Effects of phosphate rock products on soil pH

Abstract

Summary. Changes to soil pH (CaCl₂ ) following annual applications of phosphate rock (PR) and water-soluble phosphorus products were investigated in the National Reactive Phosphate Rock Project. It was difficult to measure small changes in pH due to variation in pH within each site and across years. pH (the change over time from the initial soil pH at that plot) was significantly influenced by fertiliser product at 13 of the 27 sites examined. At 5 sites, one or more of the PR products had pH of 0.07–0.21 units greater than the pH of the control. At the other 8 sites, the pH of the control plot was greater than or equal to the that of the PR plots, or significant increases in pH occurred in the single superphosphate plots. The changes in soil pH following application of the fertiliser products were inconsistent both within and between sites. Chemically the PR products have the potential to reduce the rate of acidification in soils where the products dissolve readily, however, this was not generally reflected in the field, where the application of PR products only increased soil pH at a limited number of sites.