| Objective:Gray desert soil in Xinjiang is rich in calcium carbonate,which is the main reason for low soil P availability,and soil P availability is closely related to the type and form of P fertilizer.Due to the widespread application of drip irrigation technology in Xinjiang,the application mode of phosphorus fertilizer has gradually changed from traditional basal application to drip application.However,A large body of evidence showed that phosphorus will be absorbed by the top soil and difficult to be absorbed by the deep roots of crops.Polyphosphate phosphate fertilizer had shown some advantages in crop phosphate application,but its production cost was high and its application on drip irrigated cotton had been rarely reported..This study was conducted to investigate the fertilization effect of polyphosphate and diammonium drip irrigation on drip irrigated cotton from the perspective of high production cost and low acceptance of polyphosphate fertilizer by farmers,with the aim of achieving both"economic"and"efficient use of phosphate fertilizer"..At the same time,to address the problem of imperfect application technology and unclear fertilization efficiency of polyphosphate phosphate fertilizer on drip irrigated cotton fields,the optimal application strategy of polyphosphate phosphate fertilizer on cotton fields in Xinjiang and its fertilization efficiency differences were further investigated and fertilization recommendations were made accordingly.Methods:（1）A field trial study of economic polyphosphate blending ratios was conducted in 2021.Ammonium polyphosphate 1（APP1,polymerization degree 2.3,polymerization rate 75%）ammonium polyphosphate 2（APP2,polymerization degree 1.8,polymerization rate 75%）and potassium tripolyphosphate（KTPP,polymerization degree 3.0,polymerization rate 95%）were blended with conventional drip irrigation at 10%,30%and 50%of the total phosphorus application（P2O5 120 kg/hm2）with polyphosphate carryover P2O5content,respectively.Diammonium was blended and applied,while no phosphorus fertilizer（P0）and conventional drip-diammonium application（DAP）were used as controls.The effects of drip irrigation application of different polyphosphate blended phosphate fertilizers on cotton growth and yield formation were investigated by monitoring soil phosphorus effectiveness,cotton biomass and phosphorus uptake,yield and yield components.（2）A field study on the application technology of polyphosphate phosphate fertilizer with different basal topdressing ratios was conducted in 2022.Ammonium polyphosphate（polymerization degree 1.8,polymerization rate 75%）and potassium tripolyphosphate（polymerization degree 3.0,polymerization rate95%）were blended with drip diammonium at a P2O5 carry-over ratio of 3:7 to form two blended phosphate fertilizers,and conventional drip diammonium was selected as the control,for a total of three phosphate fertilizers.Three different basal topdressing ratios application strategies were set up under each phosphorus fertilizer type,namely 7:3,1:1 and 3:7.The farmers’conventional full drip phosphorus application strategy（CK,with DAP as the phosphorus source）and no phosphorus application（P0）were also used as controls.The effects of different base-to-chase phosphorus application strategies of polyphosphate fertilizer on cotton growth and yield formation were investigated by monitoring the growth traits,yield composition and soil effective phosphorus content of cotton under different base-to-chase phosphorus application strategies.（3）An experimental study on the hydrolysis and release of polyphosphate phosphorus in different soils was carried out in 2022.At constant temperatures of 30℃and 15℃,five kinds of phosphate fertilizers were cultivated in calcareous soil in Xinjiang（p H 8.12）and latosol in southern China（p H 5.23）.The phosphorus sources were ammonium polyphosphate 1（APP1,degree of polymerization 2.3,polymerization rate 75%）,ammonium polyphosphate 2（APP2,degree of polymerization 1.8,polymerization rate 75%）,and ammonium polyphosphate 3（APP3,degree of polymerization 2.7,polymerization rate 98%）,potassium tripolyphosphate（KTPP,degree of polymerization 3.0,polymerization rate 95%）and conventional drip irrigation（DAP）,with no phosphate fertilizer as the blank control.Soil phosphatase activity and soil available phosphorus content were determined by incubating and fertilizing soil for 2,24,240 and 720 h,respectively.The time range and characteristics of phosphorus hydrolysis and release of different polyphosphates in different types of soils were studied.Results:（1）The content of available phosphorus in 0-20 cm soil,the aboveground biomass and phosphorus absorption of cotton,the number of bolls per plant,the yield of seed cotton,the number of pre-summer boll,the agronomic utilization rate of phosphorus fertilizer and the ratio of yield to input increased with the increase of the proportion of polyphosphate.The value of each index was generally APP2>KTPP>APP1 in the three polyphosphate treatments.At the full flowering and boll stage of cotton,the content of available phosphorus in 0-20 cm soil and the amount of phosphorus absorbed by cotton under APP2-50 