Soil fertility is defined as the ability of the soil to produce and sustain high crop yields indefinitely. In other words, fertility is a measure of the available nutrients in the soil and the proportion in which they occur. The soil is able to do this only if it can adequately supply the nutritional requirement of the crop plants in question.
Some of the factors are as listed below:
In farming soil fertility may be lost in many ways. The common ways include the following:
In plant nutrients, you may discover that certain elements are essential for plant growth. Those being required in the largest quantity are known as major or macro elements while those needed in small amounts are known as minor or micro elements, and those needed in very minute quantities are known as trace.
The elements needed in large amounts are carbon, hydrogen and oxygen, obtained mainly from air and water. Nitrogen, Phosphorus, potassium, calcium, magnesium, sulphur and iron are obtained from the soil dissolved in water, or from application of foliar sprays. Essential trace elements are copper, manganese, zinc, molybdenum, boron and chlorine which can be made available to plants either through their roots or their leaves.
The table below summarises the importance of major and minor nutrients to the plants, deficiency symptoms and their sources.
Table 3.3
NUTRIENT | IMPORTANCE TO PLANT | DEFICIENCY SYMPTOMS | SOURCES |
NITROGEN | Constitutes of proteins | Stunted growth in plants | Ammonium nitrate Urea Ammonium sulphate |
PHOSPHORUS | Protein formation and good root formation | Stunted growth. Purple colour in the leaves | Single and triple super phosphate |
POTASSIUM | For flower and fruit formation | Yellow leaves with brown edges | Potassium sulphate Potassium chloride |
CALCIUM | Formation of cell wall | Weak plants | Ground limestone |
MAGNESIUM | Formation of chlorophyll | Yellowing of leaves | Magnesium sulphate |
SULPHUR | Formation of proteins | Yellowing of plants | Ammonium sulphate Calcium sulphate |
As for Inorganic Fertilisers, these are artificially made fertilisers which are manufactured to supply the chemical nutrient needs of plants. The proportions of the main contents are stated on the container. Fertilisers which supply one main element such as nitrogen, phosphorus and potassium are known as straight fertilisers. Those containing mixtures in definite proportions are known as compound fertilisers.
The table below shows examples of straight fertilisers:
Fertiliser | % of Nitrogen |
Ammonium sulphate | 21 |
Ammonium Nitrate | 34 |
Urea | 46 |
Fertiliser | % of Phosphorus |
Single super phosphate | 19 |
Triple super phosphate | 44 |
Fertiliser | % of Potassium |
Muriate of potash (KC1) | 60 |
Sulphate of potash (KS04) | 50 |
It is necessary to note that top dressing fertiliser is sometimes applied with fertilisers of nitrogen. Plants, which are adequately supplied with potassium, are better able to withstand drought conditions than those suffering from a shortage.
On the other hand, Compound fertilisers are fertilisers containing more than two major elements along with minor elements. They are mostly applied as basal dressing fertilisers.
The table below shows the percentage constituents of Nitrogen, Phosphorus and potassium present in the different compound fertilisers
Compounds | % N | % P20S | % K20 | Other |
A | 2 | 18 | 15 | 65 |
C | 6 | 18 | 12 | 64 |
D | 10 | 20 | 10 | 60 |
R | 20 | 20 | 0 | 60 |
V | 4 | 18 | 15 | 63 |
X | 20 | 10 | 5 | 65 |
As for organics, these are the waste and residues of plants and animals. These organics can be in many forms such as poultry manure, cow dung/animal manures, farm yard manure, green manure and compost. They are natural manures and their decomposition is achieved by bacteria to form humus. Organic manures have bad and good effects on the soil.
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