Improving Soil Water and Nitrogen Management to Facilitate Growth and Water-nitrogen Use Efficiency of Cotton in Saline-alkali Soils

【Objective】 Soil salinity is an abiotic stress faced by agricultural production in many countries. Improving agronomic practices to alleviate the detrimental effect of soil salinity is essential to sustaining crop production in salt-affected areas. This paper aims to study the combined effect of soil water, nitrogen and salt content on physiological and ecological indexes as well as yield of cotton under mulched drip irrigation in saline-alkali soils. 【Method】 The study was based on pot experiment. It consisted of four irrigation amounts: 1 575 (W0), 2 100 (W1), 2 625 (W2) and 3 150 m3/hm2 (W3); four nitrogen fertilizations: 0 (N0), 150 (N1), 300 (N2) and 450 kg/hm2 (N3), and four salt stress treatments: non-salinity (S0), light salinity (S1), moderate salinity (S2) and heavy salinity (S3). All pots were irrigated by mulched irrigation and for each pot, we measured the growth, water-nitrogen utilization efficiency of the cotton. 【Result】 Change in irrigation amount, nitrogen application and soil salinity had a significant impact on plant height, stem diameter, LAI, Pn, Tr and Gs (P<0.05). When soil nitrogen application, soil salinity and irrigation amount were the same, increase in soil water or nitrogen content boosted plant height, stem diameter, LAI and cotton yield significantly. When soil irrigation amount and nitrogen application were the same, there was a threshold soil salt content beyond which the effect of soil salinity on cotton growth ushered in. Interaction analysis showed that soil water, nitrogen and salt content had a combined significant effect on growth index, yield, WUE and PFP of the cotton (P<0.01). Among all treatments, N1+S1+W2 gave the highest yield, WUE and PFP, while N2+S2+W0 was the worst, with its yield, WUE and PFP reducing by 172.01%, 60.71% and 444.08%, respectively, compared to CK (without salinity). The yield of N2+S2+W3 was 71.46% higher than that of N1+S2+W1. That is, when soil salinization was high, increasing irrigation amount and nitrogen application could offset the detrimental impact of soil salinity and increased cotton yield. Path analysis showed that irrigation amount and soil salt content had the most positive and negative effect on cotton yield, respectively. 【Conclusion】 For the slightly salinized soil, irrigating 2 625 kg/hm2 of water coupled with 150 kg/hm2 of nitrogen fertilization was effective to alleviate the effect of soil salinity, while for the severely salinized soils, irrigating 3 125 kg/hm2 of water combined with 300 kg/hm2 of nitrogen fertilization worked better to ameliorate the effect of soil salinization and maximize cotton yield.