Fruit quality of pomegranate grown in arid environment and irrigated with saline water

Authors: CENTOFANTI, TIZIANA - California State University; Banuelos, Gary; Wallis, Christopher

Submitted to: Sustainable Water Resources Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2017
Publication Date: 10/1/2017
Citation: Centofanti, T., Banuelos, G.S., Wallis, C.M. 2017. Fruit quality of pomegranate grown in arid environment and irrigated with saline water. Sustainable Water Resources Management. 1-14. https://doi.org/10.1007/s40899-017-0191-7.
DOI: https://doi.org/10.1007/s40899-017-0191-7

Interpretive Summary: In arid regions, utilizing saline soils and waters naturally rich in trace elements requires identifying new crops for sustaining crop production under poor growing conditions. Poor quality water produced from such soils can be utilized to grow specialty crops, e.g., pomegranates, that are specifically selected for tolerance to high salt and boron (B). The goal of this micro-plot field study was to evaluate the physiological responses related to nutritional quality in fruit from one-year old pomegranate trees irrigated for three years with typical poor quality water found in the western San Joaquin Valley, CA). Results from this study showed that the young pomegranate trees tolerated irrigation with poor water quality at various salinity levels for three years. Under the adverse growing conditions, fruit were generally smaller than fruit collected from pomegranate trees irrigated with good quality water. The juice produced from fruit collected from trees irrigated with poor quality water contained Se, as well as higher concentrations of nutrients, including antioxidant phenolic compounds. The production of nutrient-enriched pomegranate fruit juice may represent higher market value crop product by using poor quality water as a source of irrigation. Longer term studies (beyond 3 years) are, however, necessary to determine if the nutritional effect in pomegranate juice is further enhanced with longer use of poor quality waters and importantly, is the soil quality still able to sustain growth of pomegranate trees.

Technical Abstract: Soils in the west side of the SJV were derived from Cretaceous shale rock and contain high levels of naturally occurring selenium (Se) oxyanions, sulfate, and boron (B) salts. With the installation of subsurface tile drainage system in such soils, leaching the salts out of the rooting zone with excessive irrigation water was a management practice and an effective tool to manage land salinization and to maintain a lower water table. Consequently, a strategy was proposed for disposing of this water by reusing the poor quality water on growing alternative crops, specifically selected for tolerance to high salt and B. One crop to consider is pomegranate (Punica granatum L.), which has been grown as a food crop under saline conditions in an arid climate throughout different regions of the world. To our knowledge there are no studies that have evaluated the response of pomegranate production and fruit quality when irrigated with poor quality water containing Se, salts, and B. The goal of this study was to evaluate the physiological responses related to nutritional quality in fruit from one-year old pomegranate trees irrigated for three years with typical poor quality water in a sandy loam soil. The trees were first irrigated with a salinity of ranging from 3,6, and 9 dS m-1 and containing 0.25 and 4 mg L-1 of Se and B, respectively. Under these irrigation treatments for three years, trees and fruit were smaller in size and showed a relatively stunted growth compared to those irrigated with good quality water. Despite the poor growth and lower fruit yield obtained from trees in this study, the fruit quality was higher in terms of concentration of phenolic compounds and Se content. Generally, effect of saline waters on polyphenols concentration was not significant for most anthocyanin and non-anthocyanin compounds analyzed, except for Cyanidin-3-hexoside, Cyanidin rutinoside, and Pelargonidin-3-glucoside; they were higher in year 3 for trees irrigated with saline water. In addition, the saline treatments did not have any significant effect on most of the tested macro- or micro-nutrient concentrations in the fruit juice, except Se. The juice produced from fruit collected from trees irrigated with salinity contained Se (up to 0.24 mg L-1). Our results demonstrate that the saline waters can be used to irrigate young pomegranate trees for at least 3 years in a sandy loam soil. Although the trees were physically stunted from saline treatments, the trees still produced healthy fruit albeit smaller but they contained higher concentrations of Se and certain phenolic compounds. More research is need to study the longer term effects on soil (e.g., accumulation of salt, B), and on tree and fruit quality when using such waters for the irrigation of pomegranate trees.