for Twenty Years in succession on the same Land. 145 
much wet weather during the winter ; or even when sown in the 
spring, if very heavy falls of rain should follow. Not only, how- 
ever, is the rain of the spring and summer generally less con- 
tinuous than that of the winter, but, as the season advances, the 
soil itself is usually in a drier state, there is more evaporation 
from it, and considerably more also from vegetation, tending to 
lessen the proportion of the rain passing below the reach of the 
roots, and carrying with it fertilizing matters. For important 
data relating to this subject we would refer to a paper by Pro- 
fessor Voelcker.* Some of the results he records we shall quote 
further on (Section IV.) ; but it may be useful to give here a 
single paragraph from our own paper above referred to. 
" Fortunately, some of the most important mineral constituents 
of soils and manures are, in the case of the heavier .soils at any 
rate, almost wholly retained by them within the range of the 
roots of our crops. Nitrogen, whether supplied in the form of 
ammonia-salts or nitrates is, however, much less completely so 
retained ; being, in whichever state supplied, carried off in greater 
or less quantity in the drainage-water, chiefly in the form of 
nitrates. According to results obtained independently by Pro- 
fessor Frankland and Professor Voelcker, on the analysis of 
drainage-water from the experimental wheat-field at Rotham- 
sted, that collected during the winter, from land manured in the 
autumn by an amount of ammonia-salts supplying 82 lbs. of 
nitrogen per acre, may contain from 2'5 to 3 parts, or even more, 
of nitrogen, as nitrates and nitrites, per 100,000 parts of water. 
Assuming that only 2"5 parts of nitrogen were so carried beyond 
the reach of roots for every 100,000 parts of water passing down- 
wards, there would still be, for every inch of rain so passing, a 
loss per acre of between 5 and 6 lbs. of nitrogen, supplied in 
manure at a cost of not much less than Is. per lb." 
Now, in December, January, and February, 1868-9, about 
10"5 inches of rain fell, being about 4'5 inches more than the 
average ; and although data are at present wanting for anything 
like an accurate estimate of what proportion of this large amount 
of rain would pass away by drainage, f it may at any rate be 
concluded that several inches would do so. It can hardly be 
wondered at, therefore, that, in the case of the wheat, the plots 
receiving nitrogen as ammonia-salts in the autumn were much 
less productive than usual, and also, in a much greater degree than 
usual, deficient compared with the plot receiving its nitrogen as 
* " On the Productive Powers of soils in relation to the loss of Plant-Food by 
Drainage." By Professor Voelcker, Ph.D., F.R.S. ('Jour. Chem. Soc. Lond.,' 
June, 1871.) 
t See evidence on this point in the paper in this Journal before referred to. 
Vol. vii. — s.s. Part I. 
VOL. IX. — S. S. L 
