THE IMPACTS OF SUSTAINED DEFICIT IRRIGATION MANAGEMENT ON MINT AND CANOLA OIL CROPS IN THE COLUMBIA BASIN, PACIFIC NORTHWEST, USA
Okwany, Romulus Okoth
MetadataShow full item record
The need for increased agricultural and industrial production, municipal use and environmental constraints is making it a critical decision to develop new technologies and improve available management options for more effective and efficient use of the available freshwater use.This dissertation is a collection of researches on the impacts of sustained deficit irrigation (SDI) on the yields of two specialty crops grown in the Pacific Northwest, USA. The main objective of these researches was to investigate the yield responses of the crops to sustained deficit irrigation. We also aimed at suggesting general and specific recommendations on the feasibility of adapting sustained deficit irrigation management for their production. The crops were subjected to season-long SDI levels for an insight in production potentials at different water supply levels. The crops' yield parameters and quality attributes were evaluated to assess the impact of water stress to the harvestable and marketable products.The spearmint investigation showed that its biotic response to water stress is by decreased biomass and oil yield. Of special interest is that the proportion of oil yield to biomass yield decreases is significantly lower signifying a productivity gain in the marketable oil yield with respect to the biomass raw material. Oil quality components also show positive improvement with water stress that would be attractive for marketers in view of the possibility to increase market premium on this oil.Canola crop study showed significant seed and oil yield reductions under water stress. The two canola cultivars show significant differences in their responses to the varied water stress levels. Study illustrates cultivar variability that would be crucial in an intensive water management system employing water deficit, requiring grower awareness of impact of management decisions that would face their enterprises under such a system.The final study showed that peppermint is not adaptable to SDI even at fairly low water stress levels. Oil quality improvement is demonstrated but is too low in relation to the seed and oil yield loss.Irrigation deficit had impacts on the yield and quality components of the crops. The impact varies between crops and cultivars. Implementation of SDI is a risky undertaking but with good management and with the prior understanding of the impacts to a crop offers better alternative to complete crop loss or fallowing due to water shortages. There is potential to adopt SDI strategies within crop-, cultivar- and market-specific considerations.