Date of Award:

5-2017

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant, Soils and Climate

Committee Chair(s)

Bruce Bugbee

Committee

Bruce Bugbee

Committee

Brent Black

Committee

Scott Jones

Committee

Corey Ransom

Committee

Niel Allen

Abstract

Tree fruit crops are of high value, but use a lot of water. Precision irrigation has the potential to save water while simultaneously improving crop quality. The timing and method of precision water stress in various tree fruit crops has been widely studied. However, in order to successfully employ precision irrigation methods in orchards, an accurate measurement of tree water status is required. Currently, stem water potential is the preferred indicator. However, this measurement is tedious and cannot be automated. Because measurements must be taken near solar noon (approximately 1:30 PM MDT in the summer in northern Utah), the number of measurements that can be recorded per day is limited. An automated, electronic measure of tree water status to replace stem water potential measurements is much sought after.

Numerous methods have been studied, including evapotranspiration models, soil water status and direct measurements of tree water use. Many of these techniques have demonstrated some level of utility, but none has been adopted for widespread use in orchards. The most widely studied include fluctuations in stem diameter, canopy temperature changes and sap flow measurements.

Canopy temperature measurements have great potential for determining tree water status. The main challenge with this technique in orchards is the heterogeneity of the orchard canopy as compared to a field crop. Exploring various methods of measuring canopy temperature changes could provide the needed plant-based metric required to successfully employ precision water stress in orchards.

Measurements of trunk hydration using time-domain reflectometry have been studied for many years, but sensor cost prohibited the widespread use of this technique. The evolution of less expensive sensors has triggered a renewed interest in this technique. Still, much needs to be learned about the best methods to obtain accurate measurements of trunk hydration.

Should precision water stress production systems become more widely used, the influence of rootstock characteristics on drought-tolerance becomes increasingly important. This research provides evidence that some rootstocks are more drought-tolerant than others. The research also presents findings in regard to canopy temperature measurements using infrared thermometry and measurements of trunk hydration using electromagnetic moisture sensors.

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