Growth and regeneration of summer-growing pasture legumes on a heavy clay soil in south-eastern Queensland

Abstract

Growth and regeneration of summer-growing pasture legumes were studied on a black earth site near Dalby on the Darling Downs. Pure swards of some annual and perennial species (i.e. Macroptilium atropurpureum cv. Siratro, Macroptilium lathyroides cv. Murray, Stylosanthes scabra CPI 55856 and Rhynchosia minima CQ2970) were found to be productive (rainfed, 2-3 t ha-1, irrigated, 4-6 t ha-1) over 3 years. A moderately severe summer drought (to be expected on a 1 in 6 frequency), while severely limiting DM production relative to irrigated plots, did not adversely affect plant survival or regeneration in the following season. Waterlogging associated with normally high autumn and winter rainfall did prevent perennation, but regeneration from soil seed reserves was excellent and sward survival was not affected (4 t ha-1 after 3 years). The soil studied has a moderate level of subsoil salinity (EC, of 3.6 dS m-1 at 11 5 cm) but levels of chloride found in legume tissues (0.5-1.5%) were found to be unlikely to limit growth or to prejudice survival. Observations taken over the same period on pure grass plots (Panicum coloratum var. makarikariense cv. Bambatsi) revealed the grass had a deeper and more extensive root system (459 cm cm-2) than did any of the legume species (e.g. Siratro 111-118 cm c m-2) and was more effective in extracting soil water during dry periods.