Effect of Phosphate-Metal-Humic Complexes on P Uptake in Hydroponics and Soil.

Humates are increasingly used in mineral fertilizers. Phosphate-metal-humate complexes have been claimed to increase P availability to plants. We assessed the complexation of P with metal(Fe/Al)-humates in solution using a P-loaded Fe oxide to buffer P concentrations. Solutions with the same free phosphate concentration with or without P-Fe/Al-HA complexes were prepared and used in short-term hydroponic plant uptake studies to assess if these complexes increase P availability. Furthermore, a pot trial was carried out to compare the effectiveness of fertilizers containing these humates to standard soluble fertilizers (MAP and SSP).