Analysis Of Soil Physicochemical Properties And Environmental Effects After 37 Years Of Organic Fertilizer Application

The application of organic fertilizer is an important measure to maintain the balance of matter and energy in ecosystem,which can improve soil fertility and the resistance and resilience of ecosystem to disturbance.Long-term location test of organic fertilizer is an important reference to judge the effect of long-term application of organic fertilizer on soil environment in production practice.Therefore,in this study,a long-term fixed-position experiment in the south of the Loess Plateau was selected,and the continuous cropping soil of wheat and alfalfa was taken as the research object.By combining field sampling and indoor analysis,the fertilization systems in grain fields(W-NPM,W-NP,W-P,W-M and W-CK)represented by wheat and grassland(A-NPM,A-P,W-CK)represented by alfalfa were analyzed.The main results are as follows:(1)Long-term application of organic fertilizer can improve soil aggregate and soil moisture characteristics,and soil water holding capacity and water supply capacity are significantly improved.The results showed that the application of organic fertilizer increased the content of soil macro-aggregates,which was more than 5mm in size.W-NPM was 9.98%higher than W-NP,and W-M was 5.28%higher than W-CK.The content of water-stable aggregates in alfalfa soil is 9.86%higher than that in wheat soil.The application of organic fertilizer can improve the geometric average diameter and average weight diameter of aggregates,reduce the destruction rate of soil aggregates and improve the stability of soil aggregates.The application of organic fertilizer can improve the water content and water holding capacity of soil.The field water holding capacity of W-M treatment was 3.26%higher than that of W-CK treatment,and that of A-NPM treatment was 4.81%higher than that of A-P treatment.The effect of organic fertilizer application on soil wilting coefficient is consistent with FC.The soil water availability under organic fertilizer application(NPM,M)is 16.20%and 7.48%higher than that under no fertilization treatment,and the water supply capacity of soil is enhanced under long-term organic fertilizer application.(2)Long-term application of organic manure can improve the chemical indexes of soil organic carbon,total nitrogen,total phosphorus and soil humus components,and change the stoichiometric characteristics of soil.The results showed that the application of organic fertilizer significantly improved the fixation and accumulation of organic carbon in soil.Compared with W-CK,the content of organic carbon in soil treated by W-NPM and W-M increased by 284%and 205%respectively.The TN content of W-M was 33.33%higher than that of W-CK,and that of A-NPM was 36.53%higher than that of A-P.The application of organic fertilizer increased the TN content of soil.The contents of Alkali-N and Olsen-P in W-NPM treatment were 23.77mg/kg and27.09mg/kg higher than those in W-NP treatment.The soil C:P ratio under organic fertilizer application is the highest,which is 24.92 and 29.55 higher than that under no fertilizer application.Long-term application of organic fertilizer significantly increased the carbon content of extractable humus,humic acid and fulvic acid in soil,and changed the Hu-Fu ratio in soil.(3)Long-term application of organic fertilizer increases the content of heavy metals and microplastics in soil,which may lead to the risk of soil pollution.The results showed that the application of organic fertilizer increased the accumulation of heavy metals in soil,increased the potential pollution risk of heavy metals in soil and reduced the environmental capacity of heavy metals in soil.Specifically,the contents of Cr,Cu,As,Cd,Pb and Mn in W-NPM treatment were 3.84%,54.15%,2.89%,9.09%,7.97%and 10.29%higher than those in W-NP treatment,while the contents of Ni,Zn and Fe in W-NPM treatment were lower than those in W-NP treatment.The single pollution index of Cr,Cu,As,Cd and Pb in A-NPM is higher than that in A-P treatment,and the order of Nemerow comprehensive pollution index is W-NPM>W-NP>W-P>W-CK,A-NPM>A-P>A-CK;The environmental capacity of heavy metals under the combined application of nitrogen and phosphorus organic fertilizers(W-NPM,A-NPM)is lower than that without fertilization(CK).Long-term application of organic manure increased microplastics abundance and average area of soil.The highest microplastics content of single application of organic manure(W-M)was 1686.67±1461.43 n/kg,and the combined application of N-P organic manure(W-NPM,A-NPM)had a larger area,with average areas of 0.233 mm~2 and 0.232 mm~2.To sum up,the application of organic fertilizer affects the physical and chemical properties and environmental effects of soil.Long-term application of organic fertilizer can increase the organic carbon content in soil,affect the humification process of soil,improve the stability of soil aggregates and soil moisture content,and help increase crop yield.At the same time,the long-term application of heavy metals and microplastics contained in organic fertilizers into the soil leads to the accumulation of heavy metals and microplastics in the soil,which increases the risk of heavy metal accumulation and microplastics pollution and reduces the environmental capacity of the soil.Therefore,the application of organic fertilizer needs strict time control measures to ensure soil quality and maintain the sustainable development of the ecosystem.