Effects Of Water And Nitrogen Coupling As Well As Planting Density On Growth And Water-Nitrogen Use Efficiency Of Cotton

In response to the shortage of water resources,low water use efficiency and soil salinization in southern Xinjiang,a field cotton drip irrigation experiment was conducted in the 31st regiment of Yuli County,Korla City,Xinjiang.The tested cotton variety was"Xinluzhong 67",with 2 planting densities,260,000 plants/hm²（D₁,local planting density,plant spacing 10 cm）,320,000 plants/hm²（D₂,plant spacing 8 cm）.2 irrigation levels,namely 80%ETc（W₁）,100%ETc（W₂,ETc is crop evapotranspiration）and 3 nitrogen levels,200 kg/hm²（N₁）,300 kg/hm²（N₂）,400 kg/hm²（N₃）.During the growth period,the cotton growth index,dry matter weight and other indicators were measured,and the yield,yield components and soil water and salt transport were also calculated at harvest period.By studying the effects of planting density and water-nitrogen interaction on cotton growth,yield and water and nitrogen use efficiency in southern Xinjiang,the technical support and theoretical basis for reasonable close planting and optimal control of water and nitrogen in southern Xinjiang cotton fields was provided.The results shows:（1）The interaction of planting density,water and nitrogen significantly affected the physiological morphological indexes of cotton（plant height,stem diameter,leaf area index and fruit branch number）（P<0.05）.Under high planting density（D₂）,increasing irrigation amount and nitrogen application rate can significantly promote the growth of various physiological morphological indexes;under low planting density（D₁）,various physiological morphological indexes are positively correlated with irrigation amount,and with the increase of nitrogen application rate showed a trend of first increase and then decrease.Plant height and stem thickness kept increasing as the growth period progressed,while LAI first increased and then decreased.In the fluffing stage,the plant height and stem thickness of the D₁W₂N₂ treatment reached the maximum,which were 105.33 cm and 11.16mm,respectively;In the boll stage,the LAI of D₂W₂N₃ treatment was the largest at 5.75,but it was only 0.8%higher than that of D₁W₂N₂ treatment.（2）The dry matter weight distribution of cotton in each treatment during the boll reeling period is as follows:"cotton boll>stem>leaf>root",the dry matter mass distribution ratio of cotton bolls is 52.29%～61.35%,at low planting density,80%ETc,and low nitrogen application（D₁W₁N₁）treatment reached the maximum value,and it was significantly higher than other treatments（P<0.05）.The accumulation of nitrogen in cotton gradually increases with the growth of cotton plants,and the proportion of accumulated nitrogen in organs changes with the advancement of the growth period.The specific performance of each period is:bud stage:leaf>stem>root>bud and boll,flowering stage:leaf>bud and boll>stalk>root,boll stage:bud and boll>leaf>stalk>root,fluffing stage:bud and boll>leaf>stalk>root,the proportion of bud and boll gradually increased.（3）The seed cotton yield,WUE and biological yield of cotton were significantly affected by planting density and water and fertilizer（P<0.05）.Under low planting density（D₁）,the indexes first increased and then decreased with the increase of nitrogen application rate.Under high planting density（D₂）,the indexes were positively correlated with nitrogen application rate.The nitrogen use efficiency（NUE）,nitrogen absorption efficiency（UPE）,and nitrogen partial productivity（NPFP）of cotton plants all decreased with the increase of nitrogen application rate.Under D₁W₂N₂,due to the relatively high product of effective boll number and single boll quality,a relatively high seed cotton yield was achieved,which was7421.0 kg/hm2,which was close to that of D₂W₂N₃ treatment The maximum yield is 7392.5kg/hm2,but it will waste manpower and fertilizer.（4）It is impossible to rank cotton fiber quality by 8 single indicators.By using principal component analysis to extract 3 principal components,a comprehensive ranking of cotton fiber quality was obtained:D₁W₂N₁>D₂W₂N₃>D₁W₂N₃,and their yields are 6607.0,7392.5,7421.0 kg/hm²,respectively.Overall planning of various physiological indicators,seed cotton yield and environmental protection purposes,using planting density of 260,000plants/hm²,100%ETc and nitrogen application rate of 300 kg/hm² irrigation is suitable for the growth of local cotton plants.（5）Water and nitrogen regulation significantly affected the distribution and accumulation of nitrate nitrogen and salt in the root zone soil.The soil layer of each treatment had salt accumulation inside and outside the membrane.In the horizontal direction,0-40 cm soil layer,The nitrate nitrogen content in the membrane is higher than the content outside the membrane,and there was no significant difference in the nitrate nitrogen content in the soil layer below 40 cm,but there was a significant difference in the amount of salt accumulation,which was expressed as:"inner membrane<outer membrane";In the vertical direction,with the increase of the depth of the soil layer,the nitrate nitrogen and salt content decreased,and the nitrate nitrogen and total salt accumulation showed an increasing trend with the increase of nitrogen application rate.