Effects Of Nitrogen Levels Under Shallow Drip Irrigation On Nitrogen Efficiency Of Spring Maize And Soil Greenhouse Gas Emissions

In order to explore the effects of nitrogen application level on nitrogen efficiency and soil greenhouse gas emissions of spring maize under shallow drip irrigation in Xiliaohe plain,two treatments of constant topdressing（T₁）and optimized topdressing（T₂:70%constant topdressing）were set under shallow drip irrigation in Horqin agricultural high tech demonstration park of Tongliao City,Inner Mongolia in 2019.With conventional constant nitrogen topdressing under traditional border irrigation（CK₁）as control and no fertilization（CK₂）as blank control,the emission fluxes of CO₂,N₂O and CH₄ from soil during the growth period of spring maize were measured by static dark box gas chromatography,The correlation between soil greenhouse gas emissions and soil temperature,humidity and nutrients was analyzed.The main results are as follows:1.Compared with traditional border irrigation CK₁ treatment,shallow drip irrigation increased grain yield and grain nitrogen accumulation after silking stage,but there was no significant difference in whole plant nitrogen accumulation under the same nitrogen application rate,thus significantly improving nitrogen harvest index,nitrogen agronomic efficiency and nitrogen partial productivity.Under shallow burying drip irrigation,the nitrogen accumulation of grain,cob and whole plant in T₁ treatment was higher than T₂ treatment,but there was no significant difference in grain yield;The agronomic efficiency and partial productivity of nitrogen fertilizer increased by 22.40%and 30.58%in T₂ and T₁ respectively.2.The diurnal variation of greenhouse gas emissions from spring maize field showed that CO₂ and N₂O emissions had obvious diurnal variation characteristics,and the diurnal variation trend was similar to that of atmospheric temperature,showing a single peak emission curve.Compared with traditional border irrigation CK₁ treatment,shallow drip irrigation increased N₂O daily flux under the same nitrogen application rate.Correlation analysis showed that the diurnal variations of N₂O and CO₂ emission fluxes were significantly（P<0.05）or extremely significantly（P<0.01）positively correlated with surface temperature and 10cm soil temperature,and soil temperature was an important factor affecting the diurnal variations of CO₂ and N₂O.3.During the growth period of spring maize,there was no significant difference in CO₂ emission between shallow drip irrigation and traditional border irrigation under the same nitrogen application rate.N₂O emission increased by 11.78%and CH₄absorption decreased by 34.78%;Under shallow drip irrigation,the CO₂ and N₂O emissions of optimized nitrogen topdressing T₂ decreased by 13.15%and 20.27%,compared with conventional nitrogen topdressing T₁,respectively,while the CH₄uptake had no significant difference.Under the same nitrogen application rate,the greenhouse gas emission intensity of shallow drip irrigation was 14.13%lower than that of traditional border irrigation,and the greenhouse gas emission intensity of optimized nitrogen topdressing T₂ was 10.46%lower than that of conventional nitrogen topdressing T₁.There was no significant difference in comprehensive warming potential between T1 and CK₁,which were significantly higher than T₂（P<0.05）;There was no significant difference between T₁ and T₂ treatments under net ecosystem economic budget drip irrigation,which were significantly higher than CK₁ treatment（P<0.05）.4.The results of correlation analysis between soil greenhouse gas emission fluxes and soil environmental factors during the growth period of spring maize showed that CO₂,N₂O and CH₄ emission fluxes were significantly positively correlated with surface temperature and soil 10cm temperature（P<0.01）,and CO₂ and N₂O emission fluxes were significantly positively correlated with soil water content（P<0.01）.Path analysis showed that soil water content had the greatest impact on CO₂,N₂O and CH₄ emission fluxes.There was a significant（P<0.05）or extremely significant（P<0.01）positive correlation between the mean CO₂ and N₂O emission fluxes and the mean contents of soil organic matter,total nitrogen,ammonium nitrogen and nitrate nitrogen during the whole growth period of spring maize.Path analysis showed that soil total nitrogen content had the greatest impact on CO₂ emission fluxes,soil ammonium nitrogen content had the greatest impact on N₂O emission fluxes,and soil organic matter content had the greatest impact on CH₄ emission fluxes.5.Compared with traditional border irrigation CK₁,T₁ and T₂ treatments under shallow drip irrigation increased maize yield,nitrogen harvest index,nitrogen partial productivity and nitrogen agronomic efficiency.Compared with the traditional border irrigation CK₁ treatment,T₁ and T₂ treatments increased the net ecosystem economic budget（P<0.05）and reduced the greenhouse gas emission intensity（P<0.05）;The comprehensive warming potential of T₁ and CK₁ was significantly higher than that of T₂（P<0.05）;Compared with T₁ treatment,T₂ treatment reduced the comprehensive warming potential and greenhouse gas emission intensity.Therefore,under shallow drip irrigation,the amount of topdressing nitrogen is reduced by 30%compared with the conventional topdressing nitrogen less than that of conventional topdressing nitrogen,which not only reduces the comprehensive warming potential and greenhouse gas emission intensity,but also ensures higher maize yield and net ecosystem economic budget,which is a water and nitrogen management mode with high yield,high efficiency and ecology.