Uncovering the contribution of cover crop belowground inputs on soil carbon and nitrogen storage

增加生物多样性和保持健康的土壤对加强加拿大的粮食系统至关重要，覆盖作物可能在其中发挥重要作用。覆盖作物是种植在主要作物（如玉米、大豆、西红柿）之间的植物，在秋季到次年春季期间提供土壤保护和肥沃，而此时田地通常是光秃秃的。大多数覆盖作物的研究都集中在覆盖作物的生长季节和次年，但使用覆盖作物的种植者是长期使用的。此外，影响碳氮动态等土壤指标的变化是长期的。因此，在了解覆盖作物对农业生态系统的真正影响方面存在重大差距。

Increasing biodiversity and maintaining healthy soil are critical to enhancing Canadian food systems, for which cover crops may play an important role. Cover crops are plants grown in-between main crops (eg corn, soybeans, tomatoes), providing soil protection and enrichment during the fall to following spring when fields would normally be left bare. The majority of cover crop research focuses on the cover crop growing season and the following year, but growers who use cover crops do so over the long term. Moreover, changes in soil indicators, such as those affecting C and N dynamics occur over the long-term. Thus there is a significant gap in knowledge the true impact of cover crops in agroecosystems. My research program is well positioned to advance knowledge in the understanding the role of cover crops on C and N cycling to evaluate ecological services (e.g. reduced synthetic fertilizer dependency) while quantifying crop productivity and resiliency by using my remarkable suite of long-term cover crop experiments. Through these one-of-a-kind in Canada long-term cover crop experiments we have observed differences in soil organic matter that cannot be explained by aboveground plant inputs alone. The mechanisms driving soil organic matter increases due to cover cropping are a significant gap in knowledge and the focus of this NSERC proposal. The short term objectives of my research program and this DG proposal are to improve scientific understanding of the mechanisms of plant above- and below-ground inputs on soil organic C and N stores. It is hypothesized that belowground inputs (roots and rhizodeposits) are contributing significant and relatively stable quantities of organic matter, which in turn facilitates C and N protection allowing for overall long-term gains in organic C with cover crops compared to the no cover crop control. Through this NSERC DG, my research program will address a significant knowledge gap of the relative contribution of, and controlling factors of, the two plant below ground inputs of importance, namely root exudates (which constitute up to 20% of plant-fixed C) and root tissues. The proposed agricultural systems-based approach is innovative as it assesses (i) soil in addition to (ii) plants, (iii) the environment, and (iv) the interconnections among these pools throughout the continuum in a long-term cover crop experiment. Novel field and laboratory experiments will be conducted through the training and mentorship of 4 graduate HQP. The proposed research has important implications for advancing competitiveness of Canadian agriculture while providing environmental benefits and soil ecosystem services. Most notably, my research program targets understanding belowground plant inputs on C and N dynamics which addresses a significant gap in scientific knowledge.