116 
Drought of 1870 and 
the porosity of a clay soil be increased by the application of 
manure, by mechanical means, or by a combination of the two, 
its power to absorb and retain water, without being wet, and in 
an available state, will be proportionately increased, and the 
necessity for artificial drainage, at any rate on some soils, 
would be greatly obviated. 
From the results adduced, it may safely be concluded, as 
already intimated, that the three plots would retain different 
amounts of water, due to the previous winter rains, at the time 
of the commencement of active vegetation in the spring. And 
although the actual amounts of excess indicated by the figures 
in Table VI. may not be true measures of the increased reten- 
tion by the manured as compared with the unmanured soil, and 
although the excess at any one time may not be sufficient to 
meet the increased requirements of the manured crop, it must 
be supposed that the soils of higher retentive power would retain 
proportionally more of every heavy shower falling from time to 
time during growth ; and hence may be accounted for the differ- 
ences, not at first sight adequately explained, in the amounts of 
water retained by the different soils at the period when they had 
supported, and nearly carried to completion, such widely different 
amounts of crop. 
Have we not, also, in the fact that the soil and subsoil, to 
a considerable depth, may frequently during the winter be 
saturated with Avater, a probable explanation, of part at least, 
of the less effect of a given amount of nitrogen applied in the 
autumn in the form of ammonia-salts, than of an equal amount 
supplied in the spring as nitrate of soda ? For although the 
ammonia of the ammonia-salts is in great part absorbed by 
the upper layers of the soil, it is well established that a portion 
of the nitrogen supplied as manure in the form of ammonia 
becomes converted into nitric acid, and reaches the drains In 
the form of a nitrate ; and It may be assumed that this action 
would, other things being equal, be the greater the greater the 
amount of water passing through the soil. Professor Voelcker, 
who has analysed many of the drainage waters collected at 
different times from the several plots in the experimental wheat- 
field at Rothamsted, has, moreover, found a greater amount of 
nitric acid in them the greater the amount of ammonia-salts 
applied as manure. 
Another reason which may in part explain the frequent less 
effect of a given amount of nitrogen applied as ammonia-salts 
than of an equal amount applied as nitrate of soda, even when 
both are sown at the same time in the spring, may be that, as 
the nitric acid of the nitrate distributes more rapidly under the 
influence of rain than does the ammonia of the ammonia-salts, 
