Plant concentrations of essential elements may exceed the critical concentrations, the minimum concentrations required for growth, and may vary somewhat from species to species. Nonetheless, the following table gives the general requirements of plants:
Please note that concentrations, whether in mg/kg (=ppm, parts per million) or Percent (%), are always based on the weight of dry matter, instead of the fresh weight. Fresh weight includes both the weight of the dry matter and the weight of the water in the tissue. Since the percentage of water can vary greatly, by convention, all concentrations of elements are based on dry matter weights.
Somewhat arbitrarily, a dividing line is drawn between those nutrients required in greater quantities, macronutrients, and those elements required in smaller quantities, micronutrients. This division does not mean that one nutrient element is more important than another, just that they are required in different quantities and concentrations. On the table above, the dividing line is typically drawn between S and Cl, meaning that:
Macronutrients: N, K, Ca, Mg, P, and
Micronutrients: Cl, Fe, B, Mn, Zn, Cu, Mo, and Ni
The prefix "micro" is well-understood from its use in terms such as "microscope". The term "macro" is somewhat less common, but indicates objects of a somewhat large size. Intermediate sizes are sometimes indicated by "meso". For example, the fauna (animal life) of soil may be divided into macrofauna (moles, mice, etc.), mesofauna (earthworms, burrowing insects, etc.), and microfauna (nematodes, etc.)
This page was last modified by Phillip Barak, Univ. of Wisconsin, on 11 Jan 1999. All rights reserved.