The Effects Of Ammonium Polyphosphate Combined With Improved Materials On Phosphorus Form And Soybean Growth In Coastal Saline Soil

The area of coastal saline soil in the Yellow River Delta is about 4445.05 km².Salinization reduces soil fertility and soil compaction,resulting in crop yield reduction,which seriously restricts the sustainable development of coastal saline-alkali agriculture.For a long time,domestic and foreign scholars have put forward effective improvement measures for coastal saline soil,focusing on the effects of improvement measures on water and salt transport and soil structure,but there are few studies on soil fertility and nutrient utilization of coastal saline soil.Salinity affects the morphology,transformation and availability of soil nutrients,especially the transformation,migration and absorption of phosphorus.The key to improve the utilization efficiency and availability of phosphorus in coastal saline soil is to understand the process of phosphorus transformation and its influencing factors.In this study,the coastal saline soil in the Yellow River Delta was used as the research object.Through indoor culture experiments and pot experiments,phosphorus chemical fractionation,³¹P-NMR technology,fluorescence quantitative PCR technology and high-throughput sequencing technology were used to explore the effects of ammonium polyphosphate combined with biochar and straw on the physical and chemical properties of coastal saline soil,phosphorus morphological changes,alkaline phosphatase activity,phoD,pho X coding gene abundance,microbial community structure and soybean growth.In order to provide a new perspective for the study of phosphorus literacy cycle and regulation in coastal saline soil,and provide theoretical support for the application of ammonium polyphosphate in coastal saline soil.The main results are as follows:（1）Application of ammonium polyphosphate combined with biochar or straw in coastal saline soil can reduce soil pH and increase soil organic matter and available phosphorus content.Compared with the control,the pH value decreased significantly by 0.23～0.30 units,and the organic matter increased significantly by 23.86%～59.80%.The content of available phosphorus in the treatment of ammonium polyphosphate combined with biochar and straw was significantly increased by 13.45%and 17.60%compared with the treatment of ammonium polyphosphate combined with biochar and straw,respectively.（2）During the incubation period,compared with the control,single application of ammonium polyphosphate and combined application of biochar and straw could significantly increase the content of six inorganic phosphorus,but could not change the trend of Na HCO₃-Pi and C.HCl-Pi content.The treatment of only adding ammonium polyphosphate and ammonium polyphosphate combined with biochar was more conducive to increasing the content of Resin-P and D.HCl-P;ammonium polyphosphate combined with biochar significantly increased Na OH-Pi content by37.29%compared with ammonium polyphosphate alone.Single application of ammonium polyphosphate significantly reduced the content of C.HCl-Po by 20.91%compared with the control.The content of Residue-P showed a downward trend,and the decrease of Residue-P content in the treatment of only adding ammonium polyphosphate and ammonium polyphosphate combined with straw was higher than that in the treatment of adding biochar.The content of phosphate monoester in the treatment of ammonium polyphosphate and ammonium polyphosphate combined with improved materials was significantly higher than that in the control.The contents of Resin-P,Na HCO₃-Pi and Na OH-Po in the treatment of ammonium polyphosphate were significantly higher than those in the treatment of monoammonium phosphate,while the content of Residue-P was significantly lower than that in the treatment of monoammonium phosphate.（3）From the distribution characteristics of soil phosphorus pool,the application of ammonium polyphosphate can significantly increase the proportion of active phosphorus（Resin-P,Na HCO₃-Pi,Na HCO₃-Po）in coastal saline soil,reduce the proportion of medium active phosphorus（Na OH-Pi,Na OH-Po,D.HCl-P）in phosphorus pool,and have no significant effect on the proportion of stable phosphorus（C.HCl-Pi,C.HCl-Po,Residue-P）.The proportion of active phosphorus in the soil treated with ammonium polyphosphate was significantly increased by 18.69%～33.22%compared with that treated with monoammonium phosphate,while the change between medium active phosphorus and stable phosphorus was not significant.（4）The copy number of phoD gene and pho X gene in the treatment of ammonium polyphosphate combined with biochar and straw was significantly increased by 87.50%～213.05%and 420.22%～591.35%,respectively,compared with the treatment of ammonium polyphosphate alone.The community richness of phoD gene was the highest in the treatment of ammonium polyphosphate alone,and the species diversity of pho X gene was the highest in the treatment of ammonium polyphosphate combined with straw.The phoD gene defined 14 genera at the genus level,with Saccharopolyspora,Aeromicrobium,Sinorhizobium,Streptomyces,and Skermanella as the main dominant genera.The pho X gene defined 22 genera at the genus level,with Pseudosulfitobacter,Skermanella,Methylobacterium,Starkeya,and Mesorhizobium as the main dominant genera.（5）For soybean yield,the yield of soybean treated with ammonium polyphosphate alone was significantly lower than that of monoammonium phosphate alone by 11.79%.After the application of modified materials,the yield of soybean treated with ammonium polyphosphate was significantly higher than that of monoammonium phosphate.The treatment of ammonium polyphosphate combined with straw had the highest soybean yield,which was 60.68%higher than that of monoammonium phosphate combined with straw.In summary,the combined application of ammonium polyphosphate and improved materials can reduce soil pH value,increase soil organic matter content and phosphorus availability in coastal saline soil,increase the abundance of phosphorus cycle functional genes in coastal saline soil,enrich microbial community diversity,and increase the phosphorus absorption and yield of soybean in coastal saline soil.