Items

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  Root litter decomposition in a sub-Sahelian agroforestry parkland dominated by Faidherbia albida

  In agroforestry systems, fine roots grow at several depths due to the mixture of trees and annual crops. The decomposition of fine roots contributes to soil organic carbon stocks and may impact soil fertility, particularly in poor soils, such as those encountered in sub-Sahelian regions. The aim of our study was to measure the decomposition rate of root litter from annual and perennial species according to soil depth and location under and far from trees in a sub-Sahelian agroforestry parkland. Soil characteristics under and far from the trees were analysed from topsoil to 200 cm depth. Faidherbia tree, pearl millet and cowpea root litter samples were buried in litterbags for 15 months at 20, 40, 90 and 180 cm depths. Root litter decomposition was mainly impacted by soil moisture and soil depth. Faidherbia decomposed more slowly (36 ± 12% remaining mass after 15 months) than cowpea and pearl millet roots (23 ± 7% and 29 ± 11% respectively). Pearl millet aboveground biomass, at harvesting time, was twice as high under (992 g m−2) than far (433 g m−2) from the tree, and belowground biomass (0–200 cm of depth) was 30.9 g m−2 and 19.6 g m−2 under and far from the tree, respectively. Faidherbia fine roots contributed slightly (p-value < 0.1) to higher stocks of C under the tree (7761 ± 346 g m−2) than far from it (5425 ± 558 g m−2) and from 0 cm down to 200 cm depth.
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  Carbon sequestration capacity in no-till soil decreases in the long-term due to saturation of fine silt plus clay-size fraction

  The capacity of soils to stabilize carbon (C) may decrease over time, limiting the potential of no-till soil to act as a C sink in the long-term. Our objectives were to evaluate the effects of long-term no-till cropping systems on (i) C storage in soil, (ii) C stabilization in the fine silt plus clay-size (<20 μm) fraction and its relationship with the decrease of C saturation deficit (CSD) in this fraction, and (iii) on C accumulation in labile fractions of soil organic matter (SOM) in 0–2.5, 2.5–5, 5–10 and 10–20 cm layers of a subtropical Acrisol. The study was based on a long-term (36 years) no-till experiment where five cropping systems, with variable annual C inputs, were assessed: [i] bare-soil, [ii] black oat/maize, [iii] black oat + vetch/maize + cowpea, [iv] lablab + maize and [v] pigeon pea + maize. Cropping systems including maize and tropical legumes (lablab, pigeon pea and cowpea) with high C input led to the highest C storage in the top layers (up to 10 cm depth) of this no-till soil. Also, a decrease of CSD in fine silt plus clay-size fraction was observed in all soil layers to 20 cm depth, but the most expressive impact on CSD occurred in the topsoil (0–2.5 cm), where the capacity to further stabilize more carbon decreased by 90–97% when compared to bare soil. Considering the full C saturation level of the silt plus clay-size fraction and the current C contents in the soil, the remaining capacity of C sequestration up to 20 cm was estimated as ranging from 22.5 to 32.8 Mg C ha−1, and much of it (58–75%) was in the 10–20 cm layer. Our results highlight the importance of diversified cropping systems with high input (quantity and quality) crop residues to C sequestration in soil. Moreover, although the mineral-associated SOM of the top layer reached a C stabilization limit, C accumulation continues in non-saturated labile fractions, and in non-saturated fine silt plus clay-size fraction in deeper layers of subtropical no-till soils.
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  Will fungi solve the carbon dilemma?

  Soils are hotspots of diversity and sustain many globally important functions. Here we focus on the most burning issue: how to keep soils as carbon sinks while maintaining their productivity. Evidence shows that life in soils plays a crucial role in improving soil health yet soil ecological processes are often ignored in soil sciences. In this review, we highlight the potential of fungi to increase soil carbon sequestration while maintaining crop yield, functions needed to sustain human population on Earth and at same time keep the Earth livable. We propose management strategies that steer towards more fungal activity but also high functional diversity of fungi which will lead to more stable carbon sources in soil but also affects the structure of the soil food web up to ecosystem level. We list knowledge gaps that limit our ability to steer soil fungal communities such that stabilising carbon in top soils becomes more effective. Using the natural capacity of a biodiverse soil community to sequester carbon delivers double benefit: reduction of atmospheric carbon dioxide by storing photosynthesized carbon in soil and increasing agricultural yields by restoring organic matter content of degraded soils.
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  Chapitre 8. Dynamique de stockage du carbone dans les sols du Sénégal : Acquis de la recherche et perspectives

