Preparation Of Concentrated Biogas Slurry Formula Fertilizer And Its Effect On The Growth Of Chinese Cabbage

Biogas engineering is an effective way to utilize livestock and poultry manure,but the treatment and utilization of fermentation by-product-biogas slurry has become a key factor limiting the further development of biogas engineering.In order to solve the problems of large yield,difficult transportation and low added value of biogas slurry,this experiment used reverse osmosis membrane process to concentrate biogas slurry,and used the concentrated liquid after three times of concentration(volume of 12.50% of the influent liquid)as raw material to carry out different formulations.The application effect of concentrated biogas slurry formula fertilizer was determined by cabbage cultivation experiment.With no fertilizer(CK)and conventional application of chemical fertilizer(HF)as control,the treatment group set up different concentrated biogas slurry formulations: concentrated biogas slurry(P1),concentrated biogas slurry + magnesium sulfate(P2),concentrated biogas slurry + boric acid(P3),concentrated biogas slurry + humic acid(P4),Concentrated biogas slurry + chelated iron(P5),concentrated biogas slurry + magnesium sulfate + boric acid + humic acid + chelated iron(P6).The effects of different concentrated biogas slurry formula fertilizers on the growth and soil properties of Chinese cabbage were studied,and the best concentrated biogas slurry formula fertilizer was selected to provide theoretical basis and data support for the resource utilization of biogas slurry.The main results are as follows:(1)Membrane concentration of biogas slurry was carried out.It was found that the contents of total nitrogen,total phosphorus,total potassium,nitrate nitrogen,ammonium nitrogen,organic matter,calcium ion,magnesium ion and trace elements in biogas slurry increased with the decrease of the volume of concentrated solution.The content of heavy metals meets the limit requirements of toxic and harmful substances in fertilizers(GB 38400-2019).The nutrient content of the concentrated biogas slurry with a volume of 12.50% of the influent stock solution was the highest,and the contents of total nitrogen,total phosphorus,total potassium and organic matter were significantly increased by 166.90%,183.61%,94.21% and 484.82%,respectively,which could be used as raw materials for formulation.(2)The results of Chinese cabbage cultivation experiment showed that compared with chemical fertilizer,the fresh weight of Chinese cabbage with concentrated biogas slurry formula fertilizer increased by 1.57%-9.69%;the contents of soluble sugar,soluble protein and vitamin C increased by 4.55%-19.70%,3.95%-11.30% and 6.00%-15.84%,respectively,and the nitrate content decreased by 17.07%-25.92%.The contents of nitrogen,phosphorus and potassium increased by 5.40%-23.33%,2.83%-21.42% and 3.86%-22.02%,respectively.The activity of antioxidant enzymes and the content of medium and trace elements in Chinese cabbage were improved to varying degrees.(3)The application of concentrated biogas slurry formula fertilizer could increase soil total nitrogen and organic matter content,which were significantly increased by 14.13%-30.43% and3.50%-9.31%,respectively,compared with chemical fertilizer.The biogas slurry formula fertilizer can transform the nutrient elements in the soil into forms that are more easily absorbed by crops,thereby increasing the content of available phosphorus,available potassium,watersoluble calcium,water-soluble magnesium and available trace elements in the soil.Compared with chemical fertilizer,it significantly increased the activities of soil urease,sucrase,catalase and alkaline phosphatase,significantly improved soil fertility,and alleviated soil acidification.(4)Compared with the treatment of only applying concentrated biogas slurry(P1),the treatment of adding additional nutrients in concentrated biogas slurry(P2,P3,P4,P5,P6)can improve the yield,quality,enzyme activity,mineral element content and soil nutrient,enzyme activity,water-soluble calcium and magnesium and available trace element content of Chinese cabbage to varying degrees.Among them,the treatment of adding four substances in concentrated biogas slurry(P6)significantly increased the yield of Chinese cabbage by 4.76 %-7.99 % compared with the other biogas slurry treatments.Through principal component analysis,the application effect of different concentrated biogas slurry formula fertilizers was ranked as follows : P6 > P4 > P2 > P5 > P3 > P1 > HF > CK.(5)The contents of heavy metals in Chinese cabbage and soil applied with concentrated biogas slurry formula fertilizer met the ’ national food safety standard food pollutant limit ’(GB2762-2022)and ’ soil environmental quality agricultural land soil pollution risk control standard’(GB 15618-2018),respectively.On the whole,the treatment of adding magnesium sulfate,boric acid,humic acid and chelating iron to the concentrated biogas slurry(P6)can optimize the growth effect and soil improvement effect of Chinese cabbage within the controllable range of environmental safety risks.