Effects Of Fertilization Methods On Soil Nutrients,Resistance Genes And Microbial Communities

With the increasing scale of livestock farming in China,a large amount of manure is generated during the farming process and needs to be addressed urgently.In the context of promoting green farming,although returning manure to the field can relieve some of the pressure of manure pollution,manure containing antibiotic resistance genes(ARGs)can cause potential harm to the environment by enriching in the soil.Therefore,in this study,we conducted a field experiment by planting a classic crop of cabbage to investigate the effects of different manure application patterns,such as conventional fertilizer(CF)and half-volume application of conventional fertilizer(T1),and at half-volume application of manure(T2)and half-volume application of chemical fertilizer(T3),on soil nutrients,antibiotics,resistance gene enrichment and microbial communities,and comprehensively assessed the effectiveness of manure return to the field by calculating the nutrient uptake and yield increase of cabbage.The following conclusions were obtained:(1)Manure return to the field caused an overall increase in soil and crop nutrients and heavy metal pollutants,and the half-volume fertilization model reduced soil N surplus by reducing N and P inputs,thereby improving the efficiency of soil N and P use by cabbage.The yield of cabbage was less affected by the amount of nitrogen applied.Application of swine farm manure enhanced total soil N.The T1 treatment enhanced the total soil N content up to1.96 times that of the CK treatment,but did not significantly enhance the total soil N content in the deeper layers.Conventional fertilizer application had lower N and P utilization because of the insignificant effect on nutrient carry-over from cabbage plants.Nitrate N leaching was significantly increased compared to other treatments.Ammonium N in surface and intermediate soils responded strongly to the fertilization effect,but the leaching effect of soil depth on ammonium N was significant in deeper soils.Application of swine farm manure could cause an increase in soil p H.The contents of heavy metals Zn,Cu,Cr,As,Cd and Pb in cabbage plants and soil after application of swine farm manure were in accordance with national standards.Considering the economic benefits,soil nutrient utilization and heavy metal pollution,fertilizer reduction is an effective measure for efficient resource utilization under the combined farming model.(2)After manure application,the residues of antibiotics increased among treatments and soil layers,mainly tetracyclines,and the residues of antibiotics showed an overall decreasing trend with increasing soil depth.16 ARGs and 3 MGEs were found in the surface,middle and deep soil layers,and the detection rate reached 100%.Among them,two ARGs,sul2 and erm B,had higher relative abundance in the three-layer soil profile;among the three MGEs,the ISCR1element was the MGE with the highest relative abundance of 10~8-10~9 copies/g.None of the antibiotics were detected in the cabbage samples,while 16 ARGs and three MGEs had higher relative abundance in the cabbage samples.Combining the accumulation of antibiotics and resistance genes in soil and crop,reasonable fertilization would not cause antibiotic enrichment migration into the food chain,but the risk of ARGs entering the food chain still needs attention.Manure return to the farm significantly increased the number of unique OTUs of soil bacteria,with larger increases in all three soil layers;Alpha-diversity and Beta-diversity analyses showed that fertilizer application increased soil microbial community diversity and concentrated in the topsoil and middle soil layers.The dominant phyla in the soil for all treatments were Actinobacteria,Aspergillus,and Green Campylobacter,and the application of manure from pig farms caused a decrease in the abundance of Acidobacteria in the soil.The dominant bacterial genera in the soil were MB-A2-108,Vicinamibacteraceae and RB41,among which the relative abundance of Vicinamibacteraceae was more affected by fertilizer application.(4)The changes in the abundance of ARGs in soil after manure return to the field were influenced by several factors,and the microorganisms,the phylum Synechococcus,explained30.6%of the changes in ARGs,the environmental factors,the heavy metal Zn,explained 21.6%of the changes in ARGs,p H was also the main influencing factor and explained 7.3%of the changes in ARGs,and the antibiotic SDMD explained reached 1.6%,indicating that the changes in ARGs were jointly influenced by environmental factors,heavy metals,antibiotics and microbial communities.