Selenium Accumulation in "Jose" Tall Wheatgrass (Thinopyrum ponticum) Irrigated with Saline Drainage Water .

Utilization of saline drainage water (DW) for irrigation in the western San Joaquin Valley (SJV) of California is limited by the presence of selenium (Se) in the DW and potential risks to the environment. ‘Jose’ tall wheatgrass (Thinopyrum ponticum; TWG) is a highly salt tolerant forage that is suitable for reuse systems, but in some cases Se accumulated to >10 mg/kg DM in the herbage.  High levels of Se in the forage raised concerns for its safety for animal feeding, but it also presented an opportunity to use this Se-enriched hay in areas where Se  is deficient and dairy cattle are commonly administered Se in the form of sodium selenite. A greenhouse study was conducted to assess Se accumulation in TWG herbage as impacted by different cutting heights (CH 20, 40, 60 cm) and irrigation water combinations (salinities of 3 and 12 dS/m EC_w and Se concentrations  of 350 and 1000 µg/L) arranged in a split-plot design.

            For plants cut at 40 or 60 cm, Se concentrations >10 mg/kg DM in the herbage were obtained with high Se irrigation waters that were either high or low in salinity. However, for plants cut at 20 cm, Se accumulation was greater when the high Se water was low in salinity. Dry matter yield was highest for TWG plants cut at 60 cm and a greater mass of Se accumulated in these plants, as compared to those cut at 40 or 20 cm. Most minerals were at or near optimum levels; however, high concentrations of S and Cu in the herbage may require that care be taken when feeding to ruminant animals.