest the conversion of dry croplands to rice paddies and returning of crop residue to soils. © 2015 Society of Chemical Industry

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... However, many of these results are fraught with regional data uncertainty resulting in unreliable data at larger scales, for the following reasons. First, many previous studies mainly focused on top 20 cm soil (Li et al., 2016;Pan et al., 2009;Zhao et al., 2015), despite a considerable fraction of total SOC stock stored in the subsoil (Jandl et al., 2014;Jobbagy and Jackson, 2000) should not be neglected. Second, SOC content or soil bulk density (BD) data were often deficient when estimating SOC stock in regional scale studies. ...
... The main crops include maize (Zea mays L.), soybean (Glycine max L.), and rice. Other detailed description can be seen in Li et al. (2016). ...
... In our study, the maximum county value of SOCD was located at north for Lindian, central in Hailun, and southwest in Baoqing Counties. The distribution pattern is likely owing to the difference in the air temperature, monsoon circulation, intensive cultivation, and land reclamation time (Li et al., 2016;Liu et al., 2006a). However, these related data (e.g., cultivation history) are lacking in our study area, and thus future studies are needed to allow future enhancements to the soil C model. ...
... Mollisols are widely distributed in northeastern China (i.e., black soil region) with a dark soil surface. In this region, maize production accounts for approximately 31.2% of the total national maize yield, where Mollisols are an important regulator for high crop production in order to maintain national food security (Wang et al. 2014;An et al. 2015;Li et al. 2016). However, improper management in addition to the large-scale use of small agricultural machines has compacted the soil layer, resulting in a plow pan in the subsoil (Batey 2010;Feng et al. 2018), which degrades soil fertility. ...
... However, improper management in addition to the large-scale use of small agricultural machines has compacted the soil layer, resulting in a plow pan in the subsoil (Batey 2010;Feng et al. 2018), which degrades soil fertility. Consequently, productivity mainly depends on the proper soil structure and soil organic matter (SOM) that is currently less than half of its initial amount (Yang et al. 2003;Li et al. 2016). Although subsoiling can partially resolve the problem, soil quickly returns to the sticky state because of the stickiness of the soil. ...
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PurposeSubsoil has great potential for increasing soil organic carbon (SOC) stock. Soil compaction decreases the content of SOC in the topsoil layer and leads to the formation of a plow pan in subsoil. However, measures for improving poor soil structure mainly concentrate on topsoil. This study aims to understand the effect of subsoiling management practices on soil aggregation and accumulation of SOC in both topsoil (0–20 cm) and subsoil (20–35 cm).Materials and methodsA field experiment was carried out in a Mollisol in northeastern China. The treatments included conventional tillage (CT), subsoiling tillage (ST), and subsoiling with residue incorporation tillage (SST).Results and discussionThe results showed that in comparison to CT, ST and SST not only had lower subsoil bulk densities (reduced by 9.42% and 13.61%, respectively) but also promoted the formation of macroaggregates (> 250 μm) in both soil layers; thus, soil structure stability increased. In the topsoil layer, the content of the > 53 μm aggregate-associated carbon (C) under ST and SST was greater than that under CT. In the subsoil layer, compared with CT, SST increased the organic C content (increased by 0.73–12.32%) in all the aggregate classes, but ST decreased the content of the < 2000 μm aggregate-associated C (6.09–18.96%) on day 150. The soil structure stability decreased by 13.06% and 22.21% under ST and SST after day 150, respectively, which was probably due to the clayey characteristics of the subsoil.Conclusions We concluded that subsoiling would only improve the soil structure while increasing the loss of organic C. However, the effect of subsoiling on structure improvement was enhanced by residue incorporation, not only promoting soil aggregation but also increasing SOC accumulation.
... In China, SOCD increased in eastern and northern China and decreased in northeastern China[43,54]. In Lindian, Hailun and Baoqing of Heilongjiang Province, northeast China, the SOCD in croplands between 1981 and 2011 decreased by 6.6, 14.7 and 5.7 Mg·C·ha −1 , respectively[55]. However, the topsoil of SOCD in croplands increased significantly from 1980 to 2010, with an average increase of 0.56 kg·C·m −2 in the Songnen Plain of Northeast China[8]. ...
... This decrease was also observed by earlier studies in the northeastern part of China. In Heilongjiang, the total SOC storage of croplands decreased by 11.3% and 19.1% from 1981 to 2011 in Lindian and Hailun, respectively[55], whereas, in China, it increased with exception of Northeast China[43]. A declining trend was also found in Europe, including Finland[7], England and Wales[59]. ...
