Haile Negash*, Wondosen Wondimu, Abdisa Abraham, Zenabu Belay
Maize (Zea mays L.) is a highly valued crop in the national diet of Ethiopia, in general and southwest Ethiopia in particular. However, its productivity is constrained by low plant-available soil nitrogen due to depleting soil organic matter content and high leaching losses of mineralized nitrogen during the growing seasons. This problem is compounded by low rates and ill-timing of nitrogen fertilizer applications in the country. Therefore, a field experiment was carried out during the 2017 main cropping season in Yeki, Menit Goldia and Adiyokaka districts on a farmer’s field in southwest Ethiopia with the objectives to evaluate the effects of time and rate of nitrogen application on yield and yield components of maize. The treatments consisted of three levels of nitrogen rates, i.e. 23, 46 and 69 N kg ha-1 and five levels of nitrogen application timing, i.e. 1/2 at planting+1/2 at knee height, 1/3 at planting+1/3 at knee height+1/3 at near tasseling, 1/3 at planting+2/3 at knee height, 1/4 at planting+2/4 at knee height+1/4 at tasseling and 1/4 at planting+1/4 at knee height+2/4 at near tasseling time of nitrogen application and unfertilized plot as an absolute control treatment were arranged in factorial combinations. Cob number per plants did not respond to the rates, time of N fertilizer application and their interactions. Days to tasseling, slicking and physiological maturity were delayed as the rate of nitrogen fertilizer was increased. The highest biomass yield, grain yield, straw yield, total nitrogen uptake, apparent nitrogen recovery, and agronomic efficiency were recorded at 46 kg N ha-1 applied 1/4 dose at sowing, 2/4 dose at knee height growth stage and 1/4 dose at tasseling stage. Most of the parameters including the grain and straw yields exhibited maximum performance under this N treatment level. Thus, application of N fertilizer at a rate of 46 kg ha-1 by splitting the dose into three and applying 1/4 dose at sowing 2/4 dose at knee height growth stage and 1/4 dose at tasseling stage of the maize crop can be recommended for the study areas and similar agro ecologies.