Masters Thesis

Investigating Various Continuous Measures of Plant Water Status for Avocado Trees to Guide Irrigation Scheduling

There is an urgent need in many water-limited regions for new irrigation strategies to minimize water use in agriculture and horticulture. Such strategies largely rely on atmospheric measures to determine plant water needs, but direct plant-based measures are argued to be better for assessing water needs of orchard trees. The aim of this study was to identify plant-based measures of water status in Fuerte avocado, Persea americana, that can be continuously monitored to guide irrigation decisions. the experiment was conducted in an orchard at the Fullerton Arboretum in southern California. Avocado trees were subjected to temporary drought conditions during which several water status parameters were monitored, including soil water content and soil water potential. the state of water stress was determined directly by measuring leaf water potential. Additional measurements included trunk diameter variations (TDV), maximum daily trunk shrinkage (MDTS), trunk water potential (TWP), trunk water content (TWC), and sap flux density (SFD). To determine the best continuous plant- and/or soil-based measures for irrigation scheduling, correlations were assessed between daily means or daily totals of plant-based measures and soil water potentials. Daily TWC and TWP clearly and consistently declined during drought conditions and produced the strongest correlations with soil water potentials. Measurements of soil water potential, trunk water potential and trunk water content appear to be the best tools for detecting changes in plant water status reliably in avocado trees, ideally when used in combination.

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