Research On The Use Of Farmland Disposal Technology By Biogas Slurry And Soil Environmental Effects

Biogas project is one of the main technology for China's handling with wastes of animal husbandry, which's made an important contribution to the decontamination of wastes of animal husbandry breeding. Biogas slurry is a liquid from decomposition of methane fermentation in biogas project technology, rich in COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand) and SS (Suspended Substance), rich in nutrient such as total nitrogen, ammonia nitrogen and total phosphorus, which still can't reach breeding emission standards of the state. Most biogas slurry has no effective use, without economy and subsequent processing technology, biogas direct discharge has become one of the main water eutrophication sources, and one of the major bottleneck to agricultural non-point source pollution control.In order to solve the difficulty of biogas slurry disposal, in this paper, combining with field experiment, the pot experiment and soil column simulation experiment, we study the effect on crop growth, yield, quality and safety with biogas slurry's farmland disposal on vegetable land and leisure season farm land, explore the effect of the different biogas slurry disposal way on soil fertility and microbial flora, and make the evaluation on the environmental effect of soil disposal.These are all for providing theory basis for popularization and application of biogas farmland disposal technology. Preliminary results were shown as follows:1, Vegetables crop yield increased significantly with the biogas'watering disposal on vegetable land. Cabbage yield treated with biogas slurry and the chemical fertilizer has increased to 0.7%-20.7%, compared with the chemical fertilizer, and the most biogas slurry amount that can be disposed up to 300t/hm2; peper yield treated with biogas slurry and the chemical fertilizer has less than that treated with the chemical fertilizer, and peper yield treated with 2-3 time amount of the biogas slurry and the chemical fertilizer has equal yield to that treated with the chemical fertilizer, and its most biogas slurry amount that can be disposed up to 1350t/hm2.2, Biogas slurry treatment can increase the absorption of nutrients in cabbage, peper, increase nitrogen, phosphorus and potassium contents in plant and edible part, and significantly increase the vitamin C content of vegetables; Even in lots of application of biogas slurry, the equivalent of nitrogen is 2-3 times of the the chemical fertilizer's, also caused no nitrate accumulation in vegetables; After biogas slurry application, Cu content and As content in peper increase slightly,the Cu content in peper has increase by 4.2% and 8.5% than that of chemical fertilization application, Cu,Pb,Cr,Hg content in broccoliin treated with biogas slurry are higher than that treated with chemical fertilization, which are all below national standards; with the rice planting farmland's biogas slurry irrigation in leisure season, the harmful heavy metal content of rice has no significant increase.3, Biogas slurry with watering in vegetable farmland disposal can increase the content of organic matter, available nitrogen (N), phosphorus and potassium, rich in humic acid and so on.The more the biogas slurry amount is, the more the effect is.After the lots of biogas slurry application in vegetable land, the biogas slurry brings increased risk of secondary salinization with the soil electrical conductivity (EC) increasing; the soil columns simulation results show that, biogas slurry irrigation in leisure farm season can make use of the leisure farm land in winter to dispose, but also completely meet rice growth's demand of NPK for next season, irrigating field, the method of biogas slurry disposal, especially its interval irrigation has a great effect on the farming soil fertility.4, The quantity of microorganism (bacteria, fungi and actinomycetes) in biogas slurry treatment is much more than that in chemical fertilizers treatment. From the results of microbial diversity index (Shannon, Simpson and Pielou's index), the degree of dominance, richness, and evenness of soil microorganism in the treatment of biogas slurry application are better than that in the chemical fertilizer treatment.5, Compared with the whole fertilizer treatment, application of equal nitrogen biogas slurry treatment can greatly reduce the nitrate in shallow groundwater; phosphorus concentration in shallow groundwater increase sightly compared with whole fertilizer treatment, and the increment of the amount is small and within the framework of water quality national standards,which shows the feasibility of biogas farmland disposal; Furthermore, volatilized ammonia increases with the amount of biogas slurry application, and the volume into the atmosphere is below national standard for air quality.6, Experiments show that, biogas slurry disposal whether on vegetables, or in leisure farm irrigation season, has an increase trend of Pb and Cd, Cr, As, Hg contents in soil, just a season of biogas slurry disposal on soil will not lead heavy metal content to surpass the national standard of soil environmental quality of limited range.It's a long term to reseach for appropriate biogas slurry disposal amount and disposal cycle; irrigation disposal of biogas slurry can increase the Cu and Zn content in every level of soil, as essential elements for crops, in this experiment, we can use the biogas slurry for farmland disposal without considering the risk of the accumulation of Cu, Zn content.7, Considered the full use of the soil with the maximum biogas slurry farmland disposal, and avoid of such a risk that biogas slurry disposal amount may lead to pollutants concentration increasing in soil runoff and leakage, heavy metal, the recommended safe application of disposal biogas slurry volume is 900t/hm2, which equals to the reduction of emission N 530.6kg/hm2, P2O5 37.8kg/hm2, K2O 311.4kg/hm2, COD 900 kg/hm2.