Phosphorus agronomic efficiency in maize-based cropping systems: A focus on western Kenya

Phosphorus (P) is facing a quantity and quality supply issue and increasing its use efficiency is important for its continued use and profitability in crop production. The objective of this study was to determine how agronomic efficiency of P (PAE) in different environments and management systems in western Kenya is affected by N application, inherent soil fertility and organic resources. We used data constituting over 2700 data points from 126 farm fields of 25 different studies conducted from 1996 to 2009. Potassium (K) deficiency is negligible in western Kenya while ommission of P and N result in a 50% and 43% reduction in yield, respectively, relative to a full NPK treatment. In poor fields (low control yields) PAE was low in the absence of fertilizer N. Overall, lack of N application decreased PAE from 29 to 19 kg grain kg−1 P. Boundary analysis indicate that maximum yields are reached at about 50 kg P ha−1. Using a marginal rate of return of 100%, maximum P application rate for western Kenya should be 38 kg P ha−1. Without chemical N fertilizer application, organic resources increased PAE by 60-100% compared to continuous maize system without organic resources. Maximum PAE decreased at increased plant-available soil P and soil coarsiness. Our analysis represents best management practices and PAE may be lower than the reported values under farmer's conditions.