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Soil is the largest pool of terrestrial organic carbon in the biosphere and interacts strongly with the atmosphere, climate and land cover. Remote sensing (RS) and geographic information systems (GIS) were used to study the spatio-temporal dynamics of croplands and soil organic carbon density (SOCD) in the Sanjiang Plain, to estimate soil organic carbon (SOC) storage. Results show that croplands increased with 10,600.68 km² from 1992 to 2012 in the Sanjiang Plain. Area of 13,959.43 km² of dry farmlands were converted into paddy fields. Cropland SOC storage is estimated to be 1.29 ± 0.27 Pg·C (1 Pg = 10³ Tg = 10¹⁵ g) in 2012. Although the mean value of SOCD for croplands decreased from 1992 to 2012, the SOC storage of croplands in the top 1 m in the Sanjiang Plain increased by 70 Tg·C (1220 to 1290). This is attributed to the area increases of cropland. The SOCD of paddy fields was higer and decreased more slowly than that of dry farmlands from 1992 to 2012. Conversion between dry farmlands and paddy fields and the agricultural reclamation from natural land-use types significantly affect the spatio-temporal patterns of cropland SOCD in the Sanjiang Plain. Regions with higher and lower SOCD values move northeast and westward, respectively, which is almost consistent with the movement direction of centroids for paddy fields and dry farmlands in the study area. Therefore, these results were verified. SOC storages in dry farmlands decreased by 17.5 Tg·year⁻¹ from 1992 to 2012, whilst paddy fields increased by 21.0 Tg·C·year⁻¹.
... The region of black soils accounts for approximately 14% of crop production and 40% of soybean (Glycine max (L.) Merrill.) nationwide (Liu et al., 2005), and thus an important soil resource for crop production in China and plays a unique and central role in national food security (Li et al., 2016). Nevertheless, the region contributes heavily to climate change due to its high soil organic C (SOC) content and high potential of CO 2 evolution (Li et al., 2013). ...
... Nevertheless, the region contributes heavily to climate change due to its high soil organic C (SOC) content and high potential of CO 2 evolution (Li et al., 2013). Due to intensive cultivation combined with lack of organic material inputs, however, the black soils have experienced increased degradation over the past several decades, especially evident in decline of SOC (Li et al., 2016), which resulted in decreased soil fertility as well as exerted an adverse effect on climate change. In order to maintain and improve soil fertility of the degraded black soils, application of organic amendments was advocated in this region to increase SOC content and crop yield. ...
... higher under application of manure, chemical fertilizers, and manure plus chemical fertilizers than without fertilizer application. The C sequestration per unit area in equilibrium based on SOC balance modeling indicated that the C stabilization potential would be 8.98 kg m −2 ( Li et al. 2016). The results may not reach the maximum C sequestration under the saturation state, but they can provide a realistic basis for the study of regional C sequestration through the simulation of SOC sequestration potential in different fertility regions ( Jiang et al. 2018). ...
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Purpose Mollisols are the most fertile, high-yielding soils in the world. During the past several decades, Mollisols have lost about 50% of their antecedent organic carbon (C) pool due to soil erosion, degradation, and other unsuitable human activities. Therefore, restoring soil organic C (SOC) to Mollisols via reasonable management is crucial to sustainable development and is important for environmental stability. However, the existing literature on SOC and soil quality has focused on one soil type or on a given region where Mollisols occur, and the degree of SOC depletion and stabilization in Mollisols have not been comprehensively evaluated. Overall, we propose to develop an optimum scheme for managing Mollisols, and we outline specific issues concerning SOC restoration and prevention of SOC depletion. Materials and methods In this review, we identify the uncertainties involved in analyses of SOC in Mollisols as related to management practices. According to the existing literature on SOC in Mollisols at the global scale, we analyzed the results of SOC depletion research to assess management practices and to estimate the C amount stabilized in Mollisols. Results and discussion The review shows that the SOC stocks in Mollisols in North America under cropped systems had 51 ± 4 (equiv. mass) Mg ha⁻¹ in the top 30 cm soil layer. The SOC contents in Northeast China decreased from 52 to 24 g kg⁻¹ (46%) after 150 years of cultivation management. All of the Mollisols regions in the world are facing the challenge of SOC loss, and this trend could have a negative influence on global climate change. Hence, it is very important to take proper measures to maintain and enhance organic C contents in Mollisols. Conclusions We concluded that reasonable management practices, including no-tillage, manure and compost fertilization, crop straw returning, and mulching cultivation, are the recommended technologies. The C restoration in Mollisols is a truly win-win strategy for ensuring the security of food and soil resources while effectively mitigating global climate change. Thus, more attention should be given to protective management and land use for its impacts on SOC dynamics and soil properties in Mollisols regions.
