EFFECTIVENESS OF ECOPHOS COMPARED WITH SINGLE AND COASTAL SUPERPHOSPHATES

Ecophos is a possible alternative phosphorus (P) fertilizer to single and coastal superphosphate for clover pasture (Trifolium subterraneum) on P leaching, sandy, humic podzols in the > 800 mm annual average ra infall areas of south-western Australia. Ecophos and coastal superphos phate are partially acidulated rock phosphates (PARP) fertilizers. Eco phos is made from calcium iron aluminium (crandallite millisite) rock phosphate. Coastal superphosphate is made from apatite. The sandy humi c podzols are known to promote extensive dissolution of rock phosphate s, including the untreated rock phosphate present in PARP fertilizers. In this field study (early April 1992 to end of October 1994), the ef fectiveness of the PARP fertilizers was calculated relative to the eff ectiveness of single superphosphate (relative effectiveness or RE), us ing yield and P content of dry clover herbage. The RE of the PARP fert ilizers varied markedly between assessments, both within and between y ears, from being much less effective than single superphosphate, to eq ually or much more effective. This great diversity in RE is attributed to the different extents P can be leached in the soil, depending. on seasonal conditions. It is concluded that Ecophos is a suitable altern ative P fertilizer for the soil and environment studied.