EFFECTS OF PH AND ALUMINUM ON THE GROWTH OF TEMPERATE PASTURE SPECIES .2. GROWTH AND NODULATION OF LEGUMES

Ten temperate pasture legumes inoculated with appropriate rhizobia were grown for 31 days in flowing solution culture. Solution ionic strength was approximately 2 700-mu-M and contained inorganic nitrogen (150-mu-M NO3BAR) only at the commencement of the experiment. Solution pH was maintained at 4.5, 5.0, 5.5 and 6.0. Also, five aluminium (Al) treatments were imposed, with nominal Al concentrations of 0, 3, 6, 12 and 24-mu-M (2.5, 7.1, 8.3, 11.2 and 24.7-mu-M Al measured) at pH 4.5. Solution pH < 6.0 markedly reduced total dry mass (TDM) in all cultivars of white clover (Trifolium repens) cvv. 'Grasslands Pitau, Huia, G18 and Tahora' and red clover (Trifolium pratense) cvv. 'Grassland Turoa and Pawera', and to a lesser extent in the two subterranean clover (Trifolium subterraneum) cvv. 'Tallarook and Woogenellup'. In contrast, solution pH had no effect on the growth of Lotus corniculatus cv. Maitland, while Lotus pedunculatus cv. Maku grew best at pH 4.5. Lotus pedunculatus cv. Maku grew best in solution where the sum of the activities of the monomeric Al species {Al(m)} was maintained at 5.9-mu-M. The growth of all other species was decreased with Al in solution, a 50% reduction in TDM being associated with c. 6-mu-M {Al(m)} for white clover and subterranean clover, and c. 3-mu-M in red clover and Lotus corniculatus cv. Maitland.