| The problem of global warning caused by human activities is increasingly serious.Agroecosystem is an important source of greenhouse gas emission.Fertilization can ensure the grain yield,and it is also a key factor that affect greenhouse gas emission.In order to explore the efficient and scientific measures of reducing greenhouse gas emission,the two of rice and wheat field experiments were conducted,to investigate the effects of reduced nitrogen input and combined application of different fertilizers on CH4 emissions from paddy soil and N2O-N direct and indirect(NH3 volatilizations and nitrogen leaching)emissions from the rice-wheat field and relevant driving factors.Eight treatments in the field emperiment were applied,including(1)control without fertilizer,(2)reduced nitrogen input and combined with increased potassium treatment,(3)reduced nitrogen input plus topdressing urea ammonium treatment,(4)formula fertilization treatment,(5)combined application of organic-inorganic fertilizer,(6)stability urea with dicyandiamide and hydroquinone treatment,(7)urea formaldehyde treatment,(8)conventional fertilization treatment.The corresponding codes of rice season experiment were(1)RCK,(2)RN190CF+U+K,(3)RN230CF+UA,(4)RN230CF+U,(5)RN230OF+U,(6)RN230UHD,(7)RN230UF and(8)RN270CF+u,respectively,and the codes in the wheat field experiment were correspondingly used as follows:(1)WCK,(2)WN150CF+U+K,(3)MWN180CF+UA,(4)WN200CF+u,(5)WN180OF+U,(6)WN200UHD,(7)WN20OUF and(8)WN230CF+U;the number in the code represents the amount of nitogen applied.The fertilizer varieties used is exactly the same in rice season and wheat season,in which the urea ammonium(UA)and organic fertilizer(OF)and stability urea with dicyandiamide and hydroquinone(UHD)and urea formaldehyde(UF)are new nitrogen fertilizers.The results of rice season experiments showed that:(1)Cumulative CH4 emissions from different treatments ranged from 72.52?181,96 kg/hm2.All fertilizer treatments except for RN230UHD reduced CH4 emissions by 32.01%?49.65%relative to the RN270CF+U treatment.The RN190CF+U+K,RN230CF+UA,RN230CF+u and RN230OF+u had the better CH4 mitigation effect among all fertilizer treatments.(2)Cumulative N2O-N direct emissions from the paddy field was very low ranged from 0.14?0.33 kg/hm2,and the ranged of emission factors were 0.02%?0.09%.With the exception of RN230CF+UA,N2O-N direct emissions for all fertilizer treatments were decreased in comparison with RN270CF+U treatment.Cumulative N2O-N indirect emissions caused by NH3 volatilizations ranged from 0.10?0.30 kg/hm2,while those caused by nitrogen leaching ranged from 0.036?0.057 kg/hm2.The NH3 volatilization was the main way of paddy N2O-N indirect emissions.RN190CF+U+K and RN230UHD increased NH3 volatilization loss,while RN230UHD increased the paddy nitrogen leaching loss.Calculating the total N2O-N emissions(direct+indirect),the result showed that only RN230UHD increased the total N2O-N emissions by 11.31%,other fertilizer treatments decreased them by 8.64%-26.74%in comparison with RN270DCF+U treatment.RN230CF+u,RN230OF+u and RN230UF showed the priority among all fertilizer treatments.(3)Calculating the aggregate emission of N2O-N and CH4 in the CO2 equivalent(GWP)for the 100-year horizon of each treatment,the result showed that RN230UHD treatment increased GWP,while the other treatments decreased the GWP by 31.36%?47.33%compared to RN270CF+U.The RN230CF+UA,RN230OF+U,RN190CF+U+K and RN230CF+U treatments performed the best reducing effiency.(4)CH4 emissions in paddy field were positively correlated with water depth and soil temperature,while N2O-N direct emissions and NH3 volatilizations were positively correlated with the inorganic nitrogen concentrations of field surface water.However,the nitrogen leaching was positively correlated with NH4+-N value of the surface water and N03---N of the topsoil.The results of wheat field experiments showed that(1)Cumulative N2O-N.direct emissions from the wheat field ranged from 0.4?2.50g/hm2,and the emission factors is ranged from 0.50%?1.00%.All fertilizer treatments reduced N2O-N direct emissions by 2.32%?46.75%relative to the WN230CF+u treatment.Cumulative N2O-N indirect emissions caused by NH3 volatilizations ranged from 0.14?0.30 kg/hm2.With the exception of WN200UHD and WN200CF+U,all fertilizer treatments decreased NH3 volatilizations by more than 20%compared with WN230CF+u.Cumulative N2O-N indirect emissions caused by nitrogen leaching ranged from 0.31?1.42 kg/hm2,and the rate of reduction for all fertilizer treatments were up to 0.89%?39.04%.Nitrogen leaching was the main contributor for N2O-N indirect emissions.(2)Calculating the total N2O-N direct and indirect emissions,the result showed those ranged from 0.87?4.22 kg/hm2 and total N2O-N emissions for all fertilizer treatments were decreased by 6.91%y37.35%in comparison with VWN230CF+u treatment.In especial,the WN180Of+u and WN150Cf+u+K treatments significantly reduced N2O-N emissions among all fertilizer treatments.(3)The N2O-N direct emissions and nitrogen leakage peaks in wheat field were related to rainfall,and also positively correlated with soil WFPS and soil NO3--N concentrations(P<0.05).However,NH3 volatilizations were positively correlated with soil temperature(P<0.05).The effects of differen fertilization treatments on greenhouse gas intensity and nitrogen use efficiency were analyzed.Four fertilizer treantments including reduced nitrogen input and combined with increased potassium treatment,reduced nitrogen plus topdressing urea ammonium treatment,formula fertilization treatment and combined application of organic-inorganic fertilizer treatment decreased the greenhouse gas intensity in the rice and wheat seasons.The reduced nitrogen plus topdressing urea ammonium treatment,both reducing the greenhouse gas emission and increasing the nitrogen use efficiency,was the most suitable fertilizer application strategy for rice and wheat planting. |
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