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Abstract

Rubber-based agroforestry (Hevea brasiliensis) systems are considered the best way to improve soil properties and the overall environmental quality of rubber monoculture, but few reports have examined soil aggregate stability in such systems. The objective of this study was to examine the management and landscape effects on water stable soil aggregates, soil aggregate-associated carbon, nitrogen content and soil carbon, and nitrogen accumulation in Xishuangbanna, southwestern China. Treatments were rubber monoculture (Rm) and four rubber-based agroforestry systems: H. brasiliensis–C. arabica (CAAs), H. brasiliensis–T. cacao (TCAs), H. brasiliensis– F. macrophylla (FMAs) and H. brasiliensis–D. cochinchinensis (DCAs). The results showed that, with the exception of CAAs, the rubber-based agroforestry treatments significantly increased total soil organic carbon (SOC) and N contents and enhanced the formation of macroaggregates compared to the rubber monoculture treatment. SOC and N contents in all water-stable aggregate fractions were significantly higher in rubber-based agroforestry systems (except CAAs) compared to rubber monoculture. The macroaggregate fractions contained more organic carbon and nitrogen than the microaggregate fractions. The proportions of C and N loss from slaking and sieving were shown to have significantly negative correlations with the mean weight diameter and the SOC and N concentrations in bulk soil. The results suggest that soil surface cover with constant leaf litter fall and extensive root systems in the rubber-based agroforestry systems increased soil organic carbon and nitrogen, helped improve soil aggregation, reduced soil erosion, decreased carbon and nitrogen loss, and ultimately improved the carbon and nitrogen accumulation rates. Given that the soil physical-chemical properties improvement and the patterns of the intercropping system played key roles in managing artificial forests, we recommend that local governments and farmers should prefer T. cacao, F. macrophylla and D. cochinchinensis and not C. arabica as the alternative interplanted tree species within rubber plantations.

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... While rubber plantations in China, Vietnam, and Thailand are mainly small-holdings, large-scale economic enterprises are dominant in Cambodia, Laos, Indonesia, and Myanmar (Fox and Castella, 2013;Fox et al., 2014). The conversion of rainforests to rubber plantations has many environmental consequences, e.g., decreases in water reserves (Ziegler et al., 2009), exacerbation of seasonal drought (Tan et al., 2011), disrupted local carbon budgets (Song et al., 2014), increases in water-induced soil erosion (Chen et al., 2017), declines in soil productivities and ecosystem biodiversity (Ahrends et al., 2015;Warren-Thomas et al., 2015). The current tendency for rubber plantations to expand may therefore threaten biodiversity and the livelihoods of local inhabitants and may result in ecosystem instability and drought (Song et al., 2017). ...
... Because of the intensive management and trampling by farmers during the rubber tapping period, the soil is more tightly packed in the rubber plantation than in the tropical rainforest. In addition, there is more seasonal variation in soil erosion in the rubber plantation than in the tropical rainforest (Chen et al., 2017). Consequently, more seasonal variation in the soil carbon substrate is present in the rubber plantation than in the tropical rainforest (Zhang et al., 2010). ...
... In the rubber plantation, soil water content was generally higher than that in the rainforest (Fig. 1), making water content the primary control on the CH 4 flux. This result is in line with Fang et al. (2010) and Werner et al. (2006) and this may relate to lower soil porosity (Chen et al., 2017) and a heavy soil structure. Net CH 4 fluxes (emission or uptake) are the result of both CH 4 consumption and production. ...
Article
With large area of primary tropical rainforest converted into rubber (Hevea brasiliensis) plantation in Southeast Asia, it is necessary to examine the change in soil CO2 and CH4 emissions, and their underlying drivers in tropical rainforest (TRF) and rubber plantation. In TRF and RP in Xishuangbanna Southwest China, we measured the soil CO2 , CH4 , temperature, and water content once each week from 2003 to 2008, and twice weeks in 2013 and 2014. Additionally, the concentrations of soil carbon (C) and nitrogen (N) fractions from 2013 to 2014 were observed. Inputs of litter and live, dead, decomposed fine roots dynamics were also included. TRF transplanted to RP did not change significantly the annual soil CO2 emissions (TRF, 359 ± 91 and RP 352 ± 41 mg CO2 m⁻² h⁻¹) but decreased soil CH4 uptake significantly (TRF, −0.11 ± 0.18 mg CH4 m⁻² h⁻¹) RP, −0.020 ± 0.087 mg CH4 m⁻² h⁻¹). The most important influence on soil CO2 and CH4 emissions in the RP was the leaf area index and soil water content, respectively, whereas the soil water content, soil temperature, and dead fine roots were the most important factors in the TRF. Variations in the soil CO2 and CH4 caused by land-use transition were individually explained by soil temperature and fine root growth and decomposition, respectively. The results show that land-use change varied the soil CH4 and CO2 emission dynamics and drivers by the variation of soil environmental and plant's factors.
... Although it secures homogeneity in latex production, the lack of genetic diversity increases susceptibility to phytosanitary problems and reduces rubber latex yielding. Producers are creating new plantations in areas that were covered by natural tropical forests [3], avoiding common diseases such as the South American leaf blight (SALB), caused by Pseudocercospora ulei (Henn.), with negative consequences for natural ecosystems. Others are developing new rubber genotypes with more resistance to diseases and good latex production [4] for cultivation in traditional areas. ...
... According to Chen et al. [3], agroforestry systems for rubber trees are the best alternative for improving soil properties. Our results indicated that none of the rubber plantations improved the degraded condition of the soils. ...
... A higher AM fungal diversity will enhance the external mycelial network, improving the nutrition of the plant community [16]. Additional traits (e.g., soil aggregation, soil organic C, biomass C sequestrated) and ecological services (plant, enthomofauna, and bird diversity) have been evaluated on different rubber plantations and genotypes [3,22,62], corroborating the importance of this plant species for soil restoration. ...
Article
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Rubber (Hevea brasiliensis, (Willd. Ex Adr. de Juss) Muell. Arg, Euphorbiaceae) is an important commercial latex-producing plant. Commercially, rubber is reproduced from a limited number of grifting genotypes. New promising genotypes have been selected to replace traditional genotypes. In addition, rubber has been promoted to recuperate Amazon soils degraded by extensive cattle ranching. Arbuscular mycorrhizal (AM) symbiosis is an important alternative for improving plant nutrition in rubber trees and recuperating degraded soils, but AM fungal communities on different plantations and in rubber genotypes are unknown. Spore abundance, root colonization and AM fungal community composition were evaluated in rubber roots of Colombian and introduced genotypes cultivated in degraded soils with different plantation types. Traditional (spore isolation and description; clearing and staining roots) and molecular techniques (Illumina sequencing) were used to assess AM fungi. Rubber roots hosted a diverse AM fungal community of 135 virtual taxa (VT) in 13 genera. The genus Glomus represented 66% of the total AM fungal community. Rubber genotype did not affect the arbuscular mycorrhization, hosting similar AM fungal communities. The composition of the AM fungal community on old and young rubber plantations was different. Diversity in AM fungi in rubber roots is an important characteristic for restoring degraded soils.
... In this context, several studies have reported that agroforestry or integrated production systems, when compared to conventional systems, result in improvements in soil quality regarding the physical (Chen et al. 2017;Moreira et al. 2018;Cabral Filho et al. 2017), chemical (Schwab et al. 2015;Araújo et al. 2017;Pardon et al. 2017) and biological properties (Udawatta et al. 2014;Portilho et al. 2018;Guillot et al. 2019). These conservationist systems are also considered as a strategy for mitigating climate change, as they can promote atmospheric C sequestration (Lorenz and Lal 2014;Srinivasarao et al. 2014;Abbas et al. 2017;Tumwebaze and Byakagaba 2016;Dhillon and Rees 2017;Franzluebbers et al. 2017). ...
... The constant litter inputs and soil cover associated with the existence of extensive root systems in intercropped forest systems contribute to the increase in the levels of soil organic C and N, improving soil quality over time (Chen et al. 2017;Rodrigues et al. 2015) reported a reduction in the soil organic C in a monoculture of grass (Brachiaria brizantha) and increase when the cultivation was intercropped with trees. Gelaw et al. (2014) also reported significant increases in the C and N stocks after the introduction of a silvopastoral system. ...
... Our results can be related to the deposition of the aerial and subsoil residues (leaf and root exudates, leaves, stems, flowers, seeds and roots) from the forest component (double rows of eucalyptus), contributing to the SOM accumulation. Chen et al. (2017) reported that the constant inputs of litter and the presence of extensive root systems increase the levels of soil C and N contents. In addition, Dhillon and Van Rees (2017) also highlighted that the age of the stand and characteristics such as height and diameter of trees, canopy diameter and inputs of litter showed a positive correlation with increases in soil C contents. ...
Article
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There is insufficient information about the dynamics of soil organic matter in integrated production systems. Therefore, we aimed to evaluate the variations in soil C and N stocks and microbial attributes as a function of the distances apart from the eucalyptus double rows within a silvopastoral system in the Brazilian Cerrado. Four treatments were considered, consisting of four distances (0.5 m, 1.6 m, 3.8 m and 6 m) apart from the double rows of eucalyptus for soil sampling within the silvopastoral system. The soil C and N contents and stocks, C/N ratio, microbial C (Cmic), soil basal respiration, metabolic quotient and microbial quotient were evaluated. Our results showed that soil C contents and stocks were significantly higher near the eucalyptus trees. Soil C stocks ranged from 99.91 (6.0 m) to 119.64 Mg ha−1 (0.5 m) up to 100 cm soil depth, with an increase of 19.73 Mg ha−1 nearest of the forest component. The same pattern was observed for N stocks, with values ranging from 9.52 (0.5 m) to 7.95 Mg ha−1 (6.0 m) and representing an increase of 1.57 Mg ha−1 near the eucalyptus. We also found an increase of 51.32% in the Cmic at 0.5 m apart from the forest component. Thus, we can infer that the presence of eucalyptus improved the soil quality within the silvopastoral system, indicating that the correct soil sampling and measurements must be performed considering all the transect cultivated with forage grass and double rows of eucalyptus.
... Due to the cactus pear high wateruse efficiency, the addition of organic manure and irrigation may have enhanced the water availability and root absorption of both water nutrients, which consequently enable greater growth of cactus pear roots and cladodes and increased the soil organic matter (SOM) caused by root activity [47,48]. SMBC is highly affected by SOM, and this significant positive relationship was reported by many researchers [49][50][51][52]. High variability in the relationship between manure application and soil acidity was found in the literature [53]. ...
... Due to the cactus pear high water-use efficiency, the addition of organic manure and irrigation may have enhanced the water availability and root absorption of both water nutrients, which consequently enable greater growth of cactus pear roots and cladodes and increased the soil organic matter (SOM) caused by root activity [47,48]. SMBC is highly affected by SOM and this significant positive relationship was reported by many researchers [49][50][51][52]. High variability in the relationship between manure application and soil acidity was found in the literature [53]. ...
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Study of appropriate planting time and response to agronomic management practices is imperative for the newly introduced cactus pear (Opuntia ficus-indica (L.) Mill.) into a semi-arid region of India. Responses of cactus pear to agronomic practices (planting time, and irrigation and fertilizer application) were evaluated to determine the potential for fodder production and livestock feed in a semi-arid environment of India. We assessed four planting times (February, March, July, and October) and two agronomic managements (with and without irrigation and fertilizer application) during 2016–2020 at Jhansi, India. Cactus pear establishment and growth improved with planting time in July and October due to favorable soil moisture and congenial temperature. However, plant height (19 cm) and cladode weight (118 g) were greater in July than in October planting. Nutrient uptake and crude protein contents, however, were higher for the earlier plantings of February and April compared to June and October. Irrigation and nutrients application had little effect on the cactus pear plant growth, except on plant width and cladode length and width. Cactus pear can be planted during July in moderately fertile soils without any agronomic intervention in semi-arid situations of India and has potential as an effective alternative source of forage for livestock during the summer months.
... These microaggregates, in turn, build macroaggregates due to transient and temporal agents such as polysaccharides, roots, and fungal hyphae (Spohn and Giani 2011). Due to the various aggregate binding agents, the stability of soil aggregates and the allocated C and N in differentsize aggregates have different sensitivities to land use and cover change (Tisdall and Oades 1982;Chen et al. 2017). Land cover change from natural forests to intensively managed plantations has been well known to strongly affect soil aggregation and C and N pools (Ashagrie et al. 2005;Chen et al. 2017;Goma-Tchimbakala 2009;He et al. 2008). ...
... Due to the various aggregate binding agents, the stability of soil aggregates and the allocated C and N in differentsize aggregates have different sensitivities to land use and cover change (Tisdall and Oades 1982;Chen et al. 2017). Land cover change from natural forests to intensively managed plantations has been well known to strongly affect soil aggregation and C and N pools (Ashagrie et al. 2005;Chen et al. 2017;Goma-Tchimbakala 2009;He et al. 2008). However, fewer studies have focused on the efficiency and mechanism of aggregate C and N turnover associated with the input of plant residues and output of microbial mineralization. ...
