Fertilizer is a substance that is added to soil to help plants grow. Farmers use various fertilizers to help produce abundant crops. Home gardeners use fertilizers to raise large, healthy flowers and vegetables. Landscapers spread fertilizers on lawns and golf courses to help grow thick, green grass.
Fertilizers contain nutrients (nourishing substances) that are essential for plant growth. Some fertilizers are made from such organic materials as manure or sewage sludge. Others are manufactured from certain minerals or are produced as synthetic compounds.
People have used fertilizer for thousands of years. They used it even though at one time they did not know why it was beneficial for plants. Long before they gained an understanding of plant nutrition, people noticed that certain substances helped plants thrive. These beneficial substances included animal droppings, wood ashes, and certain minerals. During the 1800’s and early 1900’s, scientists identified chemical elements that are essential for plant nutrition.
Today, farmers throughout the world use billions of dollars worth of fertilizer yearly. Increased production resulting from the use of fertilizers accounts for about a fourth of all crop production. Without fertilizers, greater amounts of land and labor would be needed to produce the same quantity of food and fiber.
The importance of fertilizer
Green plants produce the food they use. They produce it by means of the process of photosynthesis (see Photosynthesis). This process requires large amounts of nine chemical elements—carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. It also requires smaller amounts of several other elements. These elements are called micronutrients because so little of each is needed. The micronutrients include boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc. Certain kinds of plants also require small amounts of cobalt and silicon.
Air and water provide most of the carbon, hydrogen, and oxygen that green plants need for growth. The other elements must come chiefly from the soil.
The elements plants receive from soil are normally provided by decaying plant and animal matter and dissolved minerals. But sometimes soil does not have enough of these substances. In such cases, plants need fertilizer to thrive. The harvest of crops, for example, involves removing plants from the soil before they decay. The mineral elements contained in the harvested portions of the crops do not return to the soil. As a result, fertilizer must be added to replace the elements. Nitrogen, phosphorus, and potassium are the elements that soil most often lacks.
Kinds of fertilizers
There are two chief kinds of fertilizers, inorganic and organic. Manufacturers produce inorganic fertilizers from certain minerals or synthetic substances. Organic fertilizers come from decayed plant or animal matter.
Inorganic fertilizers
are the most widely used fertilizers. They supply three main elements: nitrogen, phosphorus, and potassium.
Nitrogen fertilizers
are the most widely used inorganic fertilizers. They are produced mainly from ammonia gas. Manufacturers convert the gas into liquid forms. Both gas and liquid forms may be applied directly to the soil. Manufacturers also use ammonia in producing solid fertilizers. Solid fertilizers include ammonium sulfate, ammonium nitrate, ammonium phosphate, and an organic compound called urea. Each of these fertilizers provides the soil with large amounts of nitrogen. Some, including ammonium sulfate and ammonium phosphate, furnish other elements as well as nitrogen.
Phosphorus fertilizers
are also called phosphates. Finely ground apatite may be applied to soil as a solid fertilizer called rock phosphate. Apatite also may be treated with sulfuric acid or phosphoric acid to make liquid fertilizers called superphosphates.
Potassium fertilizers
come largely from deposits of potassium chloride. Manufacturers mine the deposits or extract them with water. The manufacturers then produce such fertilizers as potassium chloride, potassium nitrate, and potassium sulfate.
Other inorganic fertilizers
provide soil with various elements. Those containing gypsum, for example, supply sulfur. Manufacturers also produce fertilizers that provide specific micronutrients.
Organic fertilizers
are made from a variety of substances. They include manure, plant matter, sewage sludge, and wastes from meat-packing plants. These fertilizers contain a smaller percentage of nutrients than do inorganic fertilizers. Therefore, they must be used in larger quantities to obtain the same results. Some organic fertilizers may also cost more. However, they solve a disposal problem because much organic waste has little use other than as fertilizer. Plant matter is used as fertilizer in two main ways: after treatment in a compost pile or as green manure.
A compost pile consists of various types of plant matter mixed together in proportions designed to speed up decomposition (decay). Soil, fertilizer, or lime may also be added. The pile is allowed to decay for several months before being used as fertilizer. See Compost.
Green manure consists of certain crops that farmers use as fertilizer. For example, some plants have bacteria in nodules (knotlike growths) on their roots. These bacteria take nitrogen out of the air and convert it into a form that plants can use. Such plants, called legumes, include alfalfa, beans, and clover. Farmers may plant a crop of legumes and then plow the young plants into the soil. As the plants decay, nitrogen and other elements are released into the soil. They enrich the soil so it can nourish other crops.
The fertilizer industry
The majority of the fertilizers produced in the world are used on farm crops. China, India, Russia, and the United States are the world’s leading producers of fertilizers. Other leading fertilizer producers include Belarus, Canada, Germany, and Indonesia.
Raw materials
for fertilizers come from several sources. Ammonia, the basic source of nitrogen fertilizers, is formed by combining nitrogen from the air with hydrogen from natural gas. Many petroleum companies produce ammonia because they have large supplies of natural gas.
The world’s leading producers of phosphate rock include China, Morocco, and the United States. China and Morocco have the largest reserves of phosphate rock. Florida is the leading phosphate rock producer in the United States.
Large deposits of potassium chloride, the major source of potassium fertilizer, occur in Canada. Saskatchewan is the leading Canadian province in potassium chloride production. New Mexico is the leading U.S. state.
Production and sale.
Fertilizer is produced in four basic forms. Straight goods fertilizer is any chemical compound that contains one or two fertilizer elements. Bulk blend fertilizer is a mixture of straight goods fertilizers. Manufactured fertilizer consists of two or more chemicals that are mixed and then formed into small pellets. Each pellet may contain nitrogen, phosphorus, and potassium and perhaps certain micronutrients. Liquid fertilizer consists of one or more fertilizer materials dissolved in water. It may be sprayed on plants or soil, injected into soil, or added to irrigation water.
Most fertilizers release their plant nutrients into the soil almost immediately. Manufacturers also produce a special type of fertilizer called controlled-release fertilizer. Controlled-release fertilizer gives up its nutrients gradually. This type has been found useful when plants need a constant supply of nutrients over a long period.
Problems of the fertilizer industry.
Every year, large amounts of fertilizer must be produced to meet the world’s growing need for food. The fertilizer industry tries to match its production with this need. If it does not do so, severe food shortages might result.
A shortage of raw materials could cause a low supply of fertilizer. Some materials, such as natural gas and phosphorus, have uses other than in making fertilizer. Their use by other industries could cause a shortage for fertilizer manufacturers.
The mining and processing of the raw materials needed to make fertilizer may damage the environment. Many minerals used in making fertilizer come from open-pit mines. Such mines leave large unproductive areas unless properly landscaped. In addition, the excessive use of fertilizer can contribute to water pollution. For example, erosion may carry fertilized soil into lakes and streams. The nutrient elements in the soil then increase the growth of algae (simple plantlike organisms) in water. When the algae die, they decay and use up the oxygen supply in the water.
