FERTILIZERS. The words fertilizer and manure denote any substance that increases the productiveness of the soil, but in scientific agricultural literature the word fertilizer is confined to materials prepared artificially that supply nutrients to the plant, the word manure being more generally applied to sub stances like farmyard manure and lime that improve the soil in other ways besides supplying nutrients. Both groups will be dealt with in this article. (See also SOIL; FEEDING STUFFS ; GRASS AND GRASSLAND; and the further list of headings under AGRICULTURAL ARTICLES.) The use of farmyard manure is probably as old as agriculture itself. Its discovery was already mythical in Roman times, and its properties and particularly those of composts were known in great detail to the Arabs and are fully described in their loth century text book, Kitab al-Falahali, with some gruesome detail, as when the writer, in emphasizing the value of blood as manure says, quite calmly, "the best of all is human blood." Lime was known from ancient times to the Celtic peoples and wood ashes both to them and to the Arabs. The older treatises in agri culture give much information also about substances like waste wool, bones, etc.
In the first 4o years of the i9th century chemists and botanists began studying the phenomena of plant growth and by 1844 the labours of Theodore de Saussure and other plant physiologists of the Geneva school, of Justus von Liebig in Germany, and of J. B. Lawes and J. H. Gilbert at Rothamsted had shown that all these substances fell into five groups, containing as their respec tive fertilizing constituents one or more of the following, namely, (I) nitrogen, (2) phosphorus, (3) potassium, (4) organic matter (mainly cellulosic material), and (5) calcium oxide. Of these the first three could be supplied from sources not previously drawn upon by farmers, and they could be manufactured into products easy to transport and to handle on the farm. These manufactured products became known as "artificial manures," or "artificial fertilizers," since shortened to "artificials." Their introduction into farming was in large part due to the enterprise of J. B. Lawes (q.v.) of Rothamsted, who in 1843 set up the first fertilizer fac tory and at Rothamsted afforded the first and still one of the most complete demonstrations of their value. They greatly improved the agricultural production of the time and played no small part in enabling Europe in general and England in particular to main tain the rapidly increasing population. They are now used all over the world in increasing quantities, not only to increase crop yields, but also to modify the composition or habit of growth of the crop so as to enable it better to withstand adverse condi tions. The five groups will be dealt with in the order set out above.