Received for publication 1 Apr. 1985. We thank Robert B. Peters, Peters Fertilizer Co., W.R. Grace Co., Inc., for supplying 25–3.9–14 fertilizer, and Barbara Gustavson, Dept. of Experimental Statistics, LSU Baton Rouge for statistical analysis assistance. Mention of a commercial product is done with the understanding that no discrimination is intended and no endorsement is given by the authors. 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.