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Plants require nutrients to grow. The higher the crop yield the
higher is as well the demand for nutrients. In well balanced systems, only the quantity of nutrients which has been extracted by the plant has to be returned. Additional fertilisation requirements arise usually through intensive farming methods.
On-farm ressources may not always be sufficient to keep the fertility
of soil and therefore fertilisers have to be added.
Primary, or more specific, macro-nutrients required for growth can be
divided into two different groups, one composed of C-H-O (Carbon, Hydrogen, Oxygen) which is freely available by air and the other group with N-P-K
(Nitrogen, Phosphorus, Potassium) which might have to be added to maintain a sufficient soil level.
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