A COMPARISON OF 5 SOIL-PHOSPHORUS TESTS FOR 5 CROP SPECIES FOR SOIL PREVIOUSLY FERTILIZED WITH SUPERPHOSPHATE AND ROCK PHOSPHATE

The P(i), Colwell, Bray 1, calcium acetate lactate (CAL) and Truog pho sphorus (P) soil test reagents were assessed in two field experiments on lateritic soil's in Western Australia that had been fertilized four years previously (1984) with triple superphosphate, North Carolina ro ck phosphate, Queensland rock phosphate, and in one experiment, Calcip hos. Soil samples to measure soil P test were collected February 1987. Soil P test was related to seed (grain) yields measured later in 1987 . Different crop species were grown on different sections of the same plot at each site. The species were lupins (Lupinus angustifolius), ba rley (Hordeum vulgare) and oats (Avena sativa) at one site, and lupins , oats, triticale (x Triticosecale) and rapeseed (Brassica napus) at t he other site. For each reagent, the soil P test calibration, which is the relationship between yield, expressed as a percentage of the maxi mum yield, and soil P test, generally differed for different plant spe cies and for different fertilizer types. Variations in soil P test req uired to produce half the maximum yield of each species at each site w as least for the CAL reagent followed by the Colwell reagent.