Effect of different aluminium and phosphorus levels on aluminium‐tolerant and aluminium‐susceptible genotypes of white clover ( Trifolium repens L.)

Abstract Two genotypes of white clover ( Trifolium repens L.) selected for either tolerance or sensitivity to soil aluminium (Al), were grown in an acid soil with factorial combinations of four Al and four phosphorus (P) levels. Plants of the Al‐tolerant genotype were larger and leafier than the susceptible plants despite containing more Al. Shoot Al concentrations were lower in the tolerant plants. Al x P interactive effects on growth were normal, with P ameliorating the effects of increased Al. Shoot and root magnesium (Mg) levels were much higher in the tolerant plants suggesting that in white clover, as for some other species, Mg plays a key role in Al tolerance. Increasing Al application rates from 20 to 50 (μg Al/g soil stimulated several of the plant growth parameters that were recorded but the mechanism was not apparent. The Al‐tolerant genotype had a lower shoot P concentration and shoot P content and was more responsive to applied P than the susceptible genotype. These characteristics which are associated with improved P efficiency in white clover, suggest that screening white clover for Al tolerance may produce plants well adapted to acid soils and intermittent P fertiliser use.