Received for publication 22 Apr. 1985. Florida Agr. Expt. Sta. J. Ser. No. 6371. We thank the Tennessee Valley Authority, Muscle Shoals, AL 35660 for supplying radioactive superphosphate under contracts TV-61031A and TV-61046A. We are also grateful to Drs. Hannah and Zack for assistance with scintillation counting; Robin Reddick for typing this manuscript; Carolyn Bartuska, Claudia Larsen, and Jan Weinbrecht for their excellent technical assistance; and Dr. Cornell for statistical assistance. Trade names are mentioned with the understanding that no discrimination is intended and no endorsement by the authors or Univ. of Florida is implied. This research was funded in part by a donation from the Frontrunners Chapter of the Florida Nurserymen and Growers Assoc. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.