76 



GAINS AND LOSSES OF NITEOG-EN 



Way found from O3 to 3'1 parts K 2 O and up to 1*7 parts P 2 5 

 per million of drainage water. 1 



Schloesing 2 states that the amount of phosphoric acid in the water 

 impregnating soils is usually about 1 milligram per litre, but sometimes is 

 as much as 2 or 3 milligrams. 



The composition of drainage water naturally varies with many 

 circumstances, e.g., rainfall. Complete analyses have not recently 

 been published. The average of analyses by Way (1856), Krocker 

 (1853), and Zoller (1857) gave the following: 



Potash, K 2 O . 

 Phosphoric acid, P 2 5 

 Lime, CaO . 

 Soda, Na 2 . 

 Silica, SiO 2 . 

 Sulphuric acid, S0 3 

 Organic matter 

 Nitric acid, N 2 5 

 Ferric oxide and alumina 

 Chlorine 



Parts per million. 

 . 2 to 60 

 traces to 2 

 68 to 180 

 . 5 to 46 

 . 5 to 25 

 . 18 to 130 

 . 16 to 180 

 . 2 to 210 

 0-7 to 7 

 . 1 to 57 



Total solids (average) 



365 



In conclusion, it may be useful to summarise the chief sources of 

 gain and loss of nitrogen to soils, apart from the agriculturists' efforts. 

 The chief sources of gain are 



(1) The ammonium compounds and nitric acid brought down in 

 the rain (see Chap. II). 



(2) Gaseous ammonia absorbed from the atmosphere by the soil 

 constituents. This is probably a comparatively unimportant source. 



(3) Compounds of nitrogen (chiefly nitric acid, probably) formed 

 by micro-organisms existing in the soil itself, air furnishing the neces- 

 sary nitrogen and oxygen. 



(4) Similar compounds produced by the micro-organisms (or by 

 the enzymes resulting from them) frequenting the tubercles or 

 nodules on the rootlets of leguminous plants. 



(5) The products of the nitrification of organic compounds already 

 present in the soil. This is also the work of micro-organisms, and is 

 often limited by the abundance and activity of protozoa present, 

 which feed upon the ammonia-forming bacteria. 



(6) The small quantity of nitrogenous matter (in solution or sus- 

 pension) brought in occasionally by flood water, and its subsequent 

 nitrification, if necessary. 



While the losses are chiefly due to 



(1) Denitrification the liberation of free nitrogen or of nitrous or 

 nitric oxide from the nitrogen compounds. This is due to the action 

 of micro-organisms in the absence of oxygen and therefore occurs 

 most readily in soils rich in decaying carbonaceous matter, or par- 

 tially water-logged. 

 0| (2) In the drainage water, by which nitrates and, to a much less 



1 Jour. Koy. Agric. Soc. $ 1856, 133. 



2 Compt. Bend., 127, 236; Jour. Chem. Soc., 1899, Abstracts, ii. 119. 



