Vegetative approach for improving the quality of water produced from soils in the westside of central California

Abstract

Water reuse is a proposed strategy for utilizing or disposing of poor quality drainage water produced in the westside of central California. This 2-year field study evaluated the ability of two potential forage species to tolerate irrigation with water high in salinity, boron (B), and selenium (Se). The species used were: Sporobulus airoides var. salado (alkali sacaton) and Medicago sativa var. salado (alfalfa). After first year establishment with good quality water (<1 dS m⁻¹), the two species were furrow-irrigated with drainage effluent that had an average composition of sulfate-dominated salinity ((electrical conductivity (EC) of 6.2 dS m⁻¹)) B (5 mg l⁻¹), and Se (0.245 mg l⁻¹). Both crops were clipped monthly from June to October of each year. Total dry matter yields averaged between 11 and 12 mg ha⁻¹ for both crops irrigated with effluent for two growing seasons. Plant concentrations of Se ranged from a low of 1.3 mg kg⁻¹ in alkali sacaton to a high of 2.5 mg kg⁻¹ in alfalfa, while B concentrations ranged from a low of 60 mg kg⁻¹ in alkali sacaton to a high of 170 mg kg⁻¹ in alfalfa. Chemical composition of the soil changed as follows from preplant to post-irrigation after two seasons with drainage effluent: EC from 2.78 to 6.5 dS m⁻¹, extractable B from 1.9 to 5.6 mg l⁻¹, and no change in extractable Se at 0.012 mg l⁻¹ between 0 and 45 cm. Between 45 and 90 cm, EC values increased from 4.95 to 6.79 dS m⁻¹, extractable B from 2.5 to 4.8 mg l⁻¹, and no change in extractable Se at 0.016 mg l⁻¹. Increased salinity and extractable B levels in the soil indicate that management of soil salinity and B will be necessary over time to sustain long term reuse with poor quality water.