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  Deliberation and Diversity: Perceptions of Small Group Discussions by Race and Ethnicity

  One of the challenges facing public deliberation scholars and practitioners is to identify deliberative processes that address inequities in interaction and foster active participation among all members of ethnically or racially diverse groups. This study draws from cocultural communication theory and uses mixed methodology to examine the experiences of citizens assigned to racially/ethnically diverse small groups who participated in “By the People: Dialogues in Democracy”—a national/local initiative and public deliberation event. One hundred participants in a local deliberation in Omaha, Nebraska, completed a postevent questionnaire, and 20 participants were subsequently interviewed. Data were analyzed to compare the perceptions of White participants and participants of color (African American, Hispanic, Native American, Asian American). Analysis of variance indicated that participants of color perceived greater communication quality and group effectiveness and experienced more satisfaction with their small groups than did Whites. Both White interviewees and interviewees of color said they valued being exposed to diverse group members and perspectives, the respectful tone of the group interaction, the facilitators’ ability to guide the interaction, and the opportunity to learn. Consistent with cocultural communication theory, participants of color specially praised the equal opportunity to speak in their groups and the experience of being heard. The results fortify the importance for public deliberation practitioners to take concerted steps to ensure racial/ethnic diversity and egalitarian interaction of members in deliberative small groups.
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  Deliberations about deliberative methods: issues in the design and evaluation of public participation processes

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  Apports de l’évaluation délibérative dans la gestion concertée des ressources communes. L’exemple des marais Tanoé-Ehy

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  Which public and why deliberate? – A scoping review of public deliberation in public health and health policy research

  Deliberative methods are of increasing interest to public health researchers and policymakers. We systematically searched the peer-reviewed literature to identify public health and health policy research involving deliberative methods and report how deliberative methods have been used. We applied a taxonomy developed with reference to health policy and science and technology studies literatures to distinguish how deliberative methods engage different publics: citizens (ordinary people who are unfamiliar with the issues), consumers (those with relevant personal experience e.g. of illness) and advocates (those with technical expertise or partisan interests). We searched four databases for empirical studies in English published 1996e2013. This identified 78 articles reporting on 62 distinct events from the UK, USA, Canada, Australasia, Europe, Israel, Asia and Africa. Ten different types of deliberative techniques were used to represent and capture the interests and preferences of different types of public. Citizens were typically directed to consider community interests and were treated as a resource to increase democratic legitimacy. Citizens were preferred in methodological studies (those focused on understanding the techniques). Consumers were directed to focus on personal preferences; thus convened not as a source of policy decisions, but of knowledge about what those affected by the issue would accept. Advocatesdwho are most commonly used as expert witnesses in juriesdwere sometimes engaged to deliberate with consumers or citizens. This almost always occurred in projects directly linked to policy processes. This suggests health policymakers may value deliberative methods as a way of understanding disagreement between perspectives. Overall however, the ‘type’ of public sought was often not explicit, and their role not specified. This review provides new insight into the heterogeneity and rising popularity of deliberative methods, and indicates a need for greater clarity regarding both the constitution of publics and the relative usefulness of different deliberative techniques.
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  Deliberation as a catalyst for reflexive environmental governance

  Ecological or ecosystemic reflexivity involves the capacity of social-ecological systems to reconfigure themselves in response to reflection on their performance. In this paper we argue that deliberation is central to reflexive governance, mainly because it can reconcile many if not most of the sometimes contradictory claims that are made in the literature about its drivers. We take four key dimensions along which reflexivity may be sought, each of which features a binary that puts two plausible drivers of reflexivity in tension with one another: (i) sources of knowledge (public participation versus expertise); (ii) composition of public discourse (diversity versus consensus); (iii) institutional architecture (polycentricity versus centralization); (iv) institutional dynamics (flexibility versus stability). In each case, we demonstrate that deliberative ideas can manage the tension between the two plausible drivers of reflexivity.
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  Sustainability as a cultural transformation: the role of deliberative democracy

  What might break the ‘glass ceiling’ that has so far prevented a deep sustainability transformation? I consider the cultural dimension of such a transformation. Cultural meanings not only provide the building blocks of individuals’ life stories, but collectively construct social reality, powerfully shaping how people think and act. Any glass ceiling to societal transformation is partly cultural, and can be reproduced by a society’s ‘political grammar,’ which constrains what can be perceived and politically advanced. Contesting these limits is vital for making glass ceilings visible and opening up new transformative potentials. Consequently, overcoming the glass ceiling of the environmental state must be understood as a cultural transformation: a process of ‘meaning-making’ that re-orientates people’s fundamental norms and outlooks. This adds nuance to the debate around democracy and sustainability; it is not democracy in general, but only a particularly vibrant and critical deliberative sphere that can provide the necessary political foundation.
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  Deliberative Democracy or Agonistic Pluralism

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  Transforming Rural Water Governance: Towards Deliberative and Polycentric Models?

