NITROGEN MANAGEMENT USING MULTI-SPECIES COVER CROP MIXTURES

Open Access
- Author:
- Raggazino, Robert Thomas
- Area of Honors:
- Agroecology
- Degree:
- Bachelor of Arts
- Document Type:
- Thesis
- Thesis Supervisors:
- Charles Macaulay White, Thesis Supervisor
Dr. Heather D Karsten, Thesis Honors Advisor - Keywords:
- nitrogen management
cover crops
agroecology - Abstract:
- Nitrogen management is an important part of any farm system; nitrogen is typically the most limiting nutrient for plant growth, the most expensive nutrient applied to crops as fertilizer, and is easily lost from soil through processes such as leaching, denitrification, and volatilization. Nitrogen deficiency can lead to poor yields and nitrogen overabundance can cause nitrate leaching. Losses of nitrogen to the environment cause issues such as ground water pollution, eutrophication of water bodies, and can act as greenhouse gases. Nitrogen fertilizer is extremely energy intensive to manufacture and accounts for a large portion of agriculture’s carbon footprint. Cover crops provide a potential tool in farm system nitrogen management, lessening the need for expensive chemical fertilizer inputs and reducing nitrate leaching. Cover crops can be used for nitrogen management in three scenarios: to retain nitrogen against leaching, to fix nitrogen from the atmosphere to supply to the following crop, or to do both. This thesis examines the third scenario, utilizing mixed-species cover crop plantings composed of various combinations of a winter hardy legume, a winter killed legume, and a winter hardy grass. The main goal of the research is to determine the optimal species composition and seeding rates of a cover crop to balance the nitrogen retention and nitrogen supply functions. We used a response surface design to study how different plant densities of fava bean (winter killed legume), red clover (winter hardy legume), and triticale (winter hardy grass) interacted to influence nitrogen retention and supply. Using the response surface design, we created 20 unique cover crop treatments, each replicated three times. Fava bean was grown at four different densities (0, 56, 112, and 168 kg/ha) in monocultures and in bicultures with red clover planted at 13 kg/ha. Four different densities of triticale were crossed with the fava bean/red clover bi-cultures (0, 22, 45, 67 kg/ha) to form tri-cultures with different rates of fava bean and triticale plant densities. We measured cover crop biomass in October 2012 and soil nitrate concentrations in November 2012 and March 2013 as indicators of potential nitrogen retention and supply. There was a positive relationship between fava bean plant density and nitrogen content, with a hyperbolic yield-density model showing the best fit to the data. Increasing fava bean plant density reduced red clover biomass nitrogen in the bi-culture plantings, however. No negative relationship was observed between triticale and red clover; the relationship requires future research as neither species had reached full maturity at the October sampling date. Increased fall N uptake by triticale in the tricultures was correlated with lower soil nitrate concentrations in early spring, suggesting that including triticale as a component of a mixture may be effective at reducing nitrate leaching.