EFFECT OF WATERLOGGING AND SOIL-PH ON THE MICRODISTRIBUTION OF NATURALIZED ANNUAL LEGUMES

Variation in the size and composition of the soil seed bank of 3 natur alised legumes, subterranean clover (Trifolium subterraneum L.), wooll y clover (T. tomentosum L.), and cluster clover (T. glomeratum L.), wa s related to soil characteristics on a transect that ascended from a w inter waterlogged area in a wheatbelt pasture. Growth of the 3 species was compared with other species from section Vesicaria (T. resupinatu m and T. clusii) in waterlogged and freely drained pots for 34 days. O f the 3 naturalised legumes present in the transect, cluster clover wa s rare, and woolly and subterranean clovers were separated on the basi s of their response to soil pH and the likelihood of winter waterloggi ng. Subterranean clover was absent from soil with pH > 7 . 0; these ar eas were dominated by woolly clover. Areas with pH < 7 . 0 were domina ted by subterranean clover, except where winter waterlogging was likel y, in which case they were once again dominated by woolly clover. The waterlogging tolerance of woolly clover, together with that of other s pecies in section Vesicaria, was confirmed in the pot experiment. Afte r 34 days, shoot drg weight of the waterlogged Vesicaria species was a n average of 39% greater than the beery drained controls. Root length continued to increase for the duration of the waterlogging treatment w ith much of the new root growth as laterals. Conversely, shoot and roo t growth in subterranean and cluster clovers was severely reduced by w aterlogging. The patchy distribution of woolly clover in many wheatbel t pastures can be explained by its response to high pH and winter wate rlogging compared with subterranean clover.