Optimization Of Water And Nitrogen Management For High-Yield-Cotton In South Xinjiang

The edge of Tarim basin of south Xinjiang is one of the most important cotton production regions in China. Unreasonable water and N fertilization application is a common problem in high-yield-cotton system in this region. It causes the decreasing of water and nitrogen use efficiency. In this study, An investigation was conducted in Cele and Yuli, to have the first hand results about farmer's practice in water and nitrogen managements. And two field experiments were conducted in Cele and Yuli Counties. Real time soil nitrate and water monitoring were used for the optimized nitrogen and water treatments in these two sites, to recommend the application amount of nitrogen and water at different cotton growth periods for synchronizing the demands of water and nitrogen by cotton and their supplies by irrigation and soil or fertilization. The effects of the optimized water and nitrogen treatments on growth, yield, fiber quality, water and nitrogen use efficiencies and nitrogen balances were studied in the experiments. The results showed as followed:The investigation result showed that 39.5% (Cele) and 72.8% (Yuli) of the investigated field applied excessive N fertilizer, but only 6.2-7.9% investigated field suffered by N deficiency; N balance result indicated that an average nitrogen surplus was 248 kg N-hm-2 in Cele and 108 kg N.hm-2 in Yuli, respectively.Compared with the conventional treatments, the optimized N and water treatments dramatically reduced N fertilizer application amount from 432 kg-hm-2 to 256 kg-hm-2 at Cele and 310 kg.hm-2 to 137 kg.hm-2 at Yuli site. Meanwhile, irrigation water decreased from 660 mm to 427 mm at Cele and 600mm to 402 mm at Yuli. The seedcotton yield in the optimized treatments was 4.74 thm-2 in Cele and 5.99 t-hm-2 in Yuli, and compared with 4.88 thm-2 in Cele and 5.64 thm-2 in Yuli in conventional treatments, there was no significant difference between them.N uptake of cotton in the optimized treatments were 243 kg-hm-2 in Cele and 270 kg-hm-2 in Yuli respectively, which were similar to the conventional treatments, 216 kg-hm-2 in Cele and 269 kg-hm-2 in Yuli, but both of these two treatments significantly higher than the treatments with no N fertilization at two experimental sites.Compared with the conventional treatments, the optimized treatments dramatically increased N recovery from 28.2% to 57.9% in Cele and 27.7% to 66.2% in Yuli respectively, and as well as increased water use efficiency from 7.4 kg.hm-2.mm-1 to 11.1 kg.hm-2.mm-1 in Cele and from 9.4 kg.hm-2.mm-1 to 14.9 kg.hm-2.mm-1 in Yuli, respectively.The apparent N losses was reduced drastically from conventional treatments (294 kg-hm-2 in Cele and 163 kg-hm-2 in Yuli) to the optimized treatments (87kg-hm-2 in Cele and 19 kg-hm-2 in Yuli). Soil NO3-N movement out of the effective root zone was one of the most imporment pathways of N losses in the conventional high-yield-cotton system in South Xinjiang, the optimized treatments could dramatically reduced soil NO3--N movement out of the effective root zone.In conclusion, in the optimized water and nitrogen management system, a high productivity could be maintained with less application of mineral N fertilizer and irrigation water and reduce N losses compared with the farmer's practice.