Search

Cocoa production is a leading driver of deforestation in the humid-tropics of West Africa. Reconciling climate change mitigation with livelihoods of farmers requires identification of production strategies to concurrently improve yield and profit while curtailing emissions of greenhouse gases (GHG). Using a 2021 plot-survey conducted in Ghana's Eastern region, we evaluated yields, GHG emissions, and value of production (VOP) (a profit indicator) across a typology representing the diversity of systems at plot-level. The typology was constructed by first stratifying plots according to shade levels and variety (hybrid vs. Amazonia) which resulted in three systems: Hybrid sun , hybrid variety under full-sun (little to no shade); Hybrid shade , hybrid and moderate shade (13–25 shade trees ha−1); and Amazonia, Amazonia under predominantly moderate shade. Next, factor analysis and clustering were used to group plots within each system according to cocoa yield, vegetation, management, and (local) climate conditions. Cluster analysis showed that fertiliser, weeding, pruning, hand pollination, cocoa tree density, and shade tree densities of differing heights were most influential for determination across systems. Hybrid shade had the highest net GHG removal rate at −6.8 ± 1.7 (± 95% CI) Mg CO 2 eq ha−1 yr−1: 48% and 127% higher (emissions more negative) respectively over Amazonia and Hybrid sun. Hybrid shade additionally had the highest average and least variable VOP among production systems at 669 ± 564 USD ha−1 yr−1, compared to Hybrid sun and Amazonia at 404 ± 442 and 213 ± 280 USD ha−1 yr−1 respectively. These results point to hybrid cocoa grown under moderate shade of 13–25 shade trees ha−1 as optimal for reconciling climate change mitigation with development in West African cocoa. • Study concurrently evaluates financial profits and GHG balances (N 2 O & CH 4 emissions, CO 2 removals) in West African cocoa. • Plot-level indicators are evaluated across a typology obtained from sample-stratification and clustering. • Hybrid cocoa under moderate shade (13-25 shade trees ha-1) had GHG removal increment of 127% over same variety without shade. • This system too had higher mean profits, thus best reconciling GHG mitigation and economic development for the region. [ABSTRACT FROM AUTHOR]

The cultivation of deep-rooted vegetation greatly alters the tradeoffs between water and carbon dynamics, yet their impact on microbial carbon sequestration (MCS) remains inadequately documented, particularly in thick vadose zones. This information is crucial for global climate mitigation and ecosystem service enhancement. As such, we collected triplicate samples for each land use type, exploring the abundance and structure of cbbL -harboring microbial communities within 10-m deep profiles under cultivated farmland and two apple orchards of varying ages (n = 72). Our findings indicated a shift from water-dominated (improved water retention at the expense of reduced carbon sequestration) to carbon-dominated benefits (enhanced carbon sequestration at the expense of decreased water retention) in deep soil layers (2–10 m) after the transformation from farmland to apple orchards. Despite the lack of significant differences among the three land use types, the gene abundances and microbial diversity indices reduced with soil depths because of variations in substrates, resources, and microenvironments. The cbbL -harboring microorganisms consisted of 5 phyla, 7 classes, 19 orders, 30 families, and 55 genera, with Proteobacteria as the predominant bacterial phylum. The relative contributions of different genera varied with soil depths, reflecting their distinct survival strategies. The microbial network was positively connected in various soil layers under farmland and apple orchards. Furthermore, the results of correlation, redundancy analysis, and structural equation modeling jointly indicated that plant roots and soil properties, including total nitrogen and organic carbon, governed MCS processes in deep unsaturated zones. Specifically, the low microbial variation between farmland and apple orchards can be attributed to the predominant effects of climatic and pedogenic factors on soil properties, the restricted contribution of plant roots to soil nutrient levels per unit depth, and the adverse effects of plant-induced ecohydrological consequences on root systems and microbial populations. This study offers new insights within thick vadose zones containing deep-rooted plants, thereby contributing to a better understanding of global terrestrial carbon cycle processes. [Display omitted] • Microbial carbon sequestration processes were explored in 10-m deep profiles. • The farmland-to-apple orchards conversion led to water-carbon tradeoffs. • Microbial carbon sequestration differed with depths rather than land use types. • Depth-dependent plant roots and soil nutrients affects carbon sequestration. [ABSTRACT FROM AUTHOR]

