| In order to enhance the livestock manure agricultural application and to reduce the resulting potential soil environment heavy metal pollution risk, pig manure from a pig feeding plant was selected as raw material in the experiments, and mixed with corn stalk powder before composting in an aerobic reactor for90days. And the experiments were conducted to:(1) Study effects of pig manure compost agricultural application on the soybean planting and its environmental risk,(2) Evaluate the effect of different amounts (at0,2.5,5.0,7.5and10%in weight ratio) heavy metal passiving agent such as flyash, weathered coal and bentonite on the compost physicochemical properties during the swine manure composting,(3) Reveal the organic matter degradation during composting by using Fourier Transform Infrared Spectroscopy analysis method,(4) Investigate the Influence of passiving agent variety and proportion on the nutrient transformations during aerobic composting process,(5) explore the effects of flyash, weathered coal and bentonite on Cu and Zn chemical speciation and fractionation changing during aerobic composting,(6) detect the composts potential agricultural application on wheat cultivatation, and (7) to estimate the compost crop land application rate and the potential environment risk. The results showed that:1. After90days composting, the compost product was a potential organic fertilizer with plenty of NPK, and contained256.31mg Cu/kg and474.40mg Zn/kg but no other heavy metals such as Ni, Cd, Cr, Pb, Hg and As. The futher research conducted by the soybean planting pot experiments indicated that the application of the organic fertilizers had significant effect on the growth and yield of soybean within10%compost application rate, and increased the Zn content in the seeds of soybean. Rational application rate of swine compost in Yongshou zinc lack soil was90.28t/(hm2.a) and can be used for20years. The further pollution index and geoaccumulation index evaluation indicated that it would not cause soil environmental risk with the rational application rate of the compost in5%. The study implicated that the high Znic contaminated swine manure exhibit a potential agricultural application valve.2. The results showed that the pile temperature of all the treatments could rise to nearly70℃quickly and maintained above55℃more than a week. The moisture content gradually reduced with the composting time extension and was around30%after90days composting for all the treatments. Adding fly ash would present a strong alkaline composting environment, while adding the bentonite could significantly increase the compost water soluble salinities and the increasing were significant correlated with the amount of bentonite. The Potherb mustard seeds germination rate reached90%after90days composting in the control and weathered coal adding treatment, and the germination index were above1.0finally. While for the bentonite and flyash added treatments, after90days composting the germination index were lower than0.5except2.5%and5.0%treatments. The results implicated that add passive agents had no notable effect on compost temperature and moisture content. pH, EC and Potherb mustard roots growth were strongly influenced by the variety and adding proportion of the passive agents, although the Cu and Zn could be stabilized by adding the passive agents during the composting. The passive agent selection and dosage control should be considered in the pig manure aerobic composting process.3. The Fourier Transform Infrared Spectroscopy analysis showed that the organic matter decomposition would be continued for more than60days during the composting process. Addtion of flyash, weathered coal and bentonite had no effect on the compost raw material decomposition. During the composting, the peaks of polysaccharides at1640cm-1and1160cm-1declined, and the peaks of aromatic cylces at1460and1546cm-1, and the asymmetric stretching vibration peaks of Si-O-Si were increased. The peak of C-H vibration in methylene at2853cm-1and C=O stretching in aldehyde, acetone and carboxylic acid at1740cm-1, could be used to evaluate the decomposition of organic matter of compost. The final compost products were better than the compost product quality control standards in China, and these compost products could be used as organic fertilizer or soil amendments.4. Addition of fly ash, weathered coal and bentonite, lead the C/N ratio decrease according to composting time, whereas total N showed an opposite trend for all treatments except10%flyash was amended. NH4-N concentration increased during the first several weeks and later rapidly decreased as composting progressed. At the end of composting, only small amounts of NH4-N were detected. There was no significant loss of NH4-N during the thermophilic phase by ash amendment. While, addition of fly ash also inhibited the nitrification process as indicated by the lower soluble NO3-N contents in ash-amended swine manure composts but had no effect on TP increasing. While, the NO3-N concentration in the weathered coal and bentonite addition treatments, remained very low for the first several weeks, and followed by a steady increase. For the bentonite-adding treatment, the final NO3-N contents were1.09,1.04,1.01,0.94,0.87g/kg, respectively. Compared with the control, no significant loss of nitrogen was found with bentonite-added treatments.With the prolonging of composting time, fly ash and bentonite-adding could accelerate organic matter reduction slightly. For example, from the control to10%bentonite treatment, the organic matter decreased by21.33%,21.97%,23.52%,26.56%, and28.19%, respectively for the bentonite-adding treatments. Total P content showed an increasing trend with extended composting time for all the treatments.5. The total Cu and Zn concentration in compost piles were concentrated during the composting process, while the percentages of DTPA extractable Zn and Cu in compost piles were decreased. Adding5%fly ash,10%weathered coal, and10%bentonite in the compost raw material would reduce DTPA-Cu significantly, while the addition of5%fly ash,2.5%weathered coal, and10%bentonite10%weathered coal would reduce DTPA-Zn remarkably. The Sposito’s chemical speciation analysis showed that the fractionation were in the order of residue＞sulfide＞organic bound＞organic complexed or carbonate＞exchangeable and soluble form for Cu, and residue＞organic complexed or carbonate＞organic bound＞exchangeable and soluble form for Zn, respectively.6. Compared with control, adding of weathered coal treatments had no significant effect on the wheat seedling survival rate, while the wheat seedling survival rate was remarkably affected wiht the bentonite addition amount increase. Addtion of2.5%and5.9%fly ash had lower effect on wheat seedling growth but the fly ash addion above7.5%and10%influenced the wheat seedling growth significantly. The Cu and Zn accumulation were reduced in the wheat sedling growth periods with the fly ash, weathered coal or bentonite addition, but the effects were different among the heavy metal paasiving reagent types. Later research was expected to extend the crop planting time and expand the planting species of the crops.7. The compost application rate could be estimated by using the nitrogen amount demaonded during the crop growth periods. In this study, except the compost of10%fly ash treatment, other compost sould be application in rate of10.83～22.03t/(hm2.a). And it would no heavy metal environmental risk occurr in the application rate recommended in many years’ applications in crop cultivation. If the organic fertilizer farmland application rate was estimated by considering the biological toxicity of heavy metals, the application amount would be excessive according to the nitrogen and phorphrous plant needed in growth, and it would be easy to cause the risk of soil secondary salinization. In the actual compost agricultural application experience, the further research should be carried out in the long-term field location test, and the balance of the increasing agricultural products and the influence on the quality of soil environment shoule be comprehensive investigated. |
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