treatment were significantly higher than those under other phosphorus application treatments.There was no significant difference between the cotton biomass of APP2-50 treatment and DAP at the full flowering stage,but the cotton biomass of this treatment was significantly higher than that of other phosphorus application treatments at the full boll stage.The boll number of cotton in all polyphosphate and phosphate fertilizer treatments was significantly higher than that in DAP,while the single boll weight of cotton had no difference among the phosphorus fertilizer treatments.Compared with DAP,the yield of seed cotton,the agronomic utilization rate of phosphate fertilizer and the ratio of output to input of APP2-50 treatment increased by 10.7%,88.3%and 7.6%respectively,significantly higher than other treatments.（2）The type of phosphorus fertilizer,the basal-topdressing ratio and their interaction had significant effects on the content of available phosphorus in soil.Properly adjusting the basal-topdressing ratio of phosphorus fertilizer significantly affected the availability of soil phosphorus,and the content of available phosphorus in 0-20 cm soil layer was the highest in APP treatment under the basal-topdressing ratio of 1:1.In addition,the cotton biomass and phosphorus uptake of APP at 1:1 basal-topdressing ratio were significantly higher than those of other treatments.At full boll stage,the cotton biomass and phosphorus uptake of APP at 1:1 basal-topdressing ratio were 37.2%and 9.6%higher than CK cotton,respectively.Under three different phosphorus source treatments,partial basal application of phosphorus fertilizer helped to increase the number of cotton bolls and reduce the rate of cotton boll abscission.Under the 1:1 basal-topdressing ratio of APP,the number of pre-summer boll before dormancy increased by 77.7%compared with DAP,the abscission rate of cotton buds and bolls in P0 and CK treatments was 71.2%and 56.1%,respectively,while the abscission rate of cotton buds and bolls was 47%under the ratio of 7:3 base and top dressing in APP.Under the 1:1 basal-topdressing ratio,the yield and agronomic utilization rate of phosphate fertilizer of APP were significantly higher than those of other treatments.（3）Different degree of polymerization of polyphosphate phosphate fertilizers with different hydrolysis time periods in soil.Orthophosphate phosphate fertilizer（DAP）was rapidly fixed after being applied to soil,and its soil available phosphorus content was significantly decreased;the content of available phosphorus gradually increased with the increase of incubation time,but the hydrolysis time of KTPP was long;The content of phosphorus in the soil of low degree of polyphosphate fertilizer（APP2）was the highest at the initial stage of cultivation,and then showed a downward trend.Its hydrolytic phosphorus supply period was short.At 30℃,with the increase of incubation time,the activity of acid phosphatase in the two soils decreased first and then increased slightly.The activity of alkaline phosphatase increased significantly in calcareous soil,and increased significantly in lateritic soil and then decreased significantly.The content of available phosphorus in the soil of all phosphate fertilizer treatments except KTPP decreased.Under the condition of 15℃,the activity of acid phosphatase in both soils increased first and then decreased with time,while the activity of alkaline phosphatase in lateritic soil increased slowly and remained basically unchanged after 24 hours.Conclusion:（1）Among the blended phosphate fertilizer treatments,chose ammonium polyphosphate with a polymerization degree of 1.8 at a rate of 50%over conventional drip diammonium gave the best cotton yield and was also a more economical choice for phosphate fertilizer application;（2）Applying polyphosphate mixed with phosphate fertilizer at the basal-topdressing ratio 1:1 could promote the early growth of cotton,increase cotton pre-harvest peach and reduce cotton boll abscission rate,so as to increase the yield of cotton.Among them,ammonium polyphosphate with a degree of polymerization of 1.8 was the best choice for the mixed phosphorus source.（3）The traditional water-soluble orthophosphate fertilizer（DAP）will be quickly fixed by the soil after it was applied to the soil,and the polymerized phosphate fertilizer reduces the risk of soil phosphorus fixation due to its slow hydrolysis characteristics.Although polyphosphates with higher degree of polymerization could reduce the risk of rapid fixation of phosphorus in soil,its hydrolysis time was long.If the existing multi-frequency drip irrigation of polyphosphate fertilizer was applied,it was not conducive to the balance of supply and demand of phosphorus nutrients in cotton Therefore,in the cotton drip irrigation phosphorus application system,the method of selecting low degree of polymerization of polyphosphate phosphate fertilizer and partial basic application of phosphate fertilizer could coordinate the absorption of phosphorus nutrients in cotton early stage and reduce the loss of soil phosphorus fixation to promote cotton growth and yield formation. |
PDF Full Text Request