Agricultural management can influence soil organic carbon (SOC) stocks and thus may contribute to carbon sequestration and climate change mitigation. The soil depth to which agricultural management practices affect SOC is uncertain. Soil depth may have an important bearing on soil carbon dynamics, so it is important to consider depth effects to capture fully changes in SOC stocks. This applies in particular to the evaluation of carbon farming measures, which are becoming increasingly important due to climate change. We sampled and analysed the upper metre of mineral cropland soils from ten long-term experiments (LTEs) in Germany to quantify depth-specific effects on SOC stocks of common agricultural management practices: mineral nitrogen (N) fertilisation, a combination of N, phosphorus (P) and potassium (K) fertilisation, irrigation, a crop rotation with preceding crops (pre-crops), straw incorporation, application of farmyard manure (FYM), liming, and reduced tillage. In addition, the effects of soil compaction on SOC stocks were examined as a negative side effect of agricultural management. Results showed that 19 ± 3 % of total management effects on SOC stocks were found in the upper subsoil (30–50 cm) and 3 ± 4 % in the lower subsoil (50–100 cm), including all agricultural management practices with significant topsoil SOC effects, while 79 ± 7 % of management effects were in the topsoil (0–30 cm). Nitrogen and NPK fertilisation were the treatments that had the greatest effect on subsoil organic carbon (OC) stocks, followed by irrigation, FYM application and straw incorporation. Sampling down to a depth of 50 cm resulted in significantly higher SOC effects than when considering topsoil only. A crop rotation with pre-crops, liming, reduced tillage and soil compaction did not significantly affect SOC stocks at any depth increment. Since approximately 20 % of the impact of agricultural management on SOC stocks occurs in the subsoil, we recommend soil monitoring programs and carbon farming schemes extend their standard soil sampling down to 50 cm depth to capture fully agricultural management effects on SOC. • Ten 32- to 112-year-old long-term experiments were sampled down to 100 cm depth. • Sampling only topsoil ignores 20 % of agricultural management effects on SOC stocks. • Mineral fertilisation had the greatest effect on subsoil organic carbon stocks. • None of the agricultural measures had significant effects deeper than 50 cm. • Standard soil sampling should therefore be extended to 50 cm depth. [ABSTRACT FROM AUTHOR]

Cover crops are widely advocated for increasing soil organic carbon (SOC) levels, thereby benefiting soil health improvement and climate change mitigation. Few regional-scale studies have robustly explored SOC stocks under cover cropping, due to limited long-term experiments. We used the unique experimental data from the North American Project to Evaluate Soil Health Measurements conducted in 2019 to address this issue. This study included 19 agricultural research sites with 36 pairs of cover cropping established between 1896 and 2014. Explanatory variables related to site-specific environmental conditions and management practices were collected to identify and prioritize contributing factors that affect SOC stocks with cover crops, by coupling the Boruta algorithm and structural equation modeling. Overall, cover crops significantly (P < 0.05) improved several indicators of soil health, including greater SOC (concentration: +8%; stock: +7%), total nitrogen (+8%), water-stable aggregates (+15%), and potential carbon mineralization (+34%), on average, compared to no cover crop control. Likewise, on average, cover crops sequestered SOC 3.55 Mg C ha-1 (0–15 cm depth), with a sequestration rate of 0.24 Mg C ha-1 yr-1. In addition, we found climate (Hargreaves climatic moisture deficit) was important in explaining the variation of SOC stocks with cover crops, followed by soil properties (e.g., soil clay content). In terms of management practices, cover crop type had a significant positive (0.36) effect on SOC stocks, with non-legumes showing a greater impact, compared to legumes and mixtures. Crop rotational diversity also had a positive (0.28) effect on SOC accumulation. Our findings suggested that integrating non-legume cover crops into diverse crop rotation is likely to be a promising strategy to maximize SOC stocks with cover crops across North America. • Prioritized factors affecting soil organic carbon stocks under cover cropping. • Investigated 19 long-term experiments with cover crops in North America. • Used models coupling the Boruta algorithm and structural equation modeling. • Descending from climate > cover crop type > soil clay content > rotation > tillage. • Cover crops sequestrated carbon 3.55 Mg C ha-1, at a rate of 0.24 Mg C ha-1yr-1. [ABSTRACT FROM AUTHOR]

