Solubility and Availability of Micronutrients in Relation to Phosphorus Fertilization

Availability of B, Cu, Fe, Mn, Mo, and Zn in relation to excesses of Ca(H 2 PO 4 ) 2 was studied with sour orange seedlings as indicators for induced interactions created in 19 different soils. To separate the effect of the carrier from that due to phosphorus, Ca(H 2 PO 4 ) 2 , H 3 PO 4 , KH 2 PO 4 , and NH 4 H 2 PO 4 sources were also used in a separate experiment. Chemical analyses of water extracts from the latter experiment provided the solubility data as controlled by excesses of P. Regardless of sources, excess P resulted in acute Cu deficiency; and in the case of acid soils, reduced uptake of B and Zn usually followed excess P fertilization. Excessive P fertilization of acid soils resulted in increased Mn and Mo uptake, whereas in alkaline soils excessive P reduced the availability of Mo. Solubility of Mn, B, and Mo Paralleled uptake data. Cu and Zn Solubilities were increased by excessive P fertilization. Mechanisms pertinent to the various P interactions are discussed with the major emphasis placed on P‐Cu antagonism.