UC Delivers

Irrigation research delineates tradeoffs in fruit quality and yield

The Issue

Production of navel oranges for the early market is big business in the southern San Joaquin Valley of California. Minimum harvest standards exist for juice sweetness and fruit color within the industry. The first harvested fruit of the season that meet these minimum requirements often receive a large price premium in the marketplace. Concern exists within the industry that standards for sweetness and some other fruit quality parameters are not sufficient to meet consumer acceptability and that disappointed consumers are unlikely to return to buy navel orange fruit later in the season when the fruit is sweeter and juicier. Growers of early-maturing orange varieties approached late-season irrigation strategies differently and little scientific research existed to guide these decisions. Some growers irrigated fully until harvest, while others reduced irrigation as harvest approached. In drought years, irrigation decisions are not only made as they affect fruit quality and yield, but also with respect to water availability and cost.

What Has ANR Done?

UC Kern County farm advisors Craig Kallsen and Blake Sanden, in cooperation with a private citrus grower, developed and implemented a series of carefully monitored irrigation treatments that allowed delineation of the affects of late-season irrigation stress on fruit quality and yield. Yield and fruit quality evaluations of the fruit harvested from this trial were conducted at the experimental pack line and laboratory at the UC Lindcove Research and Extension Center. To determine if laboratory-measured differences in fruit quality parameters - such as percentages of soluble solids, titratable acid and juiciness - correlated with human sensory perception, fruit from the irrigation treatments was evaluated by a human sensory panel through a program developed by UC Extension Specialist Mary Lou Arpaia, located at the UC Kearney Agricultural Center.

Results from this project were presented at ANR-sponsored grower meetings in Kern County in 2007, 2008 and 2009 and appeared in a statewide newsletter, “Topics in Subtropics." A final report of the project appeared in the 2008 annual report of the Citrus Research Board, which is the statewide citrus commodity group in California.

The Payoff

Quantifying impacts of late irrigation stress on yield and quality

Growers specializing in producing fruit for the early navel market now have available to them knowledge of the tradeoffs related to irrigating early navel varieties in the August-through-October time period. This reasearch demonstrated, on the positive side, that late season irrigation stress saved water, increased development of early fruit color and increased the concentration of soluble solids, such as sugar, and organic acids. On the negative side, water stress, generally, reduced fruit size and yield.

Contact

Supporting Unit: Kern County

Blake Sanden, irrigation and agronomy farm advisor, (661) 868-6221, blsanden@ucdavis.edu

Craig Kallsen, citrus farm advisor, (661) 868-6221, cekallsen@ucdavis.edu

Mary Lu Arpaia, Extension specialist, (559) 646-6561, arpaia@uckac.edu