Spatial Variation Of Soil Available Nitrogen And Phosphorus And Risk Assessment Of Contamination For Vegetable Waste In Vegetable Field Of Huang-Huai-Hai Region

Non-point source pollution of vegetable plot threatens sustainable development of nature,society and economy in the Huang-Huai-Hai region.In the main vegetable producing areas of Huang-Huai-Hai,problems,including the leaching of soil nitrogen and phosphorus nutrients,the random disposal of vegetable and other agricultural wastes and so on,all are important reasons for agricultural non-point source pollution in the Huang-Huai-Hai region.A large-scale field experiment was carried out in the Huang-Huai-Hai region from August to October 2018.The total number of 0-20 cm of surface soil mixed samples collected at 12typical vegetable planting bases at 896 hm~2 representative sampling points is 788.With indexes of soil available nitrogen,available phosphorus and soil texture through indoor unified measurement,using classical statistics,geostatistics,GIS and other methods,the reasonable sampling density,spatial variability characteristics and influencing factors of soil available nitrogen and phosphorus contents were analyzed.In addition,based on statistics and literature data,the content of vegetable wastes in 58 cities in the Huang-Huai-Hai region was estimated,and their pollution risks were evaluated.The main conclusions are as follows:(1)With the classical statistical calculation,the facility/open field vegetable soil sampled representative areas were 0.24 hm~2 and 0.83 hm~2,respectively and the corresponding sampled representative areas of geostatistics were 5.06 hm~2 and 1.61 hm~2,respectively.After Kriging interpolation verification,the number of pixels with an accuracy>90%of the available nitrogen in facilities and open field soils accounted for 49.2%and 93.9%of the total pixels,respectively,and that of the available phosphorus was 43.5%and 71.0%,respectively.(2)The average contents of available nitrogen in facilities and open fields were 160.7mg/kg and 27.6 mg/kg,respectively and the coefficients of variation were 38.67%and48.37%,respectively;the available phosphorus contents were 226.2 mg/kg and 52.9 mg/kg,respectively,with coefficients of variation of 46.24%and 55.69%.Spatial variability of protected vegetable fields is caused by structural factors(such as soil parent material,soil type,terrain,and climate)and random factors(such as farming system,fertilization,and irrigation,Etc.);the nugget coefficients of soil available nitrogen and available phosphorus in open field vegetable fields were 5.2%to 49.3%,0.2%to 42.7%,and the spatial correlation of the study areas is quiet different.(3)The influence weights of altitude on available nitrogen and available phosphorus were 8.56%and 15.80%,respectively,and influence weights of slope/aspect on available nitrogen and available phosphorus were 22.44%and 16.34%,respectively.The influence weights of soil texture on available nitrogen and available phosphorus were 12.50%and11.63%,respectively.The structural factors can explain 43.50%of soil available nitrogen and43.77%of soil available phosphorus.The influence weights of cultivation methods on available nitrogen and available phosphorus are 12.38%and 12.79%,respectively.The explanatory ability of irrigation to soil available nitrogen is greater than that to available phosphorus,and the influence weights are 25.73%and 7.72%,respectively.The explanatory ability of nitrogen dosage to available nitrogen is 10.74%,and the explanatory ability of nitrogen dosage to available phosphorus is 18.77%.Human factors can explain 56.50%of soil available nitrogen and 56.23%of soil available phosphorus.(4)The total amount of vegetable wastes in Huang-Huai-Hai region in 2017 was 16.18million tons,of which the TN and TP contents were 418 and 111.8 thousand tons,respectively;the average pollution intensity of vegetable wastes in various cities was 6.45t/hm~2.The pollution intensity of TN and TP was 15.15 kg/hm~2 and 4.05 kg/hm ~2,respectively.In the Huang-Huai-Hai prefecture-level cities,the areas where the pollution load of vegetable wastes exceeds 0.6 million tons were concentrated in the central region,and the pollution load accounted for 22.85%of the total load in Huang-Huai-Hai.The pollution load of TN and TP in these areas exceeded 16 and 4 thousand t/a.The pollution intensity of vegetable wastes exceeded 10 t/hm~2.Areas with pollution intensity of TN,TP exceeding 24.20 kg/hm~2,6.40kg/hm~2 include Zaozhuang,Kaifeng,Laiwu,Tangshan,Tai'an,Anyang,Jinan,Weifang and other 10 cities.