- Plant Nutrients
There are 17 essential elements for plant growth. See box middle of page 64.
An essential element is one that is needed for the normal growth of plants.
Elements taken up by the plant in large amounts from the soil are called major or macro elements.
Elements taken up in small amounts are called minor or trace elements. 
- Nitrogen
Needed to make chlorophyll and so increased nitrogen gives increased photosynthesis which leads to increased growth.
Most important and widely used fertilizer.
Deficiency causes reduction in yield and a yellowing of the crop.
Plants can absorb nitrogen in the form of nitrate ions (NO3-) but they cannot absorb nitrogen in the form of ammonium ions (NH4+) or urea.
- Phosphorus
Involved in cell division and plant growth. Deficiency causes stunted growth and a bluish colour.
If the pH of the soil is below 5.5 or above 7.5 phosphorus is unavailable to plants. This is known as phosphorus fixation or immobilisation.
Phosphorus is most available to plants between pH 6 and pH 7.
- Potassium
Involved in plant growth and disease resistance. Deficiency causes loss of yield and scorching.
Some clay minerals can trap k+ ions and make them unavailable to plants. This is called potassium fixation or immobilisation.
Only some soils with the particular clay minerals have this problem.
- Calcium, Magnesium and Sulphur
They are major elements but are not generally added in fertiliser form because:-
–They are relatively abundant in soils.
–They are not immobilised.
–Lime adds Ca and Mg
–The main nitrogen fertiliser used, Calcium Ammonium Nitrate (CAN), adds calcium to soil.
–Sulphur is/was an impurity in most fertilisers. - Trace Elements
Deficiencies of trace elements is more common than deficiencies of major elements.
The reason may be that the element was not present in the parent material or the elements have become unavailable due to high pH.
Deficiency of trace elements causes various diseases in plants and animals.
- Soil pH and Liming
Soil pH influences the availability of elements to plants.
Most elements have maximum availability between pH 6 – 7.
Liming is essential in Ireland due to the acid leaching that occurs as a result of our climate.
Lime adds Ca++ and Mg++ ions to the soil which replace H+ ions and so raise the pH. Lime takes about 2 years to have its full effect on a soil.
Ground limestone is usually used. 
- Soil Testing
Used to determine how suitable an area is for crop growth.
Soil tests are ranked on a soil index between 1 and 4, where 1 is worst and 4 is best.
Soil tests will determine what fertiliser is needed on the land.
Soil samples are taken with a soil auger. - Taking a Soil Sample
Divide area in 2–4 ha regions.
Take at least twenty samples from a wide range of areas.
Take samples in a W shape.
Avoid areas such as headlands, gateways, entrances and exits to fields.
Take account of previous cropping and fertiliser history of area.
Do not sample for lime for two years and for P and K for three months after last application.
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