Using Decision-support Irrigation System to Reduce Nitrogen and Phosphorus Leaching and Improve Their Uptake by Cotton

【Background】 A new irrigation support system has been developed based on water stress predicted by the root zone water quality model (RZWQM2) to aid irrigation scheduling; it has been tested since 2016 for cotton fields in an oasis in Xinjiang. 【Objective】 The purpose of this paper is to examine the efficacy of the system for predicting leaching and root uptake of nitrate and phosphorus (Olsen-P) against an experiment conducted in 2019 at a cotton field, in efforts to further test if the system can reduce nutrients leaching and improve their uptake by crop compared to traditional irrigation and fertigation methods. 【Method】 The experiment consisted of three decision-aid irrigation methods: irrigation based on the new system (DSSIS), irrigation based on soil moisture dynamics (SMS) and traditional irrigation method used by local farmers (E), and two irrigation levels: keeping soil moisture at 100% (FI) and 75% (DI) of the field capacity (DI) respectively. All treatments were organized in two-factor randomized blocks in the field. In each treatment, we measured NO3-­N and Olsen-P in the soil, cotton biomass, nitrogen and phosphorus in the cotton, as well as the cotton yield. 【Result】 ① Traditional irrigation was more likely to result in NO3-­N leaching, and the risk of NO3-­N leaching in DSSSIS was higher than that in SMS. However, changing irrigation methods did not lead to a noticeable difference in Olsen-P distribution in the soil. ② Compared with E and SMS, DSSIS increased nitrogen content in the above-ground part of the cotton by 28.5% and 40.0% respectively. ③ DSSIS increased the yield of cotton seed by 33.7%, water productivity by 80.7%, partial productivity of nitrogen and phosphorus by 25.2% and 25.6% respectively. 【Conclusion】 DSSIS not only reduced the risk of NO3-­N leaching and promoted root nitrogen uptake, it also improved seed yield, water productivity and partial productivity of both nitrogen and phosphorus fertilizers.