Local is hot: innovative approaches to unravel the benefits of local over broadcast applications of lime and phosphate fertilizers in weathered soils

Crop productivity in the highly weathered soils in Sub-Saharan Africa suffers from soil acidity and phosphorus (P) deficiency. The adoption of P fertilizer and lime by farmers to boost plant productivity is very small because of a very low and variable return on investment in fertilizers. It has repeatedly been found that local dosing of fertilizer granules in combination with local compost or manure doses has very strong effects on enhancing the fertilizer use efficiency when compared to the conventional broadcast spreading of soil amendments. Moreover, the effects of compost and manure in acid soils are found to be related to a local and temporal liming effect in the planting hole. Such and other findings suggest to explore the strategy of local lime application. This research proposal aims to identify why, and to what extent, the P fertilizer use efficiency may be more enhanced by local lime doses in the planting hole compared to an equivalent area based broadcast dose of lime. It is speculated that this local benefit is large for soils with high exchangeable acidity, that compost and manure boost that effect and that soil structure is involved. Novel rhizosphere visualization techniques on root development in response to locally available P and aluminum detected by LA-ICP-MS will pave the way to identify the factors involved. Field and on-farm trials performed in collaboration with a partner in Madagascar will evaluate that agronomic management in realistic conditions.