The effect of organic material addition on vegetable soil nitrogen transformation and greenhouse gases emissions
In order to explore the soil nitrogen transformation rates and their responses to different organic materials for the vegetable soil to provide a scientific basis for the rational fertilization of the vegetable soil,the vegetable soil in the Erhai Lake basin was used as the research object to carry out incubation experiment at 25℃and 60%of water holding capacity for 15 days.A paired 15N tracing incubation trial combined with a nitrogen conversion rate calculation model was conducted to investigate the vegetable soil nitrogen transformation rates and their responses to addition of organic materials(straw,biochar and cow manure).The results showed that:(1)The contents of vegetable soil ammonium nitrogen and nitrate nitrogen contents showed a decreasing trend with the increasing of time,and they decreased after the addition of three organic materials.(2)The average soil gross mineralization rate,soil gross nitrification rate,NO3-consumption rate and NH4+fixation rate during the 5-day incubation period were-28.5,-3.93,1.52 and 11.9 mg·kg-1·d-1,respectively.The soil nitrogen mineralization rate and nitrification rate were negative,and thus the vegetable soil was dominated by microbial fixation of nitrogen.(3)The nitrogen mineralization rates increased after the addition of organic materials.Although the rates were also negative,only the effect of straw addition was significant.Straw addition also significantly reduced soil gross nitrification rate.However,the soil NH4+fixation rate increased after the addition of organic materials,especially after the addition of straw and biochar.(4)Straw addition significantly increased soil N2O and CO2 emissions,while biochar had a decreasing trend but had no significant effect,and cow manure also had no significant effect.For the vegetable soil in the Erhai Lake basin,the addition of organic matter with high carbon nitrogen ratio(C/N)could increase the nitrogen microbial fixation,but with the increase of time after organic matter input,the organic materials had a tendency to increase soil mineralization rate.The biochar reduced soil CO2 and N2O emissions,and increased the inorganic nitrogen content of vegetable soil to improve soil nitrogen supply capacity.Thus,scientific and optimal input of organic fertilizers with high C/N and chemical fertilizers in the Erhai Lake basin could guarantee the sustainable utilization of vegetable soils and might reduce greenhouse gases emissions.
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