... The average annual precipitation ranges from 500 to 600 mm, with 60-70% occurring from June to August. The main soil types are Luvic Phaeozem and Haplic Phaeozem based on the United Nations Food and Agriculture Organization (FAO) classification ( Li et al., 2016). The soil is in a frozen state from late October to middle May. ...
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Automatic leaf area index (LAI) measurements are important for obtaining sufficient amounts of field data over an extended period of time. A seasonal field campaign was carried out to obtain continuous LAI measurements over maize, soybean, and sorghum fields in northeast China in 2016. Field LAI measurements were acquired with the automatic PASTIS-57 (PAI Autonomous System from Transmittance Instantaneous Sensed from 57°) instrument and two smartphone applications, PocketLAI and LAISmart. These measurements were compared with data obtained using the LAI-2200 Plant Canopy Analyzer, digital hemispherical photography (DHP), and destructive sampling measurements. The effective plant area index (PAIeff) estimates from LAI-2200 and DHP are consistent over the season, with the overall relative errors (RE) of less than 5%. The PASTIS-57 data exhibit a small underestimation of the LAI-2200 and DHP values (RE < 20%). The relative errors for the LAISmart data are between −20% and −30%. PocketLAI significantly underestimates the LAI-2200 values (RE > 40%) and saturates at around PAIeff = 3.5. The canopy clumping index (CI) exhibits an S-shaped seasonal variation that decreases with the increase of PAIeff during the vegetative growth stage but increases after this stage. PASTIS-57 shows great potential for obtaining continuous LAI measurements in agricultural crop fields, but the smartphone applications should be further examined before they can be used for research purposes. The data collected in this study are valuable for the validation of remote sensing products.
... SOC contents in cropland with long-term application of NPK fertilizers tend to decrease. Also,Li et al. (2016) showed that during 1982-2011 the mean SOC concentration decreased by more than 10% in croplands of Heilongjiang Province of northeast China, where the soil has the similar properties with that in the present long-term experiment. The decrease in SOC in this Chinese black soil can beDownloaded by [Tufts University] at 20:of global climate change and intensive agricultural managements (Zhang et al. 2016). ...
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... Manure application is an eff ective and economic way to restore eroded soils (Liu et al., 2011;Lundekvam et al., 2003;Ramos et al., 2006). Th e use of manure, compost, crop residues, and biosolids is the most common recommendation for improving SOM content, and thus enhancing SOC storage (Brejda et al., 2000;Li et al., 2015). Some studies reported that SOC declined in long-term unfertilized soils, while the application of chemical NPK fertilizers alleviated this reduction or maintained SOC constantly (Brar et al., 2013;Choudhary et al., 2013;Manna et al., 2005;Su et al., 2006). ...
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By searching literature databases, we obtained more than 200 articles published since 1993 that related to the measurements of topsoil organic carbon (SOC) in different regions. To objectively evaluate the changes in the SOC over the last two decades, we selected 132 representative articles from these documented articles. More than sixty thousand soil samples and/or sampling sites were included in the selected articles. Results from analyzing these data sets indicated that the concentration of SOC increased in 53%–59%, decreased in 30%–31% and stabilized in 4%–6% of the national croplands, respectively. A further investigation showed that the total increment of SOC in Chinese croplands ranged from 311.3 Tg to 401.4 Tg. In terms of administrative region, significant increase occurred in eastern and northern China and decrease in northeastern China, respectively. When evaluated by soil great groups, the SOC increased considerably in paddy soils and fluvo-aquic soils and reduced conspicuously in black soils. The increase of SOC is attributed to the amendments of crop residues and organic manure, the augment of synthetic fertilizer application and the optimal combination of nutrients, and the development of no-tillage and reduced-tillage practice. Water loss and soil erosion and low input induced a great decrease of the SOC in black soils. In order to effectively enhance soil C sequestrations and to greatly control the SOC reduction in northeastern China, future efforts should be made in developing new techniques, training farmers and consummating the policy of governmental compensation, by which the application of crop straw, the improvement of fertilization, the practice of no-tillage and reduced-tillage, and the control of water loss and soil erosion could be further realized. To respond to the increasing pressure from the Kyoto Protocol thenceforward, four aspects were further addressed for future research needs, including the quantification of SOC storage in the Second State Soil Survey and at present, the understanding of control mechanisms in both anthropogenic and non-anthropogenic causes that determine SOC dynamics, the investigation of options that can effectively enhance SOC sequestration and/or reduce SOC loss, and the assessments of potentials and the likely SOC dynamics in the future on a national scale.
