Phosphorus availability in soils amended with different phosphate fertilizers

Accurate measurement and characterization of phosphate rock dissolution are important for a better understanding of phosphorus (P) availability in soils. An incubation study was carried out on two New Zealand topsoils (0-15 cm; high P buffering capacity Craigieburn and low P buffering capacity Templeton) amended with North Carolina phosphate rock (NCPR) and water-soluble phosphate (WSP) at 218 mg P kg(-1) (equivalent to 60 kg P ha(-1)). Isotopic exchange kinetics was carried out after 12 h and 28 days of incubation to characterize P availability. This study showed that sensitivity of capacity factors (r(1) /R, n) to explain changes in E-1min values was affected by the P buffering capacity of the soils. The recovery of applied P in the E pool (Rec inE %) with extended incubation time was similar from the NCPR and WSP treatments (3.1-3.3%) in the Craigieburn soil compared with the Templeton soil in which Rec inE % values were greater in WSP (9%) than NCPR (1.3%) treatment. The higher values of P derived from the applied P fertilizers in the E pool (Pdff inE %>80%) suggested that the NCPR application in both soils would be efficient for increasing P availability to plants.