CAREER: Effects of Urban Agriculture Expansion and Climate on Nutrient Cycling and Loss in Urban Ecosystems

都市农业正在全球许多城市迅速扩张。由于堆肥通常被用作肥料，城市农业有可能将食物垃圾中的养分回收到人类食物系统中。然而，堆肥中养分的有效性可能与作物生产对养分的需求不匹配，不平衡或过度使用堆肥可能会导致养分通过渗滤液或径流流失。在某些情况下，都市农业可能是地下水或地表水污染的原因之一。此外，降水频率和强度的变化有可能影响城市农田的养分流失率。虽然传统农业中的养分动态已经得到了很好的研究，但对都市农业中养分循环的控制却知之甚少，这种循环发生在不同的规模上，受到不同的管理策略的影响。这项研究将对城市农业在明尼苏达州双子城城市生态系统中营养动态方面的作用进行量化和背景分析。项目成果将与当地政策制定者以及科学界分享。每年将有大约140名本科生通过课程参与项目活动，该项目将为大约15名本科生和5名高中实习生提供密集的研究经验。该项目将结合从城市农场和社区花园收集的数据，以及明尼苏达州圣托马斯大学研究场地的实验操作。观测部分将描述不同土壤管理技术的范围和频率，并评估这些不同的管理策略如何导致不同水平的养分利用效率和养分输出。研究人员将根据从农场经理那里收集的关于堆肥使用和农产品产量的信息，为10个城市农场建立养分预算，并将收集有关土壤和渗滤液营养水平的额外数据。此外，研究人员将使用一项对照的重复实验，使用96块4平方米的抬高床地，测量堆肥类型和施用量以及模拟的降雨强度对养分利用效率和渗滤液流失的影响。最后，基于这些结果的统计模型将被用来估计当前和未来情景下城市尺度上都市农业的累积养分通量。

Urban agriculture is rapidly expanding in many cities worldwide. Because compost is generally used as fertilizer, urban agriculture has the potential to recycle nutrients from food waste back into the human food system. However, the availability of nutrients in compost may not match the nutrient demands of crop production, and imbalanced or excessive application of compost could lead to losses of nutrients through leachate or runoff. In some cases, urban agriculture could be a contributor to the pollution of groundwater or surface water. Additionally, changes in the frequency and intensity of precipitation have the potential to affect nutrient loss rates from urban farm plots. Although nutrient dynamics in conventional agriculture have been well studied, little is known about controls on nutrient cycling in urban agriculture, which occurs at a different scale and is subject to different management strategies. This research will quantify and contextualize the role of urban agriculture on nutrient dynamics within the Twin Cities, Minnesota urban ecosystem. Project results will be shared with local policy-makers as well as with the scientific community. Approximately 140 undergraduate students will be engaged in project activities each year through courses, and this project will provide intensive research experiences for approximately 15 undergraduate students and 5 high school interns.This project will combine data collection from urban farms and community gardens, and experimental manipulations across study plots at the University of St. Thomas, Minnesota. The observational component will characterize the range and frequency of different soil management techniques, and to assess how these different management strategies result in different levels of nutrient use efficiency and nutrient export. Researchers will construct nutrient budgets for ten urban farms based on information collected from farm managers on compost application and produce yield, and will collect additional data on soil and leachate nutrient levels. Additionally, researchers will use a controlled, replicated experiment, using 96 four square meter raised bed plots, to measure the effects of compost type and application rate, and simulated rainfall intensity, on nutrient use efficiency and loss via leachate. Finally, statistical models based on these results will be used to estimate cumulative nutrient fluxes from urban agriculture at the city scale, under current and future scenarios.