Production and persistence of annual pasture legumes at five saline sites in southern Australia

Herbage production and persistence of 42 annual pasture legumes from 33 species were measured at five sites across southern Australia. Medicago polymorpha L. was highly productive on soils, particularly those not prone to waterlogging, with soil surface (0–10 cm soil depth) salinity [estimated by electrical conductivity (ECe)] levels in summer of up to 36 dS/m, whereas M. truncatula Gaertn. was productive on ECe levels of at least 11 dS/m. Trifolium michelianum Savi and T. resupinatum L. were highly productive on soils subject to waterlogging, but only where 0–10 cm summer ECe levels were less than 8 dS/m. No commercial species were adapted to highly saline (0–10 cm summer ECe levels >8 dS/m), waterlogged sites. However, Melilotus siculus (Turra) Vitman ex B.D. Jacks. has the potential to fulfil this role, provided an appropriate Rhizobium strain can be selected. Mixtures of species and cultivars should be sown to account for high spatial variability for salinity and waterlogging. Traits for annual legume success in saline landscapes include salinity and waterlogging tolerance in germinating seedlings and mature plants, early flowering, hardseededness and delayed softening of hard seeds. Establishment of regenerating seedlings is associated with the timing of hardseed softening in relation to rainfall events capable of leaching topsoil salts. It is proposed that salinity measurements to determine annual legume suitability for winter-dominant rainfall areas are made in summer or early autumn, when at their highest levels. Transects along salinity and waterlogging gradients are suggested as an alternative method to traditional plots for genotype evaluation.