On the Composition of Waters of Land-Drainage. IGo 



.•analyses of drainage-waters from the Experimental Wheat-field, 

 ;at Rothamsted, show that the drainage from land, manured in 

 the autumn by an amount of ammonia-salts supplying 82 lbs. 

 ■of nitrogen per acre, may contain from 2J to of parts of nitrogen, 

 as nitrates and nitrites, for every 100,000 parts of water. For 

 every inch of rain which passes through the drains and carries 

 with it 1 part of nitrogen per 100,000 parts of water, there will 

 be a loss of 2|-lbs. (2*26 lbs.) of nitrogen of manure per acre. 

 The drainage collected on the loth of January, 1868, from 

 Plot 14, contained in round numbers 3| parts of nitrogen, in the 

 form of nitrates and nitrites, per 100,000 parts of water. For 

 every inch of rain passing through the drains of that plot in 

 January there was, consequently, a loss of about 8|^ lbs. of 

 nitrogen, supplied in manure at a cost of about 1^. per lb. 

 Although we do not at present possess data from Avhich an 

 accurate estimate can be made of the proportion of the rainfall 

 which passes away by drainage, it may safely be assumed that 

 •during continued wet weather in winter several inches will pass 

 through the drains, and a very considerable amount of the 

 nitrogen supplied by the ammonia-salts, or nitrate of soda, in 

 autumn will be wasted before the wheat crop makes a start in 

 spring. 



Probably the loss is much greater than it is generally admitted 

 to be, and future quantitative analyses are likely to prove that 

 by far the larger proportion of the nitrogen of manure not 

 recovered in the crop is lost by drainage. 



Conclusion, 



Before concluding this Paper it may be of advantage to 

 recapitulate briefly the more prominent and practically inte- 

 resting points Avhich have been brought out in the course of this 

 investigation. 



1. The proportions of ammonia and nitric acid in rain-water 

 throughout the year are too trifling to afford an adequate supply 

 of nitrogenous food necessary for the luxuriant and remunerative . 

 growth of wheat and other cereal crops. 



2. Small as is the amount of ammonia in rain-water, the 

 70 samples of water from land-drainage examined by me con- 

 tained still less. Practically speaking the drainage-waters con- 

 tained only faint traces of ammonia. 



3. On the other hand all the drainage-waters contained very 

 much more nitric acid than rain-water at any time of the year. 



4. The analyses of the drainage-waters from the different 

 plots of the same field, variously treated as regards the supply 

 of manure, afford striking illustrations of the power of soils to 



M 2 



