Abstract
A pot experiment was conducted in two acidic soils (pH 4.8) with similar properties except for phosphorus (P) status to investigate the influence of different P fertilizers [Kunyang phosphate rock (KPR), monocalcium phosphate (MCP)] on ryegrass growth and different soil P fractions in the two soils. The P treatments were KPR at 50, 100, and 250 mg P kg–1 and MCP at 50 mg P kg–1. Results showed that the application of P fertilizers produced significant increase of ryegrass growth compared with no P application on soil with low P status. Dry weight of ryegrass did not increase after P application, compared with no P application on soil with high P status. Through P fractionation as modified method of CitationHedley, Stewart, and Chauhan (1982), inorganic resin P, sodium bicarbonate (NaHCO3) P, and sodium hydroxide (NaOH) P increased after MCP treatment compared with no P application. The PR application only increased resin P and hydrochloric acid (HCl) P. Soil organic P fractions were stable and less affected by P application. The average of KPR P dissolved in the two soils across all P rates was low: only about 19% of the averaged amount of KPR P applied, which was due to its low reactivity. This explains the poor agronomic effectiveness of KPR with respect to MCP.
Acknowledgments
This research was financially supported by the International Fertilizer Industry Association (IFA), the Potash and Phosphate Institute/Potash and Phosphate Institute of Canada (PPI/PPIC), and the International Potash Institute (IPI).