AFM | 小麦-玉米系统中长期秸秆还田导致表层土壤有机碳饱和和产量增加，但不刺激或减少单位产量的N2O和NO排放

题      目：Long-term straw return to a wheat-maize system results in topsoil organic C saturation and increased yields while no stimulating or reducing yield-scaled N2O and NO emissions

译      名：小麦-玉米系统中长期秸秆还田导致表层土壤有机碳饱和和产量增加，但不刺激或减少单位产量的N2O和NO排放

期      刊：Agricultural and Forest Meteorology

发表时间：2024.02.29

第一作者：姚志生 研究员

第一单位：中国科学院大气物理研究所；大气边界层物理与大气化学国家重点实验室；中国科学院大学地球与行星科学学院

研究结果

结果表明，随着时间的推移，秸秆还田后土壤有机碳储量的增加趋于平稳，表明秸秆还田后12 ~ 13年土壤有机碳达到饱和。土壤N -微量气体排放表现出较高的年际和年内变化率，主要受降雨、土壤水热条件或土壤C和N有效性的变化驱动。与秸秆焚烧或去除相比，长期秸秆还田使N2O年排放量增加9% ~ 49%，达到2.72 ~ 2.98 kg N ha−1yr−1，而NO排放量减少12% ~ 28%，达到0.83 ~ 0.90 kg N ha−1 yr−1。每年N2O的排放大致抵消了总碳汇（有机碳固存和CH4吸收）的40% ~ 46%，但随着有机碳库饱和，N2O的排放将覆盖总碳汇的气候效益。然而，由于秸秆还田处理的产量较高，按单位产量计算的年N2O排放量保持不变。

Fig. 1. Temporal dynamics of daily precipitation and soil (0–6 cm) moisture expressed as water-filled pore space (WFPS) (a), soil (5 cm) temperature (b) and soil (0–10 cm) ammonium (NH4+) (c), nitrate (NO3-) (d) and dissolved organic carbon (DOC) (e) concentrations over the years 2016–2020. NN, no synthetic and organic N fertilization; UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha-1 during the maize-growing season; UN-SB, as with UN, but stubble and harvest crop residues were burnt in each season; UN-50 %SR, as with UN, but stubble and 50 % of the harvest crop residues were returned to the cropland in each season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season. The downward arrows indicate the time of fertilization, which also apply for other panels. Vertical bars in panels (c), (d) and (e) indicate standard errors of 3 spatial replicates. The legends in the panel (c) also apply for other panels.

Table 1 Straw and grain yields (in Mg ha-1) at physiological maturity, estimated harvest index (HI, in%) and agronomic nitrogen efficiency (ANE, in kg grain kg-1 N) for the winter wheat and summer maize crops under various straw management practices during the period of 2016–2020.

Fig. 2. Temporal dynamics of topsoil (0–20 cm) organic carbon (SOC) stocks in winter wheat-summer maize rotation cropping systems under different straw management practices for the period 2005–2020 (a-d). The regression line for the NN treatment was linear, while those for the UN, UN-SB, UN-50 %SR and UN-100 %SR treatments followed the logistic regression models. NN, no synthetic and organic N fertilization; UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha-1 during the maize-growing season; UN-SB, as with UN, but stubble and harvest crop residues were burnt in each season; UN-50 %SR, as with UN, but stubble and 50 % of the harvest crop residues were returned to the cropland in each season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season. Vertical bars indicate standard errors of 3 spatial replicates.

Fig. 3. Temporal dynamics of soil nitrous oxide (N2O) (a) and nitric oxide (NO) (b) fluxes over the years 2016–2020. NN, no synthetic and organic N fertilization; UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha-1 during the maize-growing season; UN-SB, as with UN, but stubble and harvest crop residues were burnt in each season; UN-50 %SR, as with UN, but stubble and 50 % of the harvest crop residues were returned to the cropland in each season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season. The downward arrows indicate the time of fertilization. Vertical bars indicate standard errors of 3 spatial replicates. The legends in the panel (a) also apply for the panel (b).

Fig. 4. The dependence of the observed nitrous oxide (a-d) and nitric oxide (NO) (e-h) fluxes from different straw management practices on the combined effects of multivariate changes in soil temperature (ST), water-filled pore space (W), ammonium (NH4+), nitrate (NO3-) or dissolved organic carbon (DOC). Predicted results were obtained from stepwise multiple linear regression models shown in each panel. NN, no synthetic and organic N fertilization; UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha-1 during the maize-growing season; UN-SB, as with UN, but stubble and harvest crop residues were burnt in each season; UN-50 %SR, as with UN, but stubble and 50 % of the harvest crop residues were returned to the cropland in each season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season. Dashed lines represent 95 % confidence bands.

Fig. 5. Results of random forest analysis for identifying the relative importance of environmental variables (i.e., soil ammonium (NH4+), nitrate (NO3-) and dissolved organic carbon (DOC), water-filled pore space (WFPS) and soil temperature (ST)) driving temporal variations of nitrous oxide (N2O) (a-d) and nitric oxide (NO) (e-h) fluxes. UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha-1 during the maize-growing season; UN-SB, as with UN, but stubble and harvest crop residues were burnt in each season; UN-50 %SR, as with UN, but stubble and 50 % of the harvest crop residues were returned to the cropland in each season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season.

Fig. 6. Relationships between annual nitrous oxide (N2O) emissions and topsoil (0–20 cm) organic carbon (SOC) stocks and annual precipitation (a-b) and between annual nitric oxide (NO) emissions and annual grain yields and precipitation (c-d) across all winter wheat-summer maize rotation cycles of 2016–2020. UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha-1 during the maize-growing season; UN-SB, as with UN, but stubble and harvest crop residues were burnt in each season; UN-50 %SR, as with UN, but stubble and 50 % of the harvest crop residues were returned to the cropland in each season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season. Vertical and horizontal bars indicate standard errors of 3 spatial replicates. Dotted lines represent the 95 % confidence bands.

Table 2 Annual cumulative emissions of nitrous oxide (N2O), nitric oxide (NO) and N2O plus NO, as expressed either on an area basis or relative to grain yield and their direct emission factors of applied nitrogen (i.e., EFN2O, EFNO and EFN2O+NO) for various straw management practices during the winter wheat-summer maize rotation cropping systems of 2016–2020.

Fig. 7. Nitrous oxide (N2O) production rates (a) and pathways (b) in soils from different straw management practices. N2Oa, N2Od and N2Oh are contributions to N2O production rates via autotrophic nitrification, denitrification and heterotrophic nitrification, respectively. na, d and nh are autotrophic nitrification, denitrification and heterotrophic nitrification, respectively. UN, synthetic N fertilizers were applied alone at a common rate of 280 kg N ha-1 yr-1, consisting of 130 kg N ha-1 during the wheat-growing season and 150 kg N ha􀀀 1 during the maize-growing season; UN-100 %SR, as with UN, but stubble and 100 % of the harvest crop residues were returned to the cropland in each season.

该研究独特的数据集第一次使我们更好地了解有机碳固存、产量和N-微量气体排放之间的动态关系，其结果呼吁采取行动，解决秸秆还田导致长期有机碳增加后N2O排放增加的风险。