Effects Of Different Biochar Materials On Nitrogen Gaseous Loss In Alternate Wetting And Drying Irrigation Paddy Field

Alternate wetting and drying paddy field is one of the most typical water-saving/stable yield paddy ecosystem,the N uptake into significant impact on the global nitrogen cycle.However,the frequent dry-wet alternating process makes the nitrogen cycling characteristics more complex and nitrogen loss more obvious.Biochar has become an important means to improve agricultural soil fertility and reduce nitrogen loss,especially nitrogen gas loss,due to its great role in improving carbon and nitrogen cycling,reducing nitrogen loss and carbon sequestration in agricultural ecosystems,as well as its wide material sources and broad industrial development prospects.However,the physicochemical properties of biochar were significantly different with different material sources,and their potential for nitrogen reduction and emission control was even more different.Especially under dry/wet alternate irrigation with frequent changes of soil oxidation and reduction,the nitrogen loss cycle of active nitrogen state in paddy field changed significantly,and the nitrogen fixation emission reduction characteristics of different types of biochar were not clear.Therefore,in this study,three typical biochar of straw materials,husk materials and wood materials were applied to alternate dry-wet paddy fields,and the effects of biochar of different materials on NH₄⁺-N concentration,NH₃ volatilization,N₂O emission and warming potential of active nitrogen gas in surface water of paddy fields were investigated through two-year in-situ field experiments.In order to clarify the dry-wet alternate paddy NH₃ volatilization and N₂O emissions of different types of biochar application response law and mechanism of action,clear dry and wet alternate paddy NH₃ volatilization and N₂O emission rule with conventional flood irrigation paddy fields,mining of different types of biochar in dry-wet alternate paddy nitrogen emission reduction potential applications.The results show that:（1）Corn straw and wood sawdust biochar showed negative excitation effect on the NH₄⁺-N concentration in field water at different fertilization stages in the first year of carbon application,and increased the mean NH₄⁺-N concentration by 31.4%-54.8%and18.3%-35.6%,respectively.However,rice husk biochar reduced the mean concentration of NH₄⁺-N by 9.1%-30.4%.One year after biochar application,B_MS,B_RHand B_SD biochar reduced NH₄⁺-N mean concentration by 11.4%-22.5%,28.1%-61.9%and 23.7%-61.6%,respectively.The reduction effect of the three biochar on NH₄⁺-N concentration in field water was more obvious in the second year,and the rice husk biochar was more effective in controlling NH₄⁺-N concentration.（2）The total amount of NH₃ volatilization in the whole growth period under different treatments ranged from 8.97 to 17.84kg?hm^-2（2020）and 7.53 to 15.19kg?hm^-2（2021）.In the first season,the liming effect of B_MS and B_SD biochar was obvious,and the NH₃ volatilization accumulation was increased by 11.43～41.1%and 9.19～11.1%,respectively,while the B_RHbiochar was decreased by 14.88～21.71%.After field natural aging in 2021,no matter what biochar was added,the ammonia volatilization emissions showed inhibition effect in each fertilization period,and B_RH had the best effect,reducing the NH₃ volatilization accumulation by 22.49 to 38.46%.（3）Total nitrous oxide emissions under different treatments were 92.0～599.0 g?hm^-2（2020）and 138.0～610.7 g?hm^-2（2021）during the whole growth period.Compared with I_CF,the total N₂O emission under I_AWDincreased significantly by 133.21%（2020）and 114.64%（2021）.Biochar with different materials can control N₂O emission,and B_MS biochar with the highest p H value can control N₂O emission in paddy field.At the same time,the global warming potential（GWP）of active nitrogen gas increased by nearly 70%compared with conventional flood irrigation.No matter which irrigation method,biochar could effectively inhibit GWP,and the inhibition effect lasted for at least 2 seasons in paddy fields in cold northern regions.（4）In the first year of biochar application,B_SD and B_MStreatments reduced the nitrogen accumulation in rice shoot by 10.38%and 14.81%,leading to a slight yield reduction,while B_RH treatment increased the nitrogen accumulation and increased the yield.In 2021,B_MS,B_RHand B_SD treatments increased yield by 3.93%,10.30%and 7.58%,respectively,compared with those without biochar,mainly because biochar supplementation significantly increased the number of effective panicles and grains per panicle.With the aging of biochar,alkalinity gradually decreased and adsorption capacity gradually increased,and the biochar application had a positive effect on rice yield in the second year,especially the rice husk biochar,which had the potential to promote the increase of rice yield in alternate dry and wet fields.In conclusion,increased application of 20 t?hm^-2biochar in paddy fields under I_AWDshowed a long-term positive effect after the negative excitation effect in the first year,which could not only save irrigation water resources,effectively control NH₃ volatilization and N₂O emission,but also improve plant nitrogen uptake and rice yield.At the same time,the warming risk and environmental cost caused by reactive nitrogen gas can be alleviated.Based on the weight assessment based on the game theory,the comprehensive effect of B_RHbiochar under I_AWD is the best,which provides a new way to achieve green and high yield rice,reduce the consumption of water and nitrogen resources and environmental cost of rice production system.