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Out
of 92 naturally occurring chemical elements only 18 have
been identified as essential elements (or nutrients)
without which plants cannot grow and complete their life
cycles. Elements essential for plant growth include: C,
H, O, N, P, K, S, Ca, Mg (so called macronutrients, used
by plants in relatively large amounts), Fe, Mn, B, Zn,
Cu, Cl, Co, Mo, Ni (so called micronutrients, used by
plants in small amounts).
These
essential nutrients play various roles in the structure
and metabolism of plants. They are continuously cycled
through the atmosphere-soil-plant system according to
specific transformation and transport processes. Some of
these processes occur in soils and make elements
available to plant roots and soil organisms.
This
section will describe the cycles of five of these
nutrients, i.e. potassium, phosphorus, sulfur, nitrogen,
and carbon.
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