Plan B Project for Master in Statistics: The Effect of Farming Practices on Changes in Soil Organic Carbon and Nitrogen

The amount of organic carbon and nitrogen stored in the soil are thought to be related to climate change. This collaboration with researchers from the Department of Soil, Water, and Climate investigated the effects of farming practices on changes in soil organic carbon and nitrogen. Specifically, the effects of irrigation systems and the amount of manure applied were studied using soil samples collected from Fall 2006 to Fall 2013 at 98 GPS-registered sites at a large dairy in Western Minnesota. Since the data involved repeated measures over time as well as potential correlation between nearby sites, several mixed models were fit to investigate the correlation structures within individual sites between years and also the spatial correlation between sites. Results were qualitatively similar between models, but model selection procedures and information about the nature of the data were used to assess the results of the analyses and possible limitations.