Most smallholder farms in Zimbabwe are on sandy soils which are inherently infertile, with soil organic carbon (often < 0.4 %) (Grant, 1981; Mtambanengwe and Mapfumo, 2005). The soils have poor buffering capacity, are subject to nutrient leaching, and have low cation exchange capacity. A large proportion of farmers are resource-constrained, with poor capacity to purchase external mineral fertilizers. Other than the macro nutrients (N, P, K), micro nutrient deficiencies are also widespread as a result of long-term nutrient mining through crop off-take without replacement (Grant, 1981).
In many smallholder farming areas across much of sub-Saharan Africa, marked short range spatial variability in soils exists within and between farms as a result of management and or localized differences in parent material (Giller et al., 2006; Wopereis et al., 2006; Zingore et al., 2007). Recognition of the variability in soils is important for implementation of management strategies that enhance efficient use of scarce nutrient resources on smallholder farms, taking into account the distinct capacity of the different soils to supply nutrients to crops (Janssen et al., 1990). When background soil characteristics or soil fertility indicators are known, it is possible to use them and appropriately tailor fertilizer application for improved nutrient use efficiency, thus ensuring that fertilizer interventions remain economically viable for smallholder farmers.
The project will explore nutrient management strategies for optimizing maize productivity under variable soil fertility conditions in eastern Zimbabwe. Multi-location nutrient omission trials will be conducted to diagnose nutrient and non-nutrient constraints to crop productivity. The nutrient omission trials will be used as a basis for establish maximum attainable yield for heterogenous fields and develop site-specific nutrient management recommendations for reducing the gap between attainable and farmers yields. Further, the project will develop and test decision support tools, including Nutrient Expert for Hybrid Maize, and extension material for supporting farmers to make informed decisions on investment in nutrient management. Spatial analysis will also be conducted to develop a village-scale soil fertility map and spatially explicit nutrient management recommendations.