Effects Of Nitrogen-reducing And Combined Inoculants On The Loss Of Active Nitrogen In Paddy Fields

After nitrogen fertilizer is applied to the soil,in addition to being absorbed by crops,it will also be lost to the environment in the form of active nitrogen.The loss of active nitrogen mainly includes NH₃volatilization,N₂O emission and NO₃^--N leaching.This will not only reduce the efficiency of nitrogen use,but also do harm to the environment.Reducing the amount of nitrogen fertilizer is an inevitable requirement for green agriculture,but at the same time it will bring about the risk of production reduction.This study uses the inoculation of N₂O-reducing bacteria with growth-promoting effects on fertilizers to try to reduce the effect of nitrogen on the environment while ensuring yield.N₂O reducing bacteria can directly or indirectly affect the community composition and abundance of N₂O reducing microorganisms,but the effect of inoculation with N₂O reducing bacteria on NH₃ volatilization and NO₃^--N leaching is still unclear,and there is still a lack of corresponding research in rice fields in lower Yangtze River Delta.Therefore,this thesis takes the rice fields in the Chuhe Basin of the Yangtze River as the research object.A total of two years of rice season experiments were carried out,and sets up 9treatments,namely reducing nitrogen by 20%+inoculating 6 kinds of N₂O reducing bacteria,100%N,80%N and 0%N.The NH_3,N₂O and nitrogen leaching solutions are collected by the closed intermittent air extraction method,the static dark box method,and the PVC pipe measurement method respectively.The main research results of the influence of bacterial fertilizer on NH₃volatilization,N₂O emission and NO₃^--N leaching are as follows:(1)After reducing the amount of nitrogen fertilizer by 20%,rice yield decreased by 11%and22%in 2019 and 2020,respectively.But after inoculation of N₂O reducing bacteria on the basis of 20%nitrogen reduction,the inoculated strains all had a certain degree of growth-promoting effect and rice yield in 2019 and 2020 increased by 11%-16%and 5%-26%respectively.The rice yield of TSA2S and NRCB002 strains both exceeded or were equivalent to 100%N treatment.(2)There is a positive correlation between the amount of nitrogen fertilizer and NH₃ emissions.After reducing the amount of nitrogen fertilizer by 20%,the cumulative amount of ammonia volatilization decreased by 44%and 17%respectively in 2019 and 2020;Inoculation with N₂O reducing bacteria has no significant effect on NH₃ volatilization in rice fields.The peak of NH₃ volatilization in rice fields mostly occurs within 3 days after fertilization,then it decreased rapidly,and NH₃ volatilization flux basically decreased to a low level after one week.NH₃ volatilization in rice fields was significantly and strongly correlated with the concentration of NH₄⁺-N in surface water,while the p H and soil temperature of field surface water had little correlation with NH₃ volatilization.(3)There is a positive correlation between the amount of nitrogen fertilizer and N₂O emissions;After reducing the amount of nitrogen fertilizer by 20%,cumulative N₂O emissions decreased by 59%and 81%respectively in 2019 and 2020.Inoculation of N₂O reducing bacteria promotes the N₂O reduction process to reduce N₂O emissions and four strains(N2,NRCB008,NRCB010,NRCB026)have good emission reduction effects,N₂O emissions decreased by 21%-55%and 89%-216%in 2019 and 2020 respectively.Moisture and fertilizer are the main factors affecting N₂O emissions.Most of the peak N₂O emission occurs about 10days after fertilization,and N₂O emission is prone to occur when the field water is dry and the soil moisture is still high.(4)Due to the adsorption of soil colloids,nitrogen leaching in paddy fields is dominated by NO₃^--N,and the amount of NH₄⁺-N leaching is less.The amount of nitrogen fertilizer and the amount of NO₃^--N leaching are positively correlated.After reducing the amount of nitrogen fertilizer by 20%,the amount of nitrate nitrogen leaching at the three different depths decreased significantly,and decreased by 17%-61%and 39%-49%in 2019 and 2020,respectively.Inoculation of some N₂O reducing bacteria promoted the denitrification process,thereby reducing the amount of NO₃^--N leaching.The trend is more obvious at 60cm and 90cm,of which NRCB002 Strain works best.NO₃^--N leaching is greatly affected by water,so it will promote the NO₃^--N leaching process under rainfall or irrigation.In summary,after reducing nitrogen by 20%,NH₃volatilization,N₂O emission and NO₃^--N leaching are reduced at the same time,but rice yield is reduced.After inoculating some N₂O reducing bacteria on the basis of reducing nitrogen by 20%,it not only further reduces N₂O emissions and the leaching of NO₃^--N,but also ensure the yield of rice.