中国农田秸秆还田土壤N_2O排放及其影响因素的Meta分析

Meta-analysis on effects of residue retention on soil N_2O emissions and influence factors in China

农田N2O排放是全球人为温室气体主要的来源之一,了解农作措施对其排放的影响对中国农田减排具有重要的意义。该研究采用Meta分析方法,定量分析了秸秆还田对中国农田土壤N2O排放的影响,并对其影响因素进行解析。研究结果表明,在中国不同区域秸秆还田对土壤N2O排放有一定的差异,其中华东地区显著减排18.61%(P<0.05),而华中和华北地区则分别显著增加排放62.3%和27.73%(P<0.05)。同时,施氮量介于0~240 kg/hm2(以N计,下同)时,随着施氮量的增加,秸秆还田对土壤N2O影响的效应值逐渐由负值增加为正值;当施氮量介于241~300 kg/hm2时,秸秆还田有显著降低土壤N2O排放的趋势。当土壤p H值介于6.5~7.5时,秸秆还田对N2O排放影响的效应值为正值;当黏粒质量分数为15%~25%时,秸秆还田对N2O排放影响的效应值为正值,当黏粒质量分数<15%时,秸秆还田显著降低土壤N2O排放。秸秆的碳氮比与秸秆还田量对N2O的排放也有不同程度的影响,另外,秸秆还田下不同的种植制度间N2O的排放也有差异。因此,秸秆还田下实施农田N2O减排措施应综合考虑区域农业资源特点、种植制度、土壤类型和水肥管理因素。研究可为科学管理秸秆与减少农田N2O排放提出理论支撑。

Scientists have paid more and more attention to the nitrous oxide(N2O) emissions due to the great contribution of N2 O to global warming and stratospheric ozone destruction. Agricultural N2 O emissions have been estimated to more than 60%-75% of calculated annual atmospheric N2 O. Thus, it is critical to identify the effects on N2 O emission responding to residue retention(RR) in understanding how RR contributes to mitigation of climate change. In this study, a meta-analysis based on 31 published peer-reviewed papers published before 2015 was conducted to investigate the effects of RR on soil N2 O emission and 79 available comparisons were compiled into the dataset. Natural log of response ratio was used as the effect size in the random effect meta-analysis. Only field scale studies were included in this study. Original documented information, including seasonal accumulative N2 O emission flux, standard deviation, replicates, and types of land-use were obtained from each study. If seasonal accumulative N2 O emission fluxes were not directly provided, these values were calculated by multiplying time and mean N2 O emissions by the measurement period. To identify the difference from site-specific conditions, a categorical meta-analysis were adopted by dividing the comparisons into groups to assess the effects of N2 O emission responding to RR under different cropping systems, soil properties, land use types, and regions. The results presented herein showed that differences in N2 O emission under RR among regions were obvious in the categorical meta-analysis. For example, RR significantly reduced N2 O emission by 17% in the Eastern China(P<0.05), while significantly increased the emission by 95% and 34% in the Central and North China, respectively(P<0.05). Furthermore, the natural log of response ratio of N2 O emission increased with increasing N fertilization input rate but was limited, and the effect of RR on N2 O emission gradually changed from suppression to promotion. In addition, when N fertilization input rate was more than 240 kg/hm2, the effect size about N2 O emission was negative under RR. The N2 O emission were increased significantly by 21% when N fertilization input was between 180-240 kg/hm2 and decreased significantly by 16% when N fertilization was between 240-300 kg/hm2. In addition, the results showed soil p H had no significant influence on the N2 O emission. Results indicated that N2 O was significantly reduced by 29%(P<0.05) when the mass fraction of clay was less than 15%, but without significant influence when more than 15%. However, the weighted mean effect size showed a decreasing trend after increasing with p H value and mass fraction of clay. Thus, crop residue retention may increase the emission of N2 O in neutral soil, or decrease in acidity and alkalinity soil. Results also showed that the N2 O emission could increase with the increase of the amount of crop residue retention. This may due to the characteristic of residue as crop fertilizer. The C:N ratio of crop residues also affected the emission of N2 O in despite of no significant influence in this study. The retained residue with high C:N ratio could decrease N2 O emission. Significant differences in N2 O emissions were observed within the same land use type along with different cropping systems. For example, a significant decrease by 12% was observed in rice season for a rice-wheat system but a significant increase by 10% was found in rice season of rice-rape system, respectively(P<0.05). The effects of RR on N2 O emission were affected by many site-specific conditions and managements. Therefore, further research on the reduction of soil N2 O emissions with residue retention should be targeted and to specific biophysical conditions, e.g., soil type, cropping system and farming management.