Efficient Utilization Mechanism Of Phosphorus For An Annual Reduced Phosphate Fertilizer Scheme In Wheat-maize Rotation System And Coated Controlled-release Phosphate Fertilizer

Phosphorus is one of the macroelements necessary for crop growth.Phosphate fertilizer plays an irreplaceable role in ensuring food security in my country.Long-term excessive or unreasonable application of phosphate fertilizer has led to massive accumulation of soil phosphorus and low utilization of phosphate fertilizer in season,which has exacerbated the scarcity of phosphate resources in China.Therefore,it is crucial to develop a reasonable and sustainable phosphate fertilizer utilization strategy.Through long-term positioning experiments,we found and clarified the problem of excessive conventional phosphate fertilizer dosage by farmers,and we conducted research from two perspectives:reducing phosphate fertilizer application and phosphorus fixation to improve phosphate fertilizer utilization efficiency.First,this study conducted long-term field trials of winter wheat-summer maize rotation system to explore the differences in yield response,soil P availability,and rhizosphere microbial community composition diversity between wheat and maize under the application of low,medium and high levels of phosphorus fertilizer.In the second aspect,combined with the above-mentioned differences in phosphorus demand characteristics of wheat and maize,under the conditions of high and low soil available phosphorus content,the feasibility of the operation mode of reducing phosphorus fertilizer application in the maize season was studied,and the effect mechanism of soil available phosphorus content,phosphatase activity,and microbial community composition changes on annual crop yield.Third,in view of the problem that phosphorus is easily fixed by soil,considering the idea of slowing down the contact between phosphorus fertilizer and soil to reduce phosphorus fixation,a new bio-based polyurethane-coated controlled-release phosphorus fertilizer was developed.Scanning electron microscopy,gas chromatography,Fourier infrared imaging microscope and other techniques were used to characterize the microscopic morphology of the film-shell interface of the controlled-release phosphate fertilizer,the changes of the liquefied polyol components and the film-forming properties of polyurethane,and to explore the mechanism of extending the slow-release period of the coated phosphate fertilizer.The main research results are as follows:(1)The differences in the response to crop yield and soil microbial diversity of different phosphorus fertilizer application rates in the wheat-maize rotation system were investigated.This experiment was based on a long-term locational field trial for 10 consecutive years to compare the responses of wheat and maize yields,changes in soil phosphorus effectiveness,and inter-root soil microbial diversity at three phosphate fertilizer gradient levels:low(P1),constant(P2),and high(P3).The results of the experiment showed that phosphate fertilizer application was significantly correlated with wheat yield and not with maize yield based on regression analysis.Compared with the P2 treatment,long-term reduction P1 or high application P3 treatment reduced wheat yield by 20.1%and 6.2%,respectively,while the P1treatment with 50%reduction in maize resulted in an average yield increase of 6.7%.Comprehensive analysis of crop yield and grain-grass ratio found that the most suitable treatment for wheat was P2 treatment,and the most suitable treatment for maize was P1treatment.The average phosphate fertilizer utilization rate reached 48.4%in the wheat season P2 treatment for three consecutive years,while the average phosphate fertilizer utilization rate reached 51.1%in the maize season P1 treatment.Increasing phosphate fertilizer dosage significantly increased soil phosphorus effectiveness,and after 13 consecutive years of fertilizer application,the effective and total phosphorus content of the P2 treatment increased by 82.6%and 9.1%,respectively,compared to the soil at the beginning of the experiment.Soil bacterial and fungal phylum species abundance in wheat and maize showed overall seasonal differences rather than phosphate fertilizer use between seasons,where only bacterial Proteobacteria abundance was affected by both phosphate fertilizer use and season.Crop yield was significantly correlated with the alpha diversity index of the soil bacterial community,but not with fungi.This study showed that wheat was more sensitive to phosphate fertilizer uptake than maize,and that inter-seasonal changes in bacterial microbial diversity significantly affected crop yield,providing a basis for reducing and increasing the efficiency of the maize season.