Plant growth depends upon C, H, O, and at least 13 mineral elements. Six of these (N, K, Ca, Mg, P, and S) macro-elements normally occur in plants at concentrations greater than 1,000 mg kg -1 level. The remaining micro-elements (B, Cl, Cu, Fe, Mn, Mo, and Zn) normally occur in plants at concentrations less than 50 mg kg -1 . Trace amounts of other elements (e.g., Co, Na, Ni, and Si) may be beneficial for plants. Silicon concentrations may range upwards to 50,000 mg kg -1 in some forage

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... Mineral elements required by animals include the macro-elements Ca, Cl, K, Mg, N, Na, P, and S; the trace or micro-elements Co, Cu, Fe, I, Mn, Mo, Se, and Zn; and the ultra-trace elements Cr, Li, and Ni. When concentrations of these elements in forages get 'out of whack' their bioavailability to animals may be jeopardized. Interactions of K x Mg x Ca, Ca x P, Se x S, and Cu x Mo x S are briefly mentioned here because more detail will be found in the literature. Limited published information is available on Si, so we have provided more detail. Silicon provides physical support to plants and may reduce susceptibility to pests. However, Si may have negative effects on digestibility and contribute to urinary calculi in animals.