  In recent years, many countries have experienced a formal shift from command-and-control and prescriptive management of natural resources towards policy making and planning processes that build on collaboration, negotiation and deliberation among policy-makers, scientists and local stakeholders (Bouwen and Tallieu, 2004; Warner, 2006; Ansell and Gash, 2008). Public participation in environmental decision-making and implementation has become part and parcel of the environmental governance rhetoric in many industrialised countries (Sabatier et al., 2005; Messner et al., 2006; Cronin and Ostergren, 2007; Ferreyra et al., 2008; Medd and Marvin, 2008; Marshall, in press). In emerging economies and developing countries 'participatory environmental governance' has also been discussed as an alternative to centralised, top-down approaches towards natural resource conservation and management (e.g. Gupte and Bartlett, 2007; Neaera Abers, 2007; Huang et al., 2009). At the international policy level, the Rio Declaration and the Agenda 21 (1992), the World Summit on Sustainable Development (WSSD) Johannesburg Plan of Implementation (2002), and the 1998 UN Economic Commission for Europe (UNECE) "Convention on Access to Information, Public Participation in Decision-making and Access to Justice in Environmental Matters" (the so-called Aarhus Convention) have been the most important drivers for enhanced citizen participation in environmental governance.
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  Co-designing transformation research: lessons learned from research on deliberate practices for transformation

  Co-production of new knowledge can enhance open and integrative research processes across the social and natural sciences and across research/science, practice and policy interrelationships. Thus, co-production is important in the conduct of research about and for transformations to sustainability. While co-design is an integral part of co-production, it often receives limited attention in the conduct of co-produced research. This paper reports on lessons learned from an early stage of the co-design process to develop research on deliberate practices for transformative change. Key lessons learned are the need to: (1) ensure co-design processes are themselves carefully designed; (2) encourage emergence of new ways of thinking about problem formulation through co-design; (3) carefully balance risks for the participants involved while also enhancing opportunities for intellectual risk taking; (4) facilitate personal transformations in co-design as a way to stimulate and encourage further creativity; and (5) for funders to carefully and constructively align criteria or incentives through which a project or future proposal will be judged to the goals of the co-design, including for instrumental outcomes and objectives for creativity and imagination. Given that co-design necessarily involves a reflective practice to iteratively guide emergence of new thinking about the practices of change, co-design can itself be considered an important deliberate practice for transforming the conduct of research and the contribution of that research to social transformations.
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  Reasons and Inclusion: The Foundation of Deliberation

  This article provides two empirical evaluations of deliberation. Given that scholars of deliberation often argue for its importance without empirical support, we first examine whether there is a “deliberative difference”; if actors engaging in deliberation arrive at different decisions than those who think on their own or “just talk.” As we find a general convergence within deliberation scholarship around reasons and inclusion, the second test examines whether these two specific mechanisms are central to deliberation. The first evaluation looks at outcomes within a laboratory setting; the second at videotapes of decision-making processes within this setting. Our results show two things. First, in terms of outcomes, deliberation differs from other forms of interaction. Second, reasons and inclusion are central to the deliberative process. The more reasons provided within each group, the more likely participants were to change their position; similarly, the more inclusive groups were, the more likely participants were to change their position. We conclude by arguing that more work needs to be done, both in evaluating the deliberative difference and in disaggregating deliberation and examining its central explanatory mechanisms.
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  Deliberative Methods for Understanding Environmental Systems

