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Increasing soil organic carbon (SOC) stocks is increasingly targeted as a key strategy in climate change mitigation and improved ecosystem resiliency. Agricultural land, a dominant global land use, provides substantial challenges and opportunities for global carbon sequestration. Despite this, global estimates of soil carbon sequestration potential often exclude agricultural land and estimates are coarse for regions in the Global South. To address these discrepancies and improve estimates, we develop a hybrid, data‐augmented database approach to better estimate the magnitude of SOC sequestration potential of agricultural soils. With high‐resolution (30 m) soil maps of Africa developed by the International Soils Database (iSDA) and Malawi as a case study, we create a national adjustment using site‐specific soil data retrieved from 1160 agricultural fields. We use a benchmark approach to estimate the amount of SOC Malawian agricultural soils can sequester, accounting for edaphic and climatic conditions, and calculate the resulting carbon gap. Field measurements of SOC stocks and sequestration potentials were consistently larger than iSDA predictions, with an average carbon gap of 4.42 ± 0.23 Mg C ha−1 to a depth of 20 cm, with some areas exceeding 10 Mg C ha−1. Augmenting iSDA predictions with field data also improved sensitivity to identify areas with high SOC sequestration potential by 6%—areas that may benefit from improved management practices. Overall, we estimate that 6.8 million ha of surface soil suitable for agriculture in Malawi has the potential to store 274 ± 14 Tg SOC. Our approach illustrates how ground truthing efforts remain essential to reduce errors in continent‐wide soil carbon predictions for local and regional use. This work begins efforts needed across regions to develop soil carbon benchmarks that inform policies and identify high‐impact areas in the effort to increase SOC globally. [ABSTRACT FROM AUTHOR]

Food insecurity, child malnutrition, and land degradation remain persistent problems in sub‐Saharan Africa. Agricultural sustainable intensification (SI) has been proposed as a possible solution to simultaneously address these challenges. Yet there is little empirical evidence on if agricultural management practices and inputs that contribute to SI from an environmental standpoint do indeed improve food security or child nutrition. We use three waves of data from the nationally‐representative Tanzania National Panel Survey to analyze the child nutrition effects of rural households' adoption of farming practices that can contribute to the SI of maize production. We group households into four categories based on their use of three soil fertility management practices on their maize plots: "Nonadoption"; "Intensification" (use of inorganic fertilizer only); "Sustainable" (use of organic fertilizer, maize–legume intercropping, or both); and "SI" (joint use of inorganic fertilizer with organic fertilizer and/or maize–legume intercropping). The results from multinomial endogenous treatment effects models with the Mundlak–Chamberlain device suggest that use of practices in the "SI" category is associated with improvements in children's height‐for‐age and weight‐for‐age z‐scores relative to "Nonadoption," particularly for children aged 25–59 months. These effects appear to come through improvements in both crop income and productivity. [ABSTRACT FROM AUTHOR]

Understanding the challenges to increasing maize productivity in sub-Saharan Africa, especially agronomic factors that reduce on-farm crop yield, has important implications for policies to reduce national and global food insecurity. Previous research on the maize yield gap has tended to emphasize the size of the gap (theoretical vs. achievable yields), rather than what determines maize yield in specific contexts. As a result, there is insufficient evidence on the key agronomic and environmental factors that influence maize yield in a smallholder farm environment. In this study, we implemented a Bayesian analysis with plot-level longitudinal household survey data covering 1,197 plots and 320 farms in Central Malawi. Households were interviewed and monitored three times per year, in 2015 and 2016, to document farmer management practices and seasonal rainfall, and direct measurements were taken of plant and soil characteristics to quantify impact on plot-level maize yield stability. The results revealed a high positive association between a leaf chlorophyll indicator and maize yield, with significance levels exceeding 95% Bayesian credibility at all sites and a regression coefficient posterior mean from 28% to 42% on a relative scale. A parasitic weed, Striga asiatica, was the variable most consistently negatively associated with maize yield, exceeding 95% credibility in most cases, of high intensity, with regression means ranging from 23% to 38% on a relative scale. The influence of rainfall, either directly or indirectly, varied by site and season. We conclude that the factors preventing Striga infestation and enhancing nitrogen fertility will lead to higher maize yield in Malawi. To improve plant nitrogen status, fertilizer was effective at higher productivity sites, whereas soil carbon and organic inputs were important at marginal sites. Uniquely, a Bayesian approach allowed differentiation of response by site for a relatively modest sample size study (given the complexity of farm environments and management practices). Considering the biophysical constraints, our findings highlight management strategies for crop yields, and point towards area-specific recommendations for nitrogen management and crop yield. [ABSTRACT FROM AUTHOR]

