Effects Of Different Drip Irrigation Fertilizer On Soil Nitrogen And Phosphorus Content And Cotton Yield In Drip-irrigated Cotton Field

Object:Fertigation is an important measure to improve yield and water-and fertilizer-use efficiency of cotton under drip irrigation conditions in Xinjiang.Drip irrigation fertilizer（water-soluble fertilizer）is the key of fertigation technology,which is very important for the exertion of technical advantages.In recent years,drip irrigation fertilizers has developed rapidly and has a wide variety in Xijiang.On the one hand,it promotes the development and application of fertigation,on the other hand,it also leads to the widespread phenomenon of blind selection and unreasonable application of fertilizer.According to the application of drip irrigation fertilizer in drip-irrigated cotton field in Xinjiang,several representative drip irrigation fertilizers（conventional fertilizer,solid drip irrigation fertilizer and liquid fertilizer（suspended fertilizer and clear liquid fertilizer））were selected.The objective of this study was（1）to determine the dynamic change of soil N and P content under different drip irrigation fertilizer application,（2）to evaluate the effects of drip irrigation fertilizer on growth,yield and fertilizer use efficiency of cotton.This study can provide basis and reference for the rational selection and application of drip irrigation fertilizer in drip-irrigated cotton field in Xinjiang.Methods:Both a laboratory simulation experiment and a field experiment were conduced in this study.The laboratory simulation experiment included different N and P fertilizer comparative experiments.Four fertilizer treatments were set as（1）urea（TF）,（2）solid drip irrigation fertilizer（SF）,（3）suspension liquid fertilizer（LSF）,（4）clear liquid fertilizer（LCF）in the N fertilizer comparative experiment.The P fertilizer comparative experiment was consist of（1）monoammonium phosphate（MAP）,（2）ammonium polyphospphosphate（APP）,（3）solid drip irrigation fertilizer（SF）,（3）suspension liquid fertilizer（LSF）,（5）clear liquid fertilizer（LCF）.At the same time,no fertilization was used as the control（CK）in both experiments.In the field experiment,7 treatments were set as（1）no N fertilizer（N0）;（2）no P fertilizer（P0）;（3）conventional fertilizer（TF,urea+monoammonium phosphate）;（4）ammonium polyphosphate（APP,urea+ammonium polyphosphate）;（5）solid drip irrigation fertilizer（SF）;（6）Suspension liquid fertilizer（LSF）;（7）clear liquid fertilizer（LCF）.Results:（1）during the incubation period（14 d）,the concentration of NH₄⁺-N in soil increased first and then decreased,and reached the highest at 3 d.Soil NO₃^--N concentration gradually increased,and stabilized after 7 d.Compared with TF treatment（urea）,the net nitrification rate and net mineralization rate of soil under SF and LSF treatments decreased significantly,and there was no significent difference between LCFand TF treatments.The soil available P content increased slowly under APP treatment,while other fertilization treatments increased first and then decreased.During the whole incubation period,the available P content of LCF treatment was the highest,followed by APP and SF treatments,and APP treatment was the lowest.（2）During one fertigation cycle（7 d）,the NO₃^--N concentration in 0-20 cm soil of TF and SF treatments was significantly higher than that of LSF and LCF treatments,while the NO₃^--N concentration in 20-60 cm soil was significantly increased under LCF treatment.In addition,LCF treatment also significantly increased the NO₃^--N in 20-60 cm soil in the early-middle stage of cotton growth（before full boll stage）,and TF treatment had the highest of NO₃^--N in 20-60 cm soil in the later stage of cotton growth（full boll stage）.The residual amount of inorganic N in 0-100 cm soil of SF,LSF and LCF treatments were significantly lower than that of TF treatments.The lowest of inorganic N residue was found in the LCF treatment,which was 16.9%～20.8%lower than that of TF treatment.（3）Compared with TF treatment,the dry matter weight of cotton under SF and LSF treatments increased significantly,while the proportion of dry matter distribution in cotton bolls decreased.LCF treatment significantly increased the dry matter weight and N uptake of cotton,and promoted the transport of dry matter and N to cotton boll.Cotton yield and N use efficiency of SF and LSF treatments were simillar wtith TF treatment or even reduced.LCF had the highest of yield and N use efficiency,which were8.9%-10.3%and 13.0%-13.3%higher than TF treatment,respectively.（4）In one fertigation cycle（7 d）,the content of soil available P was the highest on the first day,then decreased rapidly,and leveled off after 3 d.The available P in LCF treatment always maintained a high level,the SF treatment was the lowest,and APP treatment was higher than that of TF after 3 d.The treatment of APP had the highest of available P in 0-20 cm soil at each growth stage of cotton,while LCF treatment significantly increased the available P in 20-40 cm soil,and the available P in 0-40 cm soil of LSF treatment was significantly lower than that of TF treatment.（5）The dry matter weight and P uptake of cotton of APP,SF and LCF treatments were significantly higher than those of TF treatments,but the distribution percentage of dry matter and P to cotton boll under APP and SF treatments decreased.Compared with TF treatment,the yield of cotton under LCF and APP treatments increased by 9.0%and 2.9%respectively,and the P fertilizer use efficiency increased by 5.3 and10.7 percentage points respectively.SF treatment had no significant effect on yield and P fertilizer use efficiency,while LSF treatment significantly reduced cotton yield and P fertilizer use efficiency.Conclusion:Compared with TF,SF and LSF significantly decreased the net nitrification rate and net mineralization rate of soil,increased cotton dry matter weight and P uptake,but reduced its distribution proportion to cotton bolls.LSF even significantly reduced the yield and P fertilizer use efficiency of cotton.APP can increase the available P in 0-20 cm soil,promote cotton growth and P uptake,and increase yieldand P fertilizer use efficiency.LCF significantly increased soil NO₃^--N in 20～60 cm in the early-middle stage of cotton growth,reduced soil inorganic N residue,promoted cotton dry matter and nutrient accumulation and distribution,and increased cotton yield and fertilizer use efficiency.Therefore,under the conditions of this study,clear liquid fertilizer and ammonium polyphosphate are more suitable for drip-irrigated cotton field.