| The losses of nitrogen(N)and phosphorus(P)through leaching are the main cause of agricultural non-point source pollution.It is critical to explore the mechanism and characteristics of N and P loss through leaching processTherefore,the study was conducted by sampling the soil from Zhuyu county,Zhouzhi village,Shaanxi province,to study the effect of different external materials(soil conditioner?soft rock?biochar?straw)on the leaching characteristics of soil phosphorus and nitrogen with the method of leaching soil column by indoor simulation device.Simultaneously,water samples were also collected in ten points from Yujia River to detect total phosphorus(TP),total nitrogen(TN),total dissolved phosphorus(TDP),particles of phosphorus(PP)and soluble organic phosphorus(DOP)so as to analyze the concentration changes of P and N and their influencing factors.The major conclusions were as follows:(1)Biochar addition increased the concentration of PP,DPR and DOP in leachate,resulting in the increase of the concentration of TP in the leaching solution(from 0.68 to 2.86mg/l).With the increase in the proportion of biochar(2%,4%,8%),different forms P in leachate and available P(Olsen-P)?extraction P(CaCl2)in soil increased dramatically,of which Olsen-P was increased by 141%,290%,382% respectively with 2%,4% and 8%biochar addition,and biochar significantly improved the leaching ability of P.Straw increased the concentration of DOP and PP in leachate,so as to increased the content of TP.But compared with control,the content of DRP was decreased by 50%,accounting for only 4.7%in TP.Straw decreased the content of available P in the soil,which prevented the migration of CaCl2-P to the deeper soil,and reduced the risk of phosphorus on the environment.(2)The addition of 4% and 8% biochar caused a reduction of the leaching amounts of TN by 30% and 20.7%,respectively,but the application of 2% biochar increased of the leaching amounts of TN by 5.9%.Biochar(2%?4%?8%)significantly decreased available N.Straw caused a reduction of leaching amounts of TN by 9.7%,and increased the content of available nitrogen by 59.1%.The content of total N and available N mainly remained in 0~10cm soil layer.Straw not only decreased the leaching of nitrogen,but also improved surface soil fertility.Soft rock inhibited the leaching of nitrogen and decreased the content ofavailable nitrogen within a short time.(3)The concentration of TP,PP,TDP and TN in Yujia river varied with the seasons,during crop growth period(from April to September),the average concentration of TP in every month was higher than the critical value(0.02 mg/l).PP was the main form of phosphorus in river,accounting for 67.7% of TP.The contentration of TDP?DRP and DOP was low,and mainly depending on the quality of the water itself,of which the contentration of DOP was higher in July and Auguest,referring to the temperature of the water.The concentration of TN varied from 1.6 mg/l to 14.0 mg/l,and average concentration of TP in every month was 5.8 mg/l,which was higher than the critical value(2.0 mg/l).Fertilizer with excessive input was the main source of N and P in water.Rainfall and excessive fertilization were the main factors causing the non-point pollution.To sum up.The N pollution is more serious in the water body of Yujiahe River.Biochar reduced the leaching of N,but its effect on phosphorus should also be considered when determine the application rate of biochar.Straw not only inhibited the N leaching,but also reduced the risk of P loss to the environment.The effect of soft rock and soil conditioner on the environment is not significant. |
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