To discuss how a slow release boron phosphate to mitigate boron deficiency in high rainfall environments.

• Boron phosphate compounds were synthesized by mixing boric acid and phosphoric acid (1:1 molar ratio) and heating at temperatures of 25 to 1000 °C for 1 or 24 h.
• X-ray diffraction patterns and chemical analysis results showed formation of boron phosphate compounds at low temperature • These compounds gradually crystallized with increasing temperature and heating time.
• The compounds synthesized at 300°C or less were hygroscopic, while those synthesized at 500 to 1000°C were non-hygroscopic and free-flowing.
• The solubility of all compounds decreased with increasing synthesis temperature • The solubility of compounds synthesized at 500 and 800°C increased with increasing pH.
• The compound synthesized at 1000°C was nearly insoluble and the solubility was not pH dependent.
• The release of B from the boron phosphate synthesized at 800°C for 1 hour was approximately 70% after 150 days, which confirmed its slow release.
• The characteristics of the compounds synthesized at temperatures 500 and 800°C showed that it can be used as raw materials for co-granulation with macronutrient fertilisers such as mono-ammonium phosphate.
• Such co-granulated products are currently being tested.