Date of Award
Master of Science
Christopher J Currey
Due to the increased production of local craft beers in the state of Iowa, interest in local hops has been piqued. In order to support the budding hop industry in the Midwest United States, regionally relevant empirical research is necessary, specifically regarding nitrogen (N) fertilizer recommendations. In order to refine fertilizer recommendations for the Midwest, a hop yard was established, and two experiments were conducted.
The objective of the first experiment was to determine the optimal concentration of urea (U) to maximize yield and quality, defined as the percentage of α- and β-acids in the final dried cones. It was hypothesized that a specific amount of urea would be optimal to support biomass accumulation and maintain quality. To test this hypothesis seven concentrations of U were tested, starting at 0 lb N∙a–1 to 300 lb N∙a–1 in 50 lb N∙a–1 increments. Quality and yield were measured at the end of each growing season. As the concentration of urea increased yield also increased, but quality, specifically the percentage of α-acids declined. Based on experimental results, 150 lb N∙a–1 may be recommended in order to maintain quality and support biomass accumulation.
The objective of the second experiment was to determine the optimal form of N fertilizer. It was hypothesized that a nitrate (NO3–) based fertilizer would promote biomass accumulation. To test the hypothesis, an experiment was conducted with five combinations of N fertilizer applied in split-application at a concentration of 150 lb N∙a–1. The combinations were made up of calcium nitrate (CN), urea ammonium nitrate (UAN), and U applied in the following combinations (first application-second application): CN-CN, CN-UAN, U-U, U-UAN, and UAN-UAN at 75 lb N∙a–1 per application. Nitrate-based fertilizers resulted in higher yields and may be recommended to support biomass production. Quality was unaffected by N form.
Ashly Marie Senske
Senske, Ashly Marie, "Optimization of N fertilization for hops (Humulus lupulus) in Iowa soils" (2020). Graduate Theses and Dissertations. 17896.