Effects Of Biochar Application On Nitrogen Transformation Rates And N₂O Emission In Purple Soils

The annual nitrogen fertilizer application rate in China's farmland is as high as 30 million tons of pure nitrogen,accounting for about 1/3 of the total global consumption,while the efficiency of fertilizer utilization is about 30%.Low-level nitrogen fertilizer utilization rate not only causes lower economic benefits,but also leads to a series of ecological and environmental problems such as soil acidification,water eutrophication and greenhouse gas emissions.Biochar is a carbonaceous material produced by heating under high temperature and anoxic conditions.It is with a large C/N ratio,specific surface area and pore size,and can be used as a soil amendment to improve soil structure and fertility.Biochar as a soil amendment can change the soil properties closely related to nitrogen transformation,which may have an effect on soil nitrogen transformation process and N₂O emissions.Studies have shown that biochar can affect soil nitrogen cycling by affecting soil nitrification rate,increasing nitrogen use efficiency,and inhibiting N₂O emissions.This research separately studied on the net nitrogen transformation rate,gross nitrogen transformation rate,denitrification rate and N₂O emissions of typical acidic and calcareous purple soils under different biochar addition rates in the southwestern region by short-term aerobic,anaerobic and isotope tracing experiments.The main results are follows:?1?Biochar treatments promote the average net mineralization rate of acid purple soil,and biochar application inhibit the average net nitrification rate of acid and calcareous purple soil,the inhibitory effect on nitrification in acid purple soil is enhanced with the increase of application rate.Meanwhile,no obvious correlation was observed in calcareous purple soil.Compared with the control group,the cumulative N₂O emission of acid purple soil with 1%and 2%biochar addition rate was depressed.The accumulative emission of N₂O of calcareous purple soil with 5%and 10%biochar addition rate was stimulated.Biochar addition significantly increased N₂O emission,and its value was higher than that of the control in calcareous purple soil.In general,1%biochar and 2%biochar addition are the optimal rates for inhibiting nitrification and mitigate N₂O emissions in acidic purple soil.?2?The gross mineralization rate and nitrification rate of the calcareous purple soil were significantly higher than that of the control,and increased with the biochar addition rates.Biochar treatment significantly increased the average gross mineralization rate,gross immobilization rate and gross nitrification rate.The N₂O cumulative emissions under biochar treatments were significantly higher than that of the control.The N₂O cumulative emissions under CB₁?CB₂?CB₅?CB₁₀ treatments of calcareous purple soil increased by 12.3%,16.5%,34.6%and 36.6%,respectively.The contribution rate of N₂O production in nitrification process of calcareous purple is greater than 95%,which is the dominant process of N₂O production.The fraction of nitrified emitted as N₂O from nitrification of different biochar addition rate varies from 3.28%to 4.14%.?3?During anaerobic incubation,the N₂O emission rate under different biochar treatments was significantly higher than that of the control.The average denitrification rate and N₂O cumulative emission during the incubation after the biochar and nitrification inhibitor MHPP application were higher than the control.The application of biochar in anaerobic culture condition significantly increased the amount of soil denitrifying gaseous nitrogen loss.The 1%BC and 5%BC treatments increased by 14.0%and 22.9%compared with the control;under the combination with the nitrification inhibitor MHPP The cumulative total loss of denitrification of gaseous nitrogen in 1%BC and 5%BC increased by 15.1%and 29.5%compared with the control.The application of biochar and nitrification inhibitor MHPP promoted the denitrification rate of calcareous purple soil and increased the amount of gaseous nitrogen loss.