紫色土坡耕地退耕还林对土壤N_2O排放的影响

Effect of Returning Cropland to Forestland on N_2O Emissions from Sloping Purple Soil

采用静态暗箱-气相色谱法对紫色土坡耕地常规施肥处理(CL)、坡耕地不施肥处理(CL-CK)和退耕15、30年的桤柏混交林地(FL15、FL30)的土壤N2O排放通量进行为期1年的观测,同时测定土壤温度、土壤湿度、土壤无机氮含量等。结果表明,观测期内CL、CL-CK、FL15与FL30的N2O平均释放速率分别是25.6、6.60、1.20、4.35μg N2O-N·m-2·h-1,CL小麦季N2O平均释放速率是18.0μg N2O-N·m-2·h-1,玉米季35.2μg N2O-N·m-2·h-1,CL土壤N2O排放速率显著高于CL-CK、FL15和FL30(P<0.01),且CL-CK高于FL15、FL30(P<0.01),FL30高于FL15(P<0.01)。CL、CL-CK、FL15和FL30全年的N2O排放量分别为1.01、0.400、0.050、0.310 kg N2O-N·hm-2。比较CL以及CL-CK的N2O排放总量,停止施氮的措施对土壤N2O排放的减排潜力达到0.610 kg N2O-N·hm-2。与CL-CK相比,FL15、FL30土壤N2O释放量分别减少0.350、0.090 kg N2O-N·hm-2,主要原因是退耕后土壤碳氮比升高,土壤无机养分、温度以及湿度等发生变化。

Cropland is a large source of global N2 O emissions, while forestland emits much less N2 O. Thus, returning cropland to forestland would help reduce global N2 O emissions. Here static chamber-GC technique was used to compare soil N2 O emission fluxes from sloping cropland(CL) and forestland returned from cropland for 15 and 30 years. Soil temperature, moisture, nitrate(NO-3- N) and ammonia(NH+4-N) nitrogen content in the soils were also recorded for one year. Results showed that average fluxes of soil N2 O from CL, CL-CK(CL-Check test), FL15 and FL30(15 and 30 years old forest)were 25.6, 6.60, 1.20, and 4.35 μg N2O-N·m-2·h-1, respectively, with significantly higher N2 O emissions from CL than from CL-CK, FL15 and FL30(P<0.01). The N2 O emissions from FL30 were also significantly higher than that from FL15(P<0.01). Annual cumulative N2 O emissions from CL, CL-CK, FL15 and FL30were respectively 1.01, 0.400, 0.050, and0.310 kg N2O-N·hm-2. The potential of N2 O mitigation by nitrogen fertilizer reduction was as high as 0.620 kg N2O-N·hm-2. Compared with CL-CK, FL15 and FL30reduced N2 O emissions by 0.350 and 0.090 kg N2O-N·hm-2, respectively, may due to increases in soil carbon to nitrogen ratios and changes in soil properties.