Effect of waterlogging and soil pH on the micro-distribution of naturalised annual legumes

Variation in the size and composition of the soil seed bank of 3 naturalised legumes, subterranean clover (Trifolium subterraneum L.), woolly clover (T. tomentosum L.), and cluster clover (T. glomeratum L.), was related to soil characteristics on a transect that ascended from a winter waterlogged area in a wheatbelt pasture. Growth of the 3 species was compared with other species from section Vesicaria (T. resupinatum and T. clusii) in waterlogged and freely drained pots for 34 days. Of the 3 naturalised legumes present in the transect, cluster clover was rare, and woolly and subterranean clovers were separated on the basis of their response to soil pH and the likelihood of winter waterlogging. Subterranean clover was absent from soil with pH > 7 . 0; these areas were dominated by woolly clover. Areas with pH < 7 . 0 were dominated by subterranean clover, except where winter waterlogging was likely, in which case they were once again dominated by woolly clover. The waterlogging tolerance of woolly clover, together with that of other species in section Vesicaria, was confirmed in the pot experiment. After 34 days, shoot drg weight of the waterlogged Vesicaria species was an average of 39% greater than the beery drained controls. Root length continued to increase for the duration of the waterlogging treatment with much of the new root growth as laterals. Conversely, shoot and root growth in subterranean and cluster clovers was severely reduced by waterlogging. The patchy distribution of woolly clover in many wheatbelt pastures can be explained by its response to high pH and winter waterlogging compared with subterranean clover.