Experimental Crops at Rothamstcd. 
121) 
It is remarkable that the uncropped and undrained land, 
tliougli retaining- miicli less water within 9 inches from the sur- 
face, from that point downwards retained, in June 1870, con- 
siderably more at every stage than the drained wheat soil in 
January ISGi), when the drains were running, and the land was 
supposed to be saturated. TVom this comparison, it is obvious 
that no safe conclusion can be drawn from the percentage of 
water in the subsoil of the uncropped but undrained land, as to 
the probable amount retained by the subsoil of the drained land 
at the commencement of active vegetation in the spring. The 
amount retained in the subsoil of the uncropped and undrained 
land is indeed enormous ; but the comparison of it with that in 
the adjoining cropped land shows clearly enough that it was 
readily available for the purposes of vegetation. In reference to 
this latter point, the fact of the good natural drainage by the 
chalk must not be overlooked. 
There is, upon the whole, general consistency in the results 
brought together in Table XI I. It may, perhaps, safely be 
concluded that, notwithstanding the natural drainage by the 
chalk, the pipe-drains had contributed to reduce the percentage 
of moisture retained by the subsoil of the experimental wheat field, 
to the depth examined ; but that they had, at the same time, 
rendered the clay more permeable by roots, and the water that was 
retained more readily available. The evidence is, at any rate, very 
striking as to the degree in which, in a time of drought, our crops 
are enabled to rely upon the water previously accumulated within 
the subsoil — provided the latter be of sufficient depth, of sufficient 
retentive power, and at the same time sufficiently permeable. 
Before concluding, it will be well to call attention to a very 
important bearing of some of the results adduced. Assuming, 
as we may be allowed to do for the sake of illustration, that a 
good crop of hay, wheat, or barley, will probably exhale not less, 
and perhaps more, than 700 tons of water per acre during growth, 
we still have only about 7 inches of rain, out of an average 
annual fall of say 25 inches, thus directly disposed of by the 
growing crop ; and, taking the amount retained by the soil itself 
as practically a constant quantity from year to year, there re- 
mains to be disposed of by evaporation from the surface, and by 
passage into the drains or otherwise beyond the reach of the roots 
of the crop, an average of about ]8 inches of rain annually, 
equivalent to more than 1800 tons of water per acre. 
How much of this large quantity of water passes off by 
evaporation from the surface of the soil itself, inducing by capillary 
action the withdrawal of water, carrying with it, it may be, essential 
plant-food, from the lower to the upper layers of the soil ? — or, how 
much passes downwards, carrying in solution any manurial matters 
VOL. YII. — S.S. K 
