Interactions of phosphorus, magnesium and zinc on the yield and nutrient content of maize

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Abstract
Five Zn-deficient soils designated A-E (pH 7.3-7.7) and a reference soil F (pH 7.6) were used in a glasshouse study on maize in which 5 fertilizer treatments: 75 .mu.g P/g alone and together with all combinations of 0 and 5 .mu.g/g of Mg and Zn and with 10 .mu.g Mg + 5 .mu.g Zn/g and a control were applied. The forage yield of soils A-E ranged 2.5-2.9 g when no Zn was applied and 5.1-5.6 g with added Zn, showing that Zn was the major limiting nutrient. Applied Mg significantly increased yield, the main exceptions being soils D and E which had the highest exchangeable Mg. Addition of Mg to a P but not PZn treatment significantly increased P concentration and uptake. For soils B and E, Zn addition significantly depressed P concentration in maize. The P treatment significantly depressed Zn concentration but increased Mg concentration and uptake by maize. Although Mg application either depressed or had no effect on Mg content of maize, it caused a significant increase in Zn concentration and uptake. The correlation coefficient (r) between Zn and Mg in maize was -0.61 (P < 0.001). Possibly, Mg was replacing Zn in the clay lattice or in its metallo-protein complex within the root.