THE WASTE AND CONSERVATION OF PLANT FOOD. 225 



CONSERVATION OF NITROGEN. 



Attention has been called to the manner in which the nitrogen car- 

 ried into the ocean by the waste of the land is retnrned in great part 

 through the marine, vegetable, and animal "life. Immense quantities 

 of waste nitrogen, however, are further secured, both from sea and 

 laud, by the various genera of birds. The well-known habits of birds 

 in congregating in rookeries during the nights, and at certain seasons 

 of the year, tends to bring into a coinmou receptacle the nitrogenous 

 matters which they have gathered and which are deposited in their 

 excrement and in the decay of their bodies. The feathers of birds are 

 particularly rich in nitrogen, and the nitrogenous content of the flesh 

 of fowls is also high. The decay, therefore, of remains of birds, 

 especially if it take i)lace largely excluded from the leaching of water, 

 tends to accumulate vast deposits of nitrogenous matter. If the con- 

 ditions in such deposits are favorable to the processes of nitrification 

 the whole of the nitrogen, or at least the larger part of it, which has 

 been collected in this debris, becomes finally converted into nitric acid 

 and is found combined with appropriate bases as deposits of nitrates. 

 The nitrates of the guano deposits and of the deposits in caves arise 

 in this way. If these deposits are subject to moderate leaching the 

 nitrate may become in filtered into the surrounding soil, making it very 

 rich in this form of nitrogen. The beds and surrounding soils of caves 

 are often found highly impregnated with nitrates. 



While for our purpose deposits of nitrates only are to be considered 

 which are of sufticient value to bear transportation, yet much interest 

 attaches to the formation of nitrates in the soil, even when they are 

 not of commercial importance. 



In many soils of tropical regions not subject to heavy rainfalls the 

 accumulation of these nitrates is very great. Miintz and Marcano^ 

 have investigated many of these soils to which attention was called 

 first by Humboldt and Boussingault. They state that these soils are 

 incomi^arably more rich in nitrates than the most fertile soils of Europe. 

 The samples which they examined were collected from different parts 

 of Venezuela and from the valleys of the Orinoco as well as on the 

 shore of the Sea of Antilles. The nitrated soils are very abundant in 

 this region of South America, where they cover large surfaces. Their 

 composition is variable, but in all of them carbonate and phosphate of 

 lime are met with and organic nitrogenous material. The nitric acid is 

 found always combined with lime. In some of the soils as high as 30 

 per cent of nitrate of lime has been found. Mtrification of organic 

 material takes phice very rapidly the year round in this tropical region. 

 These nitrated soils are everywhere abundant around caves, as described 

 by Humboldt, caves which serve as the refuge of birds and bats. The 



iComiit. Reud., 101, 1885, page 65 et seq. 

 SM 94 15 