(2)The mechanism of the annual transport pattern of phosphorus reduction in wheat-maize rotation system on soil phosphorus supply and microbial coupling efficiency was revealed.A pot experiment was conducted for two consecutive seasons in calcareous soils with high(30.36mg kg^-1,H)and low(9.78mg kg^-1,L)levels of effective phosphorus under a winter wheat-summer maize rotation system to evaluate the effects of phosphorus application in the wheat season only(Pw)on crop yield,soil effective phosphorus,and microbial community structure compared with conventional phosphorus fertilization in both the wheat and maize seasons(Pwm).The results showed that the HPw treatment was more effective than conventional wheat and maize fertilization.The results showed that the total crop yield was stable for two consecutive years with 1/3 less phosphate fertilizer input in the HPw treatment compared to the HPwm treatment,and the PUE increased by 10.8%in the HPw treatment.There was no accumulation of total phosphorus content in the HPw treatment compared to the base soil in both years,while HPwm increased by 20.6%.The soil water-effective phosphorus content of the Pw treatment was not significantly different from that of the Pwm treatment at the maize trumpet stage.Soil phosphorus content significantly affects soil microbial communities,especially fungal communities.The relative abundance of Proteobacteria and alkaline phosphatase(ALP)activity were significantly higher in the Pw treatment than in the Pwm treatment(11.4%and 13.3%,respectively).The contribution of soil microorganisms to yield at high phosphorus levels was greater than the effect of effective soil phosphorus.In addition,the relative abundance of Bacillus and Rhizobium was significantly higher in the Pw treatment than in the Pwm treatment.Bacillus was significantly and positively correlated with acid phosphatase(ACP)activity,and Rhizobium was significantly and positively correlated with both ACP and ALP activities,which favored soil phosphorus activation.This study showed that under high phosphorus soil conditions,phosphorus application in a winter wheat-summer maize rotation system only in the wheat season could achieve a stable crop yield throughout the year through coupling between soil phosphorus effectiveness and microorganisms.(3)The mechanism of using modified crop straw to improve the nutrient-controlled release performance of bio-based coated controlled release phosphate fertilizers was elucidated.A highly efficient transient ejection steam explosion technique was used to pretreat wheat straw(SEWS)to remove small molecules of hemicellulose and difficult film-forming ions,improve the quality of straw liquefied polyol,and extend the release period of bio-based polyurethane coated phosphate fertilizer.The results showed that the initial release rate of SEWS-treated wrapped phosphate fertilizer decreased from 4.8%to 2.5%and the release period was extended from 10d to 28d to meet the release criteria of controlled release fertilizer under the condition of 5%wrapping volume compared with wheat straw(WS)treatment.The steam explosion pretreatment straw process destroyed the cell wall,and the process reduced the hemicellulose content from 32.7%to 5.1%.The cleaning resulted in a significant reduction of the refractory film-forming ions(K⁺,Ca²⁺,and Mg²⁺)in the straw,with the greatest decrease of 85.2%in K⁺.In the straw liquefaction process,the SEWS liquefaction product decreased by 38.1%compared to the WS direct liquefaction residue rate of 5.5%,while the hydroxyl value increased by 36.5%to 125.3mg KOH g^-1.In the coating process,the SEWS-treated liquefied polyol and diphenylmethane-diisocyanate formed a tightly cross-linked,homogeneous bio-based film,reducing the formation of pores in the membrane material during the release process.Efficient pretreatment of biomass materials using transient ejection steam explosion technology is beneficial to improving the nutrient-controlled release performance of bio-based film-coated controlled release phosphate fertilizers,thereby reducing phosphorus fixation after application to the soil.In summary,under the premise of ensuring the yield of wheat and maize crops,the reduced application of phosphate fertilizer in the maize season effectively reduced the accumulation of soil phosphorus,improved the utilization rate of phosphate fertilizer,and facilitated the activation of soil phosphorus by soil microorganisms to achieve phosphorus reduction and efficiency.The research and development of the new film-coated controlled-release phosphate fertilizer significantly improved the controlled-release performance of phosphorus,making it more conducive to improving phosphorus effectiveness.