Introduction Plants require at least 16 elements for normal growth and for completion of their life cycle. Those used in the largest amounts, carbon, hydrogen and oxygen, are non-mineral elementssupplied by air and water. The other 13 elements are taken up by plants only in mineralform from the soil or must be added as fertilizers. Plants need relatively large amounts of nitrogen, phosphorus, and potassium. These nutrients are referred to asprimarynutrients, and are the ones most frequently supplied to plants in fertilizers. The three secondaryelements, calcium, magnesium, and sulfur, are required in smaller amounts than the primary nutrients. Calcium and magnesium are usually supplied with liming materials, and sulfur with fertilizer materials. Contaminants in rainfall also supply 10 to 20 pounds of nitrogen and sulfur per acre each year, depending on local air quality.
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