The influence of soil properties on the effectiveness of phosphate rock fertilisers

Abstract

Eighteen soils from south-western Australia were used to measure the effectiveness of 2 reactive phosphate rocks (RPR) [North Carolina and Sechura (Bayovar) RPRs] relative to superphosphate (relative effectiveness, or RE) using (i) yield of dried shoots of 30-day-old wheat plants (REyield ), (ii) P content of the dried shoots (RE Pcontent ), and (iii) bicarbonate soil test P (RE bicP ) as measures of effectiveness. The RE values were positively related to PR dissolution in soil, titratable acidity, and to P and Ca retention by soil, and were negatively related to soil pH. No single soil property adequately predicted REyield , RE Pcontent, or RE bicP . Stepwise multiple regression indicated that: (1) PR dissolution, soil pH, and organic carbon together accounted for about half the variation in RE yield ; (2) organic C, soil pH, and titratable acidity together accounted for about 67% of the variation in RE Pcontent ; (3) PR dissolution, P retention capacity, and titratable acidity together accounted for about 71% of the variation in RE bicP . We conclude that the agronomic effectiveness of phosphate rock fertilisers is a consequence of complex interactions of phosphate rock with soil that cannot be adequately predicted by measurements of a single soil property.