Phosphorus (P) is poorly soluble in most soils and, thus, has poor plant uptake efficiency. AVAIL® and Carbond P (CBP) are new fertilizer products shown to increase P use efficiency (PUE) and increase crop yields when grown in P limiting soils. Carbond P has specifically been seen to increases P uptake and crop yields in soils low in P, although effectiveness in regards to soil organic matter is unknown. The objectives of these studies were to determine if the mode of action for these products is related to physiological response, to determine if Carbond P is toxic to plant roots when in direct contact at high rates, and determine the limitations of Carbond P in regards to biomass (yield), P uptake and concentration. We used a hydroponic study to compare CBP to AVAIL in evaluating plant toxicity and plant philological response. AVAIL and CBP were also compared to ammonium polyphosphate (APP) at pH 6 or 8 for hydroponically grown maize (Zea mays L.). Additionally, a glasshouse study evaluated the PUE of CBP with soil in which maize was grown. Soils were moderate or high in organic matter, with 0, 5, 15, 45, or 135 kg P2O5 ha-1 applied as either APP or CBP. Both studies showed that CBP is a suitable PUE enhancing fertilizer. In the greenhouse study, the high organic matter soil revealed that both CBP and APP fertilization resulted in similar increases in biomass yield and P concentration and uptake. However, in the moderate organic matter soil, biomass and total P uptake was significantly greater for CBP than APP at the two lowest P rates of fertilization and significantly higher for APP than CBP at the highest P application rate. In the hydroponic study, neither AVAIL nor CBP had any positive or adverse effects on the plants as compared to APP. These results, coupled with this and previous soil-based greenhouse and field studies with AVAIL and CBP, show that the increase in PUE is not a physiological growth stimulant response, but rather likely the result of impacts on P solubility in the soil. However, the presence of high organic matter in the soil seemed to negate the effects of the organic acid bonded P used in Carbond P. We conclude that CBP, and possibly other organic acid based fertilizers, can assist in furthering agricultural goals, as well as environmental responsibility with these known limits.



College and Department

Life Sciences; Plant and Wildlife Sciences



Date Submitted


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AVAIL, Carbond P, copolymer, dicarboxylic acid, fertilizer, glasshouse, hydroponic, maize, organic acid, organic acid