NUTRIENT CYCLING IN PACIFIC NORTHWEST OILSEED PRODUCTION
Hammac, Warren Ashley
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Nutrient cycling is an important matter in all crop production but it is particularly important in oilseed production. The efficiency by which oilseed crops can be grown and the impact of their cultivation dictates the future of bioenergy policy. The dissertation that follows attempts to dissect the intricacies of nutrient cycling in Pacific Northwestern oilseed production to inform policy and provide farmers with valuable information. This dissertation is comprised of four chapters including 1) Nitrogen Use Efficiency In Eastern Washington Canola Production, 2) The Impact of Nitrogen Rate and Timing and Sulfur Rate On Eastern Washington Canola Grain, Oil Yield, and Oil Quality, 3) Cropping System, Nitrogen Use Efficiency, and Adoption Rate Impact on Greenhouse Gas Mitigation Potential for Pacific Northwest Canola Production, 4) High Resolution Imaging to Assess Oilseed Species’ Root Hair Responses to Soil Water Stress. Canola has the potential to be a successful crop in the dryland Pacific Northwest due to its high yield potential with little available water; however, many challenges must be overcome. Nitrogen recommendations should account for canola’s ability to access residual soil N and redeposit it for a following crop. Nitrogen timing and sulfur rate and timing appear to have little effect on grain and oil yield in spite of previous reports to the contrary. Canola nitrogen use efficiency has a major impact on life cycle greenhouse gas production when compared to that of fossil derived diesel. The Environmental Protection Agency’s Renewable Fuels policies would do well to encourage improved nitrogen use efficiency in biofuel feedstock production to magnify the greenhouse gas mitigation potential that renewable fuels offer. Utilization of simple and inexpensive imaging techniques are effective ways to conduct root research that may help in understanding the role of plant root hairs in soil carbon accumulation and storage. High resolution imaging of various root systems under varying levels of water availability indicate root surface area, density, and architecture are significantly affected by water availability. Nutrient uptake, cropping system and soil carbon sequestration models that do not account for these differences are prone to error.