Theses and Dissertations at Montana State University (MSU)
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Item Spatial patterns in soil depth and implications for offseason nitrogen dynamics in dryland wheat systems of central Montana(Montana State University - Bozeman, College of Agriculture, 2022) Fordyce, Simon Isaac; Co-chairs, Graduate Committee: Clain Jones and Craig Carr; Pat Carr, Clain Jones, Jed Eberly, Scott Powell, Adam Sigler and Stephanie Ewing were co-authors of the article, 'Exploring relationships between soil depth and multi-temporal spectral reflectance in a semi-arid agroecosystem: effects of spatial and temporal resolution' submitted to the journal 'Remote Sensing of environment' which is contained within this thesis.; Pat Carr, Clain Jones, Jed Eberly, Rob Payn, Adam Sigler and Stephanie Ewing were co-authors of the article, 'Spatiotemporal patterns of nitrogen mineralization in a dryland wheat system' submitted to the journal 'Agriculture, ecosystems, and environment' which is contained within this thesis.Shallow soils (< 50 cm) under dryland wheat (Triticum aestivum L.) production lose large amounts of inorganic nitrogen (N) to leaching. Crops grown in shallow soils may be more responsive to N fertilizer due to lower fertilizer recovery and suppressed mineralization, raising questions as to whether standard practices of N fertilizer rate determination can increase risks of leaching and groundwater contamination in these environments. Mineralized N can be a major nutritional supplement for wheat crops in dryland agroecosystems, so accurate estimates of mineralization inputs can have important economic and environmental implications. To assess the potential for suppressed N mineralization in shallow soils, we used spectral reflectance from up to three sensors (unmanned aerial vehicle, National Agricultural Imagery Program, and Sentinel 2) to spatially characterize soil depth on three fields in Central Montana (Chapter 2) and compared surface (0-20 cm) carbon and N cycling indices across soil depth classes (Chapter 3). Carbon dynamics were stable across depth classes while N mineralization was lower in the shallow class. Results confirm multispectral imagery as a valuable tool for non-destructively characterizing fine-scale spatial patterns in soil depth and corroborate previous findings of lower N mineralization in shallow soil environments. Given the potential for heightened fertilizer responsiveness due to lower mineralization in these environments, decision support systems for site-specific fertility management (e.g., variable rate fertilizer application) should assess the environmental consequences of leaching alongside the economic benefits of applied fertilizer rates which maximize responses of yield, quality and same-year net revenue.Item Factors influencing big sagebrush cover in Southwest Montana(Montana State University - Bozeman, College of Agriculture, 2010) Mendelsohn, Brittany Jennifer; Chairperson, Graduate Committee: Bok Sowell.The sagebrush steppe provides important habitat to many wildlife species. Conifer expansion of Douglas-fir and Rocky Mountain juniper into this area is a growing concern. Currently management focuses on the removal of Rocky Mountain juniper. The primary objective of this study was to determine the relationship between live sagebrush cover and aspect, slope, elevation, soil texture, soil depth and rock outcroppings. The second objective was to compare Douglas-fir and Rocky Mountain juniper's canopy areas at comparable ages. Percent cover of shrubs and conifers as well as the abiotic factors were recorded at forty Wyoming and forty mountain big sagebrush plots at each of three study sites in southwest Montana (Pipestone, Elkhorn, and Whitetail) (n = 240). The best-fit model utilizes the terms site, sagebrush subspecies, square root of conifer cover and site by sagebrush subspecies as the independent variables, with square roots of sagebrush cover as the dependent variable. The model found that abiotic factors had no correlation (p>0.05) with live sagebrush cover, but conifer cover had a negative effect on sagebrush cover. Equations were developed to predict canopy area of Douglas-fir and Rocky Mountain juniper thru time. Our findings suggest conifers should not be removed to increase sagebrush cover due to low response of sagebrush cover. Douglas-fir is the dominant conifer on these sites and has three times more canopy than Rocky Mountain juniper at similar ages (p<0.001). Rocky Mountain juniper is generally thought to have higher food and cover values for deer and elk and upland game birds compared to Douglas-fir (Gunderson 1990, Kufeld 1973). Therefore, the current practice of removing Rocky Mountain juniper to increase sagebrush cover should not be continued.