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

目前，美国中西部的降雨模式正在发生变化，暴雨事件中降雨量的比例越来越大。这种降雨模式的加剧可能会对雨水灌溉的农业产生重要影响。特别是，降雨加剧可能会改变土壤氮素的有效性和损失量。氮是一种基本的作物养分，但它也具有很强的流动性。在化肥中添加到土壤中的氮中，只有大约一半被作物吸收，其余的大部分流失到环境中。淋溶是氮素流失的最重要途径之一，可能会造成负面后果，包括地下水污染、藻类大量繁殖以及河流、湖泊和沿海海洋中的死区。这项研究探索了更强的降雨模式如何影响中西部农业生态系统的氮素淋失。该项目还试图找出在面对气候变化时可以减缓氮素淋失加剧的管理做法。这项研究将在密歇根州西南部的凯洛格生物站长期生态研究(LTER)场地进行生态系统规模的降雨操纵实验。在常规和免耕管理下的农田暴露在环境降雨以及降雨模式下，这些降雨模式延长了旱期和大量的模拟降雨事件。将使用张力式蒸渗仪来测量土壤水氮浓度，并使用模型来估计土壤水分通量，以估算淋溶。深至1.2米的土壤采样将跟踪硝酸盐在一年中沿土壤剖面的移动情况，并对个别降雨事件做出反应。结果将与推广专家、政策制定者和其他当地利益攸关方分享，并将为指导本科生提供机会。

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.