140 On the Composition of Waters of Land- Drainage. 



All soils under cultivation contain vegetable matters in the 

 sliape of decaying roots and other remains of previous crops, 

 and it is to the gradual decay and oxydation of the nitrogen 

 contained in these vegetable matters that the presence of nitric 

 acid in the drainage from the unmanured plots must be 

 ascribed. 



Farmyard-manure does not contain nitrates, nevertheless the 

 drainage-water from Plot 2, inanured with farmyard-manure, con- 

 tained 5*28 grains of nitric acid per gallon, or about three times 

 as much as the drainage from the adjoining unmanured plots. 



It appears thus that a portion of the nitrogen contained in 

 farmyard-manure passes into the drains in the shape of nitrates, 

 and, this being the case, it appears to me better policy to 

 jnanure moderately for each crop than to apply a heavy dressing 

 ol dung to one crop in a rotation and none to the succeeding 

 crops ; for it is plain that the loss in nitrogenous fertilizing 

 elements by drainage will be greater if a large quantity of dung- 

 is applied at once to the land and left for a succession of crops 

 than if each crop is manured in turn. In the former case a 

 large mass of dung is exposed to the oxydising influence of the 

 air and the solvent action of the rain at periods of the year when 

 active growth practically is at a standstill, and rain falls more 

 copiously than during the spring months and periods of active 

 growth. A larger amount of nitrates under these circumstances 

 passes into the drains than is likely to be the case if every crop 

 is manured with more moderate dressings of dung, when each 

 crop will receive a fresh supply of nitrogenous constituents that 

 will afford nitrates at a time of the year when the crop can 

 appropriate them and be benefited thereby. In other words, 

 greater chance is given to the rain to wash out the nitrates more 

 effectually when only one crop of a rotation is heavily dunged 

 than is the case if farmyard-manure in more moderate quantities 

 is applied to more than one crop. 



11. Although large quantities of ammonia-salts had been 

 applied to some of the plots, the drainage-water from these, and 

 indeed from all the plots, contained merely traces of ammonia. 



It will be noticed, however, that the drainage-waters from all 

 the plots dressed with ammonia-salts were found to contain 

 nitric acid in notable proportions ; and, further, that from those 

 plots which had been manured with the larger quantities of 

 ammonia-salts the drainage was richer in nitric acid than the 

 waters from the plots manured with a smaller quantity of 

 ammonia-salts. 



Thus whilst the drainage from the unmanured Plots, Nos. 3 

 and 4, contained only 1*75 grains of nitric acid, that from Plot 6, 

 manured with 200 lbs. of ammonia-salts per acre, contained 3'59 



