Acid soils are widespread across sub-Saharan Africa. Agricultural lime can be used to alleviate production constraints associated with soil acidity, but lime is not widely available in the region, and it is unclear if applying it would be profitable. Using lime requirement models and crop yield responses to soil acidity modelled as plateau–linear decay functions, we estimated the profitability of acid soil remediation through liming. Crop yield loss to soil acidity occurs on 32.7 Mha, or 23% of sub-Saharan Africa’s cropland. The burden of acid soils is US$6.0 billion (6% of the current production value), and 75% of that could be profitably alleviated. Under prevailing conditions, liming would be profitable in the year of application on 6.2 Mha (with an average profitability of US$278 ha−1) and on 8.8 Mha when lime’s long-term effect is considered. Intensification of crop production and lower relative lime/output prices could make liming profitable on more cropland."

We are facing a biodiversity crisis, which is largely driven by the way we produce food. In response, various approaches to ‘biodiversity-smart farming’ have been proposed, sparking debates, especially in sub-Saharan Africa, a region that was largely bypassed by the Green Revolution and is expected to experience significant biodiversity loss due to agricultural expansion. Systems agronomy, a methodological approach geared towards the design of a broad basket of options for diverse farming conditions and diverse contexts, has a critical role to play in informing these debates. My past research has explored this topic through four key directions. First, I critically examined conservation agriculture as an example of biodiversity-smart farming during my early career. Second, I explored the landscape-scale as the critical scale for biodiversity-smart farming. Third, I emphasised the need for broader evaluation metrics beyond just yield, including labour and nutrition. Finally, my more recent work aimed at guiding and prioritising interventions, whether biodiversity-smart or more broadly development-oriented. Looking ahead, I propose to expand my research in three key areas. First, I will apply systems agronomy methods developed for cereal-based systems to roots-and-tuber crop-based systems, which are critical for biodiversity-smart farming in sub-Saharan Africa. Second, I will advance research on multi-functional landscapes that work for people and nature, addressing what remains a gap in development-oriented agronomy. Lastly, while continuing to investigate the ‘where,’ ‘for whom,’ and ‘what’ of interventions, I will also explore the ‘how’, examining how systems agronomy can better inform co-design processes.

An innovative methodological approach combining statistical typologies and stochastic frontier analysis was applied to data collected from 1840 mixed crop-livestock farms in six districts of Zimbabwe, representative of semi-arid areas of the country. The average annual cereal production was 362 kg farm-1, and the average annual livestock offtake was 0.64 +/- 1.32 Tropical Livestock Units (TLU) farm-1. Our results demonstrate there is scope to increase cereal and livestock production by 90.7% and 111.9% relative to current production levels, respectively, with more efficient use of existing resources and technologies. Rainfall was found to have a strong effect on cereal production, highlighting the need for climate-smart practices. Livestock mortality (0.59 +/- 1.62 TLU farm-1) was found to be in the same order of magnitude as livestock offtake (0.64 +/- 1.32 TLU farm-1). Cereal production was supported by livestock, demonstrating the importance of crop-livestock interactions in these mixed farming systems. Three farm types were identified in our analysis. Crop-oriented mixed farms (31%) are likely to be the ones most responsive to crop-specific interventions e.g., crop rotation and integrated pest management. Livestock-oriented mixed farms (34%) are likely to benefit the most from livestock-specific interventions, e.g., home feed. Mixed farms dependent on off-farm activities (36% of the sample) may require nutrition-sensitive and laboursaving sustainable intensification technologies to benefit from their limited resources. Reducing cattle mortality is a priority for all three farm types. The method proposed here could be adapted to other contexts characterized by heterogeneous farming populations to target interventions.

Background. Evidence of the effectiveness of biofortified maize with higher provitamin A (PVA) to address vitamin A deficiency in rural Africa remains scant. Objectives: This study projects the impact of adopting PVA maize for a diversity of households in an area typical of rural Zimbabwe and models the cost and composition of diets adequate in vitamin A. Methods. Household-level weighed food records were generated from 30 rural households during a week in April and November 2021. Weekly household intakes were calculated, as well as indicative costs of diets using data from market surveys. The impact of PVA maize adoption was modeled assuming all maize products contained observed vitamin A concentrations. The composition and cost of the least expensive indicative diets adequate in vitamin A were calculated using linear programming. Results. Very few households would reach adequate intake of vitamin A with the consumption of PVA maize. However, from a current situation of 33%, 50%–70% of households were projected to reach =< 50% of their requirements (the target of PVA), even with the modest vitamin A concentrations achieved on-farm (mean of 28.3 μg RAE per 100 g). This proportion would increase if higher concentrations recorded on-station were achieved. The estimated daily costs of current diets (mean +/- standard deviation) were USD 1.43 +/- 0.59 in the wet season and USD 0.96 +/- 0.40 in the dry season. By comparison, optimization models suggest that diets adequate in vitamin A could be achieved at daily costs of USD 0.97 and USD 0.79 in the wet and dry seasons, respectively. Conclusions. The adoption of PVA maize would bring a substantial improvement in vitamin A intake in rural Zimbabwe but should be combined with other interventions (e.g., diet diversification) to fully address vitamin A deficiency.