Nitrogen fertilizer rates and supplementary irrigation effects on maize yield in Eastern Ethiopia

Maize (Zea mays L.) is an important food and nutritional security crop widely grown in Ethiopia. However, the crop yield is low due to low soil fertility, and erratic rainfall that results in moisture stress during the primary growing season. Field experiments were conducted in Haramaya district during 2019 and 2020 cropping seasons to investigate the effects of nitrogen (N) fertilizer rates and supplementary irrigation (SI) on maize productivity. The treatments consisted of six N fertilizer rates (0, 23, 46, 69, 92, and 115 kg N ha⁻¹) and (control or only rain-fed), and three SI levels (50%, 75%, and 100% crop evapotranspiration (ETc). The experiments were a split-plot design in a factorial arrangement. Irrigation was assigned to the main plots whereas N fertilizer rate was assigned to the subplots. The results indicated that the optimum grain (9.10 t ha⁻¹) and stover (12.02 t ha⁻¹) yields were recorded in response to the application of 69 kg N ha⁻¹ with 75% ETc SI. The grain and stover yields obtained at 69 kg N ha⁻¹ with 75% ETc SI exceeded the grain and stover yields obtained at nil N fertilizer rate with only rain-fed by about 356% and 144%, respectively. Furthermore, 75% ETc SI with 69 kg N ha⁻¹ resulted in the optimum (1.11 kg grain ha⁻¹ m⁻¹) water productivity. Therefore, it is concluded that under the early cessation of rainfall, 69 kg N ha⁻¹ with 75% ETc SI enhanced maize productivity in the study area.