|Du, D. Le|
Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2009
Publication Date: 3/18/2010
Citation: Banuelos, G.S.,D.D. Lee,J. Johnson.2010.Evaluation of Hybrid Poplar tree tolerance to irrigation with high salinity and boron waters under micro-plot conditions.International Journal of Phytoremediation.Vol.12:1-21 Interpretive Summary: Irrigation water quality and drainage water disposal have become priority issues for irrigated agriculture in the western San Joaquin Valley (SJV) in Central California. Sufficient evidence supports the concept of reusing poor quality water originating from agricultural drainage Instead of simply disposing of drainage waters. The successful adoption of a practical water reuse strategy requires, however, the selection of salt and B tolerant crops for use with waters high in salinity. Due to the wide diversity associated with hybrid poplar tress and their ability to transpire large quantities of water, we evaluated a large number of poplar clones for their tolerance to irrigation with increased salinity and B waters under micro-field plot condition. The majority of the clones tested during the four year evaluation were not able to tolerate the high saline and B waters during their respective growing seasons. Evidence of this intolerance was observed as early abscission of older leaves, followed by drop of younger leaves. Analyses of the leaves showed that most of the poplar clones accumulated excessive concentrations of chloride, and moderate levels of boron. Concentrations of chloride and boron were, however, lower in the tolerant clones. Increases of soil salinity and soluble B at postharvest clearly indicate that even if salt/B tolerant poplar clones are identified, salt and B management strategies for the soil are necessary for long-term use of drainage waters.
Technical Abstract: The concept of reusing salt-laden drainage water in agricultural systems was developed as part of the integrated on-farm drainage management system. The successful adoption of a practical water reuse strategy in Central California requires the selection of salt and boron tolerant crops for use with waters high in salinity (i.e., 10 ds/m) and B (i.e., 10 mg/L). Trees, i.e., Poplus species, may offer advantages over vegetative plants because they transpire larger quantities of water, produce more biomass, have longer life spans, are deeper rooted, promote a greater ecosystem diversity, and regrow new stems after they have been cut. Populus hybrid clones were evaluated for use with waters high in salt and B over a multitude of years under microplot field conditions. Individual clones were planted in 40 L pots with 58 kg soil. Each growing pot contained three different clones and was replicated six times in an unbalanced block design for irrigation with high salinity and B. The electrical conductivity (EC) was initially 10 dS/m and incurred incrementally to 30 dS/m with 10 mg B/L in the irrigation water. Harvest date was determined by the observed severity of either or both B and salt toxicity symptoms for each respective clone during each growing season. Leaf chloride (Cl) and boron (B) concentrations ranged from approximately 1200 to 60000 mg/kg and from 30 to 330 mg/kg in controls and salt/B treatments, respectively among all tested clones. Lower leaves accumulated significantly greater Cl and B concentrations than younger leaves, and the leaves from the most tolerant clones generally contained less Cl and B than those clones exhibiting toxicity symptoms. At postharvest soil B concentrations and soil EC ranged from 0.08 to 3.9 mg/L and 0.9 to 10.8 ds/m in controls and in high salinity/high B treatments, respectively. Because leaf Cl concentrations did not always increase proportionally to the amount of salt applied to soil via irrigation, it was difficult to identify a common Cl exclusion mechanism for the more tolerant clones. For B, leaf B concentrations were relatively low (<330 mg/kg) because the movement of xylem mobile ions, e.g., B, may have been restricted because of the high soil salinity. The broad variation that is the hallmark of the genes Populus may offer opportunities for introducing salt tolerance into breeding programs, even though physiological response mechanisms to excessive salt and B remain poorly understood. Reusing salt/B laden drainage water appears to be possible on a limited number of Populus clones, however, the increased soil salinity and B at postharvest clearly indicate the soil management strategies will be needed for long term use of poor quality waters.