Zinc deficiency on the shallow soils of Niue

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Abstract
The effects of zinc sulphate on the yield and chemical composition of crotalaria and sweet corn grown on two calcareous soils under green-house conditions have been examined. In the absence of applied zinc, plant growth was restricted on each soil, and the deficiency symptoms observed for each species have been described. Application of 20 lb of zinc per acre in the presence of NPK gave maximum yields of sweet corn on both soils, which amounted to double the yield of the control. At the 5 lb rate of zinc, about 85% of the maximum yield was obtained. A similar response to zinc was obtained with crotalaria on the more calcareous soil (pH 7.7). Crotalaria yields were unaffected by applications of iron (as Fe EDDHA) up to 2.4 lb of Fe per acre, but, at the 4.8 lb rate in the presence of zinc, yields were depressed due to an induced manganese deficiency. The concentration of zinc in sweet corn was not increased, provided each increment of zinc that was added increased plant yield. This concentration was 50% higher at each rate of applied zinc on the less alkaline soil (pH 7.4). Recovery of zinc was also higher on this soil, but did not exceed 0.6% of that applied. The nutrients P, K, Ca, Mg, Cu, Fe, and Mn accumulated in the tissues of zinc-deficient plants as a result of restricted growth, but fell to normal levels as zinc treatment increased plant yield. Zinc deficiency is a major factor limiting plant growth on the calcareous soils of Niue, but its correction may in turn result in deficiencies of iron and manganese.