38 On the Bain and Drainage - Waters at Rothamsted. 
sowing the manure, the nitrogen as nitrates in the drainage-water 
had reached 67*8 per million. 
The speed with which nitrification takes place is largely 
dependent on the amount of rain which falls after the ammonium- 
salts have been applied to the soil ; water is required in the 
first place for the solution and distribution of the ammonium- 
salt, and afterwards for the process of nitrification. 
The product of nitrification appears to consist entirely of 
nitrates ; traces only of nitrites have been found in the drain- 
age-waters from Broadbalk, and these are very possibly the 
result of a reduction of nitrates previously formed. 
It follows, from the quick nitrification of the ammonium- 
salts, that the drainage-waters from plots receiving ammonia are 
richest in nitrates shortly after the ammonium-salts have been 
applied. When the ammonium-salts are applied in March, as 
they are now on all plots, excepting Plot 15, the April waters are 
those strongest in nitrates. The mean of 27 analyses of waters 
collected in April from plots receiving 400 lbs. of ammonium- 
salts in March gives 29*6 of nitrogen as nitrates per million of 
water. The maximum observed has been 45*4. The average 
loss of nitrogen as nitrates in the April waters thus corresponds 
to 6*7 lbs. per acre, or to 42'81bs. of nitrate of sodium, for each 
inch of drainage.* 
When the wheat-crop commences its active growth the amount 
of nitric acid in the drainage-water greatly diminishes, and in 
the case of some of the plots receiving ammonia the nitrates 
disappear altogether in summer time. The plot in which 
nitrates first disappear from the drainage-water is naturally 
Plot 6, as here only 200 lbs. of ammonium-salts are applied. 
The various plots receiving 400 lbs. of ammonium-salts per acre 
differ very much as to the extent of the reduction in the nitrates 
effected by the growing crop, the amount of reduction depend- 
ing entirely on the power of the crop to assimilate nitrogen. 
Thus on Plots 7 and 13, which receive both superphosphate and 
potassium-salts, and thus furnish the crop in abundance with its 
most essential ash constituents, the power of the wheat to assimi- 
late nitrogen is at its highest, and the nitrates may disappear 
altogether from the drainage-waters in the course of the summer. 
In complete opposition to this stands Plot 10, to which am- 
monium-salts are applied without any of the ash constituents of 
the wheat-crop, and where, by long-continued treatment of this 
description, the available ash constituents of the soil have become 
greatly exhausted. On this plot the nitrogen applied is much 
in excess of the power of the crop to assimilate it, and conse- 
• One lb. of nitrogen ■will he conlained in G'4 lbs. of good nitrate of sodium. 
