Growth and yield compensation in sorghum (Sorghum bicolor L. Moench) as a function of planting density and nitrogen fertilizer in semi-arid areas of northeastern Ethiopia

Abstract

An experiment was conducted at two locations in northeastern (NE) Ethiopia to determine the effect of population density on the growth, yield and nitrogen use efficiency of sorghum (Sorghum bicolor L. Moench) under two levels of nitrogen fertilizer application. Eight treatments, which consisted of factorial combinations of two N fertilizer levels (0 and 80 kg ha−1) and four population densities (166 666, 88 888, 38 095 and 29 629 plants ha−1), were evaluated in a randomised complete block design with three replications. The results indicated that nitrogen fertilizer significantly enhanced leaf area index, dry mass production, crop growth rate, and grain yields. Nitrogen fertilizer also positively affected yield components. Leaf area index, crop growth rate (at the early growth stages) and leaf, stem and panicle dry mass production increased as population density increased. Grain and stover yields at harvest increased in linear responses to increases in population density. Head and seed number per unit area accounted for most of the variation in grain yield at different plant densities. It can be concluded that the conventional planting density (88 888 plants ha−1), being used in NE Ethiopia is not the optimum density, as increases in grain yield were linear up to a population density of 166 666 plants ha−1. Thus, further study to determine the optimum planting density is recommended.