Relations between plant aluminium content and the growth of lucerne and subterranean clover: their usefulness in the detection of aluminium toxicities

Abstract

ln an experiment with lucerne (Medicago sativa) and subterranean clover (Trifolium subterraneum), grown in solution cultures at two levels of phosphorus, each at five aluminium levels and pH 4, growth and aluminium transport to the leaves were comparable in both species up to the fourth aluminium level (40¦M All. The highest aluminium level (200 ¦M Al) caused a much greater growth depression in lucerne than in subterranean clover. In lucerne, aluminium concentrations in leaf dry matter peaked at the fourth aluminium level. Concentrations below this peak could indicate non-toxic as well as toxic supplies of aluminium. Leaf analysis, therefore, appears to be of little value in the detection of aluminium problems in lucerne. In subterranean clover leaves, aluminium concentrations increased to values in excess of 1 70 ppm of the dry matter at the highest aluminium level. In a second experiment, in which subterranean clover plants were grown in pots in two acid soils at two phosphorus x five aluminium levels, close, inverse, linear relations were found between relative yield (Al/no Al x 100) and leaf aluminium concentrations. These relations differed between soils, harvests and phosphorus levels, and would therefore be of little help in providing quantitative estimates of yield depressions in subterranean clover caused by aluminium. However, the lines all converged within the range of 100-1 50 ppm aluminium in leaf dry matter of plants in the no aluminium treatment, suggesting that this range represented a 'threshold' above which yield reductions due to aluminium occurred.