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Background and aims Land cover change (LCC) from natural forest (NF) to plantations (PF) has occurred worldwide over the past several decades. However, the different LCC effects on soil aggregate C and N turnover in various climatic zones remain uncertain. Methods Soil samples were taken from both NF and PF at five sites along an approximately 4200 km north-south transect in eastern China. We measured soil aggregate C and N concentrations, and δ¹³C and δ¹⁵N. Results The soil aggregate distribution is similar between NF and PF, except that the mass proportion of microaggregate is lower in NF. The impacts of LCC on soil C and N concentrations, and δ¹³C and δ¹⁵N vary among five climate zones. The changes in soil aggregate C and N concentrations and δ¹⁵N induced by LCC show nonlinear relationships with climatic factors (i.e., MAT and MAP), and there is a linear relationship between soil aggregate Δδ¹³C (calculated by subtracting PF from NF) and MAT and MAP. The soil aggregate C and N concentrations, and δ¹³C and δ¹⁵N show clear trends along the climatic transect. In addition, the impacts of LCC are more obvious in topsoil than in subsoil. Conclusion Our findings highlight that the impacts of LCC on soil C and N concentrations are related to climatic factors. Specifically, that the increased decomposition of soil C in PF than NF can be compensated by higher C inputs with increasing MAT and MAP.
... The direction of the blue arrows was determined by the functional effects of the nutrients of each node (Figure 5b). In brief, soil C determines the stability of a soil and thus affects the soil N status [36]; the arrow therefore points from the soil C concentration to the soil N concentration (Figure 5b). The litter C concentration determines the decomposition rate of the litter N and P concentrations, so the arrows therefore point from the litter C concentration to the litter N and P concentrations. ...
... The positive effects of interspecific root interactions on the soil's physical and chemical properties could help reduce soil nutrient losses and thus improve the soil's nutrient status [2,3]. For example, intercropping could help improve the stability of soil aggregates and thus prevent the leaching of soil N [36]. However, the low soil N concentration in the rubber and coffee AFS (Figure 2e) suggested that intense interspecific competition may result in less N input or more N output within the soil. ...
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Controversial competition theories may confuse the current understanding of belowground plant competition and thus result in incorrect diagnoses and mitigation strategies for nutrient competition. As such, the management of nutrient competition is a major challenge in the application and development of rubber agroforestry systems (AFSs). To explore the effects of plant competition on the nutrient status of rubber AFSs, this study measured the carbon, nitrogen, and phosphorus concentrations of the litter and soil and in plant leaves, stems, and roots from five rubber plantations (i.e., rubber monocultures and rubber mixed with cocoa, coffee, tea, and Flemingia macrophylla (Willd.) Merr., 1910)). The relative competition intensity indexes were calculated to evaluate the competition intensity of each mixed-species system, and Bayesian networks were established to investigate the linkage effects of interspecific competition for nutrients. This study demonstrated that rubber trees had weak competition with cocoa trees, moderate competition with F. macrophylla and tea trees, and intense competition with coffee trees. With the increase in competition intensity, the negative effects of interspecific competition on soil gradually offset the improvement in soil nutrients achieved with intercropping. Nitrogen and phosphorous translocation from the stems to the roots was enhanced by competition. However, enhanced nutrient allocation to roots may have led to insufficient nitrogen and phosphorous supplies in plant leaves. The quality of the litter therefore decreased because the nutrient status of fallen leaves determines the initial litter conditions. Such consequences may reduce the release of nutrients from the litter to the soil and thus increase soil nutrient depletion. This study revealed that competition effects were most obvious for the root nutrient status, followed by the stem and leaf nutrient statuses. Moreover, this study further demonstrated that the nutrient concentration of plant roots can better indicate the intensity of nutrient competition than the nutrient concentration of other plant organs.
... Rubber-F. macrophylla intercropped systems have been widely established in rubber plantations area of China (Chen et al., 2017;Liu et al., 2019b). ...
... The activities of methane-oxidizing bacteria increase under aerobic conditions, and those of methane-producing bacteria increase under anaerobic environments (Iqbal et al., 2013;Nan et al., 2020). Chen et al. (2017) reported that the introduction of F. macrophylla to rubber plantations improved total soil porosity, soil mean weight diameter, and soil hydraulic conductivity, relative to rubber monoculture. In this study, we found that the introduction of F. macrophylla to the different-aged rubber plantations significantly decreased soil bulk density. ...
Article
Rubber plantations represent 13 million hectares in the world. Many researchers have focused on the environmental sustainability of rubber plantations, with rubber-legume systems better approach for ameliorating soil environments. This study investigated the effect of introducing Flemingia macrophylla (a leguminous shrub) to different-aged rubber plantations on the emissions of CO 2 , N 2 O, and CH 4. As trees aged in the rubber plantations, the annual emissions of CO 2 , N 2 O, and CH 4 significantly decreased. The introduction of F. macrophylla to different-aged rubber plantations significantly decreased CO 2 and CH 4 flux but increased N 2 O flux. The CO 2 and N 2 O fluxes were mainly affected by soil temperature at 10 cm depth, and CH 4 flux was mainly affected by both soil water content in the 0-10 cm soil layer and soil temperature at 10 cm depth. Compared to the same-aged rubber plantations, annual total CO 2 flux of young and mature rubber-F. macrophylla plantations decreased 154,000 and 64000 kg ha − 1 , CH 4 flux decreased 0.50 and 0.78 kg ha − 1 (17.0 and 26.5 kg CO 2 eq ha − 1), and N 2 O flux increased 0.15 and 0.55 kg ha − 1 (44.7 and 163.9 kg CO 2 eq ha − 1), respectively. The rubber-leguminous shrub systems significantly improved soil organic carbon sequestration rate, relative to the same aged rubber plantations. In conclusion, the emissions of CO 2 , N 2 O and CH 4 decreased as the trees aged in the rubber plantations , and rubber-leguminous shrub systems could mitigate local climate warming by reducing reduce greenhouse gas emissions and improving soil organic sequestration rate.
... Worldwide, the AFS has shown significant soil quality improvements over time. In China, Chen et al. (2017) observed improvements in an AFS with 10 years regarding physicochemical soil quality, mainly in the macroaggregation and total organic carbon. In France and in Brazil, Cardinael et al. (2016) and Thomazini et al. (2015) also demonstrated the AFS potential on increase the soil carbon stocks. ...
... This higher TOC content came from deposition and accumulation of plant residues cultivated in the AFS-R associated to higher biomass input of the AFS-IR, which was removed annually from inter-row and deposited in the row of arboreal species. TOC positive effects on soil physical quality were observed also by Chen et al. (2017) in an AFS with 10 years in China, and TOC decrease pattern as depth increases, as observed in our study (Table 2), is the expected behavior in most agroforestry systems (Thomazini et al. 2015). ...
Article
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Concerns with environmental sustainability have promoted adoption of conservationist practices in agricultural production, mainly focused on soil quality preservation or recovery. The aim of this study was evaluating short-term soil physical quality improvements under agroforestry system management in Southern Brazil. The agroforestry system was implemented in 2013 in an Ultisol with Sandy Loam texture. Rows of agroforestry system (AFS-R) were composed by biomass producer trees intercalated with wood and fruit producer trees while in the inter-rows (AFS-IR) perennial sub-shrub, perennial grass, and summer and winter green manure annual species were implanted. Soil under native forest was used as control. Soil samples in the 0.0–0.1; 0.1–0.2 and 0.2–0.4 m depths were collected for the determination of physical attributes and the total organic carbon content in 2015, 2016 and 2017. Bulk density decreased about 9% (AFS-R) and 6% (AFS-IR) in 0.0–0.1 m between 2015 and 2017. Total porosity increased over time only in AFS-R, at a rate of 0.025 m3 m−3 year−1. The total organic carbon content of AFS increased over time only in the 0.0–0.1 m layer, although remained up to 35% less in relation to the native forest. The agroforestry system resulted in consistent improvements of several soil physical attributes over short time, particularly in rows with arboreal plants, highlighting the role of diversified tree root systems and plant residues accumulation, which implied a rapid improvement in soil quality. In this context, long-term studies with agroforestry systems are crucial to understand the benefits on soil quality.
... Os sistemas agroflorestais têm maior potencial de sequestro de C e N em comparação com os locais adjacentes de monocultura (Chen et al., 2017), sendo a proporção do estoque de carbono orgânico nas camadas do subsolo maior em sistema agroflorestal do que em monocultivo (Guo et al., 2020). O acúmulo de carbono no solo é atribuído principalmente ao aumento da biomassa de resíduos das árvores e aos exsudatos radiculares, menos distúrbios humanos e mecanismos de proteção de carbono orgânico do solo submetido a alta atividade e quantidade microbiana (Liao & Boutton, 2008). ...
... Despite all results indicating the sustainability of the ecological-based agroforestry here evaluated, it cannot be considered as a simple solution to environmental and/or pollution mitigation. An optimal strategy for these purposes depends on a wide range of technical criteria, also including yield production, economical returns to farmers, environmental issues, current and future scenarios and trade-offs among all these variables [35] However, ecological-based agroforestry systems appear to positively contribute to expand the range of possibilities of small farmers on food and wood production [36] and also regulate ecosystems functions in agricultural and boundary landscapes [24,37], by carbon and nutrient additions to soil from litter structures [38][39][40][41][42]. ...
... Specifically, the decrease in RLD resulting from LUI was parallel to the increase in soil erosion, which is consistent with previous research (Baets et al., 2007;Zheng et al., 2008). In addition, the increase in LUI led to the reduction in soil organic matter, which strongly influences the structure of the soil and reduces the stability of soil aggregates, increasing soil erodibility (Chen, Liu, Jiang, & Wu, 2017;Gould et al., 2016;Prats, Malvar, Vieira, MacDonald, & Keizer, 2013). ...
Article
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Land‐use intensification has increased soil erosion resulting from biodiversity loss, which affects ecosystem properties and services owing to changes in species compositional and structural diversity. However, information is limited on how land‐use intensity (LUI) affects soil erosion through species compositional and structural diversity and ecosystem properties. In this study we monitored soil erosion in 15 plots over 12 consecutive months on tropical Hainan Island, where land‐use changes and biodiversity loss have been severe. We quantified the direct and indirect effects of LUI, species compositional diversity (plant species diversity and evenness) and structural diversity (tree diameter and height diversity), and ecosystem properties on soil erosion using Bayesian structural equation models (BSEM). The optimal BSEM accounted for 69% of the variation in soil erosion. The LUI did not affect soil erosion directly but showed indirect impacts via species diversity, tree height diversity, and ecosystem properties. Both high species and tree height diversity reduced soil erosion directly and indirectly by promoting root length density, but tree height diversity mediated the more important indirect effect of LUI on soil erosion than species diversity and ecosystem properties. We provided evidence for loss of species diversity and tree height diversity as a result of LUI leading to aggravated soil erosion, but the impact of the latter was more serious. Therefore, we emphasize that maintenance of tree height diversity through management practices may be an effective approach to control soil erosion in the context of drastic land‐use changes in tropical areas.
... Traditionally, one way households mitigated risk to bolster livelihoods was through the use of agroforestry practices (Mulia and Lusiana 2018). The use of trees on farms provides a wide variety of ecosystem services ) such as increased cereal grain yields (Bayala et al. 2014), increased animal fodder (Hansen et al. 2008), increased soil moisture (Lott et al. 2009), and increased nutrient cycling (Chen et al. 2017). The ecosystem services provided by trees are essential to derive sustainable livelihoods and improve well-being for vulnerable populations in the Sahelian region (Brandt et al. 2018) as well as to provide essential mitigation and adaptation co-benefits (Matocha et al. 2012;) such as carbon sequestration (Luedeling et al. 2011;Pandey 2002;Takimoto et al. 2008). ...
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Farmers managing agroecological systems across sub-humid West Africa face a variety of challenges in meeting their needs. In the face of adverse conditions, farmers have successfully managed agroforestry parklands to create an ecological equilibrium. However, climate change presents a challenging and new disturbance to farmer livelihood strategies. Using a qualitative approach and a rural livelihood framework, we analyzed and assessed farmer livelihood strategies, attitudes, and responses to climate change. Results showed that farmers are constantly changing management strategies through flexible and adaptable decision-making to mitigate negative disturbances, but climate change as a primary driver to change cannot be distinguished from other normal challenges that farmers face inter- and intra-annually. Through the accumulation of knowledge and adaptive management, farmers in Kedougou derive a variety of livelihood strategies to reduce risk in the face of uncertainty and variable climatic conditions. Furthermore, farmers used trees on farms to derive a multitude of ecosystem services provided not only provisioning services such as fuel, food, and fiber, but increased biodiversity, nutrient cycling, and climate regulation. Additional research is still needed to understand to what extent the inclusion of trees on farms affect various biophysical properties as well as rationale behind species choice.
... A significant positive correlation between soil organic matter and soil microbial biomass (Table 3) in our study supports the findings of Chen et al. (2006) that soil MBC is highly influenced by soil organic matter present in different ecosystems. Such a result was supported by many researchers (Wang and Wang 2011;Chen et al. 2017;Padalia et al. 2018). Further, high soil N in the natural forest and cardamom agroforestry system is due to the presence of Alnus nepalensis which might result in a higher microbial biomass C in these sites. ...
