Rotation of Crops. 
589 
different parts of our own country ; and also to a great extent 
which are followed in many other countries. 
It is worthy of remark that, although we owe the introduc- 
tion of the essential elements of our rotations to the example of 
our Continental neighbours, we, with one or two immaterial 
exceptions, obtain more per acre of all the staple saleable 
products of rotation, grain and meat, under our landlord, 
tenant, and labourer system, than any other country in Europe, 
or than in America, under whatever advantages of climate, or 
under whatever system of holding, or of size of holdings. Thus, 
there is not a single country in Europe that reaches our average 
produce per acre of wheat ; only Belgium and Holland approach, 
but they do not equal, us in the produce of barley ; only 
Belgium, Holland, and Norway exceed us in acreage yield of 
oats ; and no country approaches us in acreage produce of 
potatoes. Again, whilst several countries exceed us in number 
of cows to a given area, and some in the number of pigs, not 
one equals us in weight per acre of other cattle than cows ; 
and not one nearly approaches us in the weight of sheep to a 
given area. Nor, notwithstanding the great depression of our 
agriculture in recent years, the result of the low prices of 
produce, is there any probability that we shall soon lose our 
pre-eminence in production per acre. 
There can be no doubt that the effect of the extension of 
the growth of green crops was — to a great extent to get rid of 
unprofitable fallows, greatly to increase the supply of stock 
food, especially for winter feeding ; so to lead to a largely 
increased production of meat and milk, to a greatly increased 
supply of manure, and thus to enrich the land for the growth 
of grain, which, accordingly, yielded much larger crops. 
We have now to endeavour to ascertain how the admittedly 
very beneficial effects of alternate, as distinguished from 
continuous, cropping are to be explained. It will be well first 
very briefly to refer to some of the chief theoretical explanations 
that have been put forward, and afterwards to discuss the 
results of various direct experimental investigations conducted 
at Rothamsted on the subject of rotation. 
The first definite theory as to the benefits of the alternation 
of crops assumed that the excreted matters of one description 
of crop were injurious to plants of the same description, but 
that they were not so, and might even be beneficial, to other 
kinds of plants. 
At first Liebig pronounced this theory of rotation to be the 
only one having any really scientific basis. Later he seems to 
