Responses of five pasture species to phosphorus, lime, and nitrogen on an infertile acid soil with a high phosphate sorption capacity

Abstract

The growth responses of Lolium pevenne L. cv. Clunes, Phalavis tubevosa L. cv. Australian Commercial, Trifolium subterraneurn L. cv. Mount Barker, Trifolium vepens L. cv. Victorian, and Medicago sativa L. cv. Hunter River to lime, superphosphate, and nitrogen were compared in a field experiment on a soil with a pH of 4.9-5.4 (115 soil/water ratio) and with the cation exchange capacity 25-50% saturated by aluminium. The soil had a high phosphorus requirement. The effects of superphosphate and lime on the sodium bicarbonate extractable phosphorus levels and on the soil pH are discussed. Lucerne was one of the least productive species at most harvests. It required more superphosphate than subterranean clover, perennial ryegrass, or white clover to attain any given percentage of maximum yield. The visual symptoms of the plants and the yield interactions showed little evidence of effects of high aluminium, which indicated that the superphosphate was needed to correct phosphorus deficiency rather than to counteract any aluminium toxicity. The initial soil pH was somewhat higher than the levels previously found to be associated with aluminium toxicity on the soil in pots. Phalaris growth was increased to the highest superphosphate level, but growth at lower levels improved with time. Subterranean clover growth was depressed by the highest superphosphate level early in the season. The other species were not affected in this way. More lime was needed for lucerne than for white clover, which in turn needed more lime than subterranean clover. Nitrogen decreased the response of clover to lime, and the evidence indicates that the response of the legumes to lime was due mainly to the effect of lime in improving nodulation and nitrogen fixation. The lime-treated subterranean clover responded to nitrogen, especially in the first few months after sowing. The grasses responded markedly to nitrogen, while lime had a small effect on their growth and response to nitrogen. In no case did lime decrease the requirement for superphosphate.