Phosphorus Fertilizer Yield Effect And Recommended Dosage Calculation Method Of Cotton Under Mulched Drip Irrigation

The low utilization rate of phosphate fertilizer in cotton production has always been an import ant factor limiting its development.Therefore,this study used a combination of indoor simulation experiments and field experiments to explore the effects of phosphorus fertilizer application on soil phosphorus availability,cotton dry matter accumulation,cotton phosphorus absorption and yield.O n this basis,combined with the three phosphorus recommended fertilization methods of fertilizer ef fect function method,phosphorus critical value method and nutrient input-output balance method,T he calculation method of recommended phosphorus application based on the balance between crop demand and phosphorus fertilizer application was formed,which provided scientific reference for ra tional application of phosphorus fertilizer.The main conclusions are as follows:（1）Effect of phosphorus application on soil phosphorus availabilityLaboratory experiments showed that phosphorus fertilizer could be fixed to varying degrees aft er being applied to the soil,and the amount of fixation increased with the increase of incubation days.The Elovich kinetic model verified the law of rapid fixation of phosphorus in the early stag e and slow fixation in the later stage.There was a linear relationship between the amount of phos phate fertilizer and the fixed amount,and the linear equation of phosphorus fixation could be used to infer the fixed amount.The results of field experiment showed that the content of soil availabl e phosphorus decreased gradually with the extension of growth period.Phosphorus application coul d significantly increase the available phosphorus content in surface soil.The linear model expressio n of soil available phosphorus content and phosphorus application rate fitted at the cotton bud stag e was y=0.06x+20.73（R²=0.882）,and the exponential model expression was y=24.55e^^{（-0.004x）}+44.12（R²=0.900）.Both mathematical models can calculate the available phosphorus content.（2）Effects of phosphorus application on dry matter accumulation and phosphorus uptake of cottonThe accumulation of dry matter increased slowly from seedling stage to bud stage.The charact eristics of the Logistic model were as follows:the period of maximum dry matter accumulation（t _m）was about 93 d～101 d after emergence.The distribution of dry matter in each organ with time was as follows:the percentage of stem increased first and then decreased,the percentage of dry matter in leaves decreased gradually,and the proportion of bud/flower/boll increased gradually.P3(160 kg·hm^-2)could significantly increase the dry matter accumulation of cotton.The phosphorus a ccumulation dynamics also conformed to the’S’curve of plant growth.The period of maximum p hosphorus accumulation（t_m）was about 76 d～100 d.The absorption proportion of leaves in vegetat ive organs was the largest at seedling stage and bud stage,and the absorption proportion of repro ductive organs increased gradually from flowering stage to boll stage.After entering the boll openi ng stage,the phosphorus proportion of cottonseed reached the maximum.P4(213 kg·hm^-2)treatment could significantly increase the phosphorus accumulation rate of cotton.（3）Calculation method of recommended amount of phosphate fertilizerThe recommended phosphorus application rates calculated by the quadratic model,square root model and linear plus platform model were 148.028 kg·hm^-2,106.629 kg·hm^-2and 84.705 kg·hm^-2,respectively.The critical value of soil phosphorus in cotton bud stage was about 28～30 mg·kg^-1,and about 102 kg·hm^-2phosphorus fertilizer should be applied to reach the critical level of soil ph osphorus.Using the nutrient input-input balance method,it was found that the soil phosphorus sup ply level was maintained at about 22 mg·kg^-1,and the phosphorus fertilizer application rate was ab out 80 kg·hm^-2to achieve the phosphorus balance.This study suggests that the application of phosphate fertilizer can effectively increase cotton yield,and the soil available phosphorus level is maintained at about 22 mg·kg^-1.It is recommende d to use the nutrient input-output balance method to calculate the recommended amount of phosph ate fertilizer（P₂O₅）.