Article
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The carbon sink capacity of the world's agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.
Article
Soil C sequestration in cropland could play an important role in mitigating the rapidly increasing CO2 emissions in China. Many efforts had been dedicated to estimating the potential for C sequestration in croplands. Potential increases in SOC in China's croplands had been recently evaluated using inventory-up-scaling simulation and crop-soil C process-based modeling. In this study, data of SOC change at monitoring sites from croplands across mainland China were collected from publications available from 1985 to 2006 to perform a statistical analysis. The data set comprises 1081 observations (404 from rice paddies, RPs and 677 from dry croplands, DCs). Frequency analysis indicates that over 70% of observations show an increase in SOC, which is higher among RPs than DCs. To quantify SOC dynamics, a Relative Annual Change Index in g kg−1 year−1 (RAC, g kg−1 year−1) is defined and calculated using the initial and final SOC values for the duration of monitored observations. RAC values ranged from −0.806 to 0.963 g kg−1 year−1 for DCs and from −0.597 to 0.959 g kg−1 year−1 for RPs, respectively. From this data, the average is estimated to be 0.056 ± 0.200 g kg−1 year−1 for DCs, and 0.110 ± 0.244 g kg−1 year−1 for RPs, with an overall estimate for China's croplands, with RPs and DCs combined, of 0.076 ± 0.219 g kg−1 year−1. A mean increase in topsoil C (0–20 cm) stock of China's croplands was estimated to be 25.5 Tg C year−1 (8 Tg C year−1 in RPs and 17.5 Tg C year−1 in DCs) between 1985 and 2006, with a total topsoil C stock increase of 0.64 Pg C over the whole period. The annual stock increase may offset ∼20%, on average, of the total CO2 emissions of China for 1994. This study suggests an important role of China's croplands, especially rice paddies, for C sequestration to mitigate climate change.
Article
Land-use change (LUC) is a major driving factor for the balance of soil organic carbon (SOC) stocks and the global carbon cycle. The temporal dynamic of SOC after LUC is especially important in temperate systems with a long reaction time. On the basis of 95 compiled studies covering 322 sites in the temperate zone, carbon response functions (CRFs) were derived to model the temporal dynamic of SOC after five different LUC types (mean soil depth of 30 +/- 6 cm). Grassland establishment caused a long lasting carbon sink with a relative stock change of 128 +/- 23% and afforestation on former cropland a sink of 116 +/- 54%, 100 years after LUC (mean +/- 95% confidence interval). No new equilibrium was reached within 120 years. In contrast, there was no SOC sink following afforestation of grasslands and 75% of all observations showed SOC losses, even after 100 years. Only in the forest floor, there was carbon accumulation of 0.38 +/- 0.04 Mg ha-1 yr-1 in afforestations adding up to 38 +/- 4 Mg ha-1 labile carbon after 100 years. Carbon loss after deforestation (-32 +/- 20%) and grassland conversion to cropland (-36 +/- 5%), was rapid with a new SOC equilibrium being reached after 23 and 17 years, respectively. The change rate of SOC increased with temperature and precipitation but decreased with soil depth and clay content. Subsoil SOC changes followed the trend of the topsoil SOC changes but were smaller (25 +/- 5% of the total SOC changes) and with a high uncertainty due to a limited number of datasets. As a simple and robust model approach, the developed CRFs provide an easily applicable tool to estimate SOC stock changes after LUC to improve greenhouse gas reporting in the framework of UNFCCC.
Article
The soil is subject to change, and this must be monitored and understood. There are various circumstances in which the change in a soil property will depend in part on the baseline value that was first measured. Such a relationship may allow us to estimate change with greater precision, but it will also reflect in part the statistical phenomenon of regression to the mean. In this paper, we describe two approaches to the analysis of how change in a variable depends on its baseline values. These methods allow for the effect of regression to the mean. We discuss their applicability to the problems of soil monitoring, and we illustrate one of them by means of a case study on change in the organic carbon content of the soils of England and Wales.