  Environmental problem solving needs science but also inevitably requires subjective judgment. Science can help in dealing with subjectivity, because scientists have long experience developing institutions and practices to address the subjective and value-laden choices that are essential to scientific progress. Democracy has also developed approaches to the problem. The underlying principles can be applied to environmental policymaking. This article explores these issues in the context of decisions about environmental risks, drawing on the work of the National Research Council and other sources. It suggests some guidelines for risk deliberation—including broad-based participation, commitment to scientific quality, explicit attention to values, transparency of deliberative processes, and rules for closure and reconsideration—and recommends that an experimental approach be employed to learn how best to use deliberative methods.
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  Precautionary Principle, Pluralism and Deliberation : Introduction

  The purpose of this book is to provide a thorough and balanced examination of the precautionary principle, considering its huge potential to express responsibility in the fields of research and innovation. The precautionary principle has a key part to play in the face of the most disruptive innovations. It is one of the most creative innovations for implementing responsibility in response to new fears surrounding environmental resilience or emerging technologies. It also constitutes one of the most original and well-received proposals of the European Union. RRI owes a certain debt to this institution, and still has a lot to learn from the precautionary principle4. In this work, we shall consider the ethics of the principle of responsibility.
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  The role of soil in regulation of climate

  The soil carbon (C) stock, comprising soil organic C (SOC) and soil inorganic C (SIC) and being the largest reservoir of the terrestrial biosphere, is a critical part of the global C cycle. Soil has been a source of greenhouse gases (GHGs) since the dawn of settled agriculture about 10 millenia ago. Soils of agricultural ecosystems are depleted of their SOC stocks and the magnitude of depletion is greater in those prone to accelerated erosion by water and wind and other degradation processes. Adoption of judicious land use and science-based management practices can lead to re-carbonization of depleted soils and make them a sink for atmospheric C. Soils in humid climates have potential to increase storage of SOC and those in arid and semiarid climates have potential to store both SOC and SIC. Payments to land managers for sequestration of C in soil, based on credible measurement of changes in soil C stocks at farm or landscape levels, are also important for promoting adoption of recommended land use and management practices. In conjunction with a rapid and aggressive reduction in GHG emissions across all sectors of the economy, sequestration of C in soil (and vegetation) can be an important negative emissions method for limiting global warming to 1.5 or 2°C This article is part of the theme issue ‘The role of soils in delivering Nature's Contributions to People’.
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  Countries’ commitments to soil organic carbon in Nationally Determined Contributions

  Soil carbon is the major active pool of terrestrial carbon, and as such, soil organic carbon (SOC) targets, policies and measures will be pivotal to achieving global climate targets. SOC sequestration may reduce the net annual greenhouse gas emissions from Agriculture, Forestry and Other Land Use by between 3% and 71%, while simultaneously supporting various ecosystem services. Accurate SOC accounting and monitoring, however, is constrained by various technical challenges related to indicators, rates of SOC change, measuring the impact of management practices on SOC, and the long-term persistence of sequestered SOC. We assessed countries’ pledges to the Paris Agreement for SOC in agriculture to better understand the level, transparency, and specificity of commitments. Reviewing 184 countries’ initial Nationally Determined Contributions (NDCs), we considered whether SOC was included, what was pledged, the level of ambition promised and the specificity of mitigation targets. Twenty-eight countries referred to SOC in their NDCs, citing quantified or unquantified mitigation targets, national policies or programs, and actions and measures to be implemented in agricultural lands (14), peatlands (6) or wetlands (14). Countries’ reasons for not including SOC in NDCs included the need to prioritize goals of sustainable development and food security above climate mitigation, a lack of incentives for farmers to improve management practices, and the difficulty of accurately monitoring changes in SOC. Including SOC targets in NDCs can improve NDCs’ comprehensiveness and transparency to track and compare policy progress across NDCs; it can also leverage SOC-related climate finance, technical support, and capacity building.Key policy insights Many NDCs specify practices known to have the potential to achieve SOC sequestration or protection without explicitly mentioning SOC. The SOC-related mitigation potential of these practices can be quantified in future NDCs.NDCs are not presently a good indicator of countries’ interest or commitment to SOC action at national level. To improve this, countries with existing SOC policies, programs, and actions can specify their SOC-related commitments in future NDCs.Increased collaboration between countries with experience managing SOC and countries needing support to develop SOC-related targets, policies, measures and incentives for land users and farmers would facilitate the provision of such needed support.To increase country commitments and attention to managing SOC, there is a need for improved SOC measurement and monitoring, for better evidence on the impacts of management practices on SOC, and for incentives for farmers to change practices and overcome barriers.
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  Mapping carbon accumulation potential from global natural forest regrowth

