不同施氮处理下旱作农田土壤CH_4、N_2O气体排放特征研究

依托甘肃农业大学布设在定西市李家堡镇的长期施氮定位实验,对不同施氮农田CH4和N2O气体通量,采用静态箱-气相色谱法进行小麦生育期的连续观测,并对影响通量变化的环境因子同期观测.结果表明:5个施氮处理下(0、52.5、105、157.5、210 kg·hm-2),旱作农田土壤在小麦全生育期内表现为CH4累积通量的汇和N2O累积通量的源;且不施氮处理时,CH4累积吸收通量最大;施氮量为210 kg·hm-2时,土壤CH4的累积吸收通量所受抑制最大,即土壤CH4累积吸收通量随施氮量升高而降低.相反,不施氮处理时,土壤N2O的累积排放通量最小,施氮量为210 kg·hm-2时,土壤N2O的累积排放通量最大,土壤N2O累积排放通量随施氮量的增加而增大.综合分析,施氮量增大会抑制全生育期旱作春小麦田土壤CH4吸收通量,提高土壤N2O的排放通量.因此,合理控制施氮量有利于生育期旱作农田土壤减排.CH4平均吸收通量随土壤温度的升高而降低,随土壤水分的升高而升高;相反,N2O平均排放通量随土壤温度的升高而升高,随土壤水分的升高而降低.5~10 cm层次的土壤温度与CH4平均吸收通量呈极显著线性负相关,与N2O平均排放通量呈显著正相关.5~10 cm层次的土壤水分与CH4平均吸收通量呈极显著线性正相关,与N2O平均排放通量呈显著负相关.

Emission characteristics of CH4 and N2O fluxes from dryland field under different nitrogen treatments

Long-term experiment was conducted in the experimental station of Gansu agricultural university in Lijiabao town of Dingxi city. The objective of the study was to determine the effects of nitrogen fertilizer on emissions of methane (CH₄) and nitrous oxide (N₂O) in an ongoing long-term experiment. The experiment was laid out in a Randomized Complete Block design in a factorial experiment with three replications. The treatments included five different nitrogen fertilizer levels; N1(0 kg·hm^-2), N2(52.5 kg·hm^-2), N3(105 kg·hm^-2), N4(157.5 kg·hm^-2) and N5(210 kg·hm^-2). Soil methane (CH₄), nitrous oxide (N₂O), temperature and moisture were measured at the same time. Methane (CH₄) and nitrous oxide (N₂O) fluxes were measured using static chamber-gas chromatography. The results showed that the five nitrogen application treatments under dry farmland during the crop growth period were sinks for CH₄. The cumulative fluxes of the five nitrogen application treatments were sources for N₂O. No nitrogen application recorded higher cumulative absorption fluxes for CH₄. The cumulative absorption fluxes suffered the greatest inhibition when nitrogen application was 210 kg·hm^-2. The cumulative absorption fluxes of soil CH₄ increased with reducing nitrogen application. On the contrary, the cumulative emission fluxes of N₂O were the lowest for no nitrogen application. The cumulative emission fluxes of N₂O increased with increasing nitrogen application, and reached the highest when nitrogen application was 210 kg·hm^-2. Based on the results of the study, the increasing nitrogen applications inhibited the absorption fluxes of CH₄, but improved the emissions fluxes of N₂O. The mean absorption fluxes of CH₄ reduced with increasing soil temperature, but increased with increasing soil moisture. The mean emissions fluxes of N₂O increased with increasing soil temperature, but reduced with increasing soil moisture. The soil temperature of 5~10 cm had negative correlation with average flux of CH₄. However, the soil temperature at a depth of 5~10 cm had significant and positive correlation with average N₂O flux. The soil moisture at a depth of 5~10 cm had positive correlation with average flux of CH₄. N₂O fluxes had significant and negative correlation with soil moisture at a depth of 5~10 cm. Therefore, a reasonable control of nitrogen application would be beneficial for a reduction in soil emission of dry farmland.