UC Riverside

In California, a multiyear drought from 2009 to 2016 forced avocado growers to re-evaluate their water management practices. Groundwater, which accounts most of the state’s water supply, was in direct competition with urban and environmental demands for water. California production accounts for 90% of the avocados produced in the United States avocado which is an economically important commodity to the state. When faced with fluctuations in water availability, reliability, and quality, avocado growers must consider the effects of these changes on long term yield and profits. The dissertation research was divided into two projects which were organized into two main chapters. Research in chapter 2 used a survey instrument distributed to growers to learn about their use of irrigation management practices. The results of this research identified key determinants underlying which combinations or “bundles” of technologies and management practices were implemented by California avocado growers during the current drought. Results indicated that the likelihood of adopting more advanced water-saving technologies and management practices increased with the shift in the location of the orchard from cooler coastal counties to hotter and drier inland areas, with the increased proportion of grower income derived from avocado production, and the greater level of importance the grower placed on information obtained from cooperative extension services; it decreased with increased irrigation complexity and grower age. Results indicated that the likelihood of adopting more advanced water-saving technologies and management practices increased with the shift in the location of the orchard from cooler coastal counties to hotter and drier inland areas, with the increased proportion of grower income derived from avocado production, and the greater level of importance the grower placed on information obtained from cooperative extension services; it decreased with increased irrigation complexity and grower age. Research in chapter 3 was a field study of the impacts of quantity and quality of irrigation water on avocado orchards. The overall goal of the research was to determine how water quality and soil hypoxia effect leaf chloride, manganese, iron and yield on ‘Hass’ avocado trees grafted on different rootstocks. A second objective was to determine whether tree uptake of iron and manganese is affected by hypoxia and whether the concentrations of these nutrients in leaf tissues may serve as surrogate markers for avocado tree exposure to hypoxia over time. The research was conducted over multiple years in three orchards, which were representative of the spatial and climatic variations of the avocado-growing regions in California. In each orchard, in situ soil monitoring equipment for continual recording of soil salinity, volumetric water content, soil temperature, soil water potential and irrigation frequency were installed. Soil hypoxia appeared to have no statistically significant effect on leaf chloride accumulation in this dataset. Leaf manganese accumulation proved to be a better marker for soil hypoxia followed by leaf iron. Results indicate that irrigation salinity may be an environmental factor that effects alternate bearing in ‘Hass’ avocado. Results may help guide avocado growers in irrigation management and emphases the importance of understanding microsite variability with an orchard. The combined results from projects one and two will help guide grower irrigation practices for optimizing both yields and profitability in relation to water quality and soil type.