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Background Soil microbial biomass, an important nutrient pool for ecosystem nutrient cycling is affected by several factors including climate, edaphic, and land-use change. Himalayan soils are young and unstable and prone to erosion and degradation due to its topography, bioclimatic conditions and anthropogenic activities such as frequent land-use change. Through this study, we tried to assess how soil parameters and microbial biomass carbon (MBC) of Eastern Himalayan soils originated from gneissic rock change with land-use type, soil depth and season. Chloroform fumigation extraction method was employed to determine MBC from different land-use types. Results Soil physical and chemical properties varied significantly with season, land-use and soil depth ( p < 0.001). The maximum values of soil properties were observed in the rainy season followed by summer and winter season in all the study sites. Annual mean microbial biomass carbon was highest in the forest (455.03 μg g − 1 ) followed by cardamom agroforestry (392.86 μg g − 1 ) and paddy cropland (317.47 μg g − 1 ). Microbial biomass carbon exhibited strong significant seasonal difference ( p < 0.001) in all the land-use types with a peak value in the rainy season (forest-592.78 μg g − 1 ; agroforestry- 499.84 μg g − 1 and cropland- 365.21 μg g − 1 ) and lowest in the winter season (forest − 338.46 μg g − 1 ; agroforestry – 320.28 μg g − 1 and cropland − 265.70 μg g − 1 ). The value of microbial biomass carbon decreased significantly with soil depth ( p < 0.001) but showed an insignificant increase in the second year which corresponds to a change in rainfall pattern. Besides, land-use type, season and soil depth, soil properties also strongly influenced microbial biomass carbon ( p < 0.001). Microbial quotient was highest in the agroforestry system (2.16%) and least in the subtropical forest (1.91%). Conclusions Our results indicate that land-use, soil depth and season significantly influenced soil properties and microbial biomass carbon. The physical and chemical properties of soil and MBC exhibit strong seasonality while the type of land-use influenced the microbial activity and biomass of different soil layers in the study sites. Higher soil organic carbon content in cardamom agroforestry and forest in the present study indicates that restoration of the litter layer through retrogressive land-use change accelerates microbial C immobilization which further helps in the maintenance of soil fertility and soil organic carbon sequestration.
... Soil aggregates are the basic units of soil structure that control the dynamics of organic matter (OM) and nutrient cycling (Chen et al., 2017). They also affect other soil properties like porosity, compaction and water retention (Regelink et al., 2015). ...
Article
We investigated the capacity of different types of agroforestry systems to promote the formation of soil mac-roaggregates through biological or physical processes. Soil macroaggregates were visually separated according to morphological patterns into invertebrate biogenic (small and large faunal aggregates), root biogenic and phys-icogenic. We evaluated organic carbon in the different types of aggregates: small and large faunal, root biogenic and physicogenic. In agroforestry systems associating shade trees and crops and sylvopastoral systems, small and large faunal aggregates comprised 58.8 and 42.1% respectively of the soil mass. In general, the highest OC contents were found in root macroaggregates (14.1 g C kg − 1 , followed by small faunal aggregated (13.7 g C kg − 1), large faunal aggregated (13.3 g C kg − 1) and physicogenic macroaggregates (10.9 g C kg − 1). Overall, the average carbon storage in the different land uses was 91.3 ± 4.1. Highest overall C contents were observed in sylvopastoral systems (131 Mg ha − 1), pasture (112.2 Mg ha − 1), home gardens (105.8 Mg ha − 1), nature regen-eration (100.6 Mg ha − 1) and secondary forest (100.1 Mg ha − 1) these being the most efficient options for storing carbon. We conclude that a sound option to increase soil C storage in aggregated structures of deforested Amazonia soils might be planting trees in pastures transformed into sylvopastoral systems.
... Since the early 2000s, rubber (Hevea brasiliensis) plantations have expanded and boomed throughout mainland Southeast Asia (MSEA) (Fox and Castella, 2013;Hurni and Fox, 2018;Ziegler et al., 2009), including the uplands of northern Laos (Manivong and Cramb, 2008;Xiao et al., 2020a). While economic benefits of rubber plantations are obvious (Qiu, 2009), it causes serious eco-environmental impacts, including disturbing hydrological regimes (Tan et al., 2011), eroding soil (Zhu et al., 2018), depleting carbon stocks (Blagodatsky et al., 2016), and threatening biological diversity (Chen et al., 2017). This extensive and controversial land use (i.e., 'rubber controversy' (Tan et al., 2011;Min et al., 2018)) has attracted much attention from international schemes, for example the Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD, later REDD+) and Sustainable Development Goals (SDGs) of the United Nations (Achard et al., 2007;Fox et al., 2014;United Nations, 2016). ...
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Rubber (Hevea brasiliensis) tree cultivation is being continuously expanded northward by replacing evergreen forests and fallow-related regenerated vegetation across mainland Southeast Asia (MSEA), e.g., Laos, a landlocked mountainous country. The non-native tree establishment in the tropical edge, or the non-traditional suitable planting area, provides stable supplies of natural latex, yet also leads to severe ecological degradation and environmental effects in water conservation, soil quality, rainforest fragmentation and biodiversity. Rubber plantations in the northern part of MSEA is normally characterized by periodic deciduous during the dry season, along with a lengthy defoliation-foliation duration, because of seasonal variations in temperature and precipitation. It thus lays a phenological and physiological base for dynamics monitoring with common multispectral (e.g., near-infrared and short-wave infrared bands) satellites, particularly Landsat. However, whether Sentinel-2 red-edge based algorithms are suitable for discriminating rubber plantations is not yet reported. Here, we developed a red-edge spectral indices (RESI) method through the normalization of three red-edge wavebands and applied it to identify and map rubber plantations at the pixel to landscape levels in Luang Namtha Province of northern Laos, where a rubber boom begun in the mid-2000s. The RESI algorithm highlights the sensitivity of red-edge bands to the changes in moisture content and canopy density of rubber plantations. The area of mature rubber was estimated to be 77.12×103 ha in this province bordering southwest China in 2018, which was nearly twice as much as that of 2011, with the overall accuracy and kappa coefficient up to 92.50% and 0.91, respectively. Our phenology-based RESI approach not only indicates that Sentinel-2 imagery holds significant potential for monitoring rubber plantations, but also improves the remotely-sensed methods of rubber boom mapping via introducing the red-edge channel.
... While the lowest pH was noticed in the ginger land use system followed by that under ginger + maize land use. Extensive root systems and more exudates by different vegetation in undisturbed forest and alder + large cardamom system affected the soil fertility status (Chen et al., 2017) and thus, were reflected in higher soil pH. In the deeper layer at 45 cm depth, the effect was less pronounced as some of the leached out bases were expected to be deposited or adsorbed in the lower soil horizons . ...
Article
Land use management exerts a tenacious impact on soil organic carbon (SOC) dynamics; however, the impact varies with climate, soils, and management practices. Therefore, an in-depth understanding of changes in SOC pools and its fractions is necessary to reduce carbon (C) emissions and adopt efficient land use planning for sustainable soil management in the North Eastern Himalayan (NEH) region of India. The soils under five prominent land uses [e.g., alder (Alnus nepalensis) + large cardamom (Amomum subulatum), alder + turmeric (Curcuma longa), ginger (Zingiber officinale) + maize (Zea mays), ginger and undisturbed forest] were sampled down to 45 cm depth to assess the impacts of land use systems on SOC content and storage, its fractions, microbial biomass carbon (MBC) and the dehydrogenase (DHA) activities. Results demonstrated that undisturbed forest soil had the highest organic carbon (OC, 145.8 Mg ha⁻¹), active C (AC, 73.7 Mg ha⁻¹), passive C (PC, 72.1 Mg ha⁻¹) pools, MBC and DHA activities followed by alder + large cardamom system (140.7 Mg OC ha⁻¹, 70.9 Mg AC ha⁻¹, and 69.8 Mg PC ha⁻¹, respectively). The soils under undisturbed forest and alder + large cardamom system had a higher share of the very labile C fractions for all depths than other land uses. Conversely, soils under sole ginger and ginger + maize land uses had a greater proportion of non-labile C (NLC) fractions; however, absolute values of the NLC pool were the highest under undisturbed forest soil. Alder + large cardamom land use system had the highest AC: PC pool ratio (1.13) and C stratification (1.02–1.05) compared to the other land uses. Of the various land uses, SOC pools (0–45 cm) in six years were reduced nominally under alder + large cardamom system (4.2%), while the reduction was maximum under the ginger system (11.2%) as compared to the SOC pools of undisturbed forest. The study demonstrated that the cultivation of crops like maize and/or ginger is more degrading and will always have a negative impact on the fertility and overall health of the Himalayan soil. Hence, alder + large cardamom system may be promoted to restore the soil C in the Sikkim Himalayan region of NEH, India, and other similar regions of the world.
... Associating a food crop during the young age can have positive effects on rubber growth and subsequent yield (Rodrigo et al. 2005), as the fertilization of the crop also beneficiates the trees, and as weeds are limited. However, the effects of permanent associations on both the latex yield and the environment are not that clear (Chen et al. 2017). ...
Article
Introducing permanently an associated crop in rubber plantations may improve biodiversity and soil cover, optimize resource use, and diversify farmer’s income. However, the associated crop may also compete with the rubber trees for resources such as space and water. The case of bamboo-rubber agroforestry system is peculiar, as bamboos present features common to both grasses and trees, they grow fast and are considered strong competitors for water. Soil organic matter and water content, bulk density, root distribution, canopy cover, and rain interception were studied on farm to understand the effects of bamboo intercropped in rubber tree plantation, compared with rubber monoculture in southern Thailand. In the rubber-bamboo association, soil water content was lower in shallow depth, whereas it increased in deeper horizons. There was no significant difference in fine root distribution of rubber trees with or without bamboo; therefore, the total root density (rubber + bamboo) was higher in the association. Canopy cover and rain interception were also higher in association with bamboo. Further studies are required to better understand in this system, the balance between higher superficial water use and increased water retention in lower soil depth, together with more specific studies on soil properties, tree development, and latex yield.
... Alley Cropping An alley cropping system is a mixed system of trees accompanied by crops in the alleyways (Gold & UMCA, 2011). A few examples of alley cropping systems successfully implemented in different parts of the world include wheat and walnuts in Southern France (Cardinael et al., 2015), coffee plantations with shading trees in Peru (Ehrenbergerová et al., 2016), and rubber and cacao in China (Chen, Liu, Jiang & Wu, 2017). Additional examples include the combination of pecan trees as the main crop with annual crops of wheat and hay in the alleys, mixed systems of apple trees with grass, or intercropped maize with fruit and nut trees and fodder grasses. ...
Thesis
This research explores the feasibility of the 4 per 1000 initiative in Colombia through the adoption of agroforestry practices. Agroforestry (AF) has the potential to provide environmental benefits through the sequestration of carbon in agricultural land that has been managed in a conventional fashion. I followed a meta-analysis approach using a comprehensive dataset with 56 studies from different regions of the world. This dataset also included environmental, physical, and management information to explore potential correlations with changes in soil organic carbon (SOC). Although all the AF practices provide a significant SOC gain in croplands, some practices did not provide the SOC rate needed to meet the annual increase required by the 4 per 1000 initiative for the Colombian context. These practices include alley cropping, agrisilviculture, shelterbelts, windbreaks, and riparian buffers. Another objective of my research was to evaluate the connection between soil C sequestration and financial benefits. The recent development of a Colombian Voluntary Carbon Market and the creation of a Carbon Tax have the potential to scale-up AF projects across the country and generate a significant number of greenhouse gas offsets. I evaluated the market value using the net present value (NPV) approach. I further explore the role that different interest rates, soil C sequestrations (low vs. high scenario), C prices, and duration of the AF project have on the GHG offset market value. Citable link to this page https://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37365373
... The reduction in the MWD and GWD in cultivated land is due to land clearing and soil physical disturbances resulting from cultivation immediately after forest conversion. Similar changes in soil aggregation have been reported under rubber agroforestry (Chen et al., 2017). A general trend of increase in bulk density and decrease in porosity, MWD, and GWD with an increase in soil depth is consistent with the findings from plantation forests in China (Ge et al., 2018) and India (Kurmi et al., 2020). ...
Article
Shifting cultivation is a globally important form of agriculture covering over 280 million hectares in the tropic, but it has often been blamed for deforestation and forest degradation. In North East India (NEI) it has been practiced for millennia and it is an important element of the cultural identity of indigenous communities. It is often practiced on slopping lands with fragile soils (mostly Acrisols), which are prone to rapid degradation with cultivation. The shortened fallow cycle as practised currently is ecologically unsustainable and economically not viable. This study aimed to quantify (i) changes in soil bulk density, aggregate stability and compaction in relation to chronosequence and soil depth, (ii) changes in the proportion of macro, meso, and micro aggregates and associated soil organic carbon (SOC) content in relation to soil depth and fallow chronosequence, and (iii) determine the minimum fallow length that achieves SOC stocks comparable with adjacent intact forest land. The proportion of soil macro-aggregates and meso-aggregates significantly varied with land-use and soil depth as well as their interactive effects. Across all soil depths, forest land had the highest proportion of macro-aggregates (75.6%), while the currently cultivated land had the least proportion (51.1%). The SOC contents in macro-aggregates increased with fallow age and decreased with soil depth; highest (1.95%) being in the top 10 cm soil of 20 years old fallows and the lowest (0.39%) in 21-30 cm depth of 5 years old fallows. Multivariate analysis identified bulk density and porosity as the most important variables to discriminate between land use practices. The analysis provided evidence for significant changes in soil compaction, aggregate stability and SOC content with the transition from undisturbed forest to slash-and-burn cultivation and fallow phases. It is concluded that a minimum of 20 years of fallow period is required to achieve SOC content and C stocks comparable with intact forest land.
