Characteristics of Spatial and Temporal Changes in Soil Salt Content in Cotton Fields under Mulched Drip Irrigation in Arid Oasis Regions

Abstract

On the basis of Penman-Monteith formula, the double factor combination experiments were designed, and the factors included certain gradients of the irrigation quotas and irrigation frequencies. Through consecutive 3 year investigations concerning field experiments of cotton under conditions of mulched drip irrigation with no winter and spring irrigation (NWSI) from 2012 to 2014, the rules for changes in soil salt content were determined, and the effects of these changes on cotton yield were analyzed. The results showed that during the growth period of cotton, soil salt content within soil layer depths of 0~30cm was more conspicuous than that within soil layer depths of 40~100cm,smaller irrigation quotas and less irrigation frequency brought about increased magnitudes of changes within soil layer depths of 0~30cm, and such changes became the most salient at seedling stage as well as blossing and boll forming stages. Effects of irrigation quotas on salt content in soil profiles were weaker than such effects exerted by irrigation frequencies. Enhancement of irrigation quotas was beneficial for reductions of salt content within soil layer depths of 0~30cm at different stages of cottons growth. Salt content in soil profiles exhibited a “C” shaped distribution: within soil layer depths of 0~40cm, salt content was 1.74% greater under 12 irrigations than that under 16 irrigations; within soil layer depths of 50~80cm, salt content was 1.71% higher under 16 irrigations than that under 12 irrigations; whereas within soil layer depths of 90~100cm, irrigation frequency exerted insignificant effects on salt content. Under the same irrigation frequency, the maximum seed cotton yield occurred under the irrigation quota of 460mm. Under favorable irrigation quotas, seed cotton yield was greater under 16 irrigations than that under 12 irrigations. Irrigation water use efficiency (IWUE) was enhanced under lowered irrigation quotas and increased irrigation frequencies, and in South Xinjiang afflicted by water deficit, the maximum IWUE can be acquired under high irrigation frequencies and low irrigation quotas. Within soil layer depths of 0~30cm, when initial soil salt content amounted to 2.03g/kg (less than 3.0g/kg), during the growth period of cotton, an irrigation quota of 460mm with 16 irrigations did not lead to the situation of soil salt accumulation. Therefore, it can be regarded as a suitable irrigation scheduling for NWSI in arid regions in South Xinjiang.

Keywords: cotton fields, arid oasis regions, no winter and spring irrigation, drip irrigation under mulch, soil salt content