Grazing exclusion has been proposed as an effective practice to enhance ecosystem carbon stocks in arid-semiarid degraded grasslands. However, in humid regions, the effects of grazing exclusion on ecosystem carbon stocks and their components in degraded grasslands remain largely unknown. Here, the effects of enclosure on ecosystem carbon stocks and their components were explored using four enclosure ages, each paired with adjacent grazed areas. Moreover, the results were synthesized with previous studies to test if enclosure's effects in semihumid-humid regions differed from those in arid-semiarid regions. The field experiment found that six months to 1 year of grazing exclusion sequestrated 14.6 % higher carbon in the enclosed grasslands than in paired-grazed grasslands as a consequence of increased carbon storage of plants and topsoils. However, compared to grazed areas, enclosures over 3–6 years contained 14.4 % less ecosystem carbon stocks, primarily due to markedly decreased soil carbon sequestration, despite increased plant carbon stocks. Structural equation models further suggested that the decrease in soil carbon stock might be owing to the decomposition of organic matter induced by low phosphorus. Additionally, compared with the northern slope of the mountain, ecosystem carbon stocks on the southern slope showed a lagged and weak response to grazing exclusion. The results, combined with a meta-analysis, revealed that plant and soil carbon stocks in semihumid-humid grasslands were more sensitive to enclosure than in arid-semiarid grasslands. These results highlight that short-term fencing (e.g., six months to 1 year), rather than long-term, is a practical strategy to foster degraded grassland ecosystem carbon sequestration in semihumid-humid regions, thus contributing to climate change mitigation. • Six months to 1 year of grazing exclusion promoted ecosystem carbon stocks • 3–6 years' fencing reduced ecosystem carbon stocks as the decrease in soil stock • The decrease in soil carbon stock was mainly owing to the imbalance of soil nutrients • Northern slope' carbon stock responded strongly compared to southern slope • Carbon stocks in humid grasslands was more sensitive than in arid grasslands [ABSTRACT FROM AUTHOR]

Highlights • Thirty years of conservation management resulted in large SOC storage in the soil profile (0–100 cm). • Greatest increase in SOC was with no-till combined with legume cover crops and N fertilization. • Rate of SOC storage was high in surface (0–30 cm) layers but decreased over time. • Subsoil (30–100 cm) contributed to half of the additional SOC storage. • Management-induced changes in SOC stocks were largely explained by plant C input. Abstract The effect of no-tillage (NT) on soil organic carbon (SOC) storage may help Brazil meet its 37% greenhouse gas emissions reduction target by 2025. When combined with legume cover crops, NT could result in even greater SOC storage than NT alone. The objective of this study was to evaluate the SOC storage potential of NT and the contribution of legume cover crops and nitrogen (N) fertilization to this potential in both the surface and subsurface soil layers of a previously degraded subtropical Acrisol of Southern Brazil. Using a split-plot design, the long-term field experiment compared the effect of NT and conventional tillage (CT), with or without legume cover crops, and with or without mineral N fertilization. Thirty years of contrasting management systems resulted in large differences (up to 35 Mg ha−1) in SOC stocks in the whole soil profile (0–100 cm). The combination that provided the greatest increase in SOC was NT combined with two legume cover crops and N fertilization (1.15 Mg ha−1 year−1 compared to CT, with no N fertilization or legume cover crop). Legume cover crops were twice as efficient in storing SOC as N fertilization, with 1 kg of residue input being converted to 0.15 kg of SOC. Overall, the variation in SOC stocks was explained largely by plant carbon input (R2 = 80%) which varied with N fertilization and cropping system. About half of the SOC storage that occurred in this 30-year-old NT system was attributable to the increase in SOC stocks in the subsurface layer (30–100 cm), which was confirmed by the contribution of C 3 cover crop residues using carbon isotope signature (from 14.8 to ∼17.5‰ in the 75–100 cm layer). Thus, the legume cover crop made a strong contribution to the potential of SOC storage in NT, and high rates of C storage occurred over a longer period in subsurface soil layers than previously believed. [ABSTRACT FROM AUTHOR]