Article
Quantifying soil organic carbon (SOC) dynamics at a high spatial and temporal resolution in response to different agricultural management practices and environmental conditions can help identify practices that both sequester carbon in the soil and sustain agricultural productivity. Using an agricultural systems model (the Agricultural Production Systems sIMulator), we conducted a high spatial resolution and long-term (122 years) simulation study to identify the key management practices and environmental variables influencing SOC dynamics in a continuous wheat cropping system in Australia's 96 million ha cereal-growing regions. Agricultural practices included five nitrogen application rates (0-200 kg N ha(-1) in 50 kg N ha(-1) increments), five residue removal rates (0-100% in 25% increments), and five residue incorporation rates (0-100% in 25% increments). We found that the change in SOC during the 122-year simulation was influenced by the management practices of residue removal (linearly negative) and fertilization (nonlinearly positive) - and the environmental variables of initial SOC content (linearly negative) and temperature (nonlinearly negative). The effects of fertilization were strongest at rates up to 50 kg N ha(-1) , and the effects of temperature were strongest where mean annual temperatures exceeded 19 °C. Reducing residue removal and increasing fertilization increased SOC in most areas except Queensland where high rates of SOC decomposition caused by high temperature and soil moisture negated these benefits. Management practices were particularly effective in increasing SOC in south-west Western Australia - an area with low initial SOC. The results can help target agricultural management practices for increasing SOC in the context of local environmental conditions, enabling farmers to contribute to climate change mitigation and sustaining agricultural production.
Article
The purpose of the study was to determine the soil organic carbon (SOC) stock for Flanders, Belgium and to evaluate various methods for assessing SOC stock. The assessment methods first determined the SOC density (C mass per unit area) for pedons in a database of soil properties, and then spatially distributed the SOC density to soil and soil/land use categories on a map. The results showed that the pedon SOC density is influenced by drainage class, texture and land use/land cover. The SOC density estimation method significantly influences results and leads to differences of up to 6% in total estimated SOC stock for Flanders. Use of various spatial distributing methods creates differences of up to 2% in total estimated SOC stock. The largest difference in SOC stock estimate between any combination of assessment methods was 7% (125.6 Tg vs 134.9 Tg). These findings emphasize the importance of complete spatial soil databases of high quality that reduce uncertainty of estimates for use in research examining the role of soils in the C cycle. The results indicate that the need for these databases is greater than the need to standardize methods to determine the spatial distribution of SOC. A map of the distribution of SOC density shows that in Flanders a large proportion of SOC is stored in sandy soils in the north of the territory.
Article
Estimates of regional and national topsoil soil organic carbon (SOC) stock change may help evaluating the soil role in mitigation of greenhouse gas (GHG) emissions through carbon (C) sequestration in soils. However, understanding of the exact mitigation role is often constrained by the uncertainty of the stock estimation associated with different methodologies. In this paper, a soil database of topsoil (0–20 cm) SOC measurements of Jiangsu Province, China, obtained from a soil survey in 1982, and from a geological survey in 2004, was used to analyze the variability of topsoil SOC among soil groups and among soil regions, and to estimate the change in SOC stocks that have occurred in the province over the last two decades. The soil survey data was obtained from measurements of 662 690 randomly collected samples, while the geological survey data was from 24 167 samples taken using a 2 km × 2 km grid. Statistical analysis was conducted on SOC values for 1982 and 2004 for different categories of soil groups, soil regions, and administrative municipalities, respectively. Topsoil SOC storage was then calculated and the provincial topsoil SOC stock was estimated for each sampling time. There were remarkable differences in SOC levels between soil groups and soil regions and different municipalities. The grid sampling with the geological survey in 2004 yielded smaller variability of topsoil SOC averages, both with soil groups and with soil spatial distribution than the random sampling method used in 1982. Variation of SOC was greater with soil groups than with soil regions in both sampling times, although it was less variable across soil taxonomic categories than within a spatial category. Little variance of the SOC level with soil groups could be explained by clay content. However, the prevalence of paddy fields in the total cropland area governed the regional and municipal average SOC levels. The average provincial topsoil SOC content increased from 9.45 g kg−1 in 1982 to 10.9 g kg−1 in 2004, and the total provincial topsoil SOC stock was enhanced from 149.0±58.1 Tg C in 1982 to 173.2±51.4 Tg C in 2004, corresponding to a provincial average SOC sequestration rate of 0.16±0.09 t C ha−1 yr−1. The SOC sequestration trend for the last two decades could be, in part, attributed to the enhanced agricultural production, symbolized by the grain yield per hectare. The results of SOC stock changes suggest a significant C sequestration in soils of Jiangsu, China, during 1980–2000, with paddy management playing an important role in regional SOC storage and sequestration capacity.
