Accumulation,Migration And Transformation Of Phosphorus In Facility Agriculture Soil And Its Safe Utilization

Facility agriculture is a typical representative of high nutrient input.Farmers often use their own subjective ideas to fertilize in actual production,resulting in a large amount of waste of nutrients.The continuous accumulation of nutrients will cause soil hardening and salinization,which will not only harm the growth of crops,but also cause pollution risks to the surrounding environment.This study takes the facility agriculture concentration area in Daxing District of Beijing as the research object,through the field questionnaire survey and relevant data collection,with the help of variogram and hot and cold spot analysis,to explore the current situation of nutrient input,expenditure and surplus of facility agriculture in Daxing District;Through the determination and analysis of total phosphorus,available phosphorus and various forms of inorganic phosphorus in the profile of facility agriculture,the accumulation,migration and transformation characteristics of soil phosphorus were explored;Based on the environmental risk index of nutrient input,carry out zoning utilization,and carry out recommended fertilization of melon within the range of ecological environment,in order to provide a scientific basis for reducing nutrient waste and reducing the risk of phosphorus loss.The main conclusions of this study are as follows:（1）The spatial accumulation effect of nutrient input in Daxing District is significant,and the high hot spots are mainly concentrated in the central region,showing a positive correlation in spatial distribution.The average input of N,P₂O₅ and K₂O in facility agriculture in the study area reached 457.55,251.71 and 345.52kg·hm^-2,and the input ratio was 1:0.55:0.76,which exceeded the normal nutrient content required by crops;Among them,the average input of N,P₂O₅ and K₂O in facility agriculture in 1～5a is the largest,which are 594.74,326.26 and 394.24 kg·hm^-2respectively,and the input ratio is 1:0.55:0.66;>The average input of 20a N,P₂O₅ and K₂O was the smallest,366.17,214.71 and 226.44 kg·hm^-2 respectively,and the input ratio was 1:0.59:0.62;The input of P₂O₅ and K₂O in facility agriculture under different planting modes was basically the same,while the input of N in cold shed was significantly higher than that in warm shed.A large amount of nutrient input has brought more available nutrients to the soil,which has produced the enrichment characteristics of surface soil.The results showed that the nutrient input in facility agriculture was excessive,and the input ratio of different nutrients was unbalanced.The surplus of N,P₂O₅ and K₂O reached 183.29,393.11 and 293.92 kg·hm^-2respectively,which exceeded 2.67,5.59 and 5.84 times of the amount taken away by crops;The average contents of available phosphorus（AP）,available potassium（AK）,organic matter（SOM）and total nitrogen（TN）in 0～20cm topsoil were 160.16 mg·kg^-1,347.96 mg·kg^-1,16.10 g·kg^-1 and 1.20 g·kg^-1 respectively.（2）The contents of total phosphorus（TP）and available phosphorus（AP）in the surface soil of facility agriculture in different planting years vary widely,which is significantly higher than that in the surrounding grain field soil,which is mainly related to the phosphorus fertilizer input of farmers in different planting years;The variation range of TP content in profile soil is 0.38-2.58 g?kg^-1,and the variation range of AP content is 1.60-256.00mg?kg^-1,showing the vertical distribution characteristics of enrichment in surface soil and decreasing downward;There are differences in the changes of TP and AP contents in different depths,in which the change ranges of0-20cm and 20-40cm are greater than those in deep soil.When the soil depth is>40cm,there is no significant difference in the changes of TP and AP contents.There are significant differences in soil phosphorus activation coefficient（PAC）between different planting years,planting patterns and different soil depths.Farmers’exogenous phosphorus fertilizer input is an important factor affecting the size of soil phosphorus pool and the availability of phosphorus.（3）The content of inorganic phosphorus is mainly concentrated in the surface soil of facility agriculture,accounting for 47.08%of TP;Among them,calcium bound phosphorus（Ca-P）is the inorganic phosphorus form with the largest proportion,reaching 98.38%,and iron phosphate（Fe-P）and closed storage phosphorus（O-P）account for a relatively small proportion;Apatite(Ca₁₀-P)is the main form of Ca-P,with the content reaching 78.70%of Ca-P,followed by dicalcium phosphate（Ca₂-P）and octacalcium phosphate（Ca₈-P）.With the increase of soil depth,the content of different forms of inorganic phosphorus showed the vertical distribution characteristics of strong enrichment in surface soil and decreasing downward;Ca₁₀-P is the inorganic phosphorus form with the largest proportion of total phosphorus in different soil layers,and the proportion of Fe-P and O-P is relatively small;There were significant differences in the content of inorganic phosphorus in different planting years and planting patterns.The results showed that the migration and transformation of different forms of inorganic phosphorus in protected agricultural soil in the study area was mainly Ca-P,while the migration and transformation of Fe-P and O-P was poor.Ca₂-P is the main source of soil AP and can be used as an effective phosphorus source for plants;Ca₈-P,Ca₁₀-P and O-P can have an indirect effect on AP through Ca₂-P,which can be used as a slow effect and potential phosphorus source for plants.Ca₁₀-P has poor availability and large accumulation.How to strengthen the bioavailability of this part of phosphorus source is an important measure to guide the management of phosphorus in facility soil.（4）The environmental risk degree of nutrient input in the study area is not optimistic.Except that the environmental risk degree of Weishanzhuang town is relatively safe,there are certain risks in other towns.There are differences in soil phosphorus loss in facility agriculture in different planting years.Among them,there is a high risk of phosphorus loss in surface soil.With the increase of soil depth,the risk of soil phosphorus loss decreases,which is mainly affected by the migration and transformation of soil phosphorus and the management mode of farmers.The zoning is carried out based on the environmental risk index of nutrient input.At the same time,the recommended fertilization proportion of West melon calculated according to soil fertility is multiplied by the environmental risk index of nitrogen,phosphorus and potassium input.On the premise that there is no risk to the environment,the recommended fertilization of West melon is carried out for each region.The results can provide some guidance for the rational fertilization of melon and reducing the risk of phosphorus loss.Figure[33]Table[29]Reference[125]...