Comparison of water‐insoluble phosphate fertilisers with superphosphate—a review

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Abstract
A series of experiments was carried out in England and Wales in the period 1972–1982, to compare the relative effectiveness of various commercially available water‐insoluble phosphate fertilisers with that of superphosphate. Most of the trials were on permanent grassland, but a few used barley and swedes as test crops. Ground Gafsa rock P, although only approximately 50% as effective as superphosphate in the year of application, gave somewhat higher responses in the following (residual) 2 years on unlimed, acid grassland. In these circumstances, grinding finer than 150 μm did not appear to be worth the extra cost. Granulation of finely ground Gafsa rock P slightly reduced its effectiveness for grass in the first year, but markedly reduced its efficiency for cereals. Mixtures of medium grade basic slag and Moroccan rock P were only slightly inferior to high grade basic slag, but mixtures of low grade slag and ground rock P (Moroccan or Gafsa) were somewhat less effective than the finely ground Gafsa rock P, especially in the first year. Granulated ground underacidulated rock P (Gafsa or Moroccan), was as effective as very finely ground Gafsa rock P, however a bulk blend of granulated Gafsa rock P and triple superphosphate was more effective than Gafsa rock P, but less so than superphosphate in the first year. Calcined aluminium calcium P was the least effective of the fertilisers tested, being especially slow in action, and only 25% as effective as superphosphate in the first year.