34G Report of Experiments on the Growth of Barleij, 
this be really so, the explanation is that, as the application of 
the ammonia-salts for the barley is made with the soil in a more 
porous condition, when there is less risk of saturation by water^ 
therefore less risk of washing out, and when growth almost im- 
mediately succeeds, the wide distribution of the ammonia (or of 
the nitrate resulting from its oxidation) is material'iy checked ; 
whilst the residue thus remaining near the surface will be the more 
easily available to the abundant surface rootlets of succeeding 
barley crops. In this there would obviously be an element in 
the explanation of the greater effect upon succeeding crops, of 
the nitrogen of manure not recovered in the immediate increase, 
when it was applied in the spring for barley than when in the 
autumn for wheat. 
The long continued effect from previous applications of 
nitrate of soda must obviously be explained in a very different 
way. As already referred to, a given surface of soil has much 
less power to retain either nitrate of soda, or other nitrates, than 
ammonia. Consequently, the nitrogen of the nitrate distributes 
much more rapidly, and widely, through the soil and subsoil, 
and, so far, is more liable to loss by drainage. On the other 
hand it has been explained (p. 140) that the effect of the nitrate, 
or its products of decomposition, is to cause the disintegration 
of the clay subsoil, and so to increase its porosity, and, there- 
fore, its surface for the absorption and retention both of 
moisture and of manurial matters, and also its permeability to 
the roots. Hence, although a given surface of the clay subsoi) 
will retain much less nitrogen as nitric acid than as ammonia, 
the surface itself being much increased, the defective power of 
retention of a given surface will, in so far, be compensated. 
Accordingly, it has been seen that the barley crop was much 
more independent of drought on the nitrated plots than on 
those manured with a corresponding quantity of nitrogen as 
ammonia-salts; and not only so, ft)r there would appear to be 
a retention of nitrates by the subsoil, beyond that which would 
be anticipated considering their solubility ; a result which is 
most probably due to the same increase of disintegration, poro- 
sity, and surface, as is assumed to account for the increased 
retention of moisture in the first instance, and subsequent ex- 
tended development of root, and yielding up of water to the 
plant. 
At any rate, whatever may be the exact explanation in either 
casCj the facts are undoubted — that there was a considerable effect 
on succeeding barley crops from previous applications of nitrogen,, 
both as ammonia-salts and as nitrate of soda ; and that much 
greater effects, due to the residue of the supplied nitrogen were 
observed when ammonia-salts were applied for barley in the- 
spring, than when for wheat in the autumn. 
