Fertilizer

Since medieval times, fertilizers have been used to help increase crop production. The earlier fertilizers were organic and consisted of decayed plant or animal matter, as well as various other items, whereas inorganic fertilizers consist largely of chemicals. Essentially, when crops are produced through the use of organic fertilizers, they are deemed to be “green,” whereas when inorganic fertilizers are used, there are certainly queries about whether the crops grown through their use can be regarded as “green.”

In ancient and early medieval times, the system of crop rotation was found to be very good in helping with crop yields. Part of this involved leaving the fields to lie fallow for a year in the process, and often being used for grazing animals. The resulting animal dung contributed to helping fields recover from intensive cultivation, and the Koreans introduced similar systems that involved fields being fallow for many years after the growing of ginseng.

Modern methods of fertilizing sometimes make use of computer technology and other instruments. This sprayer features crop canopy sensors on either side to monitor the greenness of plants and an onboard computer that adjusts the application of fertilizer accordingly.

Source: U.S. Department of Agriculture, Agricultural Research Service/James Schepers

Technically, the use of “slash and burn” (or swidden) agricultural techniques, still practiced by some people such as jungle tribes, used carbon to fertilize the soil, but as they found out, the nutrients thus provided were often rapidly used up, causing them to move to a new location. Gradually, during the late medieval and early modern period in Europe, it was determined that some forms of natural fertilizers [Page 176]could be used. The Englishman Gabriel Potts, in the 17th century, worked out that “colored water” from flooded land, and soil from streams, as well as malt dust, blood offal, and the entrails of animals helped plant nutrition. This was followed up by Walter Blith in the 1640s, who started using farmyard manure, human urine, bones, horn, fish, seaweed, and later even coarse wool clippings and soot—the latter essentially replicating some aspects of “slash and burn” agriculture. Blith also experimented with the use of chalk and lime, depending on the soil where the crops were being grown. By experimentation, agriculturalists learned that particular natural fertilizers were more suitable to specific crops and, indeed, specific species of vegetables.

During the 1730s, Viscount Charles Townshend (1674—1738) studied methods of improving crop production by having a four-year rotation system instead of the three-year system that had been used in Britain for hundreds of years. More than 100 years later, the German chemist Justus von Liebig (1803—83) recognized the importance of ammonia in helping plants grow, and he started promoting the manufacture and use of inorganic minerals involving ammonium salts to help plant nutrition and increase crop yields. He also came up with a method of using bone meal after it was treated with sulfuric acid, but it was not successful. Von Liebig's work went on to inspire the French scientist Jean Baptiste Boussingault (1802—87), who, when he returned to France from Latin America in 1832, worked on the introduction of nitrogen fixation to help in the production of legumes.

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