Study On Greenhouse Gas Emissions Under Different Biochar Application Rates In Dryland Areas

The experiment was conducted at the experimental station of Gansu agricultural university in Lijiabao town of Dingxi city. The aim of this study was to determine the effects of biochar on methane（CH₄）, nitrous oxide（N₂O）, and carbon dioxide（CO₂） emissions in a semi-arid environment. The treatments consisted of six different biochar levels; TT（0 t/ hm2）, BT1（10 t/ hm2）, BT2（20 t/ hm2）, BT3（30 t/ hm2）, BT4（40 t/ hm2） and BT5（50 t/ hm2）. CH₄ and N₂ O gas fluxes were measured bi-weekly during the whole growth period using the static chamber-gas chromatography method. CO₂ gas flux of different biochar application rates were measured by the EGM-4 portable CO₂ analyzer. Environmental factors（soil water content and temperature） were measured simultaneously with CH₄, N₂ O and CO₂ fluxes. The emission characteristics of CH₄, N₂ O and CO₂ gas fluxes and the effects of soil temperature and soil moisture on the fluxes during the growth period and all-day under the different biochar application rates are summarized below:1. Throughout the day, the absorption or emission of CH₄, N₂ O, and CO₂ was consistent with the trend in temperature changes. The lowest flux of all the 3 kinds of greenhouse gases measured occurred in the night, irrespective of treatment. The highest emission and absorption peak appeared around 4:00 am and 5:00 am. The cumulative fluxes of N₂ O and CO₂ in each treatment were sources; and the cumulative flux of CH₄ of BT3 was a sink, and the cumulative flux of CH₄ of the other treatments were weak emission fluxes. The all-day emissions of CH₄ and N₂ O gases are the largest of the control. The input of biochar at a rate less than 30 t/hm2, results in the all-day emissions fluxes of the three gases reducing with increasing biochar application rates. However, when the input exceeds 30 t/hm2, the all-day emissions fluxes of the three gases showed an increasing trend with increasing biochar application rates.2. The results of the dynamic variation showed that the soils of the wheat farmland under different biochar application rates during the crop growth period were sources for CH₄, N₂ O and CO₂.The emission of the three kinds of greenhouse gases is the most in the control. The mean emissions fluxes of CH₄ reduced with increasing biochar application rates. When the input of biochar was less than 30 t/hm2, the mean emissions fluxes of N₂ O reduced with increasing biochar application rates. However, when the input exceed 30 t/hm2, the mean emissions fluxes of N₂ O showed an increasing trend with increasing biochar application rates. But bounded by the input level of 10 t/hm2 and 30 t/hm2, the emissions fluxes of CO₂ gases of all the treatments showed a change trend “from rise to reduce to rise”. During the crop growth period, the absorption or emission of CH₄ under different biochar treatment appears alternately. The CH₄ gases of low level treatments had 2 production peaks, occurring at tillering and filling stage, and absorption peak appeared after harvest. The N₂ O gases of all the treatments showed a change trend “from rise to reduce to rise to reduce”, and the emission peak appeared in the period from tillering stage to jointing stage and from filling stage to maturity stage. The emission of CO₂ gases showed a single peak during the crop growth period, and the emission peak appeared at jointing stage.3. In the springwheat land of semi-arid region, the soil moisture and soil temperature have a linear correlation with the three greenhouse gases. During the crop growth period, the average fluxes of CH₄, N₂ O and CO₂ were negatively correlated to soil moisture at 0-5cm. The average flux of CH₄ was negatively correlated to soil temperature, but positively correlated to soil moisture at 5-10 cm. The average fluxes of N₂ O and CO₂ were negatively correlated with soil temperature at 10-15 cm, but positively correlated to soil temperature at 20-25 cm. The average fluxes of N₂ O were positively correlated to soil temperature at 15-20 cm. With all-day sampling, the average fluxes of CH₄ and CO₂ were positively correlated to soil temperature at 0-25 cm, but negatively correlated to soil moisture at 0-5cm. But the average flux of N₂ O have a low correlation coefficient with the soil moisture and soil temperature.4. In the dry farmland ecosystem, the integrated warming potential range of the three gases was from 3514.90-5222.24 CO₂-e/hm2.When the input of biocharwas less than 30 t/hm2, the global warming potentials of the three gases reduced with increasing biochar application rates. However, when the input exceeds 30 t/hm2, the global warming potentials of the three gases showed an increasing trend with increasing biochar application rates. The global warming potentials of TT is the most, BT3 is the least. So the application rate of biochar around 30 t/hm2 may be better to reducing greenhouse gas emissions.