Abstract
Pot and field trials were carried out to compare the agronomic effectiveness of single superphosphate with industrial by-products, basic slag and phos-pal, as fertilizer-P sources. The results show that the materials are equally good P sources for maize. The three sources, compared at the rates of 10—80 kg P ha-1, showed significant residual effects in the soil after the first crop of maize. The residual effects, assessed by Bray 1 extractant of 80 kg P ha-1 was highest for the basic slag followed by single superphosphate and phos-pal; this trend seemed to be supported by tissue analysis of the ear-leaf of maize. The high Bray 1 extractable P on soils treated with basic slag may be due to its ability to raise the soil pH to within the range of maximum phosphate solubility. The low P recovery by the same extractant from phos-pal treated soils, however, may be related to the inability of the Bray 1 test to assess correctly the availability of the soil reaction products of phos-pal.
