Biomass accumulation and potential nutritive value of some forages irrigated with saline-sodic drainage water

Abstract

A controlled study using a sand-tank system was conducted to evaluate 10 forage species (bermudagrass, ‘Salado’ and ‘SW 9720’ alfalfa, ‘Duncan’ and ‘Polo’ Paspalum, ‘big’ and ‘narrow leaf’ trefoil, kikuyugrass, Jose tall wheatgrass, and alkali sacaton). Forages were irrigated with sodium-sulfate dominated synthetic drainage waters with an electrical conductivity of either 15 or 25 dS/m. Forage yield was significantly reduced by the higher (25 dS/m) salinity level of irrigation water compared to the lower (15 dS/m) level. There was wide variation in the sensitivity of forage species to levels of salinity in irrigation water as reflected by biomass accumulation. With the exception of bermudagrass, which increased accumulation at the higher level of salinity, and big trefoil, which failed to establish at the higher level of salinity, ranking of forages according to the percent reduction in biomass accumulation due to the higher level of salinity of irrigation water was: Salado alfalfa (54%) = SW 9720 alfalfa (52%) > Duncan Paspalum (41%) > narrow leaf trefoil (30%) > alkali sacaton (24%) > Polo Paspalum (16%) > Jose tall wheatgrass (11%) = kikuyugrass (11%). Bermudagrass and Duncan Paspalum were judged to be the best species in terms of forage yield and nutritive quality. Kikuyugrass, which had the third highest biomass accumulation, was judged to be unacceptable due to its poor nutritional quality. Although narrow leaf trefoil had a relatively high nutritional quality, its biomass accumulation potential was judged to be unacceptably low. Alfalfa cultivar’s biomass accumulations were the most sensitive to the higher level of salinity, among forages that survived at the higher salinity level, although actual accumulations at the higher salinity were high relative to other forages. Increased salinity influenced several forage quality parameters, including organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), and in vitro gas production, generally leading to higher nutritional quality at the higher salinity level, although their significance varied amongst species and cuttings.