Biomass yield and nutritional quality of forage species under long-term irrigation with saline-sodic drainage water: Field evaluation

On the Westside of California's San Joaquin Valley, the discharge of subsurface agricultural drainage water (DW) is subject to strict environmental regulations due to its high selenium (Se) content and potential risks to wildlife. Re-use of saline-sodic DW to irrigate salt-tolerant forage crops is attractive because it reduces the volume of DW requiring disposal and the land area affected by salinity, while producing forages to satisfy the large demand for animal feed resulting from rapid expansions in dairy and beef cattle operations in this area. The biomass production and nutritional quality of six forages (‘Jose’ tall wheatgrass, creeping wildrye, alkali sacaton, ‘Alta’ tall fescue, puccinellia and ‘Salado/801S’ alfalfa) were evaluated under DW irrigation on a commercial farm near Five Points in Fresno County, California. The forage fields were in their second to fifth year of DW application and most had soil salinities higher than 12 dS/m ECe (electrical conductivity of the saturated soil paste extract). In addition to being very saline, the fields had high levels of boron (B), Se and sodicity [high sodium (Na) relative to calcium (Ca) and magnesium (Mg)]. ‘Jose’ tall wheatgrass and creeping wildrye had acceptable dry matter (DM) production (7.0 and 11.5 t/ha year) under highly saline conditions of 19 and 13 dS/m ECe, respectively. Alfalfa produced 16–20 t/ha year of DM under low salinity conditions of <7.0 dS/m ECe. The forages had estimated metabolizable energy (ME) contents of 7.9–9.9 MJ/kg DM – with the exception of alkali sacaton (6.7 MJ/kg DM) – which would make them acceptable as feeds for beef cattle, sheep and some classes of dairy cattle. Selenium levels varied from 4.4 to 10.7 mg/kg DM in forages that had received 4–5 years of DW application. Forages at the high end of this range could cause Se toxicity in ruminants when used as a sole source of forage, but they could also be used as a Se supplement if fed at a rate of 20–40 g/kg in the Se-deficient areas found along the eastern SJV. Saline-sodic DW can be used as a water resource to produce forage suitable for many classes of ruminants, although drainage waters with high levels of Se may present both problems and opportunities.