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


24 Mar 2015

2014 Annual Interpretive Summary

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 past two years, multi-locational on-farm nutrient omission trials have been conducted in pilot sites in Zimbabwe and Kenya to establish maize yield response to application of macronutrients (NPK), selected micronutrients (Zn, B), manure and liming application under variable soil fertility conditions. The experiments also sought to establish nutrient-determined maize yield gaps in maize-growing areas in Zimbabwe and assess balanced-fertilizer management strategies to optimize maize production under rainfed conditions.

Maize productivity was significantly influenced by nutrient management across sites. Maize yields across sites ranged from 0.3 to 0.8 t/ha for the control and 2.1 to 5.0 t/ha for the NPKS treatment. Using NPKS-mean yield of 3.6 t/ha as the attainable yield, the corresponding N, P and K response factors were 0.6, 0.5 and 0.1, indicating poor response to K and highest response to N application. 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. Manure alone increased yields, but only to a maximum of 2.0 t/ha at one site. Liming increased yields only at the most acidic site that had a soil pH of 4.2, with yield gains attributed to liming of 0.9 t/ha during the second season. Variable N application strategies must be an integral component of farmer management if losses related to fertilizer investment are to be minimized under the risky rainfed production system. The results showed the importance of nutrient management to enhance water use efficiency, with rain water productivity increasing from 0.38 to 1.13 kg grain/mm in the control treatments to 3.15 to 7.66 kg grain/mm in the NPKS treatment.

The results showed high variability in nutrient responses within each of the study sites, and highlight the importance of developing site-specific balanced nutrient management strategies to support sustainable maize production intensification in sub-Saharan Africa. Farmers must strategically target their limited nutrient resources to fields that are not yet degraded and maintain or improve soil fertility to guarantee returns to future fertilizer investments.