Nutritive J allies of different Crop>!. 
149 
crops ; or, according; to the figures, the same quantity of ground 
which in carrots woukl feed '200 head of cattle or sheep, in cab- 
bages would feed 179, in beet or potatoes 140, in turnips 110, 
but in wheat and oats would only feed from 50 to 55, and in 
beans or barley only 42. 
When it is farther considered how much the rotation of our 
crops generally has been improved by the introduction of root 
culture, and how greatly also the soil suffers in the constant repeti- 
tion of grain crops, from so much of its fertility finding its way to 
market in the shape of corn (the straw only being returned as 
manure), while, on the other hand, in root crops, little, though at 
last doubtless some of the staple of the soil, unless replaced by 
an equal amount from a distance, vanishes in the shape of beef 
and mutton — and when it is considered also, in root crops, that 
the manure is in proportion to the increased quantity of food pro- 
duced, and numbers of animals fed, and has circulated so much 
oltener through the soil — we cease to be surprised at the vast in- 
crease in the value of light land ; and those who cultivate heavy 
soils, hitherto unacquainted with any better rotation than wheat, 
beans, and a fallow, should be on the alert, now that thorough 
draining and subsoil ing are seen to introduce root culture on land 
heretofore unacquainted with swedes or sheep. 
There are many other details which such a calculation as the 
above will naturally suggest to those who apply it. For instance, 
the carrot, and perhaps the cabbage, if taken at a higher quantity 
per acre, are nearly as 2 : 1, while the potato and the beet are 
nearly as 3 : 2, richer than the turnip. An acre of green clover, 
which, according to Sinclair's experiments, recorded by Sir H. 
Davy, is taken as four times heavier than it is when made into hay, 
gives only 28 '29 of nourishment, while as hay it gives 37*3 — the 
laxative effect of such an excess of water in the food possibly coun- 
teracting the eff'ect which should otherwise be drawn from its 
nutritive contents. 
But the object of the present paper, as was observed before, is 
not to draw conclusions, the data of which partake more or less of 
an arbitrary character ; yet thus far we may safely conclude. If 
these data are correct, they lead to the most important results. 
Let us then apply a similar calculation to a case where our data 
are most unexceptionable. 
In Lord Spencer's valuable experiment on the relative nutri- 
tious property of swedes and mangold- wurzel, given at p. 296 of 
vol. ii. of the Society's Journal, it appears that, in feeding two 
oxen on swedes and mangold-wurzel, 2 tons of swedes gave at 
the rate of 64 lbs. of beef, while 2 tons of mangold-wurzel gave 
1021 lbs. The average of the two crops on one of the farms in 
this neighbourhood, where the most accurate accounts of produce 
