Co-chairs, Graduate Committee: Clain Jones and Craig CarrFordyce, Simon IsaacPat 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.2022-06-102022-06-102022https://scholarworks.montana.edu/handle/1/16757Shallow 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.enSoil depthWheatNitrogenGroundwater--PollutionRemote sensingSpectral imagingThesisCopyright 2022 by Simon Isaac Fordyce