Effects Of Lime On Growth Of 5 Species, On Aluminium Toxicity, And On Phosphorus Availability

Preliminary pot culture experiments indicated that the yield of phalaris relative to that of perennial ryegrass was poor on the less productive soils, particularly on some of the soils of pH <5.0 as measured in 115 soil/water suspensions. On an infertile acid soil with a high content of exchangeable aluminium, lucerne and phalaris plants responded to lime in pot experiments while subterranean clover, white clover, and perennial ryegrass were depressed by liming. The evidence, including that based on chemical analyses of extracted soil solutions and of lucerne plants, indicates that where adequate nitrogen had been applied, aluminium toxicity depressed the growth of lucerne and phalaris on this acid soil. The plant roots did not show the stunting which is obvious in cases of more severe aluminium toxicity. Subterranean clover, white clover, and perennial ryegrass resisted the toxicity. There was little evidence of a negative interaction between lime and phosphate on yields through their effects on aluminium toxicity. In general, responses to phosphate increased as the level of lime increased. Where suboptimal levels of nitrogen were applied there were responses to lime which were not clearly attributable to the alleviation of aluminium toxicity. Where nitrogen was adequate and there was no effect of lime in counteracting aluminium toxicity, in most cases lime caused a decrease in the concentration of phosphorus in the plants as well as a decrease in the yield. Lime also caused a decrease in the phosphorus level in the extracted soil solutions. However, in some cases where lime counteracted aluminium toxicity it increased the concentration of phosphorus in the tops of the plants. The significance of the results in relation to the problem of the diagnosis of aluminium toxicity is discussed.