Land Use and Management Practice Impacts on Soil Carbon and Associated Agroecosystems Services

Soil organic matter acts like a sponge within the soil, retaining water, carbon, and nutrients. It also serves as a source of carbon, or food, and nutrients, like nitrogen, for soil microbes. Because soil microbes demand carbon and nutrients in specific ratios, the quantity of soil organic matter and how nutrient rich it is compared to carbon may determine: how much nitrogen is kept within microbial bodies, how much is held within soil organic matter, and how much is transformed by microbes into a plant-available form for uptake or leaching loss. Quantifying these relationships and transformations can potentially be used to minimize excess available nitrogen lost to water ways and mitigate greenhouse gas emissions while still maximizing crop yield. Agricultural soils are responsible for 79% of the United States N2O emissions, and emissions continue to increase at a steady rate. Direct N2O emissions from agriculture are the result of two soil microbial processes, nitrification and denitrification, which transform plant available nitrogen in soil. Both processes produce N2O as a by-product that leaks into the atmosphere. The rate of nitrification is directly linked to the amount of carbon available to soil microbes and their associated nitrogen demands. This research will use two primary methods to examine the link between soil organic matter and nitrogen transformations and how that varies depending on land management practices (i.e. cover crops). The first is using stable isotopes, which trace a known amount of a less abundant isotope (i.e. 15N) through an ecosystem, and the second is microbial functional analyses, such as litter decomposition or carbon mineralization. It is a goal of this project to create metrics for farmers that link soil organic matter quantity with plant available N so as to minimize nitrogen losses from agricultural systems. We also hope to help practitioners understand how to best use cover crops to both build soil organic matter and create a timely nitrogen source for plant uptake. With a greater understanding of microbial transformations as related to soil organic matter, we can work towards altered land management practices which build soil organic matter and reduce the leakiness of agricultural soils.