Nitrogen Distribution And Leaching Risk In Soil Profile Under Different Long-term Water And Nitrogen Management Modes

In order to explore the effects of different water and fertilizer management on soil nitrogen distribution and leaching in drip irrigation cotton field under film mulch,a better water and fertilizer management model was proposed.Taking Xinjiang Cotton Field Non-point Source Pollution Prevention and Control Technology Research Demonstration Base（founded in 2008）of Baotou Lake Farm,Korla city,Xinjiang as the object,four treatments were set up at continuous monitoring sites:The spatial and temporal distribution of soil NO₃^--N and cotton growth characteristics under different water and nitrogen treatments were analyzed after 12 years of continuous production.The nitrogen profile distribution characteristics and its influence on nitrogen leaching in drip irrigation cotton field under mulching film under different water and nitrogen regulation in Southern Xinjiang were studied,and the following conclusions were drawn:（1）Under different irrigation and nitrogen application conditions,soil water content under mulch drip irrigation varied greatly from spring irrigation to bud stage,and the overall variation characteristics of soil water content in 0-100 cm soil layer at the same depth were basically the same from early flowering stage to boll stage.After spring irrigation,soil moisture in 0-100 cm soil layer was saturated.Nitrogen had a certain effect on water transport in cotton root zone.（2）Under different irrigation and nitrogen application levels,NO₃^--N content in 0～20 cm and 40～60 cm soil layers of cotton was higher.Under different nitrogen application treatments,soil NO₃^--N increased gradually with the increase of nitrogen application rate.When the irrigation amount was 4,800 m³/hm²and the nitrogen application amount was 330 kg/hm²,the soil NO₃^--N content tended to migrate to deeper soil layer gradually.When the irrigation amount was 4200 m³/hm²and the nitrogen application rate was 330kg/hm²,the NO₃^--N content in the surface soil was higher.The amount of nitrogen applied by irrigation had a significant effect on the accumulation of nitrate and ammonium nitrogen in the soil layer of 80～100 cm.（3）In drip irrigation under mulch,the study of leachate water under different irrigation and nitrogen application showed that the main form of nitrogen leaching was NO₃^--N leaching,and the leaching loss of total nitrogen and NH₄⁺-N had less influence than NO₃^--N.Long-term nitrogen application in irrigation would also lead to the occurrence of leaching risk,and the leaching risk tended to migrate downward when the irrigation amount was 330 kg/hm²and the irrigation amount was 4800 m³/hm².When the irrigation amount is 4200 m³/hm²and the nitrogen application amount is 300 kg/hm²,the risk of nitrogen leaching can be effectively prevented.（4）The optimal cotton yield can be obtained when irrigation amount is 4200 m³/hm²and nitrogen application amount is 300 kg/hm².