The Effect Of Biochar On N₂O Emission From Calcareous Arable Soil Under The Condition Of Facilitating Ammonia Oxidation

Nitrogen is an indispensable element for plant growth.Nitrous oxide(N₂O)is a potent greenhouse gas and contributes to ozone depletion.Agricultural activities are an important source of global N₂O emission,so arable soil becomes the main area of N₂O emission.Biochar is the product of high temperature pyrolysis of biomass materials in anoxic environment.The effect of biochar on N₂O emission from arable soil is a hot research topic at present.The effect of biochar on N₂O emission from arable soil is restricted by soil texture,biochar type and soil microorganisms.However,the effect and mechanism of rice husk-derived biochar on N₂O emission during the process of ammonia oxidation in calcareous arable soil in the semi-arid region of Loess Plateau are still unclear.Therefore,this study explored the effect of rice husk-derived biochar on N₂O emission from calcareous arable soil of Loess Plateau under the condition of facilitating nitrification(water-filled pore space(WFPS)being as 40%,50%,60%and 70%,and adding exogenous ammonium nitrogen).Moreover,the dynamic changes of soil pH value,electrical conductivity,inorganic nitrogen and dissolved organic carbon(DOC)contents during the incubation and the potential mechanisms were also determined.The study will provide a theoretical reference for the agricultural application of biochar in arable soils of Loess Plateau.Three biochar application rates(0%,2%and 5%;mass ratio)were set,and the indoor static soil incubation experiment was carried out.Results showed that:(1)The effect of rice husk-derived biochar on N₂O emission from calcareous arable soil was related to soil WFPS.When soil WFPS was 40%,50%and 60%,the rice husk-derived biochar inhibited N₂O emission,and the inhibition effect enhanced with the increase of biochar addition rate.The treatment of soil WFPS being as 50%and biochar addition rate being as 5%showed the lowest cumulative N₂O emission(430.93 ng N₂O-N/g dry soil),which was 62.65%lower than that of the control treatment(1153.82 ng N₂O-N/g dry soil).When soil WFPS was set as 40%,50%or 60%,the rice husk-derived biochar promoted soil nitrification,making NO₂^--N easily convert to NO₃^--N,thus reducing NO₂^--N accumulation and N₂O emission.(2)When soil WFPS was set as 70%,the rice husk-derived biochar promoted N₂O emission from calcareous arable soil,and 2%biochar addition showed relatively stronger promotion effect.Compared with the control,the cumulative N₂O emission of 2%biochar addition treatment(7287.13 ng N₂O-N/g dry soil)increased by 41.16%.The denitrification may occur in the incubation system at 70%WFPS,and the rice husk-derived biochar promoted N₂O emission.(3)When soil WFPS increased from 40%to 60%,the cumulative N₂O emission increased sharply,which indicated that the activity of ammonia oxidizing microorganisms could be stimulated at relatively high water content.(4)The regression analysis showed that N₂O emission rate was significantly positively correlated with NO₂^--N content under various soil moisture conditions.