Date of Award:

12-2013

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

Brent L. Black

Abstract

Producing fruits and vegetables in the Intermountain West can be challenging due a short growing season, extreme temperatures, and limited availability of irrigation water. This is particularly true of strawberries, where commercial production is limited due to late fall and early spring frosts that shorten the growing season. With the increasing demand for local produce as urban populations grow and as consumer buying habits change, growers are looking for ways to overcome these climatic challenges. High tunnels are one option growers can use. High tunnels are similar to greenhouses, but less expensive to construct and to maintain. Another way to protect crops against adverse climatic conditions is with low tunnels. As the name implies, they are a smaller version of a high tunnel, usually only tall enough to cover the canopy of the plant. Low tunnels can be used by themselves or in conjunction with (inside) a high tunnel. Adding heat is another option. However, heating can be expensive and may not be profitable. Targeting heat additions in the root zone may decrease cost of heat but still provide protection to the plant.
These protection methods were evaluated in Cache Valley, Utah for effectiveness of increasing strawberry yield. High tunnels increased total yield, as did high tunnels used in conjunction with low tunnels. However, low tunnels by themselves were not able to increase yield in comparison to unprotected plants in the field. Targeted root zone heating was evaluated in both high and low tunnel with two target temperatures: 7 and 15 °C. There was no difference in total yield between the two temperatures, but both increased yield above the high tunnel alone and the 15 °C heating treatment moved the harvest season approximately 6.5 weeks earlier than unheated tunnels and approximately 12 weeks earlier than field production. The additional cost associated with using supplemental heat was offset by the increased yields and the higher value of early fruit.
Separate experiments were carried out to determine susceptibility of strawberry leaves to damage from cold temperatures, which can then be used to provide guidelines for temperature management in high tunnels. Strawberry leaves were not significantly damaged when exposed to -3 °C, but significant damage occurred once leaves were exposed to -5 °C. To maximize the advantages of protected cultivation, growers should manage tunnels and heating to keep leaf temperatures above -3 °C. These results provide improved guidelines for growers interested in using protected cultivation strategies to provide fruit for local consumption in the Intermountain West.

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