70 On the Rain and Drainage-Waters at Rothamsted. 
would be very little loss from either of these sources, and that 
the loss is almost exclusively by drainage. 
31. In ordinary agriculture, with a larger proportion of the 
nitrogen supplied in farmyard-manure or animal-manures, with 
ammonia or nitrate used in smaller quantities, and with a 
variety of crops covering the 'ground with vegetation for longer 
periods of the year, the loss of nitrogen per acre by drainage 
will be considerably less than it has been shown to be in the 
Experimental Wheat-field. 
Pkactical Conclusions. 
1. Most of the nitrogen of farm-crops is derived from the 
nitric acid of nitrates within the soil. 
2. The nitric acid in the soil is produced from the nitrogenous 
compounds of the soil itself, from the nitrogenous organic 
matter of animal and vegetable-manures, from the ammonia of 
artificial-manures, and from the ammonia supplied by rain and 
condensation from the atmosphere. A very small quantity of 
ready-formed nitric acid is supplied by rain and condensation 
from the atmosphere. Nitric acid is also provided by the direct 
application of nitrates. 
3. The ammonia of ammonium-salts is rapidly converted into 
nitric acid in the soil, as also is the nitrogen of some organic 
matters, such as urine. The nitrogen of rape-cake, that of the 
less soluble parts of farmyard-manure, of stubble, of roots, &.C., 
is much more gradually converted into nitric acid, and it may 
require many years for the conversion of the whole of it. The 
nitrogenous compounds of the soil itself are very slowly con- 
verted into nitric acid, but the soil yields a certain quantity 
every year. 
4. When there is no vegetation, and there is drainage from 
the land, or even when there is vegetation, and excess of 
drainage, nitric acid is lost by drainage. 
5. As in the case of permanent grass-land the soil is always 
covered with vegetation, there will be with it the maximum 
amount of nitric acid utilised by the crop, and the minimum 
amount lost by drainage. Land without vegetation will be 
subject to the maximum loss of nitric acid by drainage. 
6. The power of a growing crop to utilise the nitric acid in 
the soil is much diminished if there be a deficiency of available 
mineral constituents, and especially of potash and phosphoric 
acid, within the reach of the roots. 
7. As the various crops grown upon a farm differ very much 
as to the period of the year of their most active growth, the 
length of time they remain on the land, and the character and 