Scattered trees in wood-pastures represent outstanding conservation value by providing microhabitats for a variety of organisms. They also diversify ecosystem services by creating shade for livestock, and capturing and storing carbon. However, trees in wood-pastures are declining Europe-wide and an appropriate legal environment to maintain them is mostly lacking. Here we looked beyond the well-documented beneficial effects of trees and assessed potential ecosystem disservices, which may drive the controversial appreciation of trees. In a grazing exclusion experiment, we assessed the effect of trees on herbage production in wood-pastures from semi-arid continental to humid montane areas in the temperate deciduous forest ecoregion, and found that trees have a suppressive effect throughout the year, although herbage nutritive value, as indicated by herbage nitrogen content, seems to be improved in spring. When we up-scaled the local ecosystem disservice on herbage yield to entire wood-pastures, the loss remained below 3%, which is lower than reported gains in livestock production due to free access to shade. Thus, the motivation for the under-appreciation of trees by land managers and decision makers may lie in that trees suppress herbage production, but the importance of this effects is offset by the magnitude of the beneficial services of trees. We recommend current wood-pasture stakeholders to revisit their attitude towards scattered trees and encourage tree planting campaigns and tree-based climate mitigation strategies to consider the protection of trees in wood-pastures and the establishment of young ones in currently open pastures up to traditionally low tree cover proportions, as livestock production is unlikely to be compromised by this action. • Wood-pastures are widespread, high nature and cultural value landscapes. • Scattered trees in wood-pastures boost biodiversity and diversify ecosystem services. • In temperate deciduous forest ecoregions, they reduce sub-canopy biomass production. • When scaled up to the whole wood-pasture, the loss of biomass remains negligible. • Climate strategies are encouraged to involve scattered trees on pastureland. [ABSTRACT FROM AUTHOR]

Policymakers and businesses in Southeast Asia are increasingly interested in using carbon markets to encourage adoption of regenerative agriculture practices by farmers. These practices are thought to mitigate climate change by reducing soil carbon loss and enhancing soil carbon sequestration. However, there is uncertainty in the ability of regenerative agriculture practices to increase soil organic carbon (SOC) stocks of croplands. We reviewed 92 empirical studies that investigated the effects of 17 regenerative farming practices across 11 broad categories of crops on SOC stock or content in Southeast Asia. Our synthesis found supporting evidence for the use of organic amendments like biochar, compost, and manure, as well as cover cropping, crop rotation, and conservation tillage to increase SOC. However, studies for practices like addition of compost and manure reported increases in greenhouse gas emissions like methane (CH 4) and nitrous oxide (N 2 O), demonstrating that increases in SOC may be offset by increases in greenhouse gas emissions. Only a few studies measured both the changes in SOC stocks and greenhouse gas emissions and none of the studies completed full greenhouse gas inventories. Estimating the net impact of SOC gains and increase of greenhouse gas emissions will be necessary to understand the overall effect of practices like compost, manure and crop residue incorporation on net atmospheric greenhouse gas concentrations. If these practices are implemented for soil carbon projects, practitioners should anticipate increases in greenhouse gas emissions from soils and implement additional practices, such as alternate wetting and drying, to optimize the climate change mitigation effects of regenerative agriculture. We encourage future research on practices, such as agroforestry and changes in crop residue management, where there are few studies and little variation in experimental design and environmental conditions. Given the interest in scaling up regenerative agriculture through voluntary carbon markets to boost SOC stocks in croplands, policymakers and businesses can support research in this area by making field-collected data from their projects accessible to researchers to further the study of the impact of these practices across different abiotic conditions and soil managements. This data sharing would alleviate the paucity and improve the quality of empirical data on regenerative agricultural practices in Southeast Asian croplands, facilitate practice-specific meta-analyses, and help to optimize climate change mitigation effects of regenerative agriculture. • Regenerative agriculture practices can increase soil carbon in Southeast Asia. • These practices can also increase cropland greenhouse gas emissions like methane. • More empirical data is needed to quantify the practices' effects on soil carbon [ABSTRACT FROM AUTHOR]

