Improved nutrient-use efficiency in cropping systems is needed to increase farm income and to minimize possible nutrient emission to the environment. Plant glutamate dehydrogenase (GDH) offers a means for improved diagnosis of the nutrient status of crops. Zea mays L. DK-68 was fertilized with nutrient solutions containing different ratios of nitrogen, phosphorus, and potassium (N, P, K). Maize shoot GDH was fractionated to its population of isoenzyme by Rotoforation followed with native PAGE. The GDH of the control maize had the complete set of 28 isoenzymes. Fertilization of the maize with N1P1K1 did not repress the 14 anodal but did repress the 14 cathodal isoenzymes. As the P content of the fertilizer increased in the sequence N0P0K0, N1P0K1, N0P1K0, N1P1K1, N0P2K0, and N0P4K0, the amination maximum velocity (V max) of the enzyme decreased curvilinearly in the sequence 310, 246, 140, 130, 108, and 83 μmol min-1 mg-1, respectively. The highest dry matter yield occurred when the fertilizer contained 1−3 mM Pi, which was thus the nutrient deficiency−sufficiency interphase. In the GDH integration of the signals from the N, P, and K so as to respond with a characteristic isoenzyme population pattern, the signal from N superseded that from K; in turn, the signal from P superseded those from N and K. Signal integration was therefore based on the dominance by the most nucleophilic nutrient. In this case, the decreasing order of nucleophilic dominance was PO4 3- > NH4 + > K+. Keywords: Zea mays; glutamate dehydrogenase; NPK signal integration

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The adsorption of zinc by six soils was determined. Soils that formed under slightly acid or neutral conditions usually adsorbed larger quantities of Zn than soils formed under very acid conditions. The stability constants for the soil‐zinc systems after displacement of Zn by KCl and Cu(OAc)2 were also higher for the near neutral soils. Soil from the Ap‐horizon was compared to soil from the Al‐horizon of the Hoytville soil series. The organic matter content did not explain the differences in the amounts of Zn adsorbed. The adsorption of Zn by the soils after extraction with hot water or C6H6‐MeOH were usually slightly less than the non‐extracted soil. However, the quantities of Zn adsorbed by the soils after extraction with NaOH were greater than the non‐extracted soils. A large percentage of this Zn was not displaced with KCl but was displaced with Cu(OAc)2.

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