Effects Of Aging Of Yak Manure Biochar On Nitrogen Loss In Farmland Soils Of Napahai Plateau Wetland

Biochar as a new type of adsorbent has a good prospect in soil improvement in recent years.The application of biochar can not only make effectively of the biomass,but also adsorb the pollutants from the environment.With the increasing use of biochar,biochar aging problem has also become an important hot topic for researchers.Based on the Napahai Plateau wetland,this thesis studied the effects of pyrolysis temperature on the physicochemical properties of yak dung biochars,and explored the adsorption and mechanism of ammonia-nitrogen(AN).Different aging methods(Freeze-thaw Cycles Physical,Biological,Chemical aging)were used to understand the physicochemical properties of yak dung biochars after aged,and adsorption batch experiments were conducted to investigate AN adsorption process of different aging yak dung biochars at different pyrolysis temperature.Finally,the effect of different input of yak dang biochars on soil leaching solution and its mechanism of inhibiting soil nitrogen loss were studied by indoor soil column simulation experiment.Main results were the following:1.Yak dung biochar under the high temperature and hypoxia conditions pyrolysis has the following characteristics:(1)The surface with a negative charge;(2)The surface is rich in oxygen-containing functional groups(-OH,-COOR,C=C,C=O etc.);(3)The surface is rough,and its pores were developed,having the basis of adsorption NH4+.As the pyrolysis temperature increased,the yield,cation exchange capacity(CEC),Zeta potential,element content(C,N,O,H)and surface functional groups(C=0,COOR,C-OH)of biochars were decreased,while the alkaline,specific surface area,pore volume/pore size of biochars were increased.These physical and chemical properties affected the adsorption of ammonia nitrogen directly,and the CEC,BET,surface acid functional groups were the main factors affecting its adsorption of NH4+ in solution.When the concentration of ammonia nitrogen was 20 mg·L-1 in the solution,the removal rates of ammonia nitrogen in these three pyrolysis temperatures were BC450(55.8%)>BC300(51.6%)>BC600(41.1%).Collectively,the BC450 has the best removal rate of AN.2.The adsorption of ammonia nitrogen on the biochars has the heterogeneous adsorption of the multi-molecular layer and monolayer adsorption.The adsorption behavior is mainly chemical adsorption,accompanied by physical adsorption.The physical aging does not change the adsorption mechanism of biochars to ammonia nitrogen.3.The physical,biological aging and H2O2 oxidation have an impact on its own physical and chemical properties.The physical and chemical properties of the changes after biochar aging were as follows:(1)C content decreased,O content increased,and C/O decreased;(2)CEC significantly increased,pH and Zeta potential decreased significantly,for example,the CEC of BBC300,BBC450 and BBC600 significantly increased by 4.2 times,4.6 times and 2.3 times respectively;(3)The COOR functional groups increased significantly,and the specific surface area of PBC and BBC were significantly increased.However,the effects of different aging methods on the physicochemical properties of biochar are different.The CEC,acidic functional groups,specific surface area and pH value of biochar were the key factors affecting their adsorption of ammonia nitrogen.The removal rate of ammonia nitrogen in aged carbon was:biological aging>physical aging>H2O2 oxidation.4、Input of biochar into soil can be effective reduced nitrogen loss from farmland soils.The input quantity of biochar and cumulative leaching volume of soil leaching solution was in inverse ratio,the conductivity is proportional to the input,and the effect of the pH value of the leachate was not obvious.The surface of biochar was loose porous,biochar can absorb water and improve soil water holding capacity,then reduce soil nutrient loss;and the biochar surface with negative charge can adsorb AN.The biochar input ratio of 0.5%could effectively reduce the ammonia nitrogen,nitrogen and total nitrogen leaching loss,and the total nitrogen leaching loss and biochar inputwas ininverse ratio.Bio-aged biochar also can reduce the loss of nitrogen and total nitrogen in the soil,but its adsorption capacity was lower than BC450.Collectively,the application of yak dung biochar can effectively control the loss of nitrogen and improve the soilfertilizer.The results of this thesis provide an important basis for the effective utilization of biomass resources in Napahai plateau wetlands,supporting to protect the water environment and soil environment of Napahai wetland.