Long-term effects of lime on pasture yields and response to phosphate fertilizers on eight acidic soils

Abstract

Eight experiments on acidic soils of the Northern Tablelands of New South Wales were carried out to measure lime effects on clover-based pastures and their response to fertilizer phosphate (P). Each experiment lasted 3 years. The seven soils deficient in P all responded to lime in the first year, and pasture yield responses were associated with lime-induced increases in isotopically exchangeable or soluble soil P or both. Three of these soils were also relatively high in soluble aluminium (Al) or manganese (Mn), and the lime-induced suppression of these toxic cations probably also contributed to the beneficial effects of lime. Negative effects of lime on fertilizer P response were more frequent than positive effects, and tended to occur on higher A1 soils. Lime eliminated the need for fertilizer P on at least three P-deficient soils during the 3 year period of the experiments, and this was also associated with increases in availability and uptake of soil P. Lime suppressed P sorptivity in all soils, but this caused an increase in fertilizer P effectiveness in only two soils (in the first year). Hence, the positive effect of lime on soluble soil P, which occurred on all soils and which would tend to lower fertilizer P effectiveness, seemed to be dominant over its negative effect on soil P sorptivity. Residual effects of lime and fertilizer P were similar, both declining after the first year, with five soils still responsive in the third year.