The study was conducted in 2018/19 main cropping season at two locations in North-western Gondar Zone, Ethiopia, to evaluate the effects of nitrogen fertilizer rates on earliness, growth, and yield and yield components of cotton varieties. The experiment was laid in a randomized complete block design with three replications in a factorial arrangement of five N rates (0, 23, 46, 69, and 92 kg ha− 1) and two cotton varieties (Sisiku-02 and Delta pine-90).
Significant main effect of N rates was observed for most of cotton phenological traits, plant height, number of main stem nodes and number of first fruiting branch nodes, average boll weight, cottonseed yield, lint yield and total cotton, whereas N fertilizer rates did not show difference regarding on days to initial flowering and lint percentage in both sites and days to initial squaring and height to node ratio at Tach-Armachiho, number of bolls per plant at Metema site. Main effect of varieties showed significant difference for all phonological traits, average boll weight, cottonseed, and lint yield and lint percentage for both sites. Significantly higher plant height, height to node ratio, number of first fruiting branch nodes and total boll numbers was recorded at Metema experimental site, while number of main stem nodes was non-significant due to main effect of varieties. However, in Tach-Armachiho main effects of varieties were non-significantly affected total boll numbers and most growth parameters except total dry matter production. The total dry matter production of the cotton plant in a plot was significantly influenced by their interaction effect at Metema. The maximum cottonseed yield, lint yield and total cotton yield were obtained at 92 kg ha-1 N rate at Metema and Tach-Armachiho sites. The higher lint yield and lint percentage were recorded on variety Sisiku-02, while higher cottonseed yield was found from variety Delta pine-90 in both sites. Similarly, the result of economic analysis showed that the maximum net benefit was obtained at main effect of 92 kg ha-1 N rate and Sisiku-02 variety.
Based on lint yield and economic analysis, use of Sisiku-02 variety with 92 kg ha-1 nitrogen rate is promising for cotton production in study areas and similar agro-ecologies