• NDVI is positively associated with both total and labile soil C pools. • Crop diversity, weed presence, and residue management enhance soil C. • Environment and management have modest or variable effects on labile soil C. • Bayesian linear regression methodology was statistically robust in this study. Soil degradation on cultivated lands of Sub-Saharan Africa is a threat to food security. Even so, drivers of soil C total and labile pools are little understood for smallholder farms. A unique opportunity to evaluate how environment conditions management drivers was afforded by a systematically representative on-farm study of 1108 cultivated plots in marginal to mesic environments across Central and Southern Malawi. Soil sample collection and analysis and surveys of farmer practice were conducted, and linked to remote-sensed data on environmental and spectral factors. Soil properties included the following ranges (mean values per site), soil clay (6.41% to 17.36%), pH (6.09 to 6.54), soil organic carbon (SOC) (6.31 g C kg soil−1 to 16.17 g C kg soil−1), and two labile soil C assays: permanganate oxidizable carbon (POXC) (291.5 mg C kg soil−1 to 504.5 mg C kg soil−1) and 24-h mineralizable C (Cmin) (28.71 mg C kg soil−1 to 65.34 mg C kg soil−1). Incorporation of domain specialists' expectation of uncertainty levels is key to carrying out a multiscale assessment of soil total and labile C status, thus a Bayesian linear regression approach was used for determining the influential drivers. Overall, the soil clay content is a strong predictor of SOC (0.479–0.517), POXC (0.139–0.266), and Cmin (0.125–0.223) at the 95% Bayesian credibility level from the Gibbs posterior samples. Vegetative cover, reflected by Normalized Difference Vegetation Index (NDVI), is also a dominant driver for SOC (0.234–0.329), POXC (0.163–0.285), and Cmin (0.249–0.38). Of the management practices studied, crop diversity, residue incorporation, and weed presence are all positive drivers for total soil C, whereas fertilizer N is not. At both regional and local scales, labile soil C pools (as reflected by POXC and Cmin) are not consistently responsive to management. The drivers of SOC are highly consistent, a strong indication of statistical robustness. This contributes to the understanding of patterns of carbon pools in intensively cultivated fields in Sub-Saharan Africa. [ABSTRACT FROM AUTHOR]

Weed abundance in cereal-based systems has increased in recent years across sub-Saharan Africa for smallholder farmers (cultivating less than two hectares). Smallholders can employ numerous practices to control weeds such as intercropping cereal crops with legumes. We conducted a review to identify the possible mechanisms responsible for weed control according to legume species, weed species and agroecosystem. In the review, we first present common weed species found in specific agroecological contexts. Then, we propose several legume intercrops that provide some control of these species and the reasons why. Finally, we highlight possible social and biophysical tradeoffs for cultivating legumes as a weed control practice in smallholder cereal systems. The review found that while many studies explained the effect a certain legume-intercrop had upon weeds (e.g., emergence rates), few identified the mechanism or mechanisms (e.g., increased predation) behind their control. Without understanding these mechanisms, it is difficult to propose management recommendations for intercropping (e.g., seeding rates). Furthermore, few studies have investigated how legume intercrops affect multiple components of farming systems, including the smallholders that cultivate them. Determining how these components connect and impose tradeoffs for smallholders unveils the drivers (or barriers) behind legume intercropping as a weed control practice. [ABSTRACT FROM AUTHOR]

• Agroecological methods improved household food security & diet diversity in 2 years. • Intercrops & crop diversification increased household food security. • Use of organic soil amendments such as compost increased dietary diversity. • Spouses discussing farming 2.4X more likely to be food secure & have diverse diets. • Participatory agroecology research linked to gender equity improved food security. This study examines whether agroecological farming practices, when employed by highly vulnerable households in sub-Saharan Africa, can improve food security and dietary diversity. The research involved a four-year study with 425 smallholder households, selected purposively based on high levels of food insecurity and/or positive HIV status. The households carried out agroecological experiments of their own choosing over a four-year period. Baseline (n = 306) and follow-up (n = 352) surveys were conducted in 2011 and 2013 respectively to assess changes in farming practices, food security, crop diversity and dietary diversity. Longitudinal mixed effects models were used with 203 matched households to estimate determinants of change in food security and dietary diversity at the population level. Qualitative interviews and focus groups were also conducted to provide depth to the survey findings. The findings show that participatory agroecology experimentation increased intercropping, legume diversification and the addition of compost, manure and crop residue amendments to the soil. Intercropping was associated with food security and the use of organic soil amendments was associated with gains in dietary diversity in bivariate analysis. Household food security and dietary diversity increased significantly over a 2-year period. Importantly, multivariate models showed that spousal discussion about farming was strongly associated with increased household food security and dietary diversity. Households who discussed farming with their spouse were 2.4 times more likely to be food secure and have diverse diets. Addition of compost or manure to the soil significantly influenced dietary diversity. These findings indicate that poor, vulnerable farmers can use agroecological methods to effectively improve food and nutritional security in sub-Saharan Africa. The study also highlights how linking agroecology to participatory research approaches that promote farmer experimentation and gender equity also lead to greater health and well-being. The study sheds light on how agroecological approaches can rapidly improve food security and dietary diversity, even under conditions of acute social, health or ecological stress. It draws attention to issues of equity and farmer-led approaches in addressing food security and nutrition. [ABSTRACT FROM AUTHOR]

