OOS 10-2 - Learning from on- and off-farm urban agriculture studies: exploring the role of experimental design in variability and insights from nitrate and phosphate leaching studies

Background/Question/Methods
Over the past 15 years, urban agriculture research has been a growing area of study in diverse disciplines, including agroecology and ecology. These studies leverage varied experimental designs, with different levels of control over variables. Off-farm studies, conducted in campus research gardens or agricultural experiment stations, have the highest level of control over all aspects of the study, from planting to measurement schedules to irrigation. On-farm studies, conducted in collaboration with urban growers, may control for some variables, but many aspects of management -- including irrigation, measurement schedules, harvest, etc. -- may be managed by growers. There have been limited studies, however, assessing the effects of experimental design on study results -- results which ultimately shape our conclusions and the possible actions we imagine. The co-authors of this presentation explore this question by comparing phosphate and nitrate leaching results obtained from multi-year on- and off-farm urban agriculture studies in Minneapolis/St. Paul, MN. The on-farm study had three replicated treatments across four farm sites, while the off-farm study had six replicated treatments in their campus garden. Lysimeters were installed one foot below the soil surface and water samples were collected weekly throughout the growing season.

Results/Conclusions
Our findings highlight the potential impacts of experimental design -- specifically, differing levels of control over variables between on- and off-farm studies -- on study results. Our findings are limited in that they compare a limited set of metrics - nitrate and phosphate concentrations in leachate - and future studies should include additional metrics. We highlight the opportunities to create paired on- and off-farm projects, such as the collaboration between researchers at the University of Minnesota and University of St. Thomas in Minneapolis/St. Paul, to leverage the strengths of diverse levels of control to better understand ecological processes in urban agriculture.