Abstract

Upland rice (Oryza spp.) yields are low in Uganda, partly because of little fertilizer use. Three on-station trials and two clusters of on-farm trials were conducted in Uganda at approximately 1000 m elevation to determine: yield response to N, P and K application; economically optimal nutrient rates (EOR); and N use efficiency components. Mean grain yield, with hulls, was 1.3 and 3.7 Mg ha^-1 with 0 and 100 kg ha^-1 N applied, respectively. Grain yield response to applied P when compared with N was less, and mean yield was not increased with K application. Depending on fertilizer cost relative to grain price (CP), mean EOR ranged from 54 to 92 kg ha^-1 N and 17 to 30 kg ha^-1 P. Equations were determined for yield response, estimation of EOR, and the benefit: cost ratio (BC) for fertilizer N and P use. Grain N concentration and N harvest index at EOR were 1.55 and 0.55 kg kg^-1, respectively. Mean recovery efficiency, partial factor productivity and agronomic efficiency declined with increasing N rate and were 0.75, 41 and 28 kg kg^-1, respectively, at the EOR. Fertilizer N and P use can be highly and moderately profitable, respectively, for upland rice production in Uganda with high N recovery and agronomic efficiency. In maximizing net return on finance-constrained investment in fertilizer use, CP and investment capacity needs to be considered.

Key words: Economic, fertilizer use, nitrogen, phosphorus, potassium, use efficiency.