Changes Of Argricultural Waste During Vermicomposting And Their Effects On Soil Properties And Crop Production

The low utilization rate and high continuous accumulation of agricultural waste cause serious resource-wasting and environmental problems,and gradually attract more and more attention by the society.Converted waste into organic soil amendments with composting technology constitutes an effective waste-management strategy.However,widely spreading of traditional composting is hindered for some restricting factors such as nutrient,effective microbial community,composting duration,appearance and transportation,etc.Vermicomposting is a low-cost technique to transform organic waste into biodegraded and stabilized by-products(vermicompost)through the combined action of earthworms and microorganisms.Compared with composting where the microorganisms degrade the organic waste,the interactions between earthworms and microorganisms strengthen the mineralization and humification of the organic matters.So that vermicompost is superior to compost in terms of nutrient and humic properties.Therefore,Numerous studies have focused on vermicompost amendment promoting soil quality,by improving soil structure,increasing plant available nutrients,and promoting microbial activity,thereby increasing plant production.In this paper,pilot-scale vermicomposting of the typical agricultural waste(cow manure,pig manure and mushroom residue)was conducted.Dynamic changes of biotic and abiotic properties of waste were under monitoring during vermicomposting.Besides,environmental risk assessment was carried out from the heavy metals composition and human pathogen of by-product.Furthermore,to evaluate the effect of vermicompost on soil chemical andbiological properties as well as crop yield and quality,the field experiment that utilization of vermicompost as soil organic amendment was set up.Finally,to investigate the synergistic effects between vermicompost and plant growth-promoting rhizobacteria(PGPR),a field experiment with a fully factorial design was conducted using three levels of vermicompost with and without PGPR.Detailed results were as follows:1.Based on vermicomposting experiment,for chemical properties,earthworm activities could accelerate mineralization and humification of organic matters,thus organic carbon was decreased and total nitrogen,total phosphorous and total potassic were increased,which led to low C/N ratio.Effect of earthworms on dissolved organic carbon and nitrogen(DOC and DON)involved two phases.Generation of micromolecular organic compounds could be facilitated and accumulating at initial stage of composting.As the composting process went on,dissolved organic matter was consumed by microbes to transform to inorganic chemical nutrients which could be readily absorbed by plants.Therefore,contents of DOC and DON decreased gradually as well as DOC/DON ratio.2.Based on vermicomposting experiment,for biotic properties,effect of earthworms on microorganisms also involved two phases.At initial stage,earthworm activities could promote microbial growth which led to higher content of microbial biomass carbon and nitrogen(MBC and MBN),as well as basal respiration(BR).As the available resources being consumed,BR decreased.While soil microbial biomass could maintain a relatively stable status due to mucus and excrement of earthworms during a certain period.On the contrary,earthworm activities inhibited fungal biomass at earlier stage while the contrary trend appeared at late stage of vermicomposting.Throughout the process,nematode abundance,especially a surge in the number of fugal-feeding nematode was inhibited by earthworms.3.Fractions of heavy metals and human pathogens in vermicompost were investigated,and we found that earthworms could strengthen the degradation of organic matter,which brought biological magnification and increased concentrations of heavy metals.Nonetheless,the availability of heavy metals extracted by DTPA significantly decreased.The shift from available to unavailable fractions of heavy metals was either due to earthworm bioaccumulation,as indicated by total heavy metal concentrations being higher in earthworm tissues,or due to the formation of stable metal-humus complexes as indicated by the promotion of humification.Meanwhile,earthworms activities appeared to be a critical factor leading to the rapid reduction of pathogens,and the current the number of fecal coliform and mortality rate of ascaris eggs of vermicompost and compost were below the threshold values formulated for compost by the China.4.As compared with traditional compost,application of vermicompost led to higher yield and better quality(improved contents of potassium,vitamin C,protein and glucose).Vermicompost increase soil available nutrients(NO3--N,available P,available K)in tomato seasons.Effects on soil biologicalproperties mainly reflected in soil microbial biomass,but not in soil basal respiration.Research based on MicroRespTM revealed that the effects of applied vermicompost and corresponding compost had little differences on soil microbial metabolism function in short term.While different types of composting material played a more significant role.Research on soil bacterial and fungal community based on T-RFLP analysis revealed that the effects of vermicomposton bacterial community appeared among CM and PM treatments,especially in tomato season.However,effects of vermicompost on fungal community had no marked trend in both crop seasons,only significantly differences found between fertilization treatments and control treatments in tomato seasons.5.Interactions between vermicompost and PGPR were investigated in the field.Our results demonstrated that applying PGPR alone had no effect on soil properties and crop performance.Vermicompost enhanced the beneficial effects of PGPR on both soil and crop,with the extent of promotion depending on the dose of vermicompost and crop types.In the presence of vermicompost,PGPR significantly reduced DOC and DON but increased MBC and MBN.PGPR also significantly increased the yield of tomato and spinach under the low dose of vermicompost,but only significantly increased tomato yield under the high dose of vermicompost.There were strongly synergistic effects between vermicompost and PGPR on crop quality,with crop nitrate concentration being significantly decreased,while the vitamin C in tomato and soluble protein in spinach was significantly increased.Our results revealed the high potential of integrating vermicompost and microbial agents to substitute for regular chemical fertilization practices.Totally,this paper focused on improvement utilization rate of agricultural waste and soil ecological system function,moreover,the relation between soil fauna and ecosystem service could be well revealed and abundant theoretical basis of organic waste utilization was provided.