Depletion of Rhizosphere Solution Phosphorus By Corn and Soybean Grown in Soil with a P-Solubilizing Copolymer.

Interest in reducing soil phosphorus (P) fixation to enhance P availability for crop plants has led to the development of commercial products intended to maintain P solubility. The objective of this controlled-climate study was to evaluate the ability of a commercial maleic-itaconic copolymer to maintain a greater pool of plant-available P in rhizosphere solution for uptake by juvenile corn (Zea mays L.) and soybean (Glycine max L. Merr.) grown in three diverse soils. Treatments included a control without P fertilizer and soil amended with ammonium polyphosphate (10-17-0; N-P-K) liquid fertilizer (49 kg P ha⁻¹) both with and without added maleic-itaconic copolymer. Following incubation, soil treatments were placed in two-chamber mini-rhizotrons. Corn seedlings were transplanted into the rhizotrons at the two-leaf stage, and grown for ten days. Soybean seeds were sown directly into the rhizotrons, and grown for 12 days. The experiments were repeated three times. Micro-suction cups (13 per chamber) were used to collect rhizosphere soil solution that was subsequently analyzed for P. Corn shoot and root dry matter production were not affected by P fertilizer applied to any of the soils. Soybean root dry matter production increased when P fertilizer, with or without copolymer, was applied to an Oxisol. Phosphorus concentrations in rhizosphere solution did not differ with distance from the root surface for either plant species, but were significantly higher in two of the P-amended soils (Haplustoll and Hapludoll), with or without the copolymer. In the Haplustoll, P concentrations in solution at the root surface of both species were higher when the copolymer was added to the P fertilizer. However, corn and soybean shoot P concentrations did not differ among the treatments. Our results are not definitive, but suggest that addition of the copolymer to P fertilizer may affect P solubility in some soils.