Enhanced phosphorus fertilizers (Carbond P® and Avail®) supplied to maize in hydroponics

Phosphorus (P) is poorly soluble in soil and has poor plant uptake efficiency. AVAIL (R) and Carbond P (CBP) are fertilizers that increase P-use efficiency (PUE) and yields on P limiting soils. The objectives of this study were to determine if mode of action for these products is related to physiological response, and to evaluate possible toxicity. AVAIL and CBP were compared to ammonium polyphosphate (APP) at pH 6 or 8 for hydroponically grown maize (Zea mays L.). Not surprisingly, biomass and P concentration increased with increasing P concentration of the solution. However, neither AVAIL nor CBP had any positive or adverse effects. These results, coupled with previous soil-based studies, show that the observed increase in PUE is not a physiological growth stimulant response, but rather the result of impacts on soil P solubility. Furthermore, these materials are not toxic when in direct contact with plant rootseven at relatively high concentrations.