International Journal of Agricultural and Natural Sciences E-ISSN: 2651-3617 15(2): 149-162, 2022 Research Article 149 INFLUENCE OF NITROGEN FERTILIZER RATE AND ITS TIME OF APPLICATION ON PRODUCTIVITY OF MAIZE (ZEA MAYS L.) IN SOUTHERN ETHIOPIA Alemayehu Adinew Abo * Mulugeta Abebe Mamo and Yohannes Erkeno Handiso 1 College of Agriculture, Department of Plant Science, Wachemo University, Hossana, Ethiopia *Corresponding Author: E.mail: aleadinw@gmail.com (Received 23 th November 2021; accepted 14 th March 2022) ABSTRACT. The study was conducted in Hadero Tunto Zuria District, Kambata Tambaro Zone, Southern Ethiopia during the main cropping season of 2019 to investigate optimum nitrogen fertilizer rate and its time of application to increase the productivity of maize crops. Soil fertility depletion and poor nutrient management are the major factors contributing to the low productivity of the crop. The treatments consisted of two factors, namely, four levels of nitrogen rates and five different application times. The experiment was laid in a randomized complete block design (RCBD) in factorial arrangements with three replications. The analysis of variance showed that the maximum grain yield (6.417 t ha -1 ) was obtained with the highest nitrogen fertilizer rate (200 kg ha -1 ) which applied 1/3 at planting + 2/3 at knee height time. While the least value (4.413 t ha -1 ) was recorded in plots that receive (50 kg ha -1 ) which applied 1/3 at planting + 2/3 at near taseling. Like grain yield, the total biomass yield of maize also increased linearly with an increase in nitrogen fertilizer rates. Thus, the results suggested that the use of the high amount of nitrogen fertilizer rate with an appropriate time of application was increased the yield of maize in the study area. Keywords: Grain Yield, growth, productivity, kernel weight INTRODUCTION Maize (Zea mays L.) is the third most important cereal crop in the world next to rice and wheat and has the highest production potential among the cereals [1]. It is the most important food for humans in South America, Africa, and China [2]. In Ethiopia, maize is grown from moisture stress to high rainfall regimes and from lowland to the highlands. It is an important cereal in human diets and animal feed, providing adequate amounts of energy and protein. It is also the most important stable crop in terms of calorie intake in Ethiopian rural families. Approximately 88% of maize produced in Ethiopia is used as food, in both green cobs and grain [3]. The average productivity of maize is 6.7 t ha -1 in developed countries and 2.4 t ha -1 in developing countries [2]. Even though its current productivity is higher than other major cereal crops, the yield productivity is below its potential. For instance, the potential yield of late- maturing hybrid maize varieties can produce up to 9.5–12 t ha −1 at the research field and 6– 8.5 t ha −1 at an on-farm field [4]. Whereas the national average productivity is 3.4 t ha −1 while in the SNNPRS is 3.075 t ha −1 [5]. Even though many biotic and abiotic factors can contribute to these big yield gaps, soil fertility depletion and poor nutrient management are among the major factors contributing to low productivity [6].