Soil Respiration and N Losses from Greenhouse Cucumber under Mulched Drip Irrigation as Affected by Reduced N Fertilizer Coupled with Biochar Incorporation
To reduce the negative effects of excessive nitrogen application in greenhouse vegetables and to clarify the characteristics of soil respiration and nitrogen gaseous emission of cucumber under mulched drip irrigation in greenhouse under reduced nitrogen and biochar application conditions.Four treatments were set up:no mulching and no biochar application(CK),mulching(M),mulching with biochar application(MB),and mulching with biochar application and nitrogen reduction(MBN80%).The effects of the reduced nitrogen application and biochar addition treatment on cucumber yield,water consumption,soil nutrient dynamics,soil respiration,N2O emissions,and ammonia volatilization were explored.The results showed that compared to the CK treatment,the M treatment reduced water consumption by 20.95%throughout the entire cucumber growth period,increased water use efficiency by 41.03%,decreased ammonium nitrogen content in the top 0‒20 cm soil layer by 48.12%,and reduced ammonia volatilization by 32.35%,N2O emissions by 14.34%,and CO2 emissions by 12.68%(p<0.05).After biochar addition,compared to the CK treatment,the MB treatment reduced water consumption by 28.37%,increased water use efficiency by 55.60%,decreased ammonium nitrogen content in the topsoil by 30.0%,increased nitrate nitrogen content by 12.37%,increased soil organic matter content by 56.28%,decreased ammonia volatilization by 36.68%,and reduced N2O emissions by 18.64%,but significantly increased CO2 emissions by 4.66%(p<0.05).Compared to the M treatment,the MB treatment further increased the content of soil organic matter and ammonium nitrogen in the topsoil,reduced ammonia volatilization,but promoted CO2 emissions.After reducing nitrogen application by 20%in the MB treatment,compared to the CK treatment,the MBN80%treatment increased yield by 25.47%,reduced water consumption by 32.43%,increased water productivity by 72.67%,decreased ammonium nitrogen content in the topsoil by 56.33%,increased soil organic matter content by 51.72%,reduced ammonia volatilization by 40.48%,and reduced N2O emissions by 20.79%(p<0.05).The global warming potential(global warming potential,GWP)and active nitrogen emissions during the entire growth period were 13.57 t·CO2-eq·hm-2 and 6.54 kg·hm-2,respectively,in the CK treatment.The M treatment significantly reduced GWP(by 14.15%)and active nitrogen emissions(by 27.37%).Adding biochar on the basis of the M treatment further reduced active nitrogen emissions but significantly increased GWP.However,reducing nitrogen application by 20%on the basis of the MB treatment significantly reduced both GWP and active nitrogen emissions(p<0.05).Compared to the CK treatment,the MBN80%treatment achieved a 25.47%increase in yield,a 32.43%reduction in water consumption,a 51.72%increase in soil organic matter content,a 17.52%increase in income,a 35.32%reduction in active nitrogen emissions,and a 2.28%reduction in GWP,with the addition of 20 t·hm-2 of biochar and a 20%reduction in nitrogen application.It also further increased yield,reduced ammonia volatilization,and addressed the issue of increased CO2 emissions in the M and MB treatments(p<0.05).This study revealed the characteristics of soil respiration and nitrogen gas emissions under the conditions of reduced nitrogen application and biochar addition in a greenhouse cucumber cultivation system,providing a theoretical basis and technical support for water-saving and yield-increasing,carbon sequestration,and emission reduction in greenhouse vegetable production.
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