The agronomic impact of enhanced weathering deployments in Sub-Saharan Africa: Insights from a smallholder field trial in Kisumu County, Kenya

Warm and humid climatic conditions in tropical regions can optimise the efficiency of enhanced rock weathering (ERW) as a carbon dioxide removal pathway. However, the potential of agronomic co-benefits (e.g., yield, nutrition, soil health) that might result from treating crops with silicate rock powder are less constrained, particularly in the context of smallholder farming that is ubiquitous throughout tropical regions like Sub-Saharan Africa. In March 2024, Flux coordinated with the United Nations Convention to Combat Desertification (UNCCD) on a pilot study to assess the impact of ERW on crop performance at 56 smallholder farms in Kisumu County, Kenya using standard farming practices. Selected plots consisted of maize and baseline measurements indicate that soils were slightly acidic (6.4 on average). Each plot was divided into control and treatment sections, with the latter amended with mafic feedstock (0-4 mm) at a rate of 20 tonnes ha-1. Differences in soil parameters (e.g., pH, nitrogen, organic carbon, phosphorus) and crop metrics (e.g., grain yield, cob length, kernels per cob) between control and treatment plots were assessed. Yield data was collected at harvest, ca. 14 weeks after rock powder application and sowing, Our findings demonstrate significant agronomic benefits, with an average yield increase of 71.17% ± 15.5% and an aggregate yield increase of 47.47% ± 5.73% in maize yield on treatment plots compared with the control plots. While confirmation via post-application soil sampling is still outstanding, the observed yield increase is potentially attributable to the liming effect of the rock powder and to the contained mineral nutrients, in particular phosphorus. The monetary value of the yield increase is substantial, exceeding on average $326 USD ha-1. Collectively, our preliminary data from the UNCCD trial appear to demonstrate rapid impacts from ERW on agronomic performance in Kenya, translating to robust economic benefits at the community level.