Article
Carbon (C) storage and sequestration in agricultural soils is considered to be an important issue in the study of terrestrial C cycling and global climatic change. The baseline C stock and the C sequestration potential are among the criteria for a region or a state to adopt strategies or policies in response to commitment to the Kyoto Protocol. Paddy soils represent a large portion of global cropland. However, little information on the potential of C sequestration and storage is available for such soils. In this paper, an estimation of the topsoil soil organic carbon (SOC) pool and the sequestration potential of paddy soils in China was made by using the data from the 2nd State Soil Survey carried out during 1979–1982 and from the nationwide arable soil monitoring system established since then. Results showed that the SOC density ranged from 12 to 226 t C ha−1 with an area-weighted mean density of 44 t C ha−1, which is comparable to that of the US grasslands and is higher than that of the cultivated dryland soils in China and the US. The estimated total topsoil SOC pool is 1.3 Pg, with 0.85 Pg from the upper plow layer and 0.45 Pg from the plowpan layer. This pool size is ∼2% of China's total storage in the top 1 m of the soil profiles and ∼4% of the total topsoil pool, while the area percentage of paddy soil is 3.4% of the total land. The C pool in paddy soils was found predominantly in southeast China geographically and in the subgroups of Fe-accumulating and Fe-leaching paddy soils pedogenetically. In comparison with dryland cultivation, irrigation-based rice cultivation in China has induced significant enrichment of SOC storage (0.3 Pg) in paddy soils. The induced total C sequestration equals half of China's total annual CO2 emission in the 1990s. Estimates using different SOC sequestration scenarios show that the paddy soils of China have an easily attainable SOC sequestration potential of 0.7 Pg under present conditions and may ultimately sequester 3.0 Pg. Soil monitoring data showed that the current C sequestration rate is 12 Tg yr−1. The total C sequestration potential and the current sequestration rate of the paddy soils are over 30%, while the area of the paddy soils is 26% that of China's total croplands. Therefore, practicing sustainable agriculture is urgently needed for enhancing SOC storage to realize the ultimate SOC sequestration of rice-based agriculture of China, as the current C sequestration rate is significantly lower than the potential rate.
Article
Land-use changes are the second largest source of human-induced greenhouse gas emission, mainly due to deforestation in the tropics and subtropics. CO2 emissions result from biomass and soil organic carbon (SOC) losses and may be offset with afforestation programs. However, the effect of land-use changes on SOC is poorly quantified due to insufficient data quality (only SOC concentrations and no SOC stocks, shallow sampling depth) and representativeness. In a global meta-analysis, 385 studies on land-use change in the tropics were explored to estimate the SOC stock changes for all major land-use change types. The highest SOC losses were caused by conversion of primary forest into cropland (−25%) and perennial crops (−30%) but forest conversion into grassland also reduced SOC stocks by 12%. Secondary forests stored less SOC than primary forests (−9%) underlining the importance of primary forests for C stores. SOC losses are partly reversible if agricultural land is afforested (+29%) or under cropland fallow (+32%) and with cropland conversion into grassland (+26%). Data on soil bulk density are critical in order to estimate SOC stock changes because (i) the bulk density changes with land-use and needs to be accounted for when calculating SOC stocks and (ii) soil sample mass has to be corrected for bulk density changes in order to compare land-use types on the same basis of soil mass. Without soil mass correction, land-use change effects would have been underestimated by 28%. Land-use change impact on SOC was not restricted to the surface soil, but relative changes were equally high in the subsoil, stressing the importance of sufficiently deep sampling.
