Novel Dicalcium Phosphate (DCP) and its key benefits
Dicalcium Phosphate (DCP) and Its Key Benefits
Several phosphorus fertilizers have been used in New Zealand, including single superphosphate (SSP), triple superphosphate (TSP), reactive phosphate rock (RPR), and dicalcium phosphate (DCP). SSP is the most commonly used due to its high-water solubility, allowing for rapid phosphorus (P) availability to plants. In contrast, lower sales of RPR (1-2%) in NZ may be attributed to its slow P release rate and inconsistent quality.
Numerous studies have shown that the effect of DCP (lime/dolomite-reverted SSP) on pastures is comparable to that of SSP, as it can supply sufficient phosphorus to plant roots. However, DCP sales remain low (<1%), likely due to limited recognition of its environmental benefits and its relatively low P content (<9%). Additionally, DCP contains phosphorus, calcium (Ca), and sulphur (S). If dolomite is used, it also contains magnesium (Mg). While the application of DCP provides essential nutrients such as P and Ca, the presence of S and/or Mg may not be suitable for certain soils.
SUPERIOR – NOVEL DCP
A novel form of DCP, produced through a specific manufacturing process, presents significant potential. This process involves the direct reaction of phosphoric acid with calcium carbonate (CaCO3), followed by a reaction with calcium hydroxide (Ca(OH)2), as outlined in the following steps:
1. 2H3PO4 + CaCO3 → Ca(H2PO4) 2 + CO2 + H2O
2. Ca(H2PO4) 2 + Ca(OH)2 → 2CaHPO4 + 2H2O
Based on these reactions, calcium hydrogen phosphate (CaHPO4) is the final product, containing a high phosphorus concentration (16.5%). Once applied, the novel DCP releases only phosphorus and calcium. With a pH close to neutral, it is suitable for both acidic and neutral soils.
The behaviour of novel DCP in soil is like that of lime/dolomite-reverted SSP. It may be effective in both high and low anion storage capacity (ASC) soils, as it releases phosphorus gradually. This prevents rapid sorption in high ASC soils while also reducing phosphorus leaching and overland flow in low ASC soils. Compared to other phosphate fertilizers, novel DCP releases phosphorus more rapidly than RPR but more slowly than SSP and TSP. This is due to its solubility in citric acid and water, which is significantly higher than RPR but lower than SSP and TSP. Consequently, novel DCP can adequately meet plant phosphorus requirements while minimizing phosphorus loss through leaching and runoff.