Research On The Environmental Effects Of Increased Application Of Organic Fertilizer In The Coastal Peri-urban Area

Peri-urban area as an important border areas of cities and villages,the food supply of urban population and livestock and poultry dung plays an important role in biological waste treatment,such as application of organic fertilizer made of livestock and poultry dung,which can improve soil physical and chemical properties,increase soil fertility and improve the quality of agricultural products and so on,but heavy metals and antibiotic resistance genes in organic fertilizer would be into the soil in the process of a large number of consecutive applying,resulting in certain environmental risks,the environmental effect of organic fertilizer increased applying would be taken more seriously.In this research,Yinjiang Town,Haishu District,Ningbo City,Zhejiang Province,a typical peri-urban area in China,was taken as the research site to explore the effects of continuous application of pig manure instead of chemical fertilizer on typical heavy metals Cu and Zn,typical antibiotic resistance genes(tet A,sul1,sul2)and int I1 under different cropping systems(rice and wheat rotation and continuous cropping of vegetables).The influence of the accumulation and migration of typical heavy metal Cu,Zn and typical antibiotic resistance genes(tet A,sul1 and sul2)and int I1 under different fertilization way(no fertilizer(CK),50% and 100%chemical fertilizer(CF)and pig manure instead of fertiliser processing(M50 and M100 approximately))of rice and wheat rotation and continuous cropping of vegetablewere studied in real-world conditions with field lysimeter system.The potential effects of soil salinization on the environmental effects of organic fertilizer application were preliminarily discussed by pot experiment in the laboratory.The main research results are as follows:1.In the rice-wheat rotation system,the application of organic fertilizer instead of chemical fertilizer promoted crop growth,improved soil physical and chemical properties,and improved soil fertility.Compared with chemical fertilizer,application of organic fertilizer significantly increased aboveground biomass of wheat,and soil p H,electrical conductivity,soil TN,TP,SOM contents and CEC.Increased organic fertilizer not only led to a lot of soil Cu,Zn accumulated and have a significant impact on the soil Cu and Zn speciation distribution,organic speciation Cu and iron and manganese oxides combined speciation Zn was accounted highest proportion in organic manure treatment,the soil Cu,Zn residue speciation content was being reduced,the availability of Cu and Zn was increased causing the grain Cu and zinc content was increased significantly.The increased application of organic fertilizer resulted in the accumulation of soil Cu and Zn in the surface and subsurface layers.The increased application of organic fertilizer increased the risk of soil Cu longitudinal migration,while the soil Zn mainly accumulated in the surface layer(0-20cm).Organic fertilizer increased application also increased the risk of antibiotic resistance genes migration in soil profile,promoted the target gene(int1,tet A,sul1 and sul2)accumulation within the soil profile,and applying fertilizer was also significantly increased the sulfa resistance genes(sul1 and sul2)abundance,and little influence on the tet A and int I1.2.In the continuous cropping system of vegetables,both organic fertilizer and chemical fertilizer treatment significantly improved the soil electrical conductivity.The increased application of organic manure also caused a large amount of Cu and Zn accumulation in the soil.The increased application of organic manure also caused a change of Cu and Zn speciation distribution in the soil.The speciation distribution pattern of Cu was changed but the distribution pattern of Zn was not changed,and the proportion of residual Cu was significantly reduced.Increasing application of pig manure organic fertilizer promoted the migration of Cu and Zn in soil profile,and increased the relative abundance of resistance genes in soil profile.Compared with rice-wheat rotation system,the accumulation and migration of Cu,Zn and resistance genes in soil were more likely to be caused by the application of organic fertilizer in continuous cropping system,and the risk of excessive nitrogen,phosphorus and soil salinization might also be caused.3.The increase of soil salinity had significant effects on plant growth,migration and transformation of soil Cu and Zn,and abundance of soil resistance genes.Low soil salinity promote plant growth and high salinity can inhibit the growth of plants,soil salinity have impact on plants absorbing nutrient elements,synthesis of photosynthetic pigment,promote soil Cu and Zn from residue speciation to the exchangeable speciation transformation,and affected the relative abundance of the resistance genes,the relative abundance of sul1 and tet A significantly reduced,but relative abundance of int1 and sul2 significantly increased with the increase of soil salinity.In conclusion,the application of organic fertilizer instead of chemical fertilizer can cause the risk of Cu,Zn and ARGs in rice-wheat rotation system and vegetable continuous cropping system.The increase of soil salinity will further improve the bioavailability of Cu and Zn and affect the abundance of resistance genes.This research provides empirical evidence for the continuous application of organic fertilizer instead of chemical fertilizer,and it is necessary to strengthen the risk prevention and control of heavy metals and resistance genes in the agricultural practice of increasing the application of organic fertilizer in the coastal peri-urban area.