The growth of improved pastures on acid soils. 2. The effect of soil incorporation of lime and phosphorus on the growth of subterranean clover and lucerne pastures and on their response to topdressing

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Abstract
Subterranean clover responds poorly to superphosphate application on some acid soils of the Southern Tablelands of New South Wales. A field experiment was undertaken, for two years, to examine the effects of incorporating large additional amounts of superphosphate or rock phosphate in the soil, with and without lime, on the growth of subterranean clover, lucerne and phalaris sown with recommended rates of lime superphosphate. Dry matter responses of subterranean clover and lucerne to superphosphate topdressing in the second year were also recorded. In the first year, subterranean clover growth was increased by the additional lime and by lime plus superphosphate. Lucerne growth was increased by additional lime. In the second year, the growth of subterranean clover was increased by the lime treatments and the superphosphate treatments applied in the previous year and by the deep incorporation into the soil of lime and superphosphate together. Subterranean clover growth also responded to the application of rock phosphate without lime. Lucerne dry matter production in the second year was increased by the lime, superphosphate and rock phosphate treatments applied in the first year. Lime application increased the yield responses of subterranean clover and lucerne to superphosphate topdressed in the second year. Lime application had no effect on the nitrogen content of the clover but increased that of lucerne. Lime application reduced the aluminium levels in the tops of all three species. The data suggest that the responsiveness of pastures to superphosphate on these soils is increased by the application of lime and rock phosphate and is related to low nitrogen fixation and high aluminium levels in the plant.