AVAILABLE NITROGEN IN THE SOIL. 



333 



875. Available nitrogen in the soil. When animal matters rich 

 in nitrogen undergo rapid putrefaction, 1 they give rise to numer- 

 ous compounds, prominent among which are those of ammonia. 

 Under certain conditions, notably the presence (1) of free oxy- 

 gen in large amount, or (2) of an alkali, or an alkaline carbonate, 

 such animal matters are also slowly broken up, and nitrates are 

 formed. The process by which various compounds of nitrogen 

 are converted into nitrates is termed nitrification. 2 



876. Vegetable matters which contain nitrogenous substance 

 in the usual amount may likewise undergo decomposition ; but 

 owing to the presence in such matters of a large proportion of 

 carbohydrates, for instance the cellulose of the cell-walls, the 

 process of decomposition is more complex than in animal matters 

 and its products more diverse. Some of the products are proba- 

 bly identical with those formed from the decomposition of albu- 

 minous matters of animal origin ; namely, ammonia, 8 or ammonia 

 compounds, and nitrates; but the larger number of them are 

 compounds which are nearly or quite insoluble and have been 

 thought to be inert. 4 But experiments have shown that under 

 certain conditions these less available compounds of nitrogen 



1 For a discussion of the various phases and conditions of decomposition the 

 student is referred to the third volume of this series, in which the different 

 forms of fermentation and putrefaction are to be treated. It is enough now to 

 note that these processes are essentially due to the presence and activity of 

 minute organisms, the lowest fungi. 



2 The student will find in Johnson's "How Crops Feed," p. 289, an ex- 

 cellent account of this most important topic. He is referred also to Boussin- 

 gault's "Agronomic," 1860, and various articles in Versuchs-Stationen. 



3 The following data indicate the amounts of nitrogen in certain soils, as 

 determined by Boussingault (Agronomic, ii., 1861, pp. 14, 18). The reduc- 

 tions to pounds per acre are from Johnson's " How Crops Feed," p. 276. 



4 Experiments by Boussingault (Agronomic, i. 1860) can hardly be in- 

 terpreted in any other way. One reason for his results has been sought in the 

 fact that he employed only very small amounts of vegetable matter in his ad- 

 mixtures of soil ; but all of his experiments are regarded as models of accuracy 



