Fertilizer, Synthetic
Soon after crops were domesticated, the need for fertilizers was realized. The first widely used fertilizer was manure, but bonemeal, fishmeal, dried blood, sewage, and seaweed all have served as fertilizers as well. In some cases green manuring is used; this takes place when crops such as clover or alfalfa are grown and then plowed under and left to rot. The first scientific study of fertilizers was conducted in 1550 when Frenchman Bernard Palissy (c.1499 or 1510-1589), voiced the opinion that since plants absorbed minerals--which he called vegetable salts--from the soil, the minerals needed to be replenished. Olivier de Serres (1539-1619), also of France, suggested crop rotation as a way of preserving soil nutrients. A 1669 paper published in England, however, suggested the use of fertilizers to replace soil minerals--phosphorus, potassium, nitrogen, sulfur, calcium, iron, and magnesium. Trace elements plants use include copper, born, zinc, manganese, and cobalt. Plants also require carbon, hydrogen, and oxygen, usually supplied through the air and water. Depending on the plant and the soil, some or all of these may need to be added. If the minerals are not replenished, the soil will not support the crop growth.
This was not such a problem in the United States or Canada during the early years of westward expansion because farmers would simply move to more fertile land when they had depleted the soil's mineral supply. However, replenishing these minerals was critical in Britain, Europe, and Asia, where arable land was in shorter supply. In general, the most commonly needed nutrients are potassium, nitrogen, and phosphorus. Natural reserves of potassium are ample. Originally the largest supplies were in Germany, but today potassium chloride mines in New Mexico and California supply much of the potassium used in synthetic fertilizers. Sulfur is present in the phosphate or ammonium fertilizers, usually as an impurity of the production process rather than as a deliberate additive. Calcium is currently supplied by dolomite, limestone, burned lime, or wood ash. Iron and magnesium are also added to fertilizers, as are the trace elements. Manure, sodium nitrate, urea, and ammonia sulphate have long been used as fertilizers for crops. Manures have a high percentage of nitrogen, as do sodium nitrate and sulphate of ammonia. Manure also improves the porosity of the soil. Unfortunately, processed manure was not in great supply while sodium nitrate, and sulphate of ammonia were available only from Chile and also were in short supply.
What was needed was a way of utilizing the nitrogen from the air, a way of fixing atmospheric nitrogen. Phosphorus is also needed in large quantities for plant growth. It was supplied as bonemeal, produced by pulverizing bones. This also became scarce. James Murray, an Irish physician, suggested that mineral phosphates from rocks could be used in place of bonemeal; however, he was not able to market his idea successfully. John Bennett Lawes (1814-1900), a English chemist, founded a research station in 1834 after inheriting his father's estate. He patented the idea of using phosphate rocks in superphosphates in 1841 and founded a superphosphate factory in 1843. Today most phosphorus is supplied in superphosphates or triple superphosphates. These are produced by applying sulphuric acid to natural phosphorus found in rocks.
In 1876 Sidney Gilchrist Thomas, also of England, used slag to develop a fertilizer for soil lacking phosphorus. A by-product of steel manufacturing, slag is also rich in phosphorus and is sometimes used. In 1802 Daniel Thaer investigated the effects of fertilizer in Saxony. At the same time other experimental farms began operation in France and Germany. Humphry Davy 's lecture in 1813 on agricultural chemistry signaled the beginning of intense study into fertilizers and the beginning of a new era in agriculture. In the 1840s a French chemist, Jean Baptiste Boussingault (1802-1887), began studying the effects of nitrogen on plant growth. He was puzzled by the fact that plants could grow in nitrogen-poor soil. At the time he presumed that the nitrogen required for their growth came from the air, but he did not know how the plants utilized the gaseous nitrogen. Actually the plants contained nitrogen-fixing bacteria at their roots. Ten years later Justus von Liebig, a German chemist, published Chemistry in its Application to Agriculture and Physiology.
While fertilizers containing phosphorus were being produced, nitrogen containing fertilizers were slower in developing. Not until the early 1900s did a German chemist, Fritz Haber, develop the technique for producing ammonia synthetically. He combined hydrogen with nitrogen and a catalyst at a high temperature and pressure to form synthetic nitrogen. By 1913 Carl Bosch, a German chemist working for BASF, developed the industrial ammonia production process. The first ammonia factory produced nine thousand tons of ammonia in its first year. The production techniques developed for the fertilizer were later applied to the petroleum industry.
Synthetic fertilizers have dramatically increased crop yields since the early twentieth century. Today, however, the amount of synthetic fertilizers in use, coupled with increased emissions from fossil fuels has resulted in a rate of excess nitrogen deposits on fields and through runoff in streams and rivers that has caused an increase in growth of algae in estuaries, oceans, and lakes. As the algae die, they deplete the oxygen supply in the water resulting in massive fish kills. Clearly, this state of affairs must be addressed, as it will have a direct effect on biodiversity, and on the health of the planet and its inhabitants.
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