Effect Of Physiology On Water And Nitrogen Of Hybrid Cotton Under Mulched Drip Irrigation

[Object] To improve water use efficiency on hybrid cotton in arid area,as a case study, we analyzed yield component of cotton and photosynthetic physiological indexes of cotton under water-nitrogen interactions.[Method] A 3 year field experiment for the effects of interaction of water and nitrogen was conducted in the year 2008,2009 and 2010.The experiment included 9 water treatments (55% FC (55% field capacity of 0-60 cm profile of 5-10 cm beside drip irrigation pipe before every irrigation time,the same as below),65% FC,75% FC, W1 (3dl8mm, irrigation with 18 mm every 3 days), W2 (3d30mm), W3 (5d18mm), W4 (5d30mm), W5 (7d42mm), W6 (10d60mm) and 4 nitrogen treatments (N1 (fertilizing nitrogen with 0 kg·hm-2),N2(150 kg·hm-2),N3(300 kg·hm-2),N4 (450 kg·hm-2)).Watermark was used to detect soil moisture dynamics at depth of 0-60cm in cotton field during flowering and boll-setting stage. Leaf area index, chlorophyll SPAD value, dry matter accumulation and distribution, canopy light distribution, were measured at different growth stages. To assess the aboveground biomass,5 plants of each treatment of each plot was sampled once per two weeks. Final yields were determined by harvesting all plants in each plot.[Result] Results showed that fluctuation of soil water content at depth of 0-20 cm,20-40 cm and 0-60 cm increased in W1 (irrigation of 6mm/d),while normal at depth of 40-60 cm,the fluctuation scope of soil water content at depth of 0-60 cm increased in W4,W5,W6。There existed significant difference in boll numbers per plant and seed cotton yield while no difference in lint percentage of water-nitrogen interactions. Seed cotton yield, boll numbers per plant, boll weight and dry matter increased with the increament of nitrogen supply under the same water management, and the yield increament more obviouly of lower nitrogen treatment (N1, N2) than that of higher nitrogen treatment (N3). There was little increament of cotton yield at high irrigation with high nitrogen supply treatment. Moderate limit of water supply may increase boll weight, while abundent water may increase boll numbers per plant. LAIMAX increaseed with the improvement of nitrogen supply under abundent water treatment, while LAIMAX decreaseed with the decreament of nitrogen supply under limit water treatment.The correlation coefficient between seed cotton yield and boll numbers per plant boll weight and dry matter accumulation,reached to extremely significant level.Dry matter accumulation(DMA)showed an indirect effect on yield through boll numbers per plant.Increase of boll number per DMA was the guarantee of a high yield with a cultivation of high boll weight.Higher maturity value of LAI and canopy light absorption, which will help the transfer of nutrients to the reproductive organs, increasing the final total dry matter in reproductive organs in proportion, and ultimately the formation of a favorable yield. Irrigation intensity 6mm/d of the periodic supply conditions, nitrogen topdressing over 150 kg·hm-2 of chlorophyll in the leaves increased to nearly a small space, while more than 300 kg·hm-2 does not increase along with decreased trend, but too much fertilizer on chlorophyll accumulation of adverse effects.The IWUE and TWUE decreased with the increase of nitrogen application under moderate water stress condition in the abundent fields,but it could increase IWUE and TWUE in a certain extent in lower fertility soil.[Conclusion] Daily average irrigation, irrigation frequency, total irrigation amount and nitrogen supplyment was 6mm,5d,500mm and 280 kg.hm-2 during cotton flowering and boll-setting stage of hybrid cotton under mulched drip irrigation. And this efficient water and nitrogen management should be recommended in the cotton areas of arid land. There was no significant difference of IWUE under changing irrigation interval(when the irrigation was applied to 6mm/d),and the maximum IWUE occured at 6.5d irrigation interval and 258.4kg·hm-2nitrogen application.