Study On Phosphorus Accumulation And Leaching From Open Field Vegetable Fields In Fluvo-Aquic Soils Under Long-Term Positioning Test

To investigate the effects of high water and fertilizer inputs on soil phosphorus leaching in vegetable growing areas,we used a combination of field experiments and soil column simulations to investigate vegetable yields,soil profile phosphorus accumulation,and the relationship between soil Ca Cl₂-P and soil Olsen-P using a segmented linear model fitted with different phosphorus fertilizer levels with organic fertilizers in the open field vegetable fields in Shunyi,Beijing.The relationship between soil Ca Cl₂-P and soil Olsen-P was investigated to explore the risk of soil phosphorus leaching.By analyzing the relationship between crop,soil,leachate and phosphorus application,exploring the characteristics of soil phosphorus cumulative leaching,clarifying the environmental threshold of soil phosphorus in tidal topsoil,and further analyzing the correlation between total phosphorus content of soil leachate and soil Ca Cl₂-P（water-soluble phosphorus）,the main conclusions of the experiment were as follows.（1）Characteristics of vegetable yield and soil phosphorus changes under different phosphorus application levels in open field vegetable fields under long-term positioning conditions:under soil conditions with high phosphorus content and long-term phosphorus fertilization,there were no significant differences in cabbage yield between fertilization treatments,but all of them were higher than those of cabbage yield in treatments without phosphorus fertilization.The surface soil Olsen-P content of the treatments without phosphorus fertilizer and with organic fertilizer only decreased significantly with increasing planting years,while the treatments with organic-inorganic combination and chemical phosphorus fertilizer only showed an increase in soil Olsen-P content with increasing planting years up to 172.27 mg·kg^-1and Ca Cl₂-P content of 13.62 mg·kg^-1.In the soil profile,the The content of soil Olsen-P and Ca Cl₂-P decreased gradually with increasing soil depth,and there was a significant cumulative increase in soil Olsen-P at all soil depths above 60cm.The Ca Cl₂-P content of top soil in the treatments without phosphorus fertilizer and with organic fertilizer only was significantly reduced,and the pattern of variation at soil depth remained consistent with the soil Olsen-P content.（2）Characteristics of oilseed rape,soil phosphorus dynamics and total phosphorus in leached water in the soil column simulation test:yield and total plant phosphorus of oilseed rape under different phosphorus application treatments were not significantly different,the lowest yield of oilseed rape in the no phosphorus application treatment,and the yield of oilseed rape in the phosphorus application treatment increased with the increase of phosphorus application.The root length of oilseed rape was significantly different among the different phosphorus application treatments,with the highest phosphorus fertilizer application treatment having a root length of11.50 cm and no significant difference among the remaining treatments.Soil Olsen-P and Ca Cl₂-P content increased with fertilizer application and gradually decreased with soil depth,with the highest Olsen-P content of 67.23 mg·kg^-1and Ca Cl₂-P content of 5.14 mg·kg^-1in the top soil.total phosphorus concentration in soil leachate increased with fertilizer application and gradually decreased with soil depth.With the increase of leaching days,the total phosphorus concentration of soil leachate in the surface layer of 0-20 cm showed a trend of increasing and then decreasing in all treatments,with the highest concentration of 7.77 mg·L^-1;while the trend of total phosphorus in soil leachate in the middle layer 20-40 cm remained the same as that in the surface layer,with the highest concentration of 5.67 mg·L^-1,but the time of increase increased compared with the surface layer,due to the In the soil depth of 40-60 cm,the concentration of total phosphorus in leachate water increased continuously with the time of leaching,reaching 3.29 mg·L^-1,while the concentration of total phosphorus in leachate water decreased continuously with the time of leaching in treatments without chemical phosphorus fertilizer.（3）Soil phosphorus leaching threshold:The environmental threshold of soil phosphorus was fitted using the relationship between soil Olsen-P content and corresponding soil Ca Cl₂-P content.The environmental threshold of soil phosphorus was 46.08 mg·kg^-1when a segmented linear function was fitted to the soil phosphorus of the open field vegetable field,and 42.09 mg·kg^-1when a soil column simulation was fitted to the soil phosphorus,and a significant positive correlation was obtained between the total phosphorus in soil leachate and soil Ca Cl₂-P.Therefore,under this test condition,the soil Olsen-P content should not exceed this level,otherwise,the risk of leaching increases.