Study On The Control Of Nitrogen Loss During Composting Of Cyanobacteria And The Preliminary Application Of Cyanobacteria Composting In Zipeng Mountain Area

Cyanobacteria is the direct product of eutrophication of water body.It has the potential to be a fertilizer resource,because it is rich in nutrients such as nitrogen and phosphorus.The cyanobacteria can be converted into organic fertilizer through the composting process,and then applied back to the farmland,which can not only reduce the pollution load in the water,but also alleviate the agricultural non-point source pollution caused by the application of excessive chemical fertilizer in agricultural production.That is of far-reaching significance.However,aerobic compost can lose a lot of nitrogen in the form of NH₃,which not only reduces the quality of compost,but also causes air pollution.Therefore,reducing nitrogen loss in aerobic composting of cyanobacteria has become one of the key problems to be solved urgently.In order to explore a better way to control nitrogen loss in the process of aerobic composting of cyanobacteria,corresponding field aerobic composting experiments were conducted,using cyanobacteria as the raw material,mushroom residues and rice hulls as conditioners.Then,the compost products were applied to maize planting experiment in the field to explore the effects of compost products replacing chemical fertilizer on maize quality and nutrient loss in field.This study is expected to provide theoretical support for the engineering and marketing of cyanobacteria composting.The main research results of this paper are as follows:（1）Corresponding field aerobic composting experiments were conducted,using cyanobacteria as the raw material,mushroom residues and rice hulls as conditioners,and four mixtures of magnesium salts and phosphates(i.e.,（Mg（OH）₂+H₃PO₄（MP）,Mg（OH）₂+KH₂PO₄（MKP）,Mg SO₄+H₃PO₄（MSP）,Mg SO₄+KH₂PO₄（MSKP））as additives.Compared to the control group,the emission of NH₃ in MP,MKP,MSP,and MSKP treatments was reduced by 48.98%,45.95%,76.91%,and 38.65%,respectively.Meanwhile,the proportion of total N（TN）increased by 66.31%,54.42%,30.15%,and 46.50%,respectively.The fixation rates of N in the four treatments were 44.26%,41.36%,71.09%,and 33.54%,respectively.Results of XRD analysis confirmed the presence of struvite（Mg NH₄PO₄·6H₂O）in the compost product in all treatments.After 42 days of composting,all the treatments（except the MSP-treated group）reached maturity and met the criterion of NY525-2012.Although the fixation rate of N in the MKP treatment was slightly lower than that in the MP treatment,the degradation rate of microcystin and total nutrient content in the MKP treatment were both relatively high.Such results indicated that the addition of MKP might be the best method for controlling N loss in cyanobacteria composting.（2）Corresponding field aerobic composting experiments were conducted,using cyanobacteria as the raw material,mushroom residues,rice hulls as conditioners and Mg（OH）₂+KH₂PO₄ as the nitrogen fixation agent,and four different proportions of biochar（i.e.,5%（B5）,10%（B10）,15%（B15）,20%（B20））as additives.Compared to the control group,the emission of NH₃ in B5,B10,B15,and B20 treatments was reduced by32.54%,39.12%,36.59%,and 33.29%,respectively.Meanwhile,the proportion of total N（TN）increased by 76.39%,92.18%,90.04%,and 80.45%,respectively.The fixation rates of N in the four treatments were 26.53%,34.43%,30.54%,and 27.95%,respectively.After 42days of composting,all the treatments reached maturity and met the criterion of NY525-2012.In general,the fixation rate of N,the degradation rate of microcystin and total nutrient content in the B10 treatment were all higher than any other group.Such results indicated that the addition of 10%biochar on the basis of MKP treatment might get better benefits in cyanobacteria composting.（3）Three treatments of the compost product（DF）,the common fertilizer（FHF）and the non-fertilizer（CK）were set up in the field maize planting experiment,the results show that,the FHF treatment and the DF treatment have different advantages in different growth indicators of maize,but both of them have achieved significant improvement compared with the CK treatment.Compared with the FHF treatment,the contents of N,P and K in maize grains under the DF treatment were increased by 4.94%,2.86%and 10.44%,respectively,and the contents of N and K in maize stalks were increased by 25.37%and 18.33%,respectively.Meanwhile,the contents of crude fat,crude protein and crude starch of maize in the DF treatment respectively increased by 4.40%,8.34%and 2.66%,but the yield decreased by 3.62%compared with the FHF treatment.And the contents of soil organic matter,total nitrogen,total phosphorus and total potassium under the DF treatment respectively increased by 7.24%,7.5%,1.33%and 14.72%compared with the FHF treatment.The last,TN loss and TK loss under the DF treatment were respectively reduced by 33.33%and 22.74%,but TP loss was increased by 1.89%compared with the FHF treatment.In conclusion,although the yield of the DF treatment was slightly lower than that of the FHF treatment,the quality of maize was improved and the nutrient loss of farmland was reduced to a certain extent.Therefore,cyanobacteria compost has the potential to replace the common chemical fertilizer on the market.