有机肥与无机肥配施对菜地土壤N_2O排放及其来源的影响

Effects of combined application of manure and inorganic fertilizer on N_2O emissions and sources in vegetable soils

该研究采用同位素自然丰度法,通过室内培养试验研究北京地区菜地有机肥和无机肥配施对土壤释放N2O及同位素位嗜值SP(site preference)的影响,以期获得不同肥料及其配比下土壤N2O的来源及变化规律。结果表明:施用无机肥释放的N2O显著高于有机肥,其累积排放量是有机肥的6.63倍,且无机肥施用比例越高,排放量越大;各肥料组合在施用后7天内均以反硝化作用生成N2O为主,贡献最高达到78.89%,SP为6.97‰,之后硝化作用逐渐增强并成为主要途径,最高占比达76.48%,SP为25.24‰;培养期内施用无机肥可以促进反硝化作用,平均占比52.98%,SP为15.52‰,而有机肥会使硝化作用增强,平均占比71.35%,SP为23.55‰。因此,在北京潮褐土地区菜地土壤施用有机肥对N2O有良好的减排效果,可为蔬菜生产中肥料的合理应用提供科学依据。

The soils are dominating source of nitrous oxide （N2O）, a greenhouse gas that contributes to stratospheric ozone destruction. In China, vegetable soils are amended with the highest level of N fertilizers among agricultural soils, causing large N2O flux. Bacterial nitrification and denitrification are thought to be the primary process for N2O emission from soil. Recently, it has been suggested that the intramolecular distribution of ^15N between central （α） and terminal （β） position in the liner N2O molecule （^βN^αNO, known as site preference or SP）, can indicate which processes contribute to N2O fluxes. The goal of this test was to confirm N2O isotopomer signature stability effects on source partitioning of N2O and the contribution of microbial process to N2O production and consumption. Here, a microcosm experiment was performed to partition N2O production pathways and its change pattern emitted from vegetable soils amended with different manure, inorganic fertilizers and their combinations by using abundant isotope technique, which mainly focused on SP. The experiments set up five different manure and inorganic fertilizers treatments： 100%M （manure fertilizers）, 100%U （inorganic fertilizers）, 80%M＋20%U, 50%M＋50%U, CK （no fertilizers）. N2O concentration,15Nαand15Nbulk were measured by an element analyzer isotope ratio mass spectrometer and a trace gas analysis system. SP was calculated by N2O isotope characteristic value, giving the contribution to denitrification and nitrification. The results showed that inorganic fertilizer drove significantly higher N2O emissions than that of manure fertilizer. The higher quantity of inorganic fertilizer was used, the more N2O was released. The cumulative emissions of N2O from manure fertilizer treatment were 6.63 folds higher than that of inorganic fertilizer. The values of SP increased first and then decreased gradually with time, suggesting that production processes of N2O were associated with different microbial pathways. Denitrification was the dominant microbial process within seven days after fertilization in each fertilizer combination, the highest proportion reached 78.89%, SP value of 6.97‰ and then nitrification became the main pathway with the highest proportion of 76.48%, SP value of 25.24‰. Denitrification was likely to occur when applying inorganic fertilizer, the average proportion reached 52.98%, SP value of 15.52‰ and the application of manure fertilizer enhanced the nitrification process with the average proportion of 71.35%and SP value of 23.55‰. Considering both values of N2O emissions and SP, it was suggested that manure fertilizer had a positive effect on reducing N2O emissions in Drab Fluvo-aquic soil of Beijing. Of course, denitrification is most important source of N2O production. The results provide scientific basis for the rational fertilization in vegetable production. At the same time, we need to make further work to explore and characterize isotopic signature of N2O to find out microbial identification of N2O.