COMPARISON OF DIFFERENT FORMS OF PHOSPHATIC FERTILIZERS PART I: RAPE AND SWEDES

Summary Eighteen experiments were carried out in Wales and the West Midland Region, between 1966 and 1971 to compare granular basic slag with powdered basic slag and superphosphate (or triple superphosphate) as phosphatic fertilizers for rape and swede crops. At the swede sites additional comparisons involving ground mineral phosphates were also made. The fertilizer treatments were applied at sowing time and at rates supplying 28 and 56 kg P/ha for rape and 28 and 56, or 44 and 88 kg P/ha for swedes. Large increases in yield of rape and swedes to the lower rate of phosphate application were recorded at most sites but, in general, only very small additional responses were obtained to the higher dressing. For both rape and swede crops, the relative effectiveness of the different phosphatic fertilizers varied somewhat between sites. Comparisons of the superphosphate and basic slag treatments show that the former gave slightly higher yields at most sites. Granular basic slag was marginally inferior to powdered slag for swedes but in general the differences between the effects of superphosphate (or triple superphosphate) and the two forms of slag were small. The effects of the Gafsa phosphate treatments for swedes were variable, being as effective as superphosphate or basic slag at some sites and much less so at others. This inconsistency detracts from their over‐all usefulness. There was no definite advantage in the finely‐ground (80 per cent through 300 mesh (50 μm)) material over the relatively coarser (60 per cent through 100 mesh (150 μm)) product. Moroccan mineral phosphate was inferior to the Gafsa phosphates for swedes, particularly at the most responsive sites.