... The introduction of F. macrophylla and Dracaena cochinchinensis (Lour.) S. C. Chen into rubber plantations increases the formation of macroaggregates, and enhances the organic carbon and nitrogen accumulation within aggregates (Chen et al., 2017). Moreover, intercropping C. sinensis and T. cacao can increase the water use efficiency in rubber plantations by improving soil water infiltration and preferential flow Zhu et al., 2019a). ...
Article
Land degradation is a global problem caused by improper agricultural practices. In tropical China, the rubber (Hevea brasiliensis) plantations are predominantly practiced on forest-cleared lands, considering their sustainable land management potential compared to annual cropping. However, all rubber plantations may not have similar land management capacity. Soil quality index (SQI) can reveal the overall soil status with a single score, which is an efficient tool to evaluate the soil quality of each category of rubber plantations. We investigated 23 soil physical and chemical parameters of three categories of rubber plantations and a primary rainforest, and derived SQI based on these parameters. Soil samples were collected from a rubber monoculture (RM), a rubber-Camellia sinensis agroforestry (RT), a rubber-Dracaena cochinchinensis agroforestry (RD), and a primary rainforest (RF). The results showed that the SQI value of the RM decreased by 15.50% compared to the RF, with a significant degree of soil nutrient loss (18.90%). This indicates that monocultural rubber cultivation is causing land degradation to some extent. However, the SQI was significantly enhanced by rubber-based agroforestry practices (25.30% by RT and 33.10% by RD) compared to the RM, suggesting that polyculture practices are suitable to recover the soil quality in degraded agricultural lands. Moreover, the chemical parameters contributed more to the SQI than did the physical parameters, indicating that nutrient management is important in soil quality recovery. Overall, our results suggest that agroforestry should be preferred over monoculture in the rubber plantations for sustainable land management in tropical China.
... By improving soil structure, the high SOM content of natural forest soils effectively eliminates this inhibitory effect of heavy clay texture on O NH4 . However, calcareous soils again become clayey when the macroaggregate fraction significantly declines, such as due to the decreased SOM content during rubber cultivation (Chen et al., 2017). This could lead to oxygen limitations in clayey soil, which in turn would inhibit the stimulatory effect of N fertilizer on O NH4 , even at a high pH. ...
Article
Investigating soil inorganic nitrogen (N) supply and availability can guide soil improvement of rubber (Hevea brasiliensis) plantations in tropical regions, but the mechanisms controlling the inorganic N supply remain unknown. In this study, three natural forests and three degraded rubber plantations located in a tropical karst region of southwestern China were sampled to determine the gross N transformation rates using a 15N tracing method. The soils of the natural forests were characterized by a high inorganic N supply capacity and a high-level nitrate (NO3􀀀 ) production potential, due to the high rates of organic N mineralization to ammonium (NH4+) (MNorg) and NH4+ oxidation to NO3􀀀 (ONH4) but relatively low rates of immobilization of NH4+ (INH4) and NO3􀀀 (INO3) to organic N and dissimilatory NO3􀀀 reduction to NH4+ (DNRA). In the soils of the degraded rubber plantations, the rates of MNorg, ONH4, INO3, and DNRA were lower but the rates of NH4+ adsorption on cation-exchange sites (ANH4) increased, resulting in reductions in the inorganic N supply capacity and N availability. In addition, NO3􀀀 turnover in the soils of the degraded rubber plantations decreased, accompanied by a high mean residence time of NO3􀀀 and low δ15N values. Soil total N, organic C, phosphorus, and potassium concentrations, waterholding capacity, cation-exchange capacity, and sand content were significantly lower in the soils of the degraded rubber plantations than in those of the natural forests, indicating a decline in soil quality in the former. The significant, positive relationships between these soil properties and the rates of MNorg, ONH4, INO3, and DNRA highlight the importance of the appropriate application of organic N fertilizers as well as phosphorus and potassium fertilizers to stimulate soil N cycling and thereby increase the inorganic N supply. A reduction of the N deficiency in soils used for rubber tree cultivation would alleviate the soil degradation that characterizes many rubber plantations in tropical karst regions.
... By improving soil structure, the high SOM content of natural forest soils effectively eliminates this inhibitory effect of heavy clay texture on O NH4 . However, calcareous soils again become clayey when the macroaggregate fraction significantly declines, such as due to the decreased SOM content during rubber cultivation (Chen et al., 2017). This could lead to oxygen limitations in clayey soil, which in turn would inhibit the stimulatory effect of N fertilizer on O NH4 , even at a high pH. ...
Article
Investigating soil inorganic nitrogen (N) supply and availability can guide soil improvement of rubber (Hevea brasiliensis) plantations in tropical regions, but the mechanisms controlling the inorganic N supply remain unknown. In this study, three natural forests and three degraded rubber plantations located in a tropical karst region of southwestern China were sampled to determine the gross N transformation rates using a 15N tracing method. The soils of the natural forests were characterized by a high inorganic N supply capacity and a high-level nitrate (NO3􀀀 ) production potential, due to the high rates of organic N mineralization to ammonium (NH4+) (MNorg) and NH4+ oxidation to NO3􀀀 (ONH4) but relatively low rates of immobilization of NH4+ (INH4) and NO3􀀀 (INO3) to organic N and dissimilatory NO3􀀀 reduction to NH4+ (DNRA). In the soils of the degraded rubber plantations, the rates of MNorg, ONH4, INO3, and DNRA were lower but the rates of NH4+ adsorption on cation-exchange sites (ANH4) increased, resulting in reductions in the inorganic N supply capacity and N availability. In addition, NO3􀀀 turnover in the soils of the degraded rubber plantations decreased, accompanied by a high mean residence time of NO3􀀀 and low δ15N values. Soil total N, organic C, phosphorus, and potassium concentrations, waterholding capacity, cation-exchange capacity, and sand content were significantly lower in the soils of the degraded rubber plantations than in those of the natural forests, indicating a decline in soil quality in the former. The significant, positive relationships between these soil properties and the rates of MNorg, ONH4, INO3, and DNRA highlight the importance of the appropriate application of organic N fertilizers as well as phosphorus and potassium fertilizers to stimulate soil N cycling and thereby increase the inorganic N supply. A reduction of the N deficiency in soils used for rubber tree cultivation would alleviate the soil degradation that characterizes many rubber plantations in tropical karst regions.
... Golbon et al. (2018) predicted the impact of climate change on rubber distribution at different time horizons using various global circulation models. Apart from climate constraints, previous studies tested the effect of monoculture rubber plantation on carbon stocks (Blagodatsky et al. 2016;Yanci et al. 2017), physico-chemical properties (Chen et al. 2017;Chen et al. 2019), land use (Hu et al. 2008;Langenberger et al. 2016), and topography (Liu et al. 2013;Nguyen 2013). Thus, it is obtrusive that soil properties and topography have a negative impact on timber yield and latex production. ...
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Commercial demand is the prerequisite for the expansion of rubber plantation, which is highly dependent on climate, topography, and soil factors. Without the contextual knowledge on these factors, the expansion of rubber plantation would remain unproductive. This study thereby aimed to evaluate the current and future suitable habitat distributions of rubber using maximum entropy (MaxEnt) species distribution model in Xishuangbanna, Southwest China. A total of 148 field-based presence locations and environmental variables (soil, bioclimatic, topography, and land use) were used to predict the suitable areas of rubber plantations using HadGEM2-ES climate model. Medium and high climatic representative concentration pathways (RCPs) (4.5 and 8.5) were selected to predict the suitable habitats for the years 2050 and 2070. Among various factors, annual mean temperature, annual precipitation, precipitation of wettest month, precipitation seasonality, precipitation of warmest quarter, and soil exchangeable H+ contributed significantly to the distribution of rubber. Currently, 1119 km2 and 2716 km2 were predicted as high and moderately suitable areas respectively. It is predicted with increase rates in the high suitable areas, 49.96% and 328.95% by 2050 and 2070 respectively under RCP 4.5. This result indicates that the medium climate change of RCP 4.5 may have a direct positive effect on the expansion of habitat suitability of rubber. We also found potential areas for rubber cultivation in Jinghong and Mengla townships, where the further expansion is anticipated with desirable land-use planning by conserving reserve forest and native vegetation.
... Ecosystem service-related benefits of rubber-based agroforest have been demonstrated in recent years; including increased soil quality, water conservation, and reduce herbicide application (Chen, Liu, Jiang, & Wu, 2017;Liu, Nie, Zhang, Tang, & Siddique, 2018). Additionally, here, we provide ecological evidence that intercropping understory crop in monoculture rubber plantations might represent a better plantation system for arthropods like ants by limiting the spread and establishment of tramp species. ...
Article
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Protected areas are increasingly threatened by biological invasions, especially in tropical Asia where extensive areas of natural habitats have been converted to monoculture plantations. Such disturbance provides a gateway for exotic species invasions, highlighting an urgent need for cross‐boundary solutions to mitigate invasion impacts. Agroforests, with multi‐storied trees and crops resembling the complex structure of natural forest, are known to promote native species compared to monoculture plantations. Yet our knowledge on their roles in controlling exotic species is limited to plant invaders, with effects on animal invaders still unknown. Given that protected areas are increasingly threatened by invaders from surrounding plantations, with a majority of them represented by insects, it is important to evaluate the effect of agroforestry practice, and mechanisms of associated management to control invasions. By using both taxonomic and functional trait‐based approaches, we studied leaf litter ant communities in 12 rubber monoculture (mono‐rubber), 9 rubber plantation with understory crops (agro‐rubber), 16 secondary, and 12 old‐growth secondary forest plots in and around protected areas in Hainan, China. Sampled ants were further classified into groups based on their invasive potential (tramp vs non‐tramp) to determine the ecological values of agro‐rubber. We found that despite mono‐rubber and agro‐rubber presenting similar species richness, the latter 1) supports species composition and functional diversity more similar to secondary forests, and 2) reduces tramp ant species occurrence, a novel management incentive. Nonetheless, agro‐rubber is not comparable to secondary forest in terms of non‐tramp ant species composition. Synthesis and applications. Against the increasing threat of biological invasions, preserving natural forests in human‐dominated landscapes is crucial. Increasing the area of agro‐rubber at the periphery of protected areas as a proactive mitigation can, however, be perceived as an additional measure to reduce invasive species’ establishment and spread across the landscape. Plantation‐based agroforestry has emerged as a potential management avenue and incentive for transforming monoculture plantations into a less “harmful” alternative.
... Plant diversity can reduce the needs for agricultural inputs such as fertilizer, pesticides (Letourneau et al., 2011;Rusch et al., 2016), and imported pollinators (Kremen et al., 2007;Orford et al., 2016;Scherber et al., 2010). Intercropped systems can provide ecosystem services which are normally lost in conventional monoculture farming (Isbell et al., 2017;Kremen and Miles, 2012;Li, 2016), increase above and belowground biodiversity (Asigbaase et al., 2019;Boinot et al., 2019) and improving soil health (Chen et al., 2017a;Froufe et al., 2020). Additionally, intercropped systems have demonstrated the potential to produce higher yields than monoculture systems (Chen et al., 2017c;Daryanto et al., 2020;Yu et al., 2015;Zhang et al., , 2019. ...
Article
Replacing conventional monocultures with high diversity agroecosystems can positively impact environmental quality, but their adoption is limited, in part, due to inadequate understanding of how these systems operate regarding belowground competition. We examined how root competition between breadfruit (Artocarpus altilis) and māmaki (Pipturus albidus) affected aboveground performance under three different establishment treatments: breadfruit first, māmaki first, and simultaneous establishment. Our 2x3 factorial design consists of two competition treatments and the three establishment treatments. Plants were grown together on either side of 47-gallon pots. For non-competition groups, a sheet of vinyl plastic was used to keep the roots of each species separate while maintaining above ground conditions. We used root cores to quantify the spatial allocation of root biomass to explore competition strategies of the two crops and measured biomass production to determine how growth was affected by competition. Our results demonstrate different effects, with breadfruit above ground biomass (AGBM) decreased and māmaki AGBM increased under competition. Below ground biomass increased for both plants under competition. Prior establishment enhanced māmaki’s response to competition, while breadfruit’s response to competition was exacerbated by post establishment and mitigated by simultaneous establishment. We suggest that māmaki’s response is due to a more aggressive strategy that targets resource patches, while breadfruit is unable to compete within established māmaki zones and employs an avoidance strategy for root allocation.
