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, taking into account that considerable variability in soil fertility exists within and between farms. Over the five years, multi-locational on-farm nutrient omission trials were conducted in pilot sites in Eastern and North-Eastern Zimbabwe to establish maize yield response to application of macronutrients [nitrogen (N), phosphorus (P), and potassium (K), or NPK), selected micronutrients [zinc (Zn), boron (B)], manure, and lime under variable soil fertility conditions. The experiments also sought to establish nutrient-limited yield gaps in major maize-growing areas in Zimbabwe and assess balanced fertilizer management strategies to optimize maize production under rain-fed conditions.

Experimental results in the fifth season showed that poor fields had soil organic carbon (SOC) levels of <0.4%. Maize grain yields were significantly higher under conservation agriculture than for conventional tillage. With conservation agriculture, significant positive treatment effects from NPKS + manure additions were observed. Grain yields increased from 0.3 t/ha (control) to 4.1 t/ha (NPKS + manure). The greatest response to nutrients was observed for N (2.2 t/ha) compared to P (1.4 t/ha), and K (0.45 t/ha). Soil analysis results were well correlated with farmers’ local indicators of soil fertility, such as soil type, texture and color. Such local indicators provide an important tool for targeting site-specific nutrient management practices in areas where farmers have limited access to soil analysis services.