Optimizing the Rate of AVAIL® Co-Polymer for Enhancing Phosphorus Availability to Corn (Zea mays).

Phosphorus is an essential plant macronutrient, but only a fraction (<40%) of phosphate applied to soils is available to plants. Our objective was to determine the application rate of a polycarboxylic acid co-polymer (AVAIL®) for optimal P uptake and corn growth at a reduced input of P fertilizer. In a greenhouse experiment, corn was grown in a P-deficient Goldsboro soil that was amended with phosphate fertilizer at 50% of the recommended rate in a horizontal band, along with AVAIL® treatments of 25, 50, 100, 150, and 200% of the soil’s estimated polymer sorption capacity. A complementary soil-sorption experiment measured dissolved P for the same P and AVAIL® treatments at pH 5.6. The corn grew for 21 days to a height of 32 ± 3 cm, with all plants showing P deficiency (purpling) after 15 days and no apparent growth trends across AVAIL® treatments. However, the soil-sorption experiment revealed a positive linear relationship (r² = 0.97) between AVAIL® input rate and dissolved P, with the average P concentration increasing from 0.03 to 0.06 mg/L.  The sustained concentration of dissolved P considered adequate for corn growth is 0.025 mg/L. Total biomass and tissue concentrations of P and other nutrients showed no trend with AVAIL® rate. Although AVAIL® increased dissolved P concentrations in the soil alone, a lack of corn growth response in the greenhouse indicates that the AVAIL® rates need to be optimized at a higher P fertilization rate.