... Hence, it is the decisive factor affecting the quality of cultivated land and crop yield (Brar et al., 2013;Hassan et al., 2016) [11,25] . However, the SOC content in Chinese farmland soil is generally low [13,14] which is lower than the world average by more than 30% and that of Europe by more than 50%. Organic C in Indian soils was estimated as 23.4-27.1 Pg (Dadhwal and Nayak, 1993) [16] . ...
... Chen, Liu, Wu, Jiang, and Zhu (2019) reported that rubber-intercropping significantly improved SMCs because of its significant moisture-holding capacity of capillary porosity in the average soil depth due to its better root distribution. The higher SMC in the average deep soil could be the complementary result of a rubber-based intercropping system as the crops shared nutrients, soil water and also the space in the soil (Langenberger et al., 2017;Wu, Liu, & Chen, 2016) that enhanced the root proliferation which improved soil porosity, hydraulic conductivity, water infiltration and soil water holding capacity (Chen, Liu, Jiang, & Wu, 2017;Elmholt et al., 2008). Table 3 represents the LAIs among the farms. ...
Article
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The study aimed to preliminarily explore the relationship of the rubber tree’s physiological status and technological properties with response to different agroecosystem components, especially leaf area index (LAI) and soil moisture contents (SMC) under three types of rubber-based intercropping, notably rubber-bamboo (RB), rubber-coffee (RC) and rubber-melinjo (RM) compared to a rubber monocrop (R). RB and RM significantly showed the highest LAI values of around 1.4, while that of R had the smallest value (about 30% lesser than the highest values). RM, RB dramatically increased the SMC with the soil depths. The rubber-based intercropping farms indicated better biochemical composition in the latex, showing efficient metabolism of the latex biosynthesis. Technological properties of the raw rubber from the rubber-based intercropping farms expressed the premium results in both non-rubber components and rheological properties with higher molecular weights. The correlation analysis revealed some significant relations among the LAI, SMC, biochemical composition and technological properties.
... This is because soil organic matter, as a substrate, directly influences soil microbial biomass (Chen et al., 2006). This was shown by the significantly positive correlation of soil microbial biomass nutrients and soil nutrients in our study (Fig. 2), as well as shown in other studies (Chen et al., 2017;Padalia et al., 2018). The change ratio of microbial biomass in the various soil layers from grassland to cropland was relatively stable (e.g., SMBC) or showed a certain degree of fluctuation (e.g., SMBN, SMBP) with time (30-59 years) since land-use shift (Fig. 6a). ...
Article
The carbon and nutrients in the soil microbial biomass (SMB) and their proportion in soil elements, namely soil microbial quotient (SMQ), are the key indicators of the soil quality and quickly respond to the shift in the land-use pattern. However, the degree of the land-use shift influences on the soil microbial biomass, and the soil microbial quotient in the meadow steppe is not well-understood. The soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorous (MBP), and SMQ were determined separately in grassland, cropland, and abandoned cropland in four sites within 50 km at a meadow steppe in northeast China. The results showed that the soil MBC, MBN, and MBP declined significantly as soil depth increased among the three land-use patterns. Agriculture has resulted in a significant decrease in the soil MBC, MBN, MBP, and SMQ compared to their corresponding values in grassland. The soil MBC content significantly was increased at the 0–10 cm soil layer after agriculture abandonment, but the SMQ had no significant improvement in the entire profile when compared to cropland. Besides, for the three types of land-use patterns, the C, N, and P stoichiometry of the soil microbial biomass was relatively stable, except for the stoichiometry in the relatively deep soil layer. Overall, the present agricultural abandonment (~ 19 years) got a certain of restoration in soil microbial biomass. Their corresponding values, however, were significantly lower than those found in native grassland. This highlighted that the restoration of the poor soil quality caused by the long term agriculture cultivation is a slow and hard process; it is important to maintain natural grasslands for protecting and maintaining soil microbial biomass and SMQ in the meadow steppe of northeast China.
... The reduction in the MWD and GWD in cultivated land is due to land clearing and soil physical disturbances resulting from cultivation immediately after forest conversion. Similar changes in soil aggregation have been reported under rubber agroforestry (Chen et al., 2017). A general trend of increase in bulk density and decrease in porosity, MWD, and GWD with an increase in soil depth is consistent with the findings from plantation forests in China (Ge et al., 2018) and India (Kurmi et al., 2020). ...
Article
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Shifting cultivation, the oldest farming system of the world and is the dominant land use in mountainous regions of South and Southeast Asia. North-East India (NEI) region, one of the world’s biodiversity hotspots, covers 17.2 million ha of land under forests, constituting ~25% of India's total forest area. The population-driven abrupt decline of the fallow period’s duration has aggravated soil erosion, depletion of nutrients, decreased productivity, reduced biodiversity, and weakening of essential ecosystem services. Therefore, the present research aims to explore whether the duration of the fallow period of up to 20-years can restore diversity of tree species, biomass carbon, and ecosystem carbon stock equivalent to those under natural forests. Based on the accessibility and availability of the fallow stands, three categories were selected for the study (1–2, 5–8, and 15–20 years), and these were replicated eight times for each age group. While the 20-years of fallow increased tree diversity, it was still 22% lower than that of the natural forest. Similarly, a 2.7-fold increase in biomass carbon storage was observed with an increase in the fallow period from 5–8-years (33.4 Mg ha-1) to 15–20-years (92.9 Mg ha-1), yet the latter was 40% lower than that under the natural forests. The very labile and labile carbon stocks decreased with an increase in the fallow period. In contrast, the less labile and non-labile carbon stocks increased with increase in the fallow age. Because of the absence of a long fallow management system in the region, and to minimize the risks of ecosystem carbon degradation, adopting an integrated approach is recommended to enhance the ecological integrity of the degraded lands under shifting cultivation while also improving the livelihood of the shifting cultivators.
... This agreed with SOC and ρ b results. Soil organic carbon was reported to improve soil aggregation (Chen et al., 2017;Novelli et al., 2017;Ojeda et al., 2018), and increase soil porosity (Dexter et al., 2008;Haruna et al., 2017;Rawls et al., 2004). Thus, the higher total pore values at the toe slope in the current study were attributed to higher SOC values at the toe slope position. ...
Article
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Soil hydraulic properties influence water and nutrient availability, as well as environmental sustainability, and these properties vary across several landscape positions. This study investigated the spatial variability and fractal characterization of soil hydraulic properties across five slope positions: summit, shoulder, back, foot, and toe slopes. Triplicate soil samples (0‐18 cm) were collected from each slope position from a pasture field planted to tall fescue (Festuca arundinacea syn. schendonorus arundinaceus). Soil bulk density (ρb), saturated hydraulic conductivity (Ksat), water retention at 0, ‐33, and ‐1500 kPa soil water matric potentials, soil organic carbon (SOC), and various pore sizes (macropores [>1,000 μm], mesopores [10‐1,000 μm], and micropores [<10 μm]) were analyzed. Results show that SOC was 26% higher, while ρb was 10% lower at the toe slope compared with the summit. Similarly, Ksat values were 3, 9, 16, and 2% greater at the toe slope compared with the summit, shoulder, back, and foot slopes, respectively. Semivariogram analysis showed that the gaussian isotropic model provided be best fit (R2 > 0.99) for hydraulic properties across all slope positions. The range of spatial variability of soil hydraulic properties was between 5.60 and 123.00 m at all slope positions. The fractal dimensions of soil hydraulic properties across all slope positions ranged from 0.784 – 1.966. Soil hydraulic properties were more similar at the foot and toe slopes which might favor improved crop productivity at these slope positions. This article is protected by copyright. All rights reserved Soil hydraulic properties vary spatially along a catena. Range of spatial variability was different for hydraulic properties along a catena Saturated hydraulic conductivity was highest at the toe slope compared with other positions Spatial autocorrelation of hydraulic properties depends on intrinsic soil properties As the soil dries, most soil hydraulic properties tend to be less self‐similar
... Soil aggregates regarded as microenvironments can determine nutrient distribution and gas (e.g., oxygen and carbon dioxide) circulation (8,27) and therefore affect microbial distribution (8,28). Studies involved in phosphorus cycling are mainly about phosphorus fractionation in environments and gene abundance of phosphate-solubilizing bacteria in different habitats (e.g., soils, sediments, and water), as well as PSB isolation (3)(4)(5)(6)(7)(8)(9)(13)(14)(15)(16)(17). ...
Article
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ABSTRACT Deciphering distribution patterns of phosphate-solubilizing bacteria (PSB) and phosphorus-cycling-related genes in soils is important to evaluate phosphorus (P) transformation. However, the linkage between PSB number and P-cycling-related gene abundance in soils, especially soil aggregates, remains largely unknown. Here, we estimated the numbers of PSB and abundances of P-cycling-related genes (i.e., gcd and bpp) in soil aggregates under different fertilization regimes as well as P-solubilizing performance and plant-growth-promoting ability of PSB. We found that tricalcium phosphate-solubilizing bacteria, phytate-degrading bacteria, and gcd and bpp abundances were more abundant in silt plus clay (silt+clay;
... This may be because a soil organic carbon and nitrogen input caused by the increase of organic matter sources in compound rubber plantation ecosystems, such as leaf litter and plant roots, prevents the aggregate loss of soil organic carbon and nitrogen and promotes its fixation. This would lead to a more benign cycle than the monoculture model (Chen et al. 2017). Another agroforestry technique may be to form a near-natural shrub-grass-rubber forest ecosystem without human disturbance between rubber plantations. ...
Article
Rubber (Hevea brasiliensis Müll. Arg.) trees have been commercialized for several decades in Asia, notably in China and form a typical plantation ecosystem in tropical areas. Although rubber trees have been planted successfully as commercial crops in many places, adapting rubber plantations to sub-optimal environments remains a challenge. Especially in young rubber plantations, populations are often not stable or sustainable because tree breakage and death are common due to frequent strong storms. Intercropping to optimize group structure has been proposed as a method to improve the overall stability of rubber plantations. The objective of our study is to explore the wind resistance and growth of individual rubber trees in an intercropped system that utilizes native tree species Michelia macclurei and Mytilaria laosensis. The density of rubber trees was the same in the monoculture and the intercrop, with additional native trees added in the intercrop. The effects of the wind resistance and growth of the system to three different planting patterns namely, the monoculture of Hevea brasiliensis, Hevea brasiliensis intercropping with Michelia macclurei, and Hevea brasiliensis intercropping with Mytilaria laosensis were analyzed using observation data from the field plots. The results show that both the maximum and average wind speeds were lower in intercropped rubber plantations than in monoculture rubber plantations, the average maximum wind speeds were lower in Hevea-Michelia and Hevea-Mytilaria intercropping systems than in the Hevea monocrop system by 8.4% and 19.6%, respectively. The average wind speeds were also lower in Hevea-Michelia and Hevea-Mytilaria intercropping systems than in the Hevea monocrop system, with daily average wind speeds 21.2% and 36.0% lower, respectively. The proportion of rubber trees showing Grade 6 wind damage in monoculture, intercropping with Michelia and intercropping with Mytilaria were 9.5%, 2.3% and 1.9%, respectively. There was a competition between the intercropping Michelia / macclurei and Hevea in soil nutrient absorption and utilization, and the competition of soil nutrient further decreased the height growth and formed small crown area opposing wind loading. This indicates that the pattern of intercropping rubber with native tree species may reduce wind speed and average wind speed in intercropped rubber systems, thereby reducing the wind damage on rubber trees and improving their health. The biomass of intercropping with Michelia and intercropping with Mytilaria systems is significantly higher than Hevea monocrop system. This result shows that the intercropping patterns of Hevea-Michelia and Hevea-Mytilaria enhance the total productivity. This indicates that intercropping rubber with native trees may construct an environment that buffers wind effects and benefits tree growth to the extent that it could also improve ecosystem stability in rubber plantations. Healthier and stronger rubber trees may lead to a more sustainable and possibly increased yield of rubber from plantations in the future. These results also enrich tropical protection science and provide a valuable reference for the sustainable management of agricultural system or other plantation.
... Therefore, our findings suggest that the enhanced SOC pool in the upland's surface layer mainly by adding OAs, and the incidental accumulation of plant residues generated during this experiment improved the overall soil physical status. Several studies demonstrated such benefits of adding OAs, e.g., stabilizing soil aggregation against slaking and dispersion and promoting soil aeration and moisture retention, in agricultural soils, which would contribute to crop yield increase in turn [47][48][49]. ...
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Some intensive farmers tend to expect short-term beneficial effects by applying soil amendments, but inconsistent fertilization practices are often conducted, causing economic losses and environmental problems. This study aimed at investigating the short-term application effects of different soil amendments on soil organic carbon (SOC) fractions, biogeochemical properties, and crop performance for finding the best land management approach using one-year field trial growing Chinese cabbages. This filed experiment was conducted in 2020 and included eight fertilizer treatments: control (w/o fertilizers), chemical fertilizer (CF), manure compost (MC), double MC amount (2MC), CF + MC, CF + rice husk (RH), MC + RH, and CF + MC + RH. As a result, the concentrations of recalcitrant to labile C forms, including Loss-On-Ignition C (LOIC), Walkley-Black C, permanganate oxidizable C (POXC), and microbial biomass C, were the highest in a mixture of MC and RH and 2MC. Additionally, the treatment with the largest difference from the control in key soil parameters was 2MC: bulk density (10%), total N (30%), available P (186%), and CO2 (433%) and N2O (825%) emissions, followed by MC + RH. Moreover, more than 20% higher fresh weight (FW) of cabbage was found in 2MC and MC + RH than in the control. Therefore, these two organic amendments appeared to benefit SOC storage and overall soil biogeochemical processes, contributing to higher biomass crop production. Moreover, LOIC significantly correlated to bulk density, available P and K, and FW, while POXC significantly correlated to N concentration in plants, indicating the short-term fertilization effects on the status of SOC fractions and the qualities of soil and plant by applying soil amendments. Overall, our findings suggest that applying MC + RH would be an alternative to replace the conventional farming practices for promoting soil quality and crop performance, but further studies to sustain the application effects of this amendment should be monitored for longer durations.
