Compensation of cotton yield by nitrogen fertilizer in non-mulched fields with deficit drip irrigation

Irrigation and fertilization are the main measures used by farmers to maintain crop yield and quality, especially in arid and semi-arid regions. To investigate the compensation of cotton yield loss due to deficit drip irrigation in non-mulched fields by increasing nitrogen (N) fertilizer application, a split-plot experiment with irrigation amount as the main plot and N application as the subplot was carried out in southern Xinjiang, China. The experiment included two irrigation amounts of 450 mm (deficit irrigation, W1) and 540 mm (full irrigation, W2) and three N application rates of 150 kg ha−1 (F1), 225 kg ha−1 (F2), and 300 kg ha−1 (F3). From the cotton seedling stage, ET0 (reference evapotranspiration) was calculated from daily meteorological data and irrigation was applied when the cumulative ET0-P reached 45 ± 3 mm. The results showed that irrigation and fertilization significantly affected soil moisture and total N, which in turn affected cotton growth, biomass formation, and yield (P<0.05). Soil water storage (SWS) increased by 15.9% on average under W2 compared to W1. F2 and F3 decreased SWS by 5.0%-5.1% and 7.7%-10.9% respectively, compared to F1. Total soil nitrogen in W2 was on average 13.3% lower than W1, and F2 and F3 were 4.4%-11.1% and 11.3%-16.5% lower than F1, respectively. Aboveground biomass increased significantly with increasing irrigation and N amounts and was 47.9% higher in W2F3 than in W1F1. However, the increased biomass was not translated into yield and excessive accumulation of root and stem biomass reduced cotton yield. Under full irrigation (W2), cotton yield increased and then decreased with increasing N application. Cotton yield in F2 increased by 3.4% and 8.6% compared to F1 and F3, respectively. Under deficit irrigation (W1), N fertilizer compensation increased with increasing N application, and cotton yield in F3 increased by 10.3% and 15.0% compared to F1 and F2, respectively (P<0.05). TOPSIS analysis showed that W1F3 had the highest rank, followed by W1F2. The results indicated that W1F3, irrigation amount of 450 mm and N application rate of 300 kg ha−1, could be proposed for cotton fields under non-mulched drip irrigation in southern Xinjiang, China.