Evaluating the Impact of Soil Fertility Heterogeneity on Maize Nutrient Requirement and Productivity in Smallholder Farming Systems

In smallholder farming areas in sub-Saharan Africa, site-specific nutrient management recommendations are important to enhance efficient use of scarce nutrient resources on smallholder farms, taking into account that considerable variability in soil fertility exists within and between farms. Over the four years of this study, multi-locational on-farm nutrient omission trials have been conducted in pilot sites in Eastern and North-Eastern Zimbabwe to establish maize yield response to application of macronutrients (NPK), selected micronutrients (Zn, B), manure and lime under variable soil fertility conditions. The experiments also sought to establish nutrient-determined maize yield gaps in major maize growing areas in Zimbabwe and assess balanced fertilizer management strategies to optimize maize production under rainfed conditions.

In Zimbabwe, maize productivity was significantly influenced by nutrient management across sites. During the fourth season (2015) maize yields across all sites were severely constrained by low rainfall, which totaled about 550 mm for the season, 200 mm less than average seasonal rainfall. Maize yields ranged from 0.1 to 1.0 t/ha for the control and 1.0 to 3.5 t/ha for the NPKS treatment. Nitrogen, P and K response factors for the fourth season were 0.65, 0.25 and 0.1, respectively, indicating poor response to K and highest response to N application. Manure application increased yields by 20 to 50%, with the effects of manure strongest on the low organic matter soils. Nitrogen and P remain the most limiting nutrients, and complementary organic nutrient management approaches should be employed to increase soil C and sustain soil productivity. Training workshops with the support of fertilizer distributors and national research partners were held to train farmers and extension workers on adaptation of site-specific fertilizer recommendations and to facilitate access to fertilizer types that match their local soil nutrient requirements.