282 BULLETIN OF THE BUSSEY INSTITUTION. 
regard to the growth of clover and the other fallow crops before grain, 
tends to support the view that it is not in the- form of nitrates alone 
that the soil-nitrogen becomes available as plant food. That wheat 
should grow freely after clover, on good land, much in the same way as 
if the land had received a dose of some nitrogenous fertilizer, can 
hardly be due solely to the accumulation of nitrates in the soil during 
the growth of the clover. For there is good reason to believe that the . 
nitrates then formed would either be consumed by the clover itself, or 
‘be washed from the soil by rains. It is far more probable that a wheat 
crop grown after clover gets its nitrogenous food directly from the 
products of the decay of the roots and stubble of the clover. The. 
growth of the fallow crop itself without the help of nitrogenous 
manure, under conditions in which a grain crop might starve, points to 
the conclusion that the soil-nitrogen must. be used by the fallow crop 
also in other forms besides nitrates. If there were nitrates at hand, a 
grain crop would thrive, and there would consequently be small need 
of growing the fallow crop. It is precisely in the power of the fallow 
crop to supply itself with nitrogen in the absence of nitrates and am- 
monium salts that its chief merit consists. 
The use of active nitrogenized manures in European field practice, 
upon rich soils, which, as has been already remarked, seems at first 
sight to cast a doubt upon the utility of the nitrogen already contained 
in those soils, is really not inconsistent with the view here presented. 
The practice in question may even be cited as an illustration of the 
importance of the soil-nitrogen, for it has often been noticed that the 
application of a very small quantity of active nitrogen in the form of 
nitrate of soda, or of an ammonium salt, produces an effect out of all 
proportion greater than the amount of nitrogen that was actually added 
to the land in the manure could of itself produce, while it is a matter of 
the commonest observation that the application to rich land of any con- 
siderable amount of such manure is actually dangerous, because of its 
liability to excite too rank a growth. An application of 112 lbs. of crude 
nitrate of soda, containing no more than 16 or 17 lbs. of nitrogen, to an 
acre of good land, has been known to double the grass crop. But a ton 
of hay contains some 25 lbs. or more of nitrogen, and a crop of 24 
tons would consequently carry off more than 60 lbs. of that element. It 
would seem, in this case, as if the driblet of active nitrogen added in the 
manure, must either help to start the crop and make it vigorous enough 
