EFFECTS OF TIME AND RATE OF NITROGEN FERTILIZER APPLICATION ON GROWTH, YIELD COMPONENTS AND YIELD OF MAIZE (Zea mays L.) AT NEDJO, WESTERN ETHIOPIA

Abstract

Maize is the major food crop in western Ethiopia and is produced in a number of agro- ecologies. However, its productivity is constrained by low rates and inappropriate timing of N fertilizer applications. Therefore, a field experiment was conducted during the 2018 main cropping season in Nedjo district of western Ethiopia on a farmer’s field. The objectives of the study were to determine the effects of time and rate of nitrogen fertilizer application on growth, yield components and yield of maize and to estimate the most economic rate and time of nitrogen fertilizer application for maize production in the study area. The treatments consisted of factorial combinations of three levels of nitrogen (46, 92 and 138 kg N ha-1) and four nitrogen (N) fertilizer application times based on days after planting (DAP) (T1=1/4 at 10-15 DAP + ¼ at 35-40 DAP +1/4 at 55-60 DAP+ 1/4 N at 75-80 DAP; T2 = 1/3 at 10-15 DAP + 1/3 at 35-40 DAP + 1/3 at 55-60 DAP; T3 = 1/2 at 10-15 DAP+1/2 at 35-40 DAP; and T4 = 1/3 at 35-40 DAP+1/3 at 55-60 DAP+1/3 at 75-80 DAP). The experiment was laid out in randomized complete block design with three replications. The result revealed that days to physiological maturity, plant height, number of ears per plant, ear length, thousand kernels weight, harvest index and agronomic efficiency were significantly affected by the main effects of N fertilizer rate and time of N application. The highest days to physiological maturity (178 days), plant height (262cm) and ear length (26.98cm) were recorded at 138 kg N ha-1, whereas the highest number of ear per plant (1.292), thousand kernels weight (421.8g) and harvest index (26.05%) were recorded at N rate of 92 kg N ha-1 and agronomic efficiency (42.44 kg grain kg-1 N) was obtained from 46 kg N ha-1respectively. Similarly, the highest plant height(261.5cm),number of ear per plant(1.356),thousand kernels weight (433.9g) and agronomic efficiency (44.23 kg grain kg-1 N) were obtained from three equal split application of nitrogen (1/3rd at 10-15DAP, 1/3rd at 35-40DAP and 1/3rd at 55-60 DAP). Days to physiological maturity (178.8days) and ear length (24.96cm) were obtained from two equal split application of Nitrogen (1/2 at 10-15DAP and ½ at 35-40DAP). The interaction of rates and time of nitrogen application had significant effect on number of kernels per ear, grain yield and aboveground dry biomass yield. The highest number of kernel per ear (481.7) and grain yield (8145 kg ha-1) were obtained under N rate of 92 kg N ha-1 in three equal split application(1/3rd at 10-15DAP, 1/3rd at 35-40 DAP and 1/3rd at 55-60 DAP) while the highest aboveground dry biomass yield (35701 kg ha-1) was obtained under N rate of 138kg N ha-1 in two times equal application of 1/2 at 10-15DAP and 1/2 at 35-40 DAP). Partial budget analysis also showed the highest net benefit of 70973.94 Birr ha-1 with marginal rate of return of 1334.38% from 92 kg N ha-1in three equal split application. Thus, it can be tentatively concluded that application of 92 kg N ha-1 in three splits (1/3rd at 10-15 DAP, 1/3rd at 35-40 DAP and 1/3rd at 55-60 DAP) to be appropriate to increase the productivity of maize in the study area. Keywords: Agronomic efficiency, G