Nutrient problems in sown pasture on an acid soil. 2. Role of lime and superphosphate

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Abstract
A study was made of the role of superphosphate and lime on subterranean clover (Trifolium subterraneum) production on an infertile acid soil in pot culture. Both fertilizers increased the exchangeable calcium in this deficient soil. Lime and superphosphate were involved in nodulation of the clover plants. There was no evidence of the direct involvement of either of them in the nitrogen fixation process, but they did increase nitrogen uptake by the plants. Once the legume functioned adequately, full expression of the yield response to phosphorus on this deficient soil followed. Most efficient phosphorus use occurred at the lime 1255, superphosphate 2000 kg ha-1 level (lime 1/2, P 16). Heavy lime dressing reduced exchangeable magnesium and the phosphorus available to the plant. Aluminium and pH were involved in the effects observed. Lime reduced CaCl2-extractable aluminium and the titratable acidity in the soil. Phosphate increased the CaCl2-extractable aluminium and apparently reduced the titratable aluminium. The combined treatments reduced these three attributes and promoted increased plant growth. Increased plant growth was associated with increased aluminium uptake by the plants, which suggests that the real effect of aluminium may have been on the calcium and phosphorus uptake by the plants, rather than on the toxic nature of the element itself.

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