Cover crops can contribute to climate change mitigation through enhanced sequestration of atmospheric carbon dioxide into soil organic carbon. Few studies, however, have estimated the total carbon (C) input to soil, i.e. derived both from plant material (shoot and root) and phyllo- and rhizodeposition. Selection of cover crop species should account for multiple objectives, such as C inputs to soil, nitrate leaching reduction and positive residual effects on the following main crop. However, trade-offs between these objectives may occur. The aim of this study was to investigate the performance of the cover crop species winter rye, hairy vetch and oilseed radish, and to assess the ability of mixtures to overcome potential trade-offs. A randomized split-plot field trial was conducted to compare cover crop treatments and a weeded control under high and low soil nitrogen (N) availability. Multiple-pulse labeling with 14C-CO 2 was carried out to trace net cover crop-derived rhizodeposition C. Soil mineral N was measured to 1.5 m depth in autumn, as well as grain and N yield in the subsequent spring barley. Cover crop species accumulated between 1250 and 2580 kg C ha−1, with significantly higher total C input (in shoot, root and phyllo- and rhizodeposits) for the mixtures compared with pure stands of either vetch or radish, while the results for rye were in between. The quantity of C lost via phyllo- and rhizodeposition (qClvPR) showed a significant positive correlation with root C and was highest for the mixtures and rye. The relative ClvPR ranged between 7% and 14% of total cover crop-derived C and tended to decrease under higher soil N availability. All cover crop treatments were able to decrease soil mineral N (0–1.5 m), with radish displaying the highest N leaching reduction potential. Despite substantial differences in cover crop total N uptake and C:N ratios, no significant differences were observed in the subsequent main crop grain or N yields. The mixtures showed the highest total C input and generally a higher or similar mineral N depletion potential than the average of the pure stands, suggesting that cover crop mixtures offer a realistic means for overcoming trade-offs among ecosystem functions. • Winter rye and cover crop (CC) mixtures produced highest total and rhizodeposition C. • Root C was the strongest predictor of rhizodeposition C. • Oilseed radish depleted soil mineral N better than winter rye and hairy vetch. • CC mixtures depleted soil mineral N as well or better than the pure stand average. • Despite dissimilar CC quantity and quality, no crop yield effect of CCs was observed. [ABSTRACT FROM AUTHOR]

Agriculture is a global contributor to greenhouse gas emissions, causing climate change. Soil organic carbon (SOC) sequestration is seen as a pathway to climate change mitigation. But, long-term data on the actual contribution of tropical soils to SOC sequestration are largely absent. To contribute to filling this knowledge gap, we measured SOC in the top 15 cm over 12 years in two agronomic long-term trials in Western Kenya. These trials include various levels – from absence to full adoption – of two widely promoted sustainable agricultural management practices: Integrated Soil Fertility Management (ISFM; i.e. improved varieties, mineral fertilizer and organic matter/manure incorporation) and Conservation Agriculture (CA; improved varieties, mineral fertilizer, zero-tillage and crop residues retention). None of the tested ISFM and CA treatments turned out successful in sequestering SOC long-term. Instead, SOC decreased significantly over time in the vast majority of treatments. Expressed as annual averages, losses ranged between 0.11 and 0.37 t C ha −1 yr −1 in the CA long-term trial and 0.21 and 0.96 t C ha −1 yr −1 in the ISFM long-term trial. Long-term application of mineral N and P fertilizer did not mitigate SOC losses in both trials. Adopting zero-tillage and residue retention alone (as part of CA) could avoid SOC losses of on average 0.13 t C ha −1 yr −1 , while this was 0.26 t C ha −1 yr −1 in response to mere inclusion of manure as part of ISFM. However, cross-site comparison disclosed that initial SOC levels of the two trials were different, probably as a result of varying land use history. Such initial soil status was responsible for the bulk of the SOC losses and less so the various tested agronomic management practices. This means, while ISFM and CA in the humid tropical agro-ecosystem of Western Kenya contribute to climate change mitigation by reducing SOC losses, they do not help offsetting anthropogenic greenhouse gas emissions elsewhere. [ABSTRACT FROM AUTHOR]