... Macroaggregates are structural units that participate in the regulation of nutrient cycling and the organic matter dynamics [101], which also depend on the carbon availability and the biological activity [48,102,103], leading to improved soil quality [104]. The presence of higher physical and root macroaggregates in pastures might be the result of macroinvertebrates, together with the dense root system of pastures, that through mechanical reinforcement, promote soil aggregation, binding the soil and releasing exudates that acts as soil binding agents [105][106][107]. ...
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Successional processes in abandoned pastures in the Amazon region have been well-documented for the floristic component; however, soil succession has been poorly studied. This study assessed the physical, chemical and biological responses of soils in the Amazon region during the natural succession process in two main landscapes of the Colombian Amazon. Soil data on soil physico–chemical (bulk density, macroaggregates, pH and minerals) and biological (soil macrofauna) composition were evaluated along chronosequence with four successional stages: (i) degraded pastures, (ii) young (10–20-year-old), (iii) middle-age (25–40-year-old) and (iv) mature forests, in two different landscapes (hill and mountain). Individual soil variables and a synthetic indicator of soil quality (GISQ) were evaluated as tools for natural succession monitoring. The results corroborated the negative impact that cattle ranching has on Amazon soils. After 10 years of natural succession, the physico–chemical and biological soil components were widely restored. Less soil compaction and organic carbon occurred in older successional stages. Soil macrofauna richness and density increased along the chronosequence, with an evident association between the macrofauna composition and the macroaggregates in the soil. None of the individual soil properties or the GISQ indicator discriminated among natural succession stages; therefore, new soil quality indicators should be developed to monitor soil quality restoration in natural successions.
... This result supports the findings of Buyanovsky et al. (1994) and could be ascribed to incomplete humified organic plant residues with a wide C:N ratio within macroaggregates. In microaggregates, however, soil organic matter under poor protection is exposed to microbial decomposition mineralization, releasing organic matter with higher bioavailability and microbial materials with lower C:N values (Callesen et al., 2007;Chen et al., 2017;Ding and Zhang, 2016). ...
Article
Soil erosion by water is a serious global ecological issue that leads to land degradation and threatens ecosystem sustainability. Splash erosion resulting from raindrop impact is the first stage of the erosion process and is mainly responsible for the detachment and migration of soil surface aggregates. In humid tropical regions, however, there has been little quantitative analysis of the relations between splash erosion and variable aggregate characteristics such as stability, particle size distribution and organic matter content. The objective of the current study was to determine how rain splash erosion is related to soil aggregate characteristics under land-use change, i.e., the conversion of tropical rainforest (TR) into rubber plantation (RP). Splash cups containing dry-sieved aggregate samples with eight size classes were exposed to natural rainfall to measure the splash erosion rate. The results showed that the initial aggregate organic carbon, water-stable aggregate index (WSA) and mean weight diameter (MWD) decreased by 31%, 9% and 48%, respectively, after 32 years of rubber cultivation. These degenerations in aggregate properties increased the susceptibility of soil aggregates to erosion and mutually contributed to a higher average splash erosion rate in RP (1.20 kg m⁻²) than in TR (1.09 kg m⁻²), regardless of aggregate size fractions. Splash erosion rates for all aggregate sizes were significantly positively correlated with rainfall kinetic energy, rainfall amount and intensity during the study period. The average splash erosion rate of aggregates first increased and then decreased with a decline in aggregate size in both TR and RP. The minimum and maximum splash rates were observed within 10–8 mm and 0.5–0.25 mm size fractions, respectively. In particular, the proportion of small-sized aggregates (i.e., 1–0.15 mm) with a relatively high splash erosion rate increased remarkably after land-use change. This exerted a negative impact on splash erosion control as well as on the sustainable development of rubber cultivation. Increasing the additional input of organic materials (e.g., intercropping cash crops with rubber trees) may help to enhance large aggregate formation and stabilization, which could minimize the risk of splash erosion at the aggregate scale for eroded rubber plantation ecosystems.
... Some authors hypothesize that the cultivation of cacao and shade trees provides the best resources for earthworms, including a favorable microclimate, food and shelter (Bottinelli et al., 2015), which allows them influence the soil through bioturbation, during which they mix the mineral layer of the soil with organic matter (Lavelle et al., 2016). In this respect, Chen et al. (2017) mentioned that agroforestry systems generally improve the accumulation of organic material thanks to the constant supply of plant residues that enable improvements in the aggregation and stability of the aggregate. However, some authors reported no increase in the stability of soil aggregates (i.e., MWD), or any significant differences in the proportions of macroaggregates, or in the storage of C with increased diversity of shade trees in cacao plots (Wartenberg et al., 2017). ...
Article
The objective of our work was to evaluate soil quality in different cacao agroforestry systems (AFS) in the Colombian Amazon. We compared soil quality of AFS at the study site with soil quality of two control systems: a pasture and a secondary forest. The study was conducted at the Macagual Amazon Research Center in western Colombian Amazon. We set up eight 600 m² plots in each study system. We collected soil samples in each plot, and assessed macrofauna diversity, aggregate morphology, and physical and chemical soil properties. We integrated these variables in a General Indicator of Soil Quality (GISQ). We found GISQ values of 0.85 for forest, 0.5, 0.65 and 0.59 for AFS and 0.21 for pasture, and the values differed significantly between land uses. The establishment of cacao AFS on degraded pasture was found to significantly improve soil fertility, i.e., by 42%. The intensification level between land uses (Pasture > AFS > Forest) negatively affected macrofauna populations due to soil compaction (physical properties). Forest had the highest physical and biological quality. Our results show that AFS not only have the capacity to maintain key soil ecological functions, but also to restore soil quality of degraded pastureland. Cacao-based AFS could therefore be a key restoration strategy for degraded pastureland. These results are very important in the context of the Colombian Amazon, where cacao is currently known as the “crop of peace”.
... Hence, it is the decisive factor affecting the quality of cultivated land and crop yield (Brar et al., 2013;Hassan et al., 2016) [11,25] . However, the SOC content in Chinese farmland soil is generally low [13,14] which is lower than the world average by more than 30% and that of Europe by more than 50%. Organic C in Indian soils was estimated as 23.4-27.1 Pg (Dadhwal and Nayak, 1993) [16] . ...
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In India, the average soil organic carbon (SOC) content of cultivated land is 30% less than the world average. Therefore, cultivation management-induced changes in SOC dynamics are necessary, especially in Typic Ustochreptsoils, where the SOC stocks are limited. Soil tillage can affect the stability and formation of soil aggregates by disrupting soil structure. Frequent tillage deteriorates soil structure and weakens soil aggregates, causing them to be susceptible to decay. SOC pools, such as coarse particulate organic matter C (CPOM-C), microbial biomass carbon (MBC), and mineralizable C (C min) respond to changes in management practices and provide sensitive indication of changes in the SOC dynamics than commonly reported total soil C alone. POC reduction was mainly driven by a decrease in fine POC in topsoil, while DOC was mainly reduced in subsoil. Fine POC, LFOC and microbial biomass can be useful early indicators of changes in topsoil organic C. In contrast, LFOC and DOC are useful indicators for subsoil. Reduced proportions of fine POC, LFOC, DOC and microbial biomass to soil organic C reflected the decline in soil organic C quality caused by tillage and straw Management practices. Average SOC concentration of the control treatment was 0.54%, which increased to 0.65% in the RDF treatment and 0.82% in the RDF+FYM treatment. Compared to F1 control treatment the RDF+FYM treatment sequestered 0.33 Mg Cha-1yr-1whereas the NPK treatment sequestered 0.16 Mg Cha-1yr-1. Relative to the control (no nutrient input CK), long-term fertilization appreciably increased SOC storage by 134, 89 and 129 kg ha–1yr–1 under CF, and 418, 153 and 384 kg ha–1yr–1under organic manure plus chemical fertilizers (MCF) in plough layer soils (0–20 cm). The mineral-associated OC (MOC) pools accounted for 72, 67 and 64% of the total SOC with sequestration rates of 76, 57 and 83 kg ha–1yr–1 under chemical fertilizers (CF) and 238, 118 and 156 kg ha–1yr–1 under MCF, respectively. Moreover, the MOC pool displayed a saturation behavior under MCF conditions. The particulate OC (POC) accordingly constituted 27, 33 and 36% of SOC, of which Light-POC accounted for 11, 17 and 22% and Heavy-POC for 17, 16 and 15% of SOC, respectively. The sequestration rates of POC were 58, 32 and 46 kg ha–1yr–1under CF, and 181, 90 and 228 kg ha–1yr–1under MCF in which Light-POC explained 59, 81 and 72% of POC under CF, and 60, 40 and 69% of POC under MCF, with Heavy-POC accounting for the balance. Compared with CK, the application of CF alone did not affect the proportions of MOC or total POC to SOC, whereas MCF application markedly reduced the proportion of MOC and increased the POC ratio, mainly in the Light-POC pool. The distribution of SOC among different pools was closely related to the distribution and stability ofaggregates. Compared to conventional tillage, conservation tillage (no-tillage coupled with straw return) increased water-stable large macro-aggregates (>2 mm) by 35.18%, small macro-aggregates (2–0.25 mm) by 33.52% and micro-aggregates by 25.10% in the topsoil (0–20 cm). The subsoil (20–40 cm) also showed the same trend. Compared to conventional tillage without straw return, large and, small macro-aggregates and micro-aggregates in conservation tillage were increased by 24.52%, 28.48% and 18.12%, respectively. Straw return also caused a significant increase in aggregate associated carbon (aggregate-associated C). No-tillage coupled with straw return had more total aggregate-associated C within all the aggregate fractions in the topsoil. But the different is that conventional tillage with straw return resulted in more aggregate-associated C than conservation tillage in the subsoil. No-tillage combined with straw return produced the highest carbon preservation capacity (CPC) of macro-aggregates and micro-aggregates in the topsoil. A considerable proportion of the SOC was found to be stocked in the small macro-aggregates under both topsoil (74.56%) and subsoil (67.09%). The review study confirmed that conservation tillage with organic manure amendment not only sequestered more SOC but also significantly altered the composition of SOC, thus improving SOC quality, which is possibly related to the SOC saturation level. Thus, straw return integrated with mineral fertilization in rice- wheat croplands leads to increase SOC stocks. However, those effects of straw return are highly dependent on fertilizer management, cropping system, soil type, duration period, and the initial SOC content.
... The higher content of SOM is an indicator of healthy soil with efficient infiltration and water-holding capacity, thus higher nutrient availability (C. Chen et al., 2017;Nannipieri et al., 2017). ...
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The replanting practice of rubber monocropping in Southern Thailand has depleted soil fertility. Most rubber planted areas in the region were under intensive chemical fertilization resulting in less soil organic matters and root proliferation. With the instability of rubber prices, some rubber farmers converted from monocropping into intercropping. Integrated fertilization in which mixed organic-inorganic fertilizers are combined with organic soil amendments could be considered in a rubber-based intercropping system to increase land productivity with cost-saving fertilization by rehabilitating soil properties. A study was conducted at a rubber-salacca intercropping farm comprised of 14-year-old mature rubber trees associated with eight-year-old salacca palms to identify the consequences of the integrated fertilization combined with two organic soil amendments: humic acid (HSA); chitosan (CSA). Changes in soil organic matter (SOM), leaf area index (LAI), fine root traits, tree physiological status, and crop productions under the two integrated fertilization were compared against the controlled application of conventional chemical fertilizer. The CSA application increased the SOM in the topsoil layer by 80%. In the 21-40 cm soil depth, the rubber roots treated with HSA and the salacca palm roots treated with CSA showed greater fine root length density (FRLD). Under CSA, the physiological status of the rubber trees showed less stress. The treatments of HSA and CSA showed 145% and 72%, respectively, higher in total production of salacca palm than that of the Zar Ni Zaw, Rawee Chiarawipa, Surachart Pechkeo and Sakanan Saelim 154 Pertanika J. Trop. Agric. Sci. 45 (1): 153-170 (2022) chemical fertilization. Improvements in the soil fertility, the root's function, the crops' yields, and the tree physiological status were consequences as complementarity in the system under the integrated fertilizations.
... Chen et al. (2017) studied effects of rubber-based agroforestry systems on soil aggregation and associated soil organic carbon in Xishuangbanna, southwestern China. Five different treatments viz., rubber monoculture (Rm) and four rubber-based agroforestry systems: H. brasiliensis -C. ...
