Greenhouse Evaluation of Phosphorus Solubilizing Compounds.

This experiment evaluated two Phosphorus (P) solubilizing products for their ability to release P from soil.   The experiment was conducted using a Fine, kaolinitic, thermic Rhodic Paleudult with a high P fixing capability.   The experiment design was a 5 x 3 factorial (3 replications) of P rate and P solubilizing materials.  P rates were 0, 34, 68 and 101 kg P₂O₅ ha^-1.  P rates were combined with one of three solubilizing materials:  1)  none, 2)  a commercial patented additive (at three rates: labeled, 2x and 4x), and, 3)  a maleic-itaconic copolymer additive.  Destructive sampling of the study was performed 3 times, at weeks 4, 8 and 12 after fertilization, and tissue and soil were analyzed for P content.  The entire experiment was repeated twice.  Addition of P solubilizing products sometimes increased plant tissue P, dry weight of ryegrass, and extractable soil P.  Differences were most often significant when the commercial product was added to soil at 4 times the recommended rate.  Differences in extractable soil P due to P amendment were more often found when CaCl₂ was the extractant, rather than the Mehlich extractant.   In this greenhouse experiment enough preliminary positive data exists that a field study is warranted.