Reactions and Availability of Banded Polyphosphate in Field Studies

Abstract The concentration of fertilizer P from both superphosphate and polyphosphate decreased rapidly with increasing lateral distance from the band. Aluminum phosphate and lesser amounts of Fe phosphates were the soil reaction products formed with essentially no difference between the two P materials. A higher proportion of the condensed phosphate ions were in the difficultly extractable form as compared with the orthophosphate ions, indicating that the condensed phosphate ions are held more strongly. The apparent hydrolysis of condensed phosphates increased with increasing lateral distance from the center of the band. Hydrolysis was greater in the Lynchburg, a low P‐fixing soil, than in the Georgeville, a high P‐fixing soil. Polyphosphate was as effective as superphosphate in supplying P for plant growth. The residual effectiveness of the polyphosphate was similar to that for superphosphate. Although condensed phosphate ions are held more strongly than orthophosphate by soil materials, there appears to be no difference in their effectiveness as sources of P for plants.