  To constrain global warming, we must strongly curtail greenhouse gas emissions and capture excess atmospheric carbon dioxide1,2. Regrowing natural forests is a prominent strategy for capturing additional carbon3, but accurate assessments of its potential are limited by uncertainty and variability in carbon accumulation rates2,3. To assess why and where rates differ, here we compile 13,112 georeferenced measurements of carbon accumulation. Climatic factors explain variation in rates better than land-use history, so we combine the field measurements with 66 environmental covariate layers to create a global, one-kilometre-resolution map of potential aboveground carbon accumulation rates for the first 30 years of natural forest regrowth. This map shows over 100-fold variation in rates across the globe, and indicates that default rates from the Intergovernmental Panel on Climate Change (IPCC)4,5 may underestimate aboveground carbon accumulation rates by 32 per cent on average and do not capture eight-fold variation within ecozones. Conversely, we conclude that maximum climate mitigation potential from natural forest regrowth is 11 per cent lower than previously reported3 owing to the use of overly high rates for the location of potential new forest. Although our data compilation includes more studies and sites than previous efforts, our results depend on data availability, which is concentrated in ten countries, and data quality, which varies across studies. However, the plots cover most of the environmental conditions across the areas for which we predicted carbon accumulation rates (except for northern Africa and northeast Asia). We therefore provide a robust and globally consistent tool for assessing natural forest regrowth as a climate mitigation strategy.
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  Small farms and development in sub-Saharan Africa: Farming for food, for income or for lack of better options? | SpringerLink

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  A global overview of studies about land management, land-use change, and climate change effects on soil organic carbon

  Major drivers of gains or losses in soil organic carbon (SOC) include land management, land-use change, and climate change. Thousands of original studies have focused on these drivers of SOC change and are now compiled in a growing number of meta-analyses. To critically assess the research efforts in this domain, we retrieved and characterized 192 meta-analyses of SOC stocks or concentrations. These meta-analyses comprise more than 13,200 original studies conducted from 1910 to 2020 in 150 countries. First, we show that, despite a growing number of studies over time, the geographical coverage of studies is limited. For example, the effect of land management, land-use change, and climate change on SOC has been only occasionally studied in North and Central Africa, and in the Middle East and Central Asia. Second, the meta-analyses investigated a limited number of land management practices, mostly mineral fertilization, organic amendments, and tillage. Third, the meta-analyses demonstrated relatively low quality and transparency. Lastly, we discuss the mismatch between the increasing number of studies and the need for more local, reusable, and diversified knowledge on how to preserve high SOC stocks or restore depleted SOC stocks.
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  ACCELERATING CARBON FARMING Joint 4 per 1000 Initiative / European Parliament webinar 8 Sept 2021

  ACCELERATING CARBON FARMING How to make Carbon Farming a Success for Climate, Environment and Farmers ? The Green Deal has been marked as the new economic strategy of the Union. It is changing our overall legislative framework to allow the deployment of technologies and unlock the investment that will make possible carbon neutrality, and a new model of prosperity. Agriculture and farmers have an essential role to play since this is the one of the few sectors that has the ability to shift from a net emitter of CO2 to a net sequestered of CO2. As part of the European Green deal, a series of initiatives can become true game changer: the reform of LULUCF regulation, the Carbon Farming initiative and the regulatory framework for certifying carbon removal. If we design the framework right, carbon farming can create a new profitable business model and support the transition. The European Green deal offers an opportunity to build a transition profitable for all: farmers would be able to get money for their contribution to climate mitigation, and also additional support to enhance their capacity to stock carbon in farmland, which is ultimately needed if we are serious about being carbon neutral by 2050. This is how we will bring everybody on board with the transition. During this panel, each speaker is asked to discuss the following questions: - How to ensure than carbon farming actually delivers the expected outcome in terms of climate mitigation and biodiversity protection on one side,and on farmers’ additional revenues on the other side? - How the carbon market, and at which price, can incentivize properly farmers? - How to ensure permanence of action in order to secure lasting climate action? - Who would be liable for the proper management and maintenance of agricultural practices benefiting the climate? (And more) Speakers: Mr. Pascal Canfin - Chair of the Committee on the Environment, Public Health and Food Safety (ENVI Committee) Mr. Norbert Lins - Chair of the Committee on Agriculture and Rural Development (AGRI Committee) Mr. Christian Holzleitner - Head of the Unit Land Use & Finance for Innovation (DG CLIMA.C.3) at DG CLIMA (Directorate General Climate Action) Ms. Claire Chenu - Director of Research Coordinator of EJP Soil "European Joint Programming Co-fund on Agricultural Soil Management" Member of the Scientific and Technical Committee of the "4 per 1000" Initiative Ms. Anne Trombini - Director "Pour une Agriculture du Vivant - Pour une Agriculture du Vivant" Ms. Léa Lugassy - Scientific Coordinator "Pour une Agriculture du Vivant - Pour une Agriculture du Vivant" Ms. Margaret Kim - CEO "The Gold Standard" Mr. Georg Goeres - Head of Europe "Indigo" Mr. Quentin Sannié Founder & CEO "Greenback"
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  Estimates of carbon stocks in sandy soils cultivated under local management practices in Senegal’s groundnut basin

