Henry Girasimoff, age 12, of San Diego, California, for his question:
When and how did farmers discover fertilizers?
For thousands of years, mankind has been a patient farmer. But the patient farmer was slow, very slow, to learn new ways. Fertilizers became fashionable only in the 1800s and the hungry world continues to need better basic soil programs. The science of agriculture is still in its infancy.
Our remote ancestors were roaming hunters and gatherers. Settled civilizations began when they learned to domesticate their wild animals and to sow and develop their wild seeds. Man The Wandering Nomad became Man The Established Farmer. The buried remains of Swiss lake settlements contain some very fine wheat. Other remains of 6,000 years ago contain seeds of flax, barley and grains that were far superior to the wild varieties.
Early farmers apparently knew how to improve their crops by selecting and planting the best seeds from year to year. But, as a rule, they depended upon the soil to feed their crops. Sometimes they strewed the fields with natural fertilizers such as manure or wood ashes, ground bones or dried blood. The Egyptians depended on rich, muddy soil from the yearly flooding of the Nile. In Europe of the Middle Ages, the crops were rotated to rest the soil. One third of the farmland was left bare and fallow each year. But if these methods improved the crops, no one knew why.
Experts of the early 19th century began to study the needs of growing plants and this new approach led to the production of chemical fertilizers. FlAnts, of course, need water and sunlight. They also need a balanced diet of at least 20 elements. However, iron and nitrogen and most of the basic plant foods must be in the .form of special chemical compounds. What's more, all the food items must be soluble because the balanced formula must be served to the roots in liquid form.
In the mid 1800s, chemical fertilizers were introduced to supply the three major groups of plant food. Ammonia is given off when coal is processed into gas and coke fuel. This ammonia by product was fixed with acid to make nitrate fertilizers. Later, abundant nitrate mines were found in Chile. This nitrogenous fertilizer is shipped around the world.
Old fashioned bone meal added traces of phosphate fertilizers to the soil. Experts of the last century treated it with sulphuric acid to add to its value as a plant food. Then natural phosphate rocks were used and later treated to yield rich superphosphate fertilizers. Plants can take their potassium from wood ash. But natural deposits of potash were found to contain more usable potassium. They were mined to provide abundant supplies of the potassium chemicals that growing plants needs.
These chemical fertilizers are cheap and plentiful and rich in usable nitrates, phosphates and potassiums. Organic fertilizers, such as manure, contain less of these essential chemicals. But they often do more to improve the texture and long term value of the soil. However, the world's major crops are fed with chemical fertilizers and more will be needed in the future. Researchers hope to find sources to supply richer, cheaper and more abundant supplies of these chemical plant foods.