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"There is no life without Plants and there are no
Plants without nutrients" |
| Crops get their nutrients or food from the soil. The bigger the crop, the
more nutrients are removed. |
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| Well-structured soils that are rich in nutrients are said to be highly
fertile. Given sufficient light, warmth and water, they will produce abundant crops.
However, the nutrients removed by crops or feeding animals must be replaced or soil
fertility will be run down. |
| Nutrients can be replaced by returning to the soil, plant, animal or human
waste, such as sewage sludge, or by adding mineral fertilisers. In some cases the soil
might simply be left to rest and recover its fertility. This process, sometimes known as
fallowing, involves the slow release of nutrients from soil minerals or the breakdown of
nutrients held in soil organic matter. |
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| The need for food will continue to increase as world population grows and
as more people can afford to improve their diets. Producing more feed depends on
maintaining or increasing soil fertility. However, achieving this gives rise to dilemmas,
concerns and choices for society. |
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| The farms of Western Europe would produce 40-50% less food if mineral
fertilisers were not used. |
| Worldwide, the reduction would be around 30%. Using organic waste (e.g.
animal manure) can reduce the need for mineral fertilisers but there is seldom-sufficient
waste in areas where the major food crops are grown. This is the case in the vast
farmlands of America, Russia and Australia. |
| If we are to feed the world’s increasing population we must grow more
food and if we are to do this without damaging wildlife and natural habitats we must make
maximum use of the suitable farm land we have. Fertilisers allow us to do that. |
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| To grow well, crops need a balanced supply of essential nutrients. The
main nutrients are nitrogen, phosphorus and potassium. These and most other nutrients are
normally dissolved in water in the soil. From there they are taken up by plant roots as
small electronically charged particles known as ions. |
| Plants also need oxygen and carbon, which they extract from the air for
respiration. That is why plant roots need well-structured soil, which allows air to flow. |
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Soil Reserves – The soil itself.
Organic manures – livestock, municipal and industrial wastes.
Atmosphere – biological nitrogen fixation.
Chemical fertilizer – mineral fertilizers. |
| Nutrients and their chemical symbols |
Plant available (ionic) form of nutrient |
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| Major Elements |
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| Nitrogen (N) Phosphorus (P)
Potassium (K) |
NH4 + NO3- H2 PO4-
K+ |
The terms major, secondary and trace elements describe the relative amounts of a
nutrient needed to carry out its specific task. Samples of soil or plant tissue
can be tested to assess whether there are sufficient nutrients available. |
| Secondary Elements |
| Sulphur (S) Magnesium (Mg)
Calcium (Ca) |
SO42- Mg2+
Ca2+ |
Samples of soil or plant tissue can be tested to assess whether there are
sufficient nutrients available. |
| Trace Elements |
| Chlorine (Cl) Iron (Fe)
Manganese (Mn)
Zinc (Zn)
Copper (Cu)
Boron (B)
Molybdenum (Mo) |
CL- Fe2+
Mn2+
Zn2+
Cu2+
H2BO3-
MoO42+ |
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