Abstract

Field experiment was conducted in 2012 and 2013 in three districts of Arsi zone, Oromia region, Ethiopia to evaluate the response of bread wheat cultivar “Damphe” under highland vertisols to treatments consisting of 20 factorial combinations of five N rates from urea and four P205 rates from triple super phosphate (TSP). The treatments were laid out in RCBD, replicated three times. All data were subjected to analysis of variance using SAS 9.0 Statistical Analysis Software. Treatment effects on the average grain yield (AGY) and average biological yield (ABY) were very highly significant. Number of spikes m-2, number of seeds/spike, and plant height were also significantly or very significantly affected. The main effects of fertilizer N on AGY, ABY, protein and wet gluten contents, and zeleny values of grains were also very highly significant. Leaf absorption of N increased with increased rates up to 92 kg/ha N. The N recovery efficiency (NRE) at 46 and 92 kg N/ha was 20.9% and 29.4% and the agronomic efficiency (AE) was 10.8 and 13.3 kg grain/ kg N applied, respectively. Above the 92 kg/ha N the increase in both NRE and AE declined or fell reaching 31.4 % and 12.6 kg grains/ kg N. Based on farmers capacity to invest and their inherent tendency to gradually adopt higher rates, a base recommendation of 92-46 (N- P₂O₅) kg/ha, which is equivalent to 160 kg/ha Urea + 100 kg/ha DAP is given. This rate was the treatment with highest marginal rate of return (MRR). Additional recommendation consisting of 138-69, and 115-46 (N- P₂O₅) kg/ha, equivalent to 240 kg/ha Urea + 150 kg/ha DAP and 210 kg/ha Urea + 100 kg/ha DAP is given, based on agronomic data, economic analysis, complexity in management history of different farms, and environmental considerations.

Key words: Average grain yield, agronomic data, N recovery efficiency (NRE), agronomic efficiency (AE), grain quality, marginal rate of return.