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Evaluating Internal Zinc Requirements of Grain Crops by Seed Analysis

Land Resources Section, National Agric. Res. Center, Park Road, Islamabad, Pakistan
Dep of Agronomy and Soil Science, Univ. of Hawaii, Honolulu, HI 96822

^* Corresponding author.

Our study tested the general opinion that foliar tissues are superior to seeds for determining the nutrient status of crops. Zinc requirements of leaves and seeds were estimated from yield response curves based on greenhouse pot culture experiments using two Zn-deficient subsoils (Paaloa silty clay; clayey, oxidic, isothermic Humoxic Tropohumult; and Keahua silty clay loam; fine, kaolinitic, isohyperthermic Torroxic Hapulstoll) of Hawaii. These were fertilized with 0, 1, 3, 9, or 27 mg Zn kg^–1 of soil. The order of grain yield response to Zn fertilization was: wheat (Triticum aestivum L.) < sorghum [Sorghum bicolor (L.) Moench] < rice (Oryza sativa L.) < millet [Pennisetum americanum (L.) Schumann] < soybean [Glycine max. (L.) Merr.] < cowpea [Vigna unguiculata (L.) Walp.] < corn (Zea mays L.). Fertilizer Zn requirements for near-maximum grain yield was highest for cowpea (7.5 mg kg^–1 soil) and lowest for wheat (0.5 mg kg^–1 soil). Zinc concentrations (mg kg^–1) in recently matured leaves associated with 95% maximum yields were similar for seven species: corn and millet, 24; soybean, 22; cowpea, 21; sorghum, 20; rice, 19; and wheat, 17. Equivalent concentrations for seeds were soybean, 43; cowpea, 26; corn, 18; millet, rice and wheat, 15; and sorghum, 10. Across all species, fertilizer levels and soils, the range of Zn concentration in leaves was 5 to 115 mg kg^–1 (both values for corn); and in grains 6 (sorghum) to 59 mg kg^–1 (wheat). Our results indicate that there was little reason to prefer leaves over grain as a diagnostic tissue for Zn; therefore, Zn should be added to the list of elements for which seed analysis may be advantageous.

Received for publication March 5, 1990.