Chairperson, Graduate Committee: Catherine A. ZabinskiNeff, Karin StocktonBruce D. Maxwell and Catherine A. Zabinski were co-authors of the article, 'Input C:N effects on soil fertility and spinach yields over three years' submitted to the journal 'Agriculture, ecosystems and environment' which is contained within this thesis.William E. Dyer, Bruce D. Maxwell and Catherine A. Zabinski were co-authors of the article, 'Organic matter effects on spinach antioxidant production' submitted to the journal 'Journal of the science of food and agriculture' which is contained within this thesis.Karin Neff, Bruce D. Maxwell, Clain Jones, Elizabeth Hummelt and Catherine A. Zabinski were co-authors of the article, 'Estimating plant available nitrogen in organic market garden systems' submitted to the journal 'Soil biology and biochemistry' which is contained within this thesis.Bruce D. Maxwell, Katie Atkinson and Catherine A. Zabinski were co-authors of the article, 'Thinking like a microbe: the biological mechanisms of fertility in sustainable mixed-vegetable production' submitted to the journal 'Applied soil ecology' which is contained within this thesis.2016-01-032016-01-032014https://scholarworks.montana.edu/handle/1/9361The increasing consumer interest in high quality foods -especially fruits and vegetables with high antioxidant phytochemicals -has led to interest in determining the effects of cropping system practices on phytochemicals over the last decade. Appropriate fertility management is critical to optimize agricultural production, both for yield and crop nutritive value, and minimize losses to the environment. In organic production systems, fertility management generally relies on soil microbial processes to decompose organic matter. To better understand the dynamics of mulch decomposition and the resulting effects on soil fertility and crop yield, a three-year randomized strip-plot experiment was implemented on the Montana State University Horticulture Research Farm. Two mulch inputs with varying carbon to nitrogen ratio (C:N), decomposition rates and microbial responses were contrasted with two non-mulched treatments, urea N fertilizer and a no-treatment control. Spinach biomass, yield, total phenolics and antioxidant capacity were measured as plant response variables to changes in soil fertility and biology due to the different inputs over three years. Water-extractable organic matter (WEOM), available nitrogen (N), phosphorus (P) and potassium (K), carbon (C) respiration, N mineralization, soil enzyme activity, microbial biomass and mycorrhizal infectivity potential were measured to assess soil fertility and biology. The hay mulch treatment increased nutrient availability and soil biological responses, and produced high spinach yields. The straw mulched treatment had a delayed effect on N availability and lower spinach yields initially, but in subsequent years both yield and biological parameters increased in the straw mulched treatments. Both mulch treatments produced cumulative spinach yields comparable to or exceeding the N-fertilizer plots. Only slight differences in total phenolic concentration and antioxidant capacity were measured among treatments indicating that other factors likely influence spinach phytochemicals more strongly than SOM. Measuring biological responses can be a sensitive measure of soil function and an important addition to farm management to better estimate how different management practices will affect soil processes, yields and the environment.enPhytochemicalsMulchingSoil fertilityResearchDissertationCopyright 2014 by Karin Stockton Neff