Effect Of Composted Sewage Sludge On Soil Quality Of Sandy Fluvo-aquic Soil

Non-hazardous composted sewage sludge(SW)applying to soil improvement play an important role in reducing the amount of urban sewage sludge and improving soil quality.The field and pot experiment were conducted in the Henan province sandy fluvo-aquic soil and the Chinese Academy of Agricultural Sciences under wheat-maize rotation system during 2013 to 2016 continuous field experiment.The experiment was designed as:applying chemical fertilizer(CK),non-hazardous composted sewage sludge 15t·hm-2(SW1),30t hm-2(SW2),45t hm-2(SW3).The experiment focused on the response of soil physical and chemical characteristics,soil fertility,soil enzyme activity and microbial diversity and community structure under the continuous application of SW to provide the theoretical support for the SW fertilizing soil.Main results for this study are as follows:1.The application of SW can significantly improve soil fertility and soil quality.Continuous application of SW can significantly increase soil moisture content,soil organic carbon(SOC),total nitrogen(TN),available phosphorus(AP)and nutrient content and reduce soil pH.SW treatments increased contents of SOC,TN and IFI by 121.2%?265.8%,93.1%?284.3%and 25.31%?55.51%,respectively,all of which increased significantly with the increase of SW application amount.At the same time,the SW did not significantly increase the content of soil heavy metals in the top 0-20cm soil layer,which ensured the environmental safety of SW to fertilize sandy fluvo-aquic soil.2.The applied amount of SW can significantly affect the content and distribution of soil active organic nitrogen.The application of SW increased the content of all active nitrogen components and promote their distribution.The increase of active organic nitrogen components by the SW application is in the following order:soil particulate organic nitrogen(PON)>light fraction organic nitrogen(LFON)>dissolved organic nitrogen(DON)>microbial biomass nitrogen(SMBN).SW promoted the distribution of particulate organic nitrogen(PON)and microbial biomass nitrogen(SMBN),and the PON/TN do not reach a significant increase.Compared with CK treatment,SMBN/TN increased 1.2-0.8-5.4-fold(P<0.05).SW reduced the distribution of LFON/TN by 17.3%-33.4%,and significantly decreased DON/TN distribution ratios by 38.5%?71.3%(P<0.05).It shows that particulate organic nitrogen and microbial nitrogen play an important role in the soil active organic nitrogen stocks in the process of improvement of soil fertility,while dissolved organic nitrogen is more easily absorbed and utilized and can replace some mineral nutrients for plants and microorganisms.Redundancy analysis(RDA)showed that the application of SW can improve soil environmental conditions,which promote the presence of organic compounds in the form of active organic components and enhance nutrient supply capacity.3.The variation characteristic of soil isotope 15N abundance can indicate the improvement of sandy fluvo-aquic soil quality with the SW treatments.Compared with CK,soil amended SW significantly reduced the abundance of soil 15N in the SW1,SW2 and SW3 treatments by 41.39%?47.71%and 59.92%,respectively(P<0.05).Both pathway analysis and RDA revealed the soil 15N abundance was significantly correlated with soil environmental conditions,soil nitrogen content and distribution which indicated the 815N abundance can be an indicator the improvement of soil quality with continuous application of SW.4.SW treatments significantly affected the soil extracellular enzyme activity.Compared with the CK treatment,soil invertase,?-1,4-glucosidase,?-1,4-N-acetylglucosaminidase,urease,?-1,4-N-acetylglucosaminidase,arylamidase and phosphatase increased by 64.6%,89.8%,202.6%,110.3%,357.8%,116.9%and 10.6%under the SW3 treatment(P<0.05).Compared CK,SW treatments significantly decreased soil phenoloxidase and peroxidase activity by 28.5%?35.4%and 31.1%?43.9%(P<0.05),respectively,but there is no significant difference among SW treatments.The correlation analysis showed that soil carbon and nitrogen enzyme activities were significantly related to the content and distribution of soil nitrogen components,indicating that soil nutrient cycling was regulated by multiple components of metabolic enzymes.Meanwhile,the correlations between soil nitrogen enzymes and soil 15N abundances were higher than with other active organic components,with correlations 0.995,respectively,indicating 15N abundances of soil were consistent with the changes of nitrogen enzyme activities and soil nitrogen components and can be used as an indicator of soil nitrogen nutrient cycling.Principal component analysis(PCA)and RDA confirmed that a positive correlation between soil enzyme activity and the applied amount of SW and environmental conditions,which in turn was conducive to the regulation of soil nutrient cycling.5.SW treatments had a significant effect on the soil bacteria diversity and community structure.SW treatments decreased the soil bacteria abundance(OTUs and Chaol)and diversity(shannon index),especially in the treatment of 45 t hm-2 SW(P<0.05),the Chao 1 and Shannon index decresed by 8.69%and 3.50%(P<0.05),respectively.Compared with the CK treatment,soil under the SW3 treatment had the highest abundance of Proteobacteria,Firmicutes,Alphaproteobacteria,Gammaproteobacteria,Bacilli,Bacteroidetes"_incertae_sedis,Acidimicrobiales,Xanthomonadales,Rhodospirillales,Bacillales with abundance increased by 27.30%,100.07%,27.52%,81.53%,106.94%,108.45%,44.40%,80.25%and 93.06%(P<0.05),respectively.While,the CK treatment had most amount of Actinobacteria,Acidobacteria,Candidatus Saccharibacteria and Verrucomicrobia,with 29.93%,12.22%,1.20%and 1.38%,respectively.Based on the analysis of differences in species composition between treatment sites and the RDA,it can be found that high amount of SW treatments change species composition into the structure dominated with nutrient cycle related species and promote nutrient cycling and energy metabolism-related gene abundance.Meanwhile,the improvement of soil environmental conditions and supplement of soil nutrition were the indirect inducers of change in the bacterial community structure and gene expression,especial the soil environmental factors DOC,DON and soil nutrient supply.In summary,under the condition of no environmental risk for land use of SW,applying SW can significantly inprove soil environmental conditions,increase soil nutrient supply capacity and soil carbon and nitrogen stocks.The improvement of soil quality in soil sandy fluvo-aquic soil is significant,especially with 45 t hm-2 SW.Further research on the metabolic characteristics and species composition of soil bacteria can confirm that SW treatments change soil microbial characteristics,promote the composition of microbial community dominating with nutrient cycle related species.This is of great significance to the SW fertilize sandy fluvo-aquic soil.