Development and Dissemination of 4R Nutrient Stewardship Knowledge to Support Crop Production Intensification in Western Kenya

The lack of appropriate site specific nutrient management recommendations is a key factor underlying low crop productivity in sub-Saharan Africa (SSA). The 4R Nutrient Stewardship Framework developed by the fertilizer industry aims to provide the context for efficient nutrient management focusing on four central components: applying the right fertilizer source, at the right rate, at the right time in the growing season, and in the right place. In 2013, on-farm nutrient omission trials were initiated on 24 farms representing the variable soil fertility conditions in Western Kenya. The trials are in the sixth season of implementation. The main objective of the study is to assess the spatial and temporal nature of nutrient limitations in heterogeneous farms in the study area.

In each season, maize is planted under five fertilizer treatments comprising of: (i) no input control, (ii) PK, (iii) NK, (iv) NP, (v) NPK. Seasonal average yield over five cropping seasons were Control < PK < NK < NP < NPK indicating that N is the most limiting nutrient in the area followed by P and K. Regression analysis of relative yields over time indicate that yield in PK and NP plots do not show much variation over time and are not linearly related to seasons, indicating that in most of the farms N was already at a very depleted status, and that K was on average not very limiting to crop growth in the study area. However, relative yield frequency plots for the 2nd to the 5th season indicate the presence of a few fields with very strong response to K omission indicating the occurrence of hotspots of K deficiency in the area.

Hierarchical clustering using seasonal relative yield data was used to identify farms with similar nutrient response. Results showed that grouping farms into five clusters accounted for 75% of the variation in responses. Further analysis has interpreted the five clusters as follows illustrating the need for site specific nutrient recommendations: Cluster 1: Fields deficient in all nutrients but with acute K deficiency (2 fields), Cluster 2: Fields low in N and P but with sufficient K levels (8 fields), Cluster 3: Fields low in P but with sufficient levels of N and K (2 fields), Cluster 4: Sufficient reserves all nutrients (N,P, and K) (1 field), and Cluster 5: Fields low in N but with sufficient levels of P and K (11 fields).