Crop diversification with grain legumes has been advocated as a means to increase agroecological resilience, diversify livelihoods, boost household nutrition, and enhance soil health and fertility in cereal-based cropping systems in sub-Saharan Africa and around the world. Soil organic carbon (SOC) is a primary indicator of soil health and there is limited data regarding SOC pools and grain legume diversification on smallholder farms where soils are often marginal. In Malawi, a range of legume diversification options are under investigation, including rotations and a doubled-up legume rotation (DLR) system in which two compatible legumes are intercropped and then rotated with a cereal. The impact of the DLR system on SOC has not yet been determined, and there is a lack of evidence regarding SOC status over a gradient of simple to complex grain legume diversified systems. We address this knowledge gap by evaluating these systems in comparison to continuous sole maize (Zea mays L.) at three on-farm trial sites in central Malawi. After six years of trial establishment, we measured SOC in bulk soils and aggregate fractions and in faster cycling SOC pools that respond more rapidly to management practices, including water extractable organic carbon (WEOC), particulate organic matter carbon (POM-C), potentially mineralizable carbon (C), and macroaggregate C. Cropping treatment differences were not seen in bulk SOC or total N, but they were apparent in SOC pools with a shorter turnover time. The DLR system of intercropped pigeonpea (Cajanus cajan (L.) Millsp.) and groundnut (Arachis hypogaea L.) rotated with maize had higher WEOC, POM-C, potentially mineralizable C, macroaggregate and microaggregate C values than continuous maize. Of the single legume rotations, the pigeonpea-maize rotation had more mineralizable C and microaggregate C compared to continuous maize, while the groundnut-maize rotation had similar C values to the maize system. Overall, this study shows the potential for crop rotations diversified with grain legumes to enhance C in management sensitive SOC pools, and it is one of the first reports to show this effect on smallholder farm sites. • Doubled-up legume rotation had more C in labile SOC pools compared to continuous maize in on-farm trials after six years. • More WEOC, POM-C, potentially mineralizable C, macroaggregate and microaggregate C in doubled-up legume rotation. • Pigeonpea-maize rotation had higher potentially mineralizable and macroaggregate C values than maize. • Groundnut-maize rotation SOC pool values similar to continuous maize. [ABSTRACT FROM AUTHOR]

• We define agronomic gain (AG) based on improvement in key performance indicators (KPIs). • KPIs include productivity, resource use efficiencies, and soil health. • AG assessment is applied to previous studies with attention to rice in sub-Saharan Africa. • Challenges in AG assessment in different research process stages are identified. • Solutions and future research areas in relation to the challenges are provided. Meeting future global staple crop demand requires continual productivity improvement. Many performance indicators have been proposed to track and measure the increase in productivity while minimizing environmental degradation. However, their use has lagged behind theory, and has not been uniform across crops in different geographies. The consequence is an uneven understanding of opportunities for sustainable intensification. Simple but robust key performance indicators (KPIs) are needed to standardize knowledge across crops and geographies. This paper defines a new term 'agronomic gain' based on an improvement in KPIs, including productivity, resource use efficiencies, and soil health that a specific single or combination of agronomic practices delivers under certain environmental conditions. We apply the concept of agronomic gain to the different stages of science-based agronomic innovations and provide a description of different approaches used to assess agronomic gain including yield gap assessment, meta-data analysis, on-station and on-farm studies, impact assessment, panel studies, and use of subnational and national statistics for assessing KPIs at different stages. We mainly focus on studies on rice in sub-Saharan Africa, where large yield gaps exist. Rice is one of the most important staple food crops and plays an essential role in food security in this region. Our analysis identifies major challenges in the assessment of agronomic gain, including differentiating agronomic gain from genetic gain, unreliable in-person interviews, and assessment of some KPIs at a larger scale. To overcome these challenges, we suggest to (i) conduct multi-environment trials for assessing variety × agronomic practice × environment interaction on KPIs, and (ii) develop novel approaches for assessing KPIs, through development of indirect methods using remote-sensing technology, mobile devices for systematized site characterization, and establishment of empirical relationships among KPIs or between agronomic practices and KPIs. [ABSTRACT FROM AUTHOR]