Article
Topsoil is very sensitive to human disturbance under the changing climate. Estimates of topsoil soil organic carbon (SOC) pool may be crucial for understanding soil C dynamics under human land uses and soil potential of mitigating the increasing atmospheric CO2 by soil C sequestration. China is a country with long history of cultivation. In this paper, we present an estimate of topsoil SOC pool and cultivation-induced pool reduction of China soils based upon the data of all the soil types identified in the 2nd national soil survey conducted during 1979–1982. The area of cultivated soils of China amounted to 138נ106ha while the uncultivated soils occupied 740נ106ha in 1980. Topsoil SOC density ranged from 0.77 to 1489tCha−1 in uncultivated soils and 3.52 to 591tCha−1 in cultivated soils with the average being 5047tCha−1 and 3532tCha−1, respectively. Geographically, the maximum mean topsoil SOC density was found in northeastern China, being of 70104tCha−1 for uncultivated soils and of 5754tCha−1 for cultivated soils, respectively. The lowest topsoil SOC density for uncultivated soils was found in East China, being of 3833tCha−1 and that for cultivated soils in North China, being of 3030tCha−1. There is still uncertainty in estimating the total topsoil SOC of uncultivated soils because a large portion of them was not surveyed during the 2nd Soil Survey. However, an estimate of total SOC for cultivated soils amounted to 5.1Pg. On average, cultivation of China’s soils had induced a decrease of SOC density of 15tCha−1 giving rise to an overall pool reduction at 2Pg. This is significantly smaller than the total SOC pool decline of 7Pg due to cultivation of natural soils in China reported by Wu et al. (Glob. Change Biol. 2003, 9: 305–315), who made a pool estimation of whole soil profile assuming 1m depth for all soils. As the mean topsoil SOC density of China was lower than the world average value given by Batjes (J. Soil Sci. 1996, 47: 151–163), China may be considered as a country with low SOC density and may have great potential for C sequestration under well defined management. However, the dynamics of topsoil C storage in China agricultural soils since 1980’s and the effects of modern agricultural developments on C dynamics need further study for elucidating the role of China agriculture in global climatic change.
Article
Despite the extensive literature on the effect on soil properties of afforestation of former arable land, we still lack full understanding of whether the changes proceed in the same direction and at the same rate, and of how long is required to achieve a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a study comparing post-arable sandy soils (Dystric Arenosols) afforested with Scots pine (Pinus silvestris L.) with arable soils and soils of continuous coniferous forests, the range and direction of changes in pH, organic carbon (Corg), total nitrogen (Ntot), ammonium (N-NH4) and nitrates (N-NO3) in soil solution, total (Ptot) and available (Pav) phosphorus were determined. The studies were carried out in south-east Poland (51°30′-51°37′N, 22°20′-22°35′E). Ten paired sites of afforested soils (five with 14- to 17-year-old stands and five with 32- to 36-year-old stands) with adjacent cultivated fields, and five sites of continuous forest with present stands of ca. 130–150years old were selected. Soil samples were taken from the whole thickness of master horizons and, in the case of the A horizon of the afforested soils, from three layers: 0–5 (A0–5), 5–10 (A5–10) and 10–20cm (A10–20). The cultivated soils in the Ap horizon showed higher pH (by ca. 1.0 unit), lower Corg and C:N, similar Ntot, lower N-NH4, higher N-NO3, higher Ptot and Pav contents compared with the Ah horizon of continuous forest soils. The results indicated decreased soil pH in the former plough layer of the afforested soils, with the greatest decrease observed in the 0–5cm layer. In these soils, the Corg content was considerably higher in the A0–5 layer, but lower in the two deeper layers and in the whole A horizon (0–20cm) compared with the Ap horizon of the arable soils. The results indicate that the Corg content, after an initial phase of decline, again achieved a level characteristic of arable soils. The Ntot content in all layers of the A horizon of the afforested soils was lower than in the Ap horizon of the arable soils, and showed a reduction with stand age, especially in deeper layers. The C:N ratios in the mineral topsoil increased with stand age. N-NH4 content increased and N-NO3 decreased after afforestation. The Ptot and Pav contents in all layers and in the whole A horizon of the afforested soils, on stands of both ages, was lower than in the Ap of the cultivated soils. From the results, it could be concluded that, after more than 30years of tree growth, the soils of the A horizon were still more similar to arable than to continuous forest soils with respect to Corg, Ptot and Pav. With respect to pH, N-NH4 and N-NO3, especially in the 0–5cm layer, they were more similar to continuous forest soils than to cultivated soils, but with respect to Ntot and C:N ratio they were somewhere in between.
Article
Loss of soil organic carbon (SOC) can cause soil degradation, which may not only undermine soil productivity, but may also-affect environmental health. In China, a huge amount of crop residues is regularly removed from the fields, and therefore China's agriculture depends on high levels of chemical fertilizer inputs. This paper aims to estimate the SOC storage in Chinese cropland, identify its changing trends under current cropping systems, and finally put forward some strategies to keep the SOC in balance. A computer simulation model of carbon and nitrogen biogeochemistry in agro-ecosystems (DeNitrification and DeComposition or DNDC) was applied to predict SOC dynamics in the upper (0–30 cm) soil layer of agricultural ecosystems at national scale. Data on climate, soil properties, cropping systems, acreage, and management practices at county scale were collected from various sources and integrated into a GIS database to support the model runs. The model results revealed (1) the total SOC storage in croplands in China is about 3968 Tg C; and (2) SOC is lost at a rate of 78.89 Tg C/year. The highest losses of SOC occur in the northeastern provinces. Chinese cropland soils release 186 Tg C as carbon dioxide into the atmosphere, and receive only 68 Tg C from crop residues annually. Considering the potential of global warming, SOC loss in cropland could be a serious contributor. Strategies to reduce the loss of SOC in Chinese cropland are proposed based on DNDC model runs for a number of scenarios under different management practices.
