Fertilizer is any substance that can be added to the soil to provide chemical elements essential for plant nutrition so that the yield can be increased. Natural substances such as animal droppings, ashes from wood fires, and straw have been used as fertilizers in fields for thousands of years, and lime has been used since Romans introduced it during the Empire. It was not until the nineteenth century, however, that chemical fertilizer became widely accepted as normal agricultural practice. Today, both natural and synthetic fertilizers are available in a variety of forms.A complete fertilizer is usually6 marked with a formula consisting of three numbers, such as 4-8-2 or 6-6-4, which designate the percentage of content of nitrogen, phosphoric acid, and potash in the order stated.Fertilizers have no harmful effects on the soil, the crop, or the customer as long as they are used according to recommendations based on the result of local research. Occasionally, however, farmers may use more fertilizer than necessary, in which case the plants do not need, and therefore do not absorb, the total amount of fertilizer applied to the soil. The surplus of fertilizer thus can damage not only the crop but also the animals or human beings that eat the crop. Furthermore, fertilizer that is not used in the production of a healthy plant is leached into the water table. Accumulations of chemical fertilizer in the water supply accelerate the growth of algae and, consequently, may disturb the natural cycle of life, contributing to the death of fish. Too much fertilizer on grass can cause digestive disorders in cattle and in infants who drink cow’s milk. Fertilizer must be used with great attention to responsible use or it can harm the environment.
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