Efficacy of Hydroxyapatite Nanoparticles as Phosphorus Fertilizer in Andisols and Oxisols

Improving phosphorus (P) fertilizer efficiency is a challenge in acidic and strongly P sorbing soils. Nanotechnology may have potential to create more efficient fertilizers. Hydroxyapatite nanoparticles (n-HAP) were evaluated as a potential fertilizer to improve P efficiency based on the hypothesis that nano-sized particles can potentially move in the soil and reach the plant roots through the mass flow of soil water to roots created by transpiration. The transport of nano-sized and bulk-sized HAP was evaluated in saturated soil column experiments. Availability of P from n-HAP, bulk-HAP, and triple superphosphate (TSP) to wheat (Triticum aestivum) was evaluated by a P-33 isotopic dilution technique in a glasshouse study with two Andisols from Chile and New Zealand and two Oxisols from Australia. Transport experiment showed that 5% of the applied n-HAP leached in the Andisol and <1% in the Oxisol. Bulk-HAP did not move in either of the soils. Across all soils, the P uptake and the percentage of P in the plant that was derived from the fertilizer followed the order: TSP > n-HAP > bulk-HAP. Although n-HAP performed better than bulk-HAP, most likely because of faster dissolution, TSP was still a more efficient P fertilizer.