Article
Most of the world’s tropical landscapes are experiencing changes in land-use and land-cover. In Yunnan Province in southwestern China, land-use changes are widespread throughout the tropics, with large areas of tropical forests being converted to banana (Musa spp.) plantations. In this study, we explored the effects of banana trees’ funnel-shaped leaves on rainfall redistribution and plant water acquisition during the 2017/2018 rainy season. Both the conventional and isotopic (δD and δ¹⁸O) methods were used to conduct rainfall partitioning, assess throughfall distribution, and predict plant water sources. We found that the mean contribution of throughfall, stemflow, and interception loss to gross rainfall (rainfall amount: 0.3–33.3 mm) were 71.8 ± 6.8 %, 17.6 ± 3.6 %, and 10.6 ± 3.8 %, respectively. The percentage of stemflow under the banana canopy was noticeably higher than previously reported for other species. The maximum amount of throughfall below the banana canopy was 1.4–4.4 times greater than the gross rainfall (rainfall amount: 14.7–70.5 mm). Soil water content and soil water δD and δ¹⁸O showed both horizontal and vertical heterogeneities within the banana plantation. Analysis of δD and δ¹⁸O indicated that banana trees absorbed 72.3 % of their water from the shallow soil stratum at 0−30 cm depth. In addition, the acquisition proportion of 0−80 cm soil water ranged from 10.2%–16.3% in the horizontal directions (0−360°). These findings indicated that banana trees’ wide and long leaves considerably altered rainfall redistribution, which in turn affected their water acquisition characteristics. As banana plantations expand in this area, there is an urgent need to further examine environmental consequences such as soil erosion and surface runoff resulting from banana cultivation.
Article
Agroforestry systems (AFSs) with oil palm are expected to have better soil quality than monocultures of this crop. The variation in soil physical quality between oil palm management zones is related to carbon input and is well known in monocultures, but poorly studied in oil palm AFSs. Here we determined whether management practices change the carbon content and physical quality of soil in oil palm AFSs. We collected undisturbed and disturbed soil samples at different management zones (weeded circle, harvest path, leaf pile, and diversified strip) from the 0–5-, 5–10-, 10–20-, and 20–30-cm soil layers in oil palm AFSs in Eastern Amazon, Brazil. We determined the soil water retention curve, density, aggregation, penetration resistance, and carbon content. We performed principal component analysis to evaluate the influence of management on carbon content and physical properties in different soil layers. Overall, the management zones where there was no machinery traffic (weeded circle, leaf pile, and diversified strip) exhibited a higher carbon content and better physical quality in the surface soil layers (0–5 and 5–10 cm). These zones differed from the harvest path, which showed worse soil physical quality, i.e., lower soil aggregation, porosity, water retention, and carbon content, and greater soil density, compaction, and penetration resistance. Management practices that increase carbon levels on the harvest path should be prioritized to reduce the degradation of soil physical quality. Therefore, our results can help guide a more sustainable management of the soil in oil palm cultivation areas in the Amazon.
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Background and purpose Volcanic eruptions of pyroclastic tephra, including the ash-sized fraction (< 2 mm; referred to as volcanic ash), have negative direct impacts on soil quality. The intensity (deposit thickness, particle-size distribution) and frequency (return period) of tephra deposition influence soil formation. Vulnerability and subsequent recovery (resilience) of the plant-soil system depend on land-uses (vegetation and management). Few previous studies covered the whole deposition-recovery cycle. We investigated the volcanic ash deposition effects on soil properties and their recovery across land-uses on a densely populated volcanic slope. Methods We measured the canopy cover and volcanic ash thickness six years after the 2014 Mt. Kelud eruption in four land-use systems: remnant (degraded) forests, complex agroforestry, simple agroforestry, and annual crops. Each system was monitored in three landscape replicates (total 12 plots). For the soil recovery study, we measured litter thickness, soil texture, Corg, soil C stocks, aggregate stability, porosity, and soil infiltration in three different observation periods (pre-eruption, three, and six years after eruption). Results Post-eruption volcanic ash thickness varied between land-use systems and was influenced by the plots slope position rather than canopy cover. The average soil texture and porosity did not vary significantly between the periods. Surface volcanic ash and soil layers initially had low aggregate stability and limited soil infiltration, demonstrating hydrophobicity. While Corg slowly increased from low levels in the fresh volcanic ash, surface litter layer, aggregate stability, and soil infiltration quickly recovered. Conclusions Different land-use management resulted in different recovery trajectories of soil physical properties and function over the medium to long term after volcanic ash deposition.
Article
Rubber plantation establishment is a common land use that can profoundly impact plant diversity and soil properties in tropical forest ecosystems, although empirical data on such effects are scarce in tropical Africa. In this study, we examined the effects of this land use on tree species diversity and soil physicochemical properties of the Awudua Forest in Ghana. We surveyed 60 25 m × 25 m plots, 20 in each of three land uses (i.e., primary forest, secondary forest and rubber plantation) of the study area. Within each plot, we identified and enumerated all trees (≥ 10 cm diameter at breast height, dbh at 1.3 m) and collected soil samples at three depths (i.e., 0-10 cm, 10-20 cm and 20-30 cm) for the determination of soil physicochemical properties (bulk density, particle size distribution, pH, OC, TN, AP, K, Mg, Ca). Soil physicochemical properties; sand, OC, AP, K, Mg, Ca in the rubber plantation decreased by 4.4%, 24.9%, 40.0%, 16.7%, 50.0% and 20.2% respectively, whereas the primary forest recorded decreases in OC (42.2%), TN (25%), AP (71.1%), K (69%), Mg (59.6%), Ca (27%) from the surface to the sub layers. Results showed significantly lower tree species richness (S, 12), diversity (H', 0.37), evenness (E, 0.43), and basal area (BA, 2.86 m²/ha) in the rubber plantation compared to those of the secondary forest (36, 1.10, 0.85 and 0.93 m² ha⁻¹, respectively) and the primary forest (46, 2.28, 0.97, and 3.32 m² ha⁻¹, respectively). Non-metric multidimensional scaling ordination also revealed distinct tree species composition among the land uses. Terminalia ivorensis (IVI = 7.1%), Musanga cecropoides (28.91%) and Hevea brasiliensis (72.03%) were the most dominant species in the primary forest, secondary forest and plantation respectively. Soil OC, TN, K, AP, Mg and bulk density differed among the land uses, but no differences were observed in pH and Ca. The findings confirmed the strong negative impacts of rubber plantation land use on plant diversity and soil properties, suggesting the need for mitigation measures such as afforestation and offsetting to ensure sustainable utilization and conservation of biodiversity in the reserve.
Chapter
Agroforestry systems play an important role in sustainable agroecosystems owing to enhanced atmospheric carbon assimilation (by soils and plants), nutrient cycling, enhanced soil biodiversity, and reduced soil disturbance (and subsequent soil erosion), all relative to monocropping systems. The magnitude of these ecosystem and provision services, however, relies on the type of agroforestry system employed (e.g., shelterbelts, silvopastures), as well as edaphic and climatic factors. Nonetheless, agroforestry’s potential to improve soil quality and soil conservation has been widely recognized as a major benefit of these managed agroecosystems, both in the tropics and temperate regions of the world. With increasing concern regarding climate change, microclimate modification with agroforestry systems such as shading to protect coffee and cacao crops in the tropics improves production resilience while maintaining ground cover, improving infiltration, and reducing erosion. The multifunctionality supported by agroforestry systems consistently underpins soil erosion prevention and overall soil health. Whether seeking to restore productivity to degraded lands, improve productivity of marginal lands, or increase the resiliency and plasticity of established agroecosystems, agroforestry practices provide direct and ancillary benefits to protect and enhance soil quality. Land managers have the opportunity to optimize and integrate tree, crop, and livestock production with regard to soil and climate variation to achieve their production goals while sustaining soil resources and supplying multiple ecosystem services. This chapter aims to provide an overview of soil conservation benefits during the production of food, fuel, and fiber in agroforestry systems.
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To alleviate the contradiction between human and land caused by the limitation of land resources and the irreversibility of land use in the development zone of urban agglomeration, 24 indexes were selected from four aspects: land use status, resource security, economic feasibility, and social acceptability to establish the level evaluation index system for the sustainable use of land resources in Baoding high-tech zone; also, the combination weighting method was used to determine the development level. The index weight of land resource utilization potential in the development zone was established. The subjective and objective linear combination was also established to obtain the proportion of subjective and objective. The multi-factor comprehensive evaluation model was used to evaluate the sustainable utilization degree of land in the high-tech zone. The comprehensive analysis of land-intensive use potential was made from five aspects: expansion potential, structure potential, intensity potential, management potential, and the number of years of land available; the analysis of the limiting factors and the combination of these factors of the land in the development zone was made to obtain the natural index after the renovation, and the natural quality potential of the cultivated land renovation was obtained according to the difference of the natural index before and after the renovation. The empirical results show that the high-tech zone’s land-use rationality index is relatively high during 2014-2018. During the evaluation period, the index continued to rise; the high-tech zone's resource security score was low, and there was no change during the evaluation period, which is basically at a low level. During the five years, the high-tech zone’s land-use sustainability has experienced the fluctuation process of first rising and then declining, which is in the stage of medium sustainable development. In the future, the potential for improvement is enormous. The prospect of the high-tech zone’s exploitable land structure is small, and the land structure is relatively reasonable, which is in line with the development orientation of the high-tech site. But the industrial land intensity in the zone also has a specific potential for excavation. The high-value areas of the natural quality potential of the land improvement in the high-tech site are mainly distributed in the west, northeast, and a few in the north and south.
Article
This paper studies the change of Soil Organic Carbon (SOC) stocks in Lixiviated Red Ferralitic soils due to the change of land use, which is new for the province of Mayabeque and for Cuba. It starts from the results previously obtained when 38 soil profiles were characterized within a period between six and fourteen years. The sampling to determine SOC contents was conducted through the method of 100-cm3 volume cylinders, in triplicate. The comparison between both samplings allows to obtain SOC gains or losses. Results were achieved under four grove sites and three cultivated soils. Regarding soils under groves, SOC gains were evidenced in all cases, whereas in cultivated soils, SOC losses were obtained in two plots under intensive cultivation; however, such SOC losses were not recorded in the third plot where agroecological practices were carried out with the systematic application of organic manure. These results lay the foundations, from the environmental point of view, since they may be useful for the province of Mayabeque to analyze SOC status in Lixiviated Red Ferralitic soils, according to the map of land use, as well as to recommend the application of organic manures, avoiding SOC losses.
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In Brazil, Haplic Ferralsols (Densic) are commonly known to have physical limitations, including higher bulk density and less drainable porosity, less water infiltration and greater resistance to root growth. However, there are extensive areas with these soils in Brazil that are important for agricultural production. Because maintaining and/or recovering the physical quality of these soils is an important task to maintain agricultural sustainability, the objective of this study was to evaluate the impact of different use and management systems on the physical quality and total organic carbon content of Haplic Ferralsols (Densic) in northeastern Brazil. The evaluated systems were: conventional planting (CC), pasture (PP) and two agroforestry systems: one 7 years (AF7) and the other 12 years old (AF12). An area of secondary forest with remnants of the Atlantic Forest Biome (SF) was selected and sampled as a reference. The total organic carbon content (TOC), flocculation index (FI) and particle density (Dp) were determined. Saturated hydraulic conductivity (Ko), macroporosity (MaP), microporosity (MiP), total porosity (TP), soil bulk density (Ds) and aggregate stability were also determined in samples collected in the 0– to 0.10, 0.10 to 0.20 and 0.20– to 0.40 m soil layers. The variables that best distinguished the agroforestry systems from the other systems were GMD, MaA, WMD and TOC. Correlations of these variables, all related to the soil structure in the AF7 and AF12 systems, contribute to maintaining or regenerating soil aggregation. None of the soil management systems were grouped with the forest area, although areas in the agroforestry systems had lower impact on the physical soil quality parameters compared to the CC and PP systems.
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n the Northeast Himalayas (NEH) region, four major conventional land-use types are forest, Jhum lands, fallow Jhum lands and plantations, but little is known about their sustainability and responses to changes. We collected soil samples at two uniform depths (0-15 and 15-30 cm) from the Zunheboto district of Nagaland (India). The dataset was statistically analyzed by conducting an ANOVA-one way, principal component analysis (PCA) and calculating an additive soil quality index (SQIa). Our results confirmed that sand content, bulk density (BD), porosity, soil organic carbon (SOC), cation exchange capacity (CEC), exchangeable calcium and potassium showed significant statistical differences among soil depths depending on the land use management. PCA results showed that soil texture, BD, porosity, SOC and exchangeable cations could be consideredthe major indicators to define soil quality. After estimating the SQIa, Jhum soils showed the highest values at the surface, while at 15-30 cm soil depth, fallow Jhum soils phase showed the highest ones. The conversion from natural forest to plantation does not hamper the SQ, but their conversion into Jhum may even increase it, for a shorter duration. However, after 1-2 year of cultivation and conversion from Jhum into fallow Jhum land, soil quality could be reduced.
