DISSERTATION RESEARCH: The effects of changing rainfall patterns on nitrogen cycling and leaching losses in agroecosystems

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Rainfall patterns are currently changing in the midwestern U.S., with an increasing proportion of rain falling in very heavy rain events. This intensification of rainfall patterns may have important consequences for rain-fed agriculture. In particular, intensification of rainfall may alter the availability and losses of soil nitrogen. Nitrogen is an essential crop nutrient, but it is also very mobile. Only about half the nitrogen added to soil in fertilizer is taken up by crops, with much of the remainder lost to the environment. Leaching is one of the most important pathways through which nitrogen is lost, with possible negative consequences including groundwater contamination and algae blooms and dead zones in rivers, lakes, and the coastal ocean. This research explores how more intense rainfall patterns may affect nitrogen leaching from Midwestern agricultural ecosystems. The project also seeks to identify management practices which may mitigate enhanced nitrogen leaching in the face of climate change. This research will be conducted using an ecosystem-scale rainfall manipulation experiment at the Kellogg Biological Station Long Term Ecological Research (LTER) site in southwest Michigan. Agricultural fields under conventional and no-till management are exposed to ambient rainfall as well as rainfall patterns with extended dry periods and large, simulated rainfall events. Leaching will be estimated with tension lysimeters to measure soil water nitrogen concentrations, and a model to estimate soil water flux. Deep soil sampling to 1.2m will trace the movement of nitrate down the soil profile over the course of a year and in response to individual rainfall events. The results will be shared with extension specialists, policymakers, and other local stakeholders and will provide opportunities for mentoring undergraduates.