Improved soil management in rainfed Mediterranean agroecosystems can be a powerful strategy to mitigate the current atmospheric CO 2 increase, through soil carbon sequestration and stabilization. In this work, we assess the effects of different soil management practices (conventional tillage, CT, reduced tillage, RT, reduced tillage plus green manure, RTG, and no tillage, NT) on soil CO 2 flux dynamics and carbon sequestration in two organic rainfed almond ( Prunus dulcis Mill.) orchards under semiarid conditions. Soil CO 2 flux, temperature, and moisture were measured monthly over two-three years, and shortly after tillage operations. The soil aggregation distribution (including micro-aggregates occluded within macro-aggregates) and associated organic carbon content were measured after four years of implementation. No significant differences in CO 2 emissions among the soils subjected to the distinct management practices were observed at either site. On the one hand, shifting from CT to RT or RTG increased the OC content by 56% on average in all aggregate sizes. On the other hand, suppressing tillage only increased the OC content (by 24%) in the macro-aggregates. Moreover, improved soil management practices modulated the response of soil CO 2 flux to temperature and moisture in these semiarid Mediterranean agroecosystems. According to our results, soil CO 2 flux under the conventional tillage treatment was more sensitive to temperature increments than with the reduced tillage treatments, indicating that bare soils will be more vulnerable to organic carbon mineralization with ongoing global warming. On the contrary, the incorporation of plant residues under the reduced tillage treatments promoted soil aggregation and organic carbon preservation, making soils more resilient to abrupt changes in temperature and moisture under these treatments. [ABSTRACT FROM AUTHOR]

Pastoral farming systems have always adapted to the seasonal availability of forage resources and climate variability by moving animals. However, the role of animal mobility as a possible mitigating strategy in response to climate change has not been clearly documented. To understand this role, we investigated (i) the major methodological challenges linked to the diversity of grazing areas and other forage resources exploited by these systems and enteric emissions of methane; (ii) the impacts of grazing practices (carbon sequestration/emission) on soil and biomass carbon fluxes. We developed an approach based on two existing models (OSTRAL: Outil de Simulation du TRoupeau ovin ALlaitant and CASA: Carnegie Ames Stanford Approach) that we adapted and used in combination. This approach was applied to three French Mediterranean sheep and crop farming systems with different degrees of flock mobility (sedentary, single transhumance and double transhumance). The preliminary results produced by the whole farm model OSTRAL showed that two systems (sedentary and double transhumance) causing low carbon emissions. In the sedentary system, higher animal productivity offsets the increase in GHG emissions (in CO 2 eq) caused by feed production. In the pastoral system, grazing reduced total GHG emissions (in CO 2 eq). The CASA model proved to be useful to simulate the carbon balance under dynamic land cover in natural environments, whether used for grazing or not. This model can help assess the impact of grazing practices and carbon fluxes in systems linked to natural environments. The results of the first application showed that seasonal mobility of livestock increases the contribution of rangeland to feeding systems and improves the non-renewable energy balance of the system. It is thus extremely important to include the specificities of animals grazing in rangelands outside the structural limits of the farm when evaluating GHG emissions. [ABSTRACT FROM AUTHOR]

