Plant Nutrients
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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.
Fertile Soils
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.
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.
The Contribution made by fertilisers
The farms of Western Europe would produce 40-50% less food if mineral fertilizers were not used. Worldwide, the reduction would be around 30%. Using organic waste (e.g. animal manure) can reduce the need for mineral fertilizers 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.
The nutrient (food) needs of plants
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.
Plant nutrients are available from four different sources
Soil Reserves
– The soil itself
Organic manures
– livestock, municipal and industrial wastes.
Atmosphere
– biological nitrogen fixation.
Chemical fertilizer
– mineral fertilizers.
| Major Elements | ||
| Nitrogen | NH4 + NO3- | The terms major, secondary and trace elements describe the relative amounts of a nutrient needed to carry out its specific task. |
| Phosphorus | H2 PO4- | Samples of soil or plant tissue can be tested to assess whether there are sufficient nutrients available. |
| Potassium | K+ | Samples of soil or plant tissue can be tested to assess whether there are sufficient nutrients available. |
| Secondary Elements | ||
| Sulphur (S) | SO42- | Samples of soil or plant tissue can be tested to assess whether there are sufficient nutrients available. |
| Magnesium (Mg) | Mg2+ | |
| Calcium (Ca) | Ca2+ |
| Trace Elements | |
| Chlorine (Cl) | CL- |
| Iron (Fe) | Fe2+ |
| Manganese (Mn) | Mn2+ |
| Zinc (Zn) | Zn2+ |
| Copper (Cu) | Cu2+ |
| Boron (B) | H2BO3- |
| Molybdenum (Mo) | MoO42+ |
There is, at present, no alternative to mineral fertilizers on a regional or global scale if food supply is to be ensured. Any potentially negative aspects associated with the production or use of such a necessary product are naturally of concern to both the EU fertilizer industry and the EU institutions, and both parties are actively engaged in addressing those concerns which arise and in ensuring that appropriate legislation is in place.
Soil Analysis
The objectives of soil testing are primarily;
- To determine soil fertility so that the correct amount of fertilizer needed to replace the nutrients removed or lost by the farming system, is applied.
- To monitor soil fertility levels.
Plant Nutrient Requirements
Plants require nutrients in order to grow, develop and complete their life cycle. The supply of nutrients to the plants should be balanced in order to maximize the efficiency of the individual nutrients so that these meet the needs of the particular crop and soil type.
The Physical Form of Fertilizer Products
The majority of the fertilizers used in Ireland are straight or compound fertilizers applied in a solid form.
Fertilizer Products
Mineral fertilizers are made from naturally occurring raw materials containing nutrients that have normally been transformed into a more plant-available form by industrial processing. Although the number of chemical processes used is relatively small, there are a wide variety of finished products.
Recommendations for Use
It is advisable for fertilizer applications to be calculated in a ‘site specific’ (soil analysis) basis, taking accounts not only of the specific crop and expected yield, but also the type of soil on which the crop is grown (including its nutrient status) and previous cropping history.
Plant Nutrient Requirements
Plants require nutrients in order to grow, develop and complete their life cycle. The supply of nutrients to the plants should be balanced in order to maximise the efficiency of the individual nutrients so that these meet the needs of the particular crop and soil type. The primary, or macro, nutrients required by plants are; –
Carbon – C Nitrogen – N
Hydrogen – H Phosphorus – P
Oxygen – O Potassium -K
Carbon, hydrogen and oxygen, which, together with nitrogen, form the structural matter in plants, are freely available from air and water. Nitrogen, phosphorus and potassium, on the other hand, may not be present in quantities or forms sufficient to support plant growth. In this case, the absence of these nutrients constitutes a limiting factor.