Site-specific nutrient management recommendations for smallholder farms in sub-Saharan Africa

Fertilizer recommendations tailored to specific climate, soil, crop, and farmer’s socio-economic status can increase farm-input use efficiency, productivity, and reduce climate-related production risks in highly heterogenous smallholder maize-based farming systems in sub-Saharan Africa (SSA). The scope for wide-scale use of soil testing in smallholder farming systems in SSA is curtailed by several challenges that include high costs of soil sampling and analysis, difficulty in taking representative soil samples, ill-equipped laboratories and considerable amount of time required to produce results. There are also limitations associated with standards of soil testing and interpretation of soil test results.

The site-specific nutrient management concept (SSNM) provides an alternative crop-based approach that is more practical for resource-constrained smallholder farming systems. The SSNM integrates soil and climate information to make field-specific decisions based on a set of nutrient management principles, which aims to supply a crop’s nutrient requirements tailored to a specific field or growing environment. Nutrient Expert for Maize (NE) was developed as an extension-based decision support tool using the SSNM concept to support cost-effective delivery of nutrient management recommendations.

The algorithms for calculating fertilizer requirements in NE is determined from a set of on-farm nutrient omission trial data under representative conditions. The N, P, and K requirements are based on the relationship between the balanced uptake of nutrients at harvest and grain yield, called internal nutrient efficiency, which are predicted using the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model. The nutrient requirement for a field or location is estimated from the expected yield response to each fertilizer nutrient, which is the difference between the attainable yield and the nutrient-limited yield. Evaluation of NE across five countries showed strong utility for guiding improved nutrient management.

The recommendations generated using NE were effective in maintaining high yields, but at a lower fertilizer input cost compared with current recommendation approaches. Agronomic nutrient use efficiencies were also increased with NE recommendations. Socio-economic and soil fertility diversity between smallholder farms had profound effects on crop productivity and nutrient management recommendations to optimize yields and profits, therefore, refinement of technologies to suit different types of farmers is essential for sustainable maize production intensification. Further improvement of NE by integration with geo-spatial soil and agronomic will enable rapid development and dissemination of recommendations for larger areas to reach millions of smallholder farmers at scale.