Afforestation of agricultural land is increasing, partly because it is an important biological method for reducing the concentration of atmospheric CO 2 and potentially mitigating climate change. Rainfall patterns are changing and prolonged dry periods are predicted for many regions of the world, including southern Australia. To accurately predict land-use change potential for mitigating climate change, we need to have a better understanding of how changes in land-use (i.e. afforestation of pastures) may change the soils response to prolonged dry periods. We present results of an incubation study characterising C and N dynamics and the microbial community composition in soil collected from two tree plantings and their adjacent pastures under a baseline and reduced frequency. While the concentration of soil C was similar in pasture and tree planting soils, heterotrophic respiration was significantly lower in soil from pastures than tree plantings. Although there was little difference in the composition of the soil microbial community among any of the soils or treatments, differences in N cycling could indicate a difference in microbial activity, which may explain the differences in heterotrophic respiration between pastures and tree plantings. Soils from pastures and tree plantings responded similarly to a reduction in wetting frequency, with a decrease in microbial biomass (measured as total PLFA), and a similar reduction in heterotrophic respiration from the soil. This suggests that the responses to changes in future wetting cycles may be less dependent on land-use type than expected. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA), comprising minimum soil disturbance, retention of crop residues and crop diversification, is widely promoted for reducing soil degradation and improving agricultural sustainability. It is also claimed to mitigate climate change through soil carbon sequestration: we conducted a meta-analysis of soil organic carbon (SOC) stock changes under CA practices in two tropical regions, the Indo-Gangetic Plains (IGP) and Sub-Saharan Africa (SSA), to quantify this. In IGP annual increases in SOC stock compared to conventional practice were between 0.16 and 0.49 Mg C ha −1 yr −1 . In SSA increases were between 0.28 and 0.96 Mg C ha −1 yr −1 , but with much greater variation and a significant number of cases with no measurable increase. Most reported SOC stock increases under CA are overestimates because of errors introduced by inappropriate soil sampling methodology. SOC increases require careful interpretation to assess whether or not they represent genuine climate change mitigation as opposed to redistribution of organic C within the landscape or soil profile. In smallholder farming in tropical regions social and economic barriers can greatly limit adoption of CA, further decreasing realistic mitigation potential. Comparison with the decreases in greenhouse gas emissions possible through improved management of nitrogen (N) fertilizer in regions such as IGP where N use is already high, suggests that this is a more effective and sustainable means of mitigating climate change. However the mitigation potential, and other benefits, from crop diversification are frequently overlooked when considering CA and warrant greater attention. Increases in SOC concentration (as opposed to stock) in near-surface soil from CA cause improvements in soil physical conditions; these are expected to contribute to increased sustainability and climate change adaptation, though not necessarily leading to consistently increased crop yields. CA should be promoted on the basis of these factors and any climate change mitigation regarded as an additional benefit, not a major policy driver for its adoption. [ABSTRACT FROM AUTHOR]

Coffee agroforestry systems (CAS) are considered as a climate change mitigation option through carbon sequestration. However, most studies on CAS have concentrated on management and productivity of the coffee plants with little known about the soil organic carbon (SOC) stocks. We conducted a study to quantify and compare the SOC stocks among Coffea arabica L. (Arabica coffee), Coffee canephora Pierre ex Froehn (Robusta coffee) agroforestry systems and Coffee monoculture (coffee monocrops) in Uganda. Soil samples were collected at 0–15 cm and 15–30 cm and tested using routine soil testing procedures. We found that there was higher SOC under CAS than coffee monocrops. When intercropped with non- fruit tree species, Robusta CAS produced higher SOC (57.564 tC/ha) compared to the Arabica CAS (54.543 tC/ha). In contrast, Arabica CAS stored more SOC (54.01 tC/ha) compared to Robusta CAS (49.635 tC/Kg) when intercropped with fruit trees like Artocarpus heterophyllus Lam. and Mangifera indica L. Under the coffee monocrop systems, Robusta coffee sequestered 4.86 tC/ha more SOC than Arabica coffee. The study showed that a farmer growing Robusta coffee intercropped with non-fruit trees is likely to benefit more from soil carbon credits than a farmer growing Arabica coffee with the same trees. Farmers growing Arabica coffee would sequester more carbon if intercropped with fruit trees. There is need for policy incentives that encourage the planting and maintenance of shade trees in coffee plantations for the benefit of carbon sequestration. [ABSTRACT FROM AUTHOR]

