Can Cover Crops Reduce Nitrous Oxide Emissions from Agricultural Soils?

尽管加拿大大多数经济部门最近都减少了温室气体的排放，但农业却落后了。这是因为在过去的几十年里，作物生产中合成氮肥的使用量翻了一番，增加了温室气体一氧化二氮（N2 O）的排放。如果作为一个国家，我们要履行减少温室气体的国际承诺，减少加拿大农业土壤的排放是势在必行的。此外，作物生产必须现代化，以限制氮素流失到环境中，并增加作物对肥料氮的利用。最终，我们必须努力创造新的农业系统，不排放温室气体，保护作物的营养。与传统系统相比，有机食品生产系统被认为可以减少温室气体净排放。然而，常见的做法，将豆科牧草作为绿色肥料的结果在冬季携带的硝酸盐氮和非常大的排放量的N2 O在以下解冻，如果土壤饱和。解冻排放也发生在传统作物生产中，占加拿大寒冷冬季气候下农业土壤年N2 O排放量的15-50%。农民们正在采用覆盖种植，即在收获一年生谷物或油料种子后播种的植物从秋季到春季提供土壤覆盖。覆盖作物有多种好处，包括降低土壤硝酸盐水平进入冬季。这种硝酸盐水平的降低对解冻排放的N2 O的影响并不为我们的气候所知。过去在温暖气候下的研究表明，覆盖作物可以通过喂养产生N2 O的土壤生物来增加排放。因此，重要的是要知道，日益流行的覆盖种植的做法是减少或增加N2 O排放量。作为我的实验室实现其长期目标的旅程的一部分，即改变食物的生产方式，使其成为土壤中温室气体的净非排放者，这项发现资助计划侧重于回答以下问题：a）在有机生产中，苜蓿犁耕后，覆盖物是否减少或增加解冻后的N2 O排放？，B）覆盖物是否减少或增加传统生产中的解冻排放？，c）可以覆盖较低的硝酸盐和土壤水分，以限制解冻排放？d）用覆盖物喂养土壤生物和降低硝酸盐对N2 O排放的净结果是什么;水分是否影响平衡？e）产生N2 O的微生物基因与解冻排放以及覆盖、管理和土壤条件的影响有何关系？f）广泛使用的模拟模型DNDC能否预测覆盖对排放的影响？该计划的成果是促进减少作物生产中N2 O排放的做法。其意义是帮助扭转最近农业土壤中N2 O排放量增加的趋势，并履行实际减少排放量的承诺。

Despite recent emission reductions of greenhouse gases (GHG) by most economic sectors in Canada, agriculture is lagging. This is because doubling in synthetic N fertilizer use in the past several decades for crop production has increased emissions of the greenhouse gas, nitrous oxide (N2O). Lowering emissions from Canadian agricultural soils is imperative if as a nation, we are to meet international commitments to greenhouse gas reductions. Further, crop production must modernize to limit nitrogen loss to the environment and increase fertilizer N utilization by crops. Ultimately, we must strive to create new agricultural systems that don't emit greenhouse gases and conserve nutrients in crops. Organic food production systems are thought to decrease net GHG emissions compared to conventional systems. However, the common practice of incorporating legume forages as green manures results in carry over of nitrate nitrogen over winter and very large emissions of N2O during the following thaw, if the soil is saturated. Thaw emissions also occur in conventional crop production accounting for 15-50% of annual N2O emissions from agricultural soils in the cold winter climates of Canada. Farmers are adopting cover cropping where plants sown following harvest of annual grains or oilseeds provide soil cover from fall through spring. There are multiple benefits to cover cropping including lowering soil nitrate levels going into winter. What the impact of this lowering of nitrate levels has on thaw emissions of N2O is not known for our climate. Past studies in warmer climates indicate that cover crops can increase emissions by feeding soil organisms producing N2O. Thus, it is important to know if the increasingly popular practice of cover cropping is decreasing or increasing N2O emissions. As part of the journey of my laboratory toward its long-term goal of changing how food is produced to be a net non-emitter of GHGs from soil, this Discovery Grant program focuses on answering the following questions; a) do covers reduce or increase thaw N2O emissions following alfalfa ploughdown in organic production?, b) do covers reduce or increase thaw emissions in conventional production?, c) can covers lower nitrate and soil moisture to limit thaw emissions?, d) what is the net result of feeding soil organisms and lowering nitrate with covers on N2O emissions; does moisture affect the balance?, e) how do microbial genes producing N2O relate to thaw emissions and effects of covers, management, and soil conditions?, and f) can the widely used simulation model, DNDC, predict cover effects on emissions?. The outcome of this program is to foster practices to decrease N2O emissions from crop production. The implications are to help in reversing the recent trend for increasing N2O emissions from agricultural soils and meet commitments to actually reduce them.