The nutritional value of such inorganic elements as calcium, phosphorus, iodine, copper, and iron has been demonstrated by many investigators, and it is generally recognized that quantitative variations of these elements in foods and feeds are important factors in human and animal health. These and other mineral elements, especially those occurring in trace amounts, are receiving greatly increased attention in both popular and scientific literature dealing with soils, fertilizers, plant growth and composition, food quality, and animal and human health and nutrition.

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