DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 389 



It is also of interest to note that investigations with soil fungi have 

 revealed the fact that certain species are even more efficient am- 

 monifiers than B. mycoides. McLean and Wilson, Waksman, Cole- 

 man and Kopeloff have worked with organisms like Trichoderma 

 koeningi which is capable of transforming more than 50 per cent of 

 the nitrogenous material added in such experimentation. 



NITRIFICATION. Experimental Study. The term nitrification refers 

 to the oxidation either of ammonia or of nitrites to nitrates. In a 

 broader sense nitrification may be defined as the production of nitrates 

 from decomposing organic matter. Saltpeter or niter, the terms 

 formerly applied to potassium nitrate, possessed, for a long time, a 

 peculiar interest because of its relation to gunpowder. Whether it be 

 true or not that gunpowder was known to the Chinese before the be- 

 ginning of the present era, there is no doubt that for several centuries 

 it played an important part in the political and economic history of 

 Europe. The large quantities of gunpowder consumed in the almost 

 incessant wars created a steady demand for saltpeter that was not 

 readily met by the saltpeter refiners of India, Hungary and Poland. 

 European nations, particularly France, were therefore thrown on their 

 own resources and were forced to develop the domestic production of 

 saltpeter. The industry came under government control and experts 

 were appointed to study the so-called saltpeter plantations and the 

 conditions affecting the appearance and increase of nitrates in com- 

 post heaps and in the soil. Much knowledge was thus gained about 

 nitrification even though it was not suspected that living organisms 

 were concerned in the process. 



With the rapid development of chemistry in the latter half of the 

 eighteenth century a nearer approach was made to the understanding 

 of the true character of nitrification. The observations of Cavendish 

 in 1784 that potassium nitrate is formed when electric sparks are passed 

 through air confined over a solution of potassium hydrate formed the 

 starting point for various theories that attempted to account for nitrate 

 formation on the basis of purely chemical reactions. The formation of 

 nitric acid and of its salts was thus assumed to be due to electric dis- 

 charges in the atmosphere, to combustion processes in nature, or to the 

 oxidation of organic matter and of calcium, magnesium, iron and man- 

 ganese compounds in the soil. Much credence was given to the latter 

 explanation because of the almost universal occurrence of nitrates in 

 arable soils. 



