Inorganic or synthetic organic materials of a concentrated nature which contain one or more plant nutrients in soluble and quickly available forms are known as Chemical Fertilizers.
Depending on the nutrient content, Fertilizers can be divided into two major categories called straight fertilizers and complex fertilizers. Straight fertilizers contain only one primary plant nutrient and the complex fertilizers contain two or more plant nutrients of which major nutrients are in chemical combination.
Being concentrated has the advantage of smaller bulk with resultant economy. Ease in storage, transport and handling are some more advantages and the application could be adjusted to supply the exact proportions of nutrients required by various crops grown in soils of varying fertility.
There are four main classes of Chemical Fertilizers – Nitrogenous, Phosphatic, Potassic and Complex.
Nitrogenous fertilizers are recently originated. With the growing awareness if optimum yields are to be achieved, it is necessary to supply a fixed amount of nitrogen. Nitrogen fertilizers became attractive in terms of cost with the break – through in retaining techniques of natural gas and Hydrogen – Nitrogen synthesis. Nitrogen fertilizers are classified into four groups based on the chemical form in which Nitrogen is present. Ammonical fertilizers contain ammonium ions, Nitrate fertilizers contain nitrate ions, Amide fertilizers contain Amide group and there is combined Ammonical and Nitrate fertilizers.
Phosphatic fertilizers were used in early days as ground animal bones. Certain grades were produced such as single super phosphates (SSP) and Triple super phosphates (TSP) but Ammonium phosphate has overtaken super phosphates. Developing countries are using more phosphate fertilizers.
During early days potash nutrients were used to crops in the forms of wood ash, sugar beet wastes and salt peter without knowing the ingredient. Later on higher grade commercial products were developed Potassium chloride being the main product. Potassium chloride is completely water soluble and when applied to soil potassium ions are absorbed and retained by soil colloids. This fertilizer has a neutral effect on soil and for crops whose quality is affected by chloride ions potassium sulphate is recommended. When applied to soil, potassium ions are absorbed by colloids and there will be no acidity or alkalinity.
Sixteen nutrient elements are recognized as essential to plants for their normal growth and development. Thirteen is obtained from soil for their normal growth. Continues cropping in the same piece of land will deplete the soil of these elements and result in lower crop yields if not artificially restored.
The progress of Chemistry during the last century contributed much to understanding the effects of chemical inputs in agriculture in the form of Chemical fertilizers and the broad principals of modern fertilizer industry was laid down by Liebig in the nineteenth century.
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