(1) Fertilizer is any substance that can be added to the soil to provide chemical elements essential for plant nutrition. Natural substances such as animal droppings and straw have been used as fertilizers for thousands of years, and lime has been used since the Romans introduced it during the Empire. It was not until the nineteenth century, in fact, that chemical fertilizers became popular. Today, both natural and synthetic fertilizers are available in a variety of forms.
(2) A complete fertilizer is usually marked with a formula consisting of three numbers, such as 4-8-2 or 3-6-4, which designate the percentage content of nitrogen, phosphoric acid, and potash in the order stated.
(3) Synthetic fertilizers are available in either solid or liquid form. Solids, in the shape of chemical granules are popular because they are easy to store and apply. Recently, liquids have shown an increase in popularity, accounting for about 20 percent of the nitrogen fertilizer used throughout the world. Formerly, powders were also used, but these were found to be less convenient than either solids or liquids.
(4) Fertilizers have no harmful effects on the soil, the crop, or the consumer as long as they are used according to recommendations based on the results of local research. Occasionally, however, farmers may use more fertilizer than necessary, damaging not only the crop but also the animals or humans that eat it. Accumulations of 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.