Article
Soil organic carbon (SOC) sequestration, methane emission, and the net carbon sink represented by rice straw incorporated into soil (RIS) were studied using long-term experimentation with rice straw incorporated into soil (LRIS) and short-term experimentation with different patterns of rice straw incorporated into soil (SPRIS). Soil organic carbon could be improved by RIS combined with soil ploughing. The increased rate of SOC deposition per cultivated layer was 0.10 t C ha(-1) for 2.625 t ha(-1) straw incorporated each season in LRIS and 0.36 t C ha(-1) for 4.5 t straw ha(-1) season(-1) incorporated in SPRIS; the apparent SOC conversion by rice straw (stubble) was reduced as the amount of incorporated straw increased. However, RIS methane emission from paddy fields also significantly exacerbated the CH(4) emission flux observed during the early and late rice growing seasons, which was increased by 75.0% (P < 0.01) and 251.5% (P < 0.01), respectively, compared with combined application of nitrogen, phosphorus and potassium fertiliser (NPK). The apparent methane conversion of straw was almost uniform with a similar rice yield and soil cultivating mode. Among the patterns of RIS, methane emission was significantly reduced under straw covering untilled land, and this property led to the lowest apparent methane conversion. RIS with ploughing and tilling resulted in negative carbon sequestration because of increased methane emissions. A combined NPK application with only rice stubble incorporation may be sustainable for a higher rice yield, but this approach has a reduced rate of negative carbon sequestration in the paddy field. Straw covering with no tillage was the best measure to realise high yield and low carbon emission for RIS.
Article
Human migration from the karst area to the non-karst area is an important approach for the restoration of degraded karst ecosystems. However, the effects of human-induced land-use change on soil properties are still unclear. The objective of this study was to investigate the effects of land use and parent material on soil organic carbon (SOC) and total nitrogen (TN) at a depth of 0-15 cm in karst and non-karst areas in southwest China. In the karst area, SOC and TN under different land uses decreased significantly in the order of secondary forestland > scrubland and abandoned farmland > farmland, commercial forestland and forage grassland. In the non-karst area, SOC and TN were the highest in scrubland and grassland, and were significantly higher than those in farmland and commercial forestland. Because of differences in parent material, SOC and TN were significantly higher in the karst area than those in the non-karst area. Abandoned farmland had the potential to increase SOC and TN significantly but land reclamation and cultivation had the opposite effect. SOC and TN were higher but cultivation-induced losses occurred more rapidly in calcareous soils than in red soils, indicating that more attention is needed for soil productivity and land use management in the karst area.
Article
There is considerable concern in Europe that soil organic matter (SOM) contents are declining, which would threaten both agriculture and the environment. We performed a trend analysis of SOM contents in sandy soils, using historic data from routine agricultural soil analyses. Data were selected from grass, grass-maize rotation and maize fields in four adjacent provinces that had been sampled four to five times during the period 1984¿2004. Absolute (at least 1%) and relative changes (SOMt=20/SOMt=0) were calculated and regressed against initial SOM contents. Mean SOM content showed a north-south gradient per cropping system. We found no single uniform trend in SOM contents for any of the three systems. Over the 20-year period, SOM declined in c. 25% of all grasslands, amounting to 185 000 of the 635 000 hectares of land under grass and forage crops in the four provinces, and increased in a total of 267 000 hectares. Carbon accumulation in grassland sandy soils was calculated at 39 g C m¿2 year¿1 (top 5 cm). For the grasslands, initial SOM contents were linearly and negatively related to absolute changes in SOM; the relation with the relative change was best explained by using log-transformed values of SOM. We conclude that in grassland soils in the Netherlands, conservation of SOM requires identification of high-risk fields rather than high-risk areas. For continuous maize on sandy soils, the entire area may be denoted as high-risk, because all fields could reach the critical limit of 3.4% SOM in the near future
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