Effects Of Different Nitrogen Application Amount On CH₄ And N₂O Emission In The Dryland Farming Of The Loess Plateau

A long term nitrogen experiment was conducted at the experimental station of Gansu agricultural university in Lijiabao town of Dingxi city. CH4 and N2 O gas fluxes of different nitrogen application rates were measured during the whole growth periodbi-weekly continuously by using the static chamber-gas chromatography method. The study started from April6, 2014 to August1,2014. Environmental factors(soil water and temperature)were measured simultaneously with CH4 and N2 O flux. The emission characteristics of CH4 and N2 O gas fluxes and the effects of soil temperature and soil moisture on the fluxes during the growth period under different nitrogen application rates are presented below. The results of the study are summarized below:1. The soil of the wheat farmland under five nitrogen application rates for the crop growth period were all sinks of cumulative fluxes for CH4 and emission sources for cumulative fluxes for N2 O. The cumulative absorption flux of CH4 was highest under nitrogen application rates of 105 kg/hm2. High nitrogen application rates inhibited the absorbing of CH4 in dryland but the cumulative emission flux of N2 O increased with increasing nitrogen application. Therefore, the greenhouse gas emissions in soils of no nitrogen application were lower than soils of nitrogen application, and significantly lower than higher nitrogen application soils.2.The wheat soil of CH4 flux with the different treatment reach full absorption three times at three stages of the crop growth; at planting, grouting and after harvest. The absorption state of N1 treatment was greater than the other treatments at the same period, whilst the CH4 absorption peak at the filling stage with different nitrogen application rates were above the two period’s peak at planting and harvest.3. The different treatments of soil N2 O flux had lower emissions at the tillering stage with flat emission peak. The N2 O recorded two times emissions peak(source) and sink peak once from the jointing stage to the mature stageunder the different nitrogen application rates of N2 O.The two complete emissions peak appeared in the jointing stage and milking stage, respectively with the whole filling stage emission peak being higher than the jointing stage emission peak. A single absorption peak appeared in the heading stage.4.The soil temperature and soil moisture during the observation period was linearly correlated with gas fluxes of CH4 and N2 O.The average emission flux of N2 O was positively correlated to soil temperature at 0-5cm. However, the average absorbed flux of CH4 was negatively correlated to soil temperature, but positively correlatedto soil water content at 5-10 cm. The soil temperature was negatively correlated to average flux of CH4, and positively correlated to average flux of N2 O.On the contrary, the soil water content was positively correlated to average flux of CH4 and negatively correlated to average flux of N2 O, but with low correlation coefficient.5. The direct effect of soil temperature on gas flux is greater than the soil water content; Thesoil moisture content by soil temperature effect on gas flux;And the direct and indirect effect of soil temperature and soil moisture of CH4 were greater than the N2 O of effect.6.Different nitrogen application rates affect the production, emission and absorption of CH4 and N2Oin the dry farmland ecosystem. Therefore, combined environmental effect of the two gases should be considered when evaluating wheat field environmental ecology. The integrated warming potential range of the two gases was from 828.24-5052.39 CO2-e kg/hm2. The integrated warming effect of the two gases under continuous cropping ecosystem of dryland wheat was increased with increasing nitrogen application rates. The integrated warming effect of N5 was higher than N2, N3 and N4 by two-four times. The warming potential of CH4 was significantly lower than N2 O during the entire growth period. High nitrogen application rates inhibited the absorbing of CH4 and promoted the emission of N2 O in dryland wheat farmland and had a significant warming effect on dryland.