  Soil organic carbon (SOC) is essential for the productivity of agroecosystems and for mitigating climate change. Because the SOC contents of sandy soils are usually small, the effects of agricultural management upon SOC stocks in such soils have been insufficiently studied. In West sub-arid Africa, the coarse-textured soils (mostly Arenosols) are diversely managed by smallholders. In this study, we aimed to quantify SOC stocks in cultivated soils of that region, in a context where agricultural practices rely mainly upon organic inputs derived from various integrated crop-livestock systems. SOC stocks were estimated for the 0–30 cm depth in 1,813 plots in Senegal’s groundnut basin. We found that SOC stocks in farmers’ fields varied between 2.3 and 59.8 Mg C ha-1 (mean ± standard deviation, 14.6 ± 0.14 Mg C ha-1). SOC stocks were influenced slightly by soil type, but were only weakly correlated to soils’ clay and silt contents. SOC stocks differed significantly among the three studied village territories due to contrasting livestock-raising systems. Average stocks were significantly higher in plots close to housings (home-fields), which receive larger amounts of organic inputs, than in plots farther from the village (out-fields). Thus, the organic inputs to home-fields improves soil C stocks of these sandy soils in the short term. Innovative agricultural practices in the studied area probably need to target options for managing all fields optimally. Those options will require continuous application of organic products—a measure that will in turn require solutions for improving availability or management of local organic resources.
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  Simulating soil organic carbon in maize-based systems under improved agronomic management in Western Kenya

  Improved management practices should be implemented in croplands in sub-Saharan Africa to enhance soil organic carbon (SOC) storage and/or reduce losses associated with land-use change, thereby addressing the challenge of ongoing soil degradation. DayCent, a process-based biogeochemical model, provides a useful tool for evaluating which management practices are most effective for SOC sequestration. Here, we used the DayCent model to simulate SOC using experimental data from two long-term field sites in western Kenya comprising of two widely promoted sustainable agricultural management practices: integrated nutrient management (i.e. mineral fertilizer and crop residues/farmyard manure incorporation) and conservation agriculture (i.e. minimum tillage and crop residue retention). At both sites, correlations between measured and simulated SOC were low to moderate (R2 of 0.25−0.55), and in most cases, the model produced fairly accurate prediction of the SOC trends with a low relative root mean squared error (RRMSE < 7%). Consistent with field measurements, simulated SOC declined under all improved management practices. The model projected annual SOC loss rates of between 0.32 to 0.35 Mg C ha-1 yr-1 in continuously tilled maize (Zea mays) systems without fertilizer or organic matter application over the period 2003–2050. The most effective practices in reducing the losses were the combined application of 4 Mg ha-1 of farmyard manure and 2 Mg ha-1 of maize residue retention (reducing losses up to 0.22 Mg C ha-1 yr-1), minimum tillage in combination with maize residue retention (0.21 Mg C ha-1 yr-1), and rotation of maize with soybean (Glycine max) under minimum tillage (0.17 Mg C ha-1 yr-1). Model results suggest that response of the passive SOC pool to the different management practices is a key driver of the long-term SOC trends at the two study sites. This study demonstrates the strength of the DayCent model in simulating SOC in maize systems under different agronomic management practices that are typical for western Kenya.
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  Reducing losses but failing to sequester carbon in soils – the case of Conservation Agriculture and Integrated Soil Fertility Management in the humid tropical agro-ecosystem of Western Kenya

  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 15cm 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 0.37tCha−1 yr−1 in the CA long-term trial and 0.21 and 0.96tCha−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 0.13tCha−1 yr−1, while this was 0.26tCha−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.