On increasing our Supplies of Animal Food. 353 



variable and unforeseeable sources of error in agricultural esti- 

 mates, still so far exceed in their effect the decimal differences of 

 which the chemist professes to take account, that the latter often 

 are hardly of that importance to the indication of results which 

 some would