The fifth assessment report of the intergovernmental panel on climate change (IPCC) estimated that by 2040 agroforestry would offer high potential of carbon (C) sequestration in developing countries. However, the role of tropical agroforestry in C sequestration and in climate change mitigation has only recently been recognized by United Nations Framework Convention on Climate Change (UNFCCC). This is partly due to the lack of reliable estimates on the sequestration potential in biomass and soil carbon pools over time. The aim of this study was to analyze the changes in the biomass and soil carbon pools of three indigenous agroforestry systems in south-eastern Rift Valley escrapment of Ethiopia using CO2FIX (v. 3.2) model. The agroforestry systems studied were Enset ( Ensete ventricosum )-tree, Enset-coffee-tree, and Tree-coffee systems. To run the model, empirical data collected from 60 farms (20 farms for each agroforestry system) and literature were used as inputs to parameterize the model. Simulations were run over a period of 50 years. Average simulated total biomass C stocks was the highest for Tree-coffee system (122 Mg C ha −1 ), followed by the Enset-coffee-tree (114 Mg C ha −1 ) and Enset-tree system (76 Mg C ha −1 ). The tree cohort accounted for 89–97% of the total biomass C stocks in all the studied systems, and the reminder was shared by Enset and coffee cohorts. The total average simulated total C stocks (biomass and soil) were 209, 286 and 301 Mg C ha −1 for Enset-tree, Enset-coffee-tree and Tree-coffee systems, respectively. The soil organic carbon (SOC) stocks accounted for 60–64% of the total carbon in the studied systems. Model validation results showed that long-term (10–40 years) simulated biomass C stocks were within the range of measured biomass C stocks for Enset-tree and Enset-coffee-tree systems, but significantly differed for the Tree-coffee system. The simulated soil and total C stocks were within the range of measured values for all the three systems. The CO2FIX model accurately predicted the SOC and total C stocks in the studied indigenous agroforestry systems, but the prediction of the biomass C stocks could be improved by acquiring more accurate input parameter values for running the model. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) sequestration by improved agricultural practices is an acclaimed strategy to combat climate change. Nevertheless, the aim of increasing of SOC encounters limitations, e.g. with regards to permanence of carbon storage or leakage effects in food production. Agroforestry systems (AFS) are a promising land use option that is able to sequester substantial amounts of SOC while addressing these challenges. With a focus on temperate climate zones worldwide, available information on SOC in AFS was reviewed to determine their SOC sequestration potential and respective controlling factors. From a total of 61 observations, SOC sequestration rates in soils of AFS were derived for alley cropping systems (n = 25), hedgerows (n = 26) and silvopastoral systems (n = 10). The results showed that AFS have a potential for substantial SOC sequestration in temperate climates. SOC stocks were higher in the topsoil (0–20 cm) than in the control in more than 70% of the observations, and higher within the subsoil (20–40 cm) for 81% of all observations, albeit large variation in the data. The mean SOC sequestration rates were slightly higher at 0–20 cm (0.21 ± 0.79 t ha-1 yr-1) compared to 20–40 cm soil depth (0.15 ± 0.26 t ha-1 yr-1). Hedgerows revealed highest SOC sequestration rates in topsoils and subsoils (0.32 ± 0.26 and 0.28 ± 0.15 t ha-1 yr-1, respectively), followed by alley cropping systems (0.26 ± 1.15 and 0.23 ± 0.25 t ha-1 yr-1) and silvopastoral systems showing a slight mean SOC loss (−0.17 ± 0.50 and −0.03 ± 0.26 t ha-1 yr-1). Moreover, SOC sequestration rates tended to be higher for AFS with broadleaf tree species compared to coniferous species. We conclude that temperate AFS sequester significant amounts of SOC in topsoils and subsoils and represent one of the most promising agricultural measures for climate change mitigation and adaption. • Agroforestry has a highly significant and positive effect on SOC sequestration in the temperate zone. • SOC stocks in temperate AFS are generally higher than in treeless agricultural sites. • The amount of sequestered SOC was slightly higher at 0–20 cm compared to 20–40 cm soil depth. • Hedgerows revealed higher SOC sequestration rates than alley cropping and silvopastoral systems. • SOC sequestration rates were higher for AFS with broadleaf tree species compared to coniferous species. [ABSTRACT FROM AUTHOR]

There has been a careless use of terminology like “climate change mitigation” and “mitigate global warming” in scientific papers on no-tillage management in agriculture. This is because it has yet to be shown unequivocally that no-tillage can lead to carbon (C) sequestration let alone climate change mitigation. I briefly summarize evidence that shows that the claims of climate change mitigation through no-tillage agriculture are highly overstated. [ABSTRACT FROM AUTHOR]