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Because of concerns about the eventual impact of atmospheric CO2 accumulations, there is growing interest in reducing net CO2 emissions from soil and increasing C storage in soil. This review presents a framework to assess soil erosion and deposition processes on the distribution and loss of C in soils. The physical processes of erosion and deposition affect soil C distribution in two main ways and should be considered when evaluating the impact of agriculture on C storage. First, these processes redistribute considerable amounts of soil C, within a toposequence or a field, or to a distant site. Accurate estimates of soil redistribution in the landscape or field are needed to quantify the relative magnitude of soil lost by erosion and accumulated by deposition. Secondly, erosion and deposition drastically alter the biological process of C mineralization in soil landscapes. Whereas erosion and deposition only redistribute soil and organic C, mineralization results in a net loss of C from the soil system to the atmosphere. Little is known about the magnitude of organic C losses by mineralization and those due to erosion, but the limited data available suggest that mineralization predominates in the first years after the initial cultivation of the soil, and that erosion becomes a major factor in later years. Soils in depositional sites usually contain a larger proportion of the total organic C in labile fractions of soil C because this material can be easily transported. If the accumulation of soil in depositional areas is extensive, the net result of the burial (and subsequent reduction in decomposition) of this active soil organic matter would be increased C storage. Soil erosion is the most widespread form of soil degradation. At regional or global levels its greatest impact on C storage may be in affecting soil productivity. Erosion usually results in decreased primary productivity, which in turn adversely affects C storage in soil because of the reduced quantity of organic C returned to the soil as plant residues. Thus the use of management practices that prevent or reduce soil erosion may be the best strategy to maintain, or possibly increase, the worlds soil C storage.
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c1 Address for correspondence: Pear Tree Cottage, Frog Lane, Ilmington, Shipston on Stour, Warwickshire, CV36 4LQ, UK. Email: mikecarr@cwms.org.uk
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This paper examines the influence of important socio-economic, institutional/policy level factors in determining the adoption/non-adoption of rubber-integrated farming systems in traditional and non-traditional rubber-growing regions in India. The empirical analysis is based on a survey of rubber growers in the traditional rubber regions of Kerala (south India) and the non-traditional rubber regions of Assam, Meghalaya, and Tripura (north east India). In sharp contrast to Kerala, where smallholder responses toward adoption of rubber-integrated farming systems have been lukewarm, the emerging rubber economies (most of which are tribal communities) of north east (NE) India have shown interest in adopting rubber as an integrated farming system along with pre-existing land-use livelihood activities. The study clearly demonstrates contrasting empirical evidence of adoption of rubber-integrated farm-livelihood systems in the rubber-growing regions in Kerala and the NE states in India. The contrasting scenarios of adoption of rubber-integrated farming systems are mostly explained by region-specific factors dominated by socio-economic, institutional variables, and policy-level constraints, as also revealed by multivariate analysis. By and large, the findings of the study have significant bearing on the socio-economic outcomes and the existing institutional development paradigm underlying the rubber-development programmes introduced in India since independence. The study shows that the existing institutional arrangements and policies, which evolved historically to facilitate rubber area expansion in the traditional regions (including Kerala), have been highly instrumental in perpetuating rubber farming as a monoculture system. However, such an institutional mechanism proves to be highly redundant in the context of the NE states which are otherwise diverse in terms of integrated farm-livelihood systems and shifting cultivation.
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The effect of soil type on carbon (C) and nitrogen (N) mineralization rates in grassland soils was investigated along with the physical and biological soil characteristics that may have caused the observed differences in mineralization rates between soil types.The percentage of mineralized organic N was higher in sandy soils than in loams and clays; this was not observed for C. In loams and clays small pores constituted a higher percentage of the total pore space than in sandy soils. Two mechanisms of physical protection of organic N were distinguished. In clay soils physical protection of organic material by its location in small pores was the main mechanism. In sandy soils, however, organic material was protected by its association with clay particles. In loams both mechanisms played a role. The protected organic material associated with clay particles consisted of amorphous undefined material that did not stain with acridine orange, indicating a high degree of decomposition, while the non-protected organic material present in the sand fraction consisted of plant debris that stained intensely with acridine orange. Physically protected organic matter had a lower C/N ratio than organic matter that was not physically protected.Grazing pressure on bacteria by bacterivorous nematodes was higher in sandy soils than in loams and clays. This coincided with a higher N mineralization rate per bacterium. The C/N ratio of the microbial biomass was higher in sandy soils than in loams and clays and was positively correlated with the N mineralization rate per unit of microbial biomass N. This is in agreement with the concepts of food webs that N mineralization is positively correlated with the C/N ratio of the consumer (bacteria) for a given sol|C/N ratio of the substrate (organic matter). It is not yet clear which of the factors investigated are the most important in determining N mineralization rates in grassland soils.
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Agroforestry and grass buffers have been shown to improve soil properties and overall environmental quality. The objective of this study was to examine management and landscape effects on water stable soil aggregates (WSA), soil carbon, soil nitrogen, enzyme activity, and microbial community DNA content. Treatments were row crop (RC), grass buffer (GB), agroforestry buffer (AG), and grass waterways (GWW). A corn (Zea mays L.)–soybean (Glycine max L.) rotation under no-till management was established in a watershed in northeast Missouri in 1991; grass buffers were implemented in 1997. Grass buffers, 4.5 m wide and 36.5 m apart, consisted of a mixture of redtop (Agrostis gigantea Roth), brome grass (Bromus spp.), and birdsfoot trefoil (Lotus corniculatus L.) on contour within the watershed. Agroforestry buffers have pin oak (Quercus palustris Muenchh.) trees distributed down the center of the grass buffers on one half of the watershed. Soils were collected from two transects extending from the summit to lower landscape positions within the grass and agroforestry portions of the watershed in June 2006. Soil enzymes studied include: fluorescein diacetate hydrolase, β-glucosidase, glucosaminidase, and dehydrogenase. Soil DNA content was determined as an alternative for microbial biomass. WSA was significantly different among treatments and landscape positions. WSA decreased from GWW > AG > GB > RC management treatments and also decreased from lower > middle > summit landscape positions. Soil carbon and nitrogen were highest for the GWW treatment and lowest for RC. The landscape position effect was significant for RC and AG treatments. Fluorescein diacetate, β-glucosidase and glucosaminidase enzyme activities were significantly higher in buffers and GWW areas than RC areas. Dehydrogenase activity was different between grass (GB and GWW) and crop areas. The landscape effect was insignificant for enzyme activity. Although soil DNA may be a good indicator of microbial biomass, it did not appear to differentiate among management systems as selectively as other microbial parameters. Results of the study show that establishment of AG, GB, and GWW increased WSA, soil carbon, soil nitrogen, and enzyme activity.
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Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered in soil will depend on the extent of physical protection of soil organic C (SOC). The main objective of this study was to characterize SOC storage in relation to soil fraction-size classes in cacao (Theobroma cacao L.) agroforestry systems (AFSs). Two shaded cacao systems and an adjacent natural forest in reddish-yellow Oxisols in Bahia, Brazil were selected. Soil samples were collected from four depth classes to 1 m depth and separated by wet-sieving into three fraction-size classes (>250 microm, 250-53 microm, and <53 microm)-corresponding to macroaggregate, microaggregate, and silt-and-clay size fractions-and analyzed for C content. The total SOC stock did not vary among systems (mean: 302 Mg/ha). On average, 72% of SOC was in macroaggregate-size, 20% in microaggregate-size, and 8% in silt-and-clay size fractions in soil. Sonication of aggregates showed that occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Considering the low level of soil disturbances in cacao AFSs, the C contained in the macroaggregate fraction might become stabilized in the soil. The study shows the role of cacao AFSs in mitigating greenhouse gas (GHG) emission through accumulation and retention of high amounts of organic C in the soils and suggests the potential benefit of this environmental service to the nearly 6 million cacao farmers worldwide.
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NewsLong infamous for heroin, opium, and other poppy products, the Golden Triangle, the mountainous, thickly forested intersection of Laos, Myanmar (formerly Burma), and China, is now becoming known for another plant: Hevea brasiliensis , the Para rubber tree. Rubber in the Golden Triangle has been a classic standoff between economics and ecology: Monocultural plantations are so much more profitable than any other lawful agricultural system in these hills that they have inevitably prevailed, no matter the environmental cost. But at least some smallholders have found out how to both make a living and restore forests to a healthier state. Surprisingly, their way forward is a return to one of the region's most ancient products: tea. Not only that, they are growing tea in a way that until recently was derided as backward and inefficient—in the forest, under the canopy of larger trees.
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Rubber plantations are expanding rapidly throughout montane mainland Southeast Asia ( 1 – 3 ). More than 500,000 ha may have been converted already in the uplands of China, Laos, Thailand, Vietnam, Cambodia, and Myanmar (see the figure, panel A). By 2050, the area of land dedicated to rubber and other diversified farming systems could more than double or triple, largely by replacing lands now occupied by evergreen broadleaf trees and swidden-related secondary vegetation ( 2 ). What are the environmental consequences of this conversion of vast landscapes to rubber?
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Communities of plants, biological soil crusts (BSCs), and arbuscular mycorrhizal (AM) fungi are known to influence soil stability individually, but their relative contributions, interactions, and combined effects are not well understood, particularly in arid and semiarid ecosystems. In a landscape-scale field study we quantified plant, BSC, and AM fungal communities at 216 locations along a gradient of soil stability levels in southern Utah, USA. We used multivariate modeling to examine the relative influences of plants, BSCs, and AM fungi on surface and subsurface stability in a semiarid shrubland landscape. Models were found to be congruent with the data and explained 35% of the variation in surface stability and 54% of the variation in subsurface stability. The results support several tentative conclusions. While BSCs, plants, and AM fungi all contribute to surface stability, only plants and AM fungi contribute to subsurface stability. In both surface and subsurface models, the strongest contributions to soil stability are made by biological components of the system. Biological soil crust cover was found to have the strongest direct effect on surface soil stability (0.60; controlling for other factors). Surprisingly, AM fungi appeared to influence surface soil stability (0.37), even though they are not generally considered to exist in the top few millimeters of the soil. In the subsurface model, plant cover appeared to have the strongest direct influence on soil stability (0.42); in both models, results indicate that plant cover influences soil stability both directly (controlling for other factors) and indirectly through influences on other organisms. Soil organic matter was not found to have a direct contribution to surface or subsurface stability in this system. The relative influence of AM fungi on soil stability in these semiarid shrublands was similar to that reported for a mesic tallgrass prairie. Estimates of effects that BSCs, plants, and AM fungi have on soil stability in these models are used to suggest the relative amounts of resources that erosion control practitioners should devote to promoting these communities. This study highlights the need for system approaches in combating erosion, soil degradation, and arid-land desertification.
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Crusting and erosion of cultivated soils result from aggregate breakdown and the detachment of soil fragments by rain, and the susceptibility of soil to these processes is often inferred from measurements of aggregate stability. Here, theories of aggregate breakdown are reviewed and four main mechanisms (i.e. slaking, breakdown by differential swelling, mechanical breakdown by raindrop impact and physico-chemical dispersion) are defined. Their relative importance depends on the nature of the rain, as well as on the soil's physical and chemical properties. The relations between aggregate breakdown, crusting and water erosion are analysed, and existing methods for the assessment of aggregate stability are reviewed. A unified framework for the measurement of aggregate stability is proposed to assess a soil's susceptibility to crusting and erosion. It combines three treatments having various wetting conditions and energies (fast wetting, slow wetting, and stirring after pre-wetting) and measures the resulting fragment size distribution after each treatment. It is designed to compare different soils, or different climatic conditions for a given soil, not to compare time-dependent changes in that soil.
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Rubber (Hevea brasiliensis L.) production systems have conserved forest biodiversity in some parts of Asia and are a threat elsewhere. A holistic view on these two sides of the coin is needed. The roles planted trees and agroforestry play in the transformation of lives and landscapes depend on the stage of “forest transition” and the spatial configuration, segregation or integration, of the landscape. “Forest transitions” need to be understood at the level of the actual pattern of change, (one level up) at the level of drivers of change, and (one level down) at the level of consequences for ecosystem goods and services. To close the loop on a feedback mechanism, forest transitions also need to be understood at the level of mechanisms that link desirable or undesirable consequences of changes in tree cover to the drivers, providing positive or negative feedback. “Forest ecosystem services” can be partially fulfilled by agroforests as a form of domesticated forest. We revisit the theoretical framing of agroforests as part of forest transition and discuss a case study of the rise and decline of complex rubber agroforests in lowland Sumatra (Indonesia) and the recent expansion of monoculture rubber in China replacing agroforestry systems. Both cases indicate a complex of driving and conditioning factors but also a current lack of incentives to reverse the trend toward landscape segregation. Complex agroforests represent an intermediate stage of intensification, between natural forest and home garden, and may occupy an intermediate stage in the way landscapes develop under the influence of land users and other stakeholders. Although complex agroforests represent considerable value (biodiversity and carbon stocks) of relevance to external stakeholders, incentive systems for the land users need to match these values; otherwise, these systems will disappear when more intensified and simplified tree crop systems take over. Current analysis of the choices in land sparing versus land sharing, and segregation versus integration, emphasizes the convex or concave nature of the bifunctional trade-off curves.