Selenium Incorporation and Partitioning in ‘Jose' Tall Wheat Grass (Thinopyrum ponticum cv. jose) Irrigated with Saline Drainage Water.

In the western San Joaquin Valley (SJV) of California, re-use of saline drainage water (DW) for irrigation has been conducted primarily to dispose of selenium (Se)-enriched DW with minimal impact to the environment.  Due to extreme water shortages in this area in recent years, this DW is now viewed as a valuable alternative water source, particularly for forage production.  ‘Jose’ tall wheatgrass (TWG) is a highly salt tolerant forage that has performed well in this area, having adequate dry matter production and quality even when grown in soils of 20 dS/m ECe.  In soils, where Se is also very high, this forage has accumulated up to 10 mg Se/kg DM when abundantly irrigated with saline DW.   Conversely, in the eastern SJV, soils are low in Se and dairy cattle producers often supplement their animals with inorganic sodium selenate.  In fact, lactating cows are responsible for an approximate annual input of 3405 kg of Se into the San Joaquin and Sacramento Valleys, primarily as feed additives.  The overall goal of the research is to evaluate the potential of utilizing TWG as a substitute for Na selenate in cattle diets.  Specifically, our objective is to identify management practices resulting in higher Se incorporation in TWG and to determine its bioavailability for cattle.  A greenhouse study was initiated with irrigation water treatments of two salinity levels (ECe 3 and 12 dSm^-1 ) and two selenium levels (250 and 1000 ppb), along with three cutting frequencies (at 15, 30, 45 cm) arranged in a split-split plot design with the forage grown in pots containing a 60:40 mix of field soil and sand.  Data on Se partitioning into young and old tissue and soil and irrigation water characteristics will be presented.