Diffusive Gradients In Thin Film Based Soil Phosphorus Supply Index And Evaluation In Xinjiang Cotton Region

DGT(Diffusive Gradients in Thin Film)is an in-situ determination method that can simulate the migration of phosphorus at the root-soil interface in different soil types,predict the response of crops to soil phosphorus supply.However,there is a lack of methods to indicate the DGT-P-based soil phosphorus supply status and phosphorus fertilizer recommended by now.In this paper,the management of phosphate fertilizers on cotton under film by drip irrigation was considered as the research object.Using the combination of field experiment and pot simulation,the migration rule of phosphorus in soil was determined in situ by DGT method.The index of soil phosphorus abundance and deficiency based on DGT-P was established,and the availability and effect of dripping phosphate fertilizer on cotton were evaluated.These results provide a theoretical basis for the accurate management of phosphorus nutrition in cotton fields.The main results are as follows:(1)A logarithmic model was used to fit the relationship between relative cotton yield and soil Olsen-P,based on the relative yield of cotton<70%,70%-80%,80%-90-%,90%-95%,>95%,soil Olsen-P was divided into five levels:extremely low,low,medium,high,and extremely high.There was a significantly positive correlation between DGT-P and Olsen-P(R2=0.88).Based on this quantitative relationship,a soil available phosphorus abundance index was established according to DGT-P in Xinjiang cotton fields.The soil available phosphorus is divided into 5 levels:<13 ?g·L-1,13-31 ?g·L-1,31-63 ?g·L-1,63-95 ?g·-1 and>95 ?g·L-1,and the critical value of cotton soil DGT-P was 58.6 ?g·L-1.The recommended index of phosphate fertilizer application for cotton in Xinjiang was put forward.(2)When DGT-P was 47.9 ?g·L-1,the application of MAP significantly increased the dry matter and yield of cotton compared with DAP,which increased by 5.82%and 3.78%,respectively.However,there was no significant difference compared with TSP,and application of MAP can increase the benefits of cotton planting.The average utilization rate of MAP,DAP,and TSP was 26%,22%and 24%,respectively,and the partial productivity was 16.41,15.81 and 16.04 kg·kg-1 respectively,but there was no significant difference between three kinds of phosphate fertilizer in soil DGT-P after cotton harvest.(3)The vertical migrate range of phosphorus in cotton field was detected by DGT method.The range of P in sandy loam is 0-15 cm,and 0-10 cm in loam.The more vicious of the soil,the less mobility of phosphorus.The vertical movement of phosphorus was 0-15 cm under drip phosphate fertilizer,and the range of movement is greater than that of phosphate fertilizer as basal.That is,drip phosphate fertilizer can increase the migration depth to 15 cm.(4)When DGT-P was 50.8 ?g·L-1,Drip phosphate fertilizer after sowing increased the DGT-P content in 0-15 cm soil layer,but drip phosphate fertilizer at bud stage only increased it in 0-8 cm soil layer.The spatial distribution of cotton roots is well matched with the distribution of DGT-P.Compared with phosphorus as basal and drip phosphorus at bud stage,the cotton yield of f drip phosphate fertilizer after sowing increased by 5.2%and 5.1%,respectively,and the utilization rate of phosphate fertilizer increased by 7.8 and 6.6 percentage points respectively,and the soil phosphorus surplus was reduced.The following conclusions were obtained from the above results:(1)The indicator system for the abundance of cotton soil available phosphorus based on DGT-P methods was established in Xinjiang,and obtained the critical value of soil DGT-P.And The recommended index of phosphate fertilizer application for cotton in Xinjiang was put forward.(2)Effects of the applied phosphate fertilizer on cotton showed that mono-ammonium phosphate(MAP)>triple superphosphate(TSP)>diammonium phosphate(DAP).(3)The mobility of P in soil was affected by the methods of phosphorus application and the proportion of sand in soil.(4)Drip phosphate fertilizer after sowing increased the migration distance of phosphorus.The spatial distribution of cotton roots was well matched with the distribution of DGT-P,which increased the cotton yield,promoted the utilization rate of phosphate fertilizer,and reduced phosphorus surplus in the soil.The above results provide theoretical and technical support for the monitoring and management of phosphorus nutrients in cotton fields,rational application of phosphate fertilizers,and reduction of soil phosphorus surplus.