CHEMISTRY OF SOILS 101 



applied to the land the loss of lime is necessarily much 

 greater. It may amount to 1,000 Ibs. per acre. 1 If the 

 soil is not naturally well supplied with lime, the reduction 

 of the quantity so effected may, in time, seriously impair 

 the productiveness. In such cases occasional liming is 

 necessary to make good the loss of lime by drainage. 



It has been pointed out that both phosphoric acid and 

 potash are found in the drainage water, but the quantities 

 of these ingredients are quite inconsiderable, even when the 

 land is heavily manured. It is estimated 1 that the mean 

 annual loss probably does not exceed 2 Ibs. of the former 

 and 10 Ibs. of the latter per acre. The phosphoric acid 

 could be replaced in the form of manure for the sum of 

 ninepence and the potash for about eighteenpence. The 

 total loss of these constituents is not, therefore, a matter of 

 serious importance. 



With regard to nitrogen it is quite otherwise. The 

 amount of the loss is greater and the substance is much 

 more costly. In fact, apart from lime, the loss by drainage 

 is practically a question ,of nitrogen. The quantity of 

 ammonia is negligible. When separated by the action of 

 lime, from the acids with which it is combined in the 

 ammonium salts, it rapidly undergoes oxidation and is con- 

 verted into nitric acid. The nitrogen of farmyard manure 

 and other organic substances ultimately suffers the same 

 fate (p. 152). Nitrates are, in effect, the only nitrogenous 

 compounds found in the drainage water. According to the 

 figures given in the table, the annual loss of nitrogen in the 

 form of nitrates from the unmanured plot must be from 

 9 to 12 Ibs. per acre, and from the plot which received 

 single ammonium salts (containing 43 Ibs. of nitrogen) 20 

 to 25 Ibs. per acre, i.e., over 40 per cent, of the amount 

 applied. The losses from the plots which received larger 



1 " Book of the Kothamsted Experiments." 



