秸秆与化肥减量配施对菜地土壤温室气体排放的影响

采用静态箱/气相色谱法,2016年11月至2017年9月通过田间原位试验,设置了无物料还田(CK)、常规化肥(F)、秸秆还田配施100%化肥(100FS)、秸秆还田配施70%化肥(70FS)、秸秆还田配施60%化肥(60FS)、秸秆还田配施50%化肥(50FS),对比分析了在化肥减量的基础上,配施秸秆处理的菜地(莴笋-卷心菜-辣椒轮作)土壤CO_2、CH_4、N_2O动态变化特征及温室效应,研究秸秆与化肥减量配施对菜地温室气体排放的影响.结果表明,土壤CO_2、CH_4、N_2O排放具有一定的季节变化规律,排放高峰主要集中在4~8月,且在施肥灌水后均会出现气体的排放峰.秸秆与化肥配施较常规施肥(F)处理提高了土壤N_2O排放量,累积排放量及其排放系数,其中100FS处理的效果最为明显,辣椒季的累积排放通量明显高于莴笋季和卷心菜季,高达60.76 kg·hm~(-2)(P0.05),N_2O的排放系数(以N_2O-N/N计)为0.138 kg·kg-1,而秸秆与化肥减量配施较100FS处理可以降低氮肥的N_2O排放系数.与对照CK和F处理相比,70FS处理降低了土壤CO_2排放量和累积排放量,分别为55.28~1 831.62 mg·(m2·h)-1和7 502.13~25 988.55 kg·hm~(-2),而其他秸秆与化肥配施处理均增加了CO_2累积排放通量,尤其是60FS和50FS处理.对土壤CH_4排放而言,辣椒季的排放波动较大,除CK外,各处理的土壤CH_4累积排放量多为负值,表现为大气中CH_4汇;秸秆与化肥减量30%~50%配施处理均降低了辣椒季的土壤CH_4排放量和累积排放通量,而100FS处理提高了CH_4排放量和累积排放通量.与CK和F处理相比,除70FS外,100FS、60FS和50FS均显著提高了GWP.总体上,从温室气体排放角度,在常规化肥施用的基础上减量30%再与秸秆配施可以降低土壤CO_2和CH_4排放,缓解温室气体的增温潜势,而对土壤N_2O减排效果不显著.

Effect of Straw Residues in Combination with Reduced Fertilization Rate on Greenhouse Gas Emissions from a Vegetable Field

Greenhouse gases mainly come from farmland soils. Re-spreading chaff (straw returning) is an effective ecological management in China. Quantitative analysis of straw residues together with reduced fertilization rates can provide a scientific basis for reducing greenhouse gas emissions. A field experiment with six different fertilizer amounts combined with straw residues was carried out in a vegetable field (lettuce-cabbage-chili rotation), including the control (CK), conventional fertilizing (F), straw returning with 100% conventional fertilizing (100FS), straw returning with 70% conventional fertilizing (70FS), straw returning with 60% conventional fertilizing (60FS),and straw returning with 50% conventional fertilizing (50FS). The dynamic characteristics and emission factors of CO₂, CH₄ and N₂O in the soil were analyzed using an in-situ, closed chamber, gas chromatography-based system, from November 2016 to September 2017. The results showed that the emission of CO₂, CH₄ and N₂O has seasonal variation characteristics. The peak value mainly occurred in April to August, and the gas emission peak would appear after fertilizing and irrigating. Compared with F treatment, straw returning with fertilizing treatments reduced the N₂O emission fluxes, cumulative emission and emission factor, especially in the 100FS treatment. The N₂O cumulative emission and emission factor was 60.76 kg·hm^-2, 0.138 kg·kg^-1 (N₂O-N/N) respectively in 100FS treatment during planting chili was more than that during planting lettuce and cabbage. Moreover, straw returning with reducing conventional fertilizing could reduce the N₂O emission factor compared with 100FS treatment. The CO₂ emission fluxes 55.28-1831.62mg·(m²·h)^-1] and cumulative emission (7502.13-25988.55 kg·hm^-2) in 70FS treatment were lower than that in CK and F treatments, while other treatments increased the CO₂ emission fluxes and cumulative emission, especially in 60FS and 50FS treatments. During planting lettuce and cabbage, the CH₄ cumulative emission mainly showed negative values in treatments except for CK, indicating that soil could adsorb CH₄. Moreover, straw returning with 30%-50% conventional fertilizing treatment could reduce CH₄ emission fluxes and cumulative emission during planting chili, but increased in 100FS. Compared with CK and F treatment, generally, straw retuning with conventional fertilizing could significantly increase the global warming potential (GWP) in the study, except for 70FS treatment. 70FS could reduce the CO₂, CH₄ emission and the GWP of greenhouse gases, but could not significantly affect N₂O emission reduction.