Responses of pasture legumes to zinc on calcareous soils in the Riverina, New South Wales

The low availability of zinc on a number of calcareous grey and brown soils of heavy texture with pH>8, in the Coleambally Irrigation and Balranald areas of New South Wales, resulted in marked deficient symptoms in, and responses to zinc by, Bacchus Marsh subterranean clover (Trifolium subterranean L.), grown on these soils. An interaction between zinc and manganese occurred but there was no yield advantage in applying manganese in place of, or together with, zinc. Healthy subterranean clover grew on the surface soil (0-4 in.) of Yooroobla clay, a gilgai puff, but plants on the subsoil, which is exposed when the soil is leveled for irrigation, were extremely, zinc deficient. The pH of the subsoil is generally about 0.5 units higher than that of the surface soil. Legume species and strains differed in their response to zinc. Ladino white clover (Trifolium repens L.) and Clare subterranean clover responded less to applied zinc than Bacchus Marsh subterranean clover, and barrel medic 173 (Medicago tribuloides Desr.) responded less than Ladino white clover. When no zinc was applied barrel medic 173 yielded better than Ladino white clover, and Ladino white clover and Clare subterranean clover better than Bacchus Marsh subterranean clover.