Effects of supplemental foliar-applied nitrogen on cotton (Gossypium hirsutum L.) yield and nitrogen efficiency under saline conditions

Nutritional management in saline conditions can offend the stressful effect of salinity by increasing the amount of nutrients availability, especially nitrogen (N). To investigate the effects of foliar application of different types of N fertilizers as a supplement at the beginning of boll development stage, a randomized complete block design in three replications was carried out at the Islamic Azad University, Sabzevar Branch, during two consecutive years of 2018 and 2019. The studied factors were control, urea (recommended -50%, recommended, and recommended + 50%), and azoteam (recommended -50%, recommended, and recommended + 50%). The recommended dose for urea and azoteam was 1% v/v and 1 l/ha, respectively. The results showed that the responses of cotton yield and yield components to the type of supplemental fertilizer were significant. Different amounts of foliar application had a significant effect on yield and yield components, as well as different N efficiency specs. The supplemental foliar application with the recommended + 50% caused 48.7% improvements in plant height, 65.6% in the number of bolls per plant, 32.3% in boll weight, 52.4% in lint yield, 61.7% in seed cotton yield, 54.9% in seed yield, 19.5% in agronomic N use efficiency, and 17.4% in N uptake efficiency and reductions of 11.6% in lint percentage and 17.4% in N use efficiency. In most of the studied traits, there was no difference between the recommended and recommended + 50%. Overall, the results of this experiment revealed that under saline conditions, the recommended dose of urea spray in the early stages of development of the boll produced a good seed cotton yield.