Effect of Rates and Time of Nitrogen Application on Growth, Yield, and Yield Components of Wheat (Triticum aestivum L.) in Eastern Hararghe, Ethiopia

Wheat is a highly valued crop in the national diet of Ethiopians, and widely produced in the country. 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 rainy seasons. This problem is compounded by low rates and inappropriate-timing of N fertilizer applications in the country. Therefore, field experiments were carried out during the 2013 main cropping season from July to November in Meta and Haramaya districts of eastern Ethiopia on a farmer’s field and on the research field of Haramaya University, respectively. The objectives of the study was to investigate the effect of rate and time of nitrogen application on growth, yield, grain protein content, and N use efficiency of bread wheat. The treatments consisted of six levels of nitrogen (0, 46, 69, 92, 115 and 138 kg N ha -1 ) and four application times ( 1 / 2 dose at planting + ½ dose at mid-tillering;½ dose at mid-tillering + ½ at anthesis; 1 / 3 rd dose each at planting, mid-tillering + anthesis, and 1 / 4 th dose at planting + ½ dose at mid-tillering + 1 / 4 th dose at anthesis. The experiments were laid out in factorial arrangement in RCBD with three replications. All the parameters evaluated were affected by the main effect of N fertilizer rate and time of N application. However, grain yield, harvest index, hectolitre weight, number of kernels per spike, total biomass yield, and total number of tillers at Haramaya and harvest index, were not significantly affected by the time of N fertilizer application. Days to heading and physiological maturity were prolonged in response to increasing the rate of nitrogen application at both sites. The highest biomass yield and plant height were recorded at 138 kg N ha -1 at both sites. Most of the parameters including grain yield exhibited maximum performances under this rate of N supply. The highest spike length was obtained at split application of 138 kg N ha -1 applied ( 1 / 4 th dose at planting, ½ at mid-tillering and 1 / 4 th at anthesis). Similarly, the tallest plants were recorded under similar rate N ha -1 applied ( 1 / 2 dose at planting and ½ dose at anthesis) at Haramaya. The nitrogen use efficiency decreased with increased N rate at both sites. In general, at Haramaya, plots treated with 46 and 115 kg N ha -1 at two equal splits at mid-tillering and at anthesis produced high grain yields, coupled with the best economic benefit or profitability. Whereas, at Meta, plots treated with 46 and 92 kg N ha -1 at two equal splits at mid-tillering and at anthesis and at three splits ( 1 / 4 th at planting + ½ at mid-tillering + 1 / 4 th at anthesis), respectively produced optimum grain yields, coupled with the best economic benefit or profitability. It could, thus, be concluded that application of 46 and 115 kg N ha -1 in two splits at mid-tillering and at anthesis and 92 kg N ha -1 in three splits ( 1 / 4 th at planting + ½ at mid-tillering + 1 / 4 th at anthesis) enhanced yield, yield components and N use efficiency of bread wheat. This implies the change of the blanket recommendation of 64 kg N ha -1 in the study area to this rate and time of application to improve the yield and N use efficiency of the crop in the study area. Keywords:- nitrogen fertilizers , yield and wheat DOI : 10.7176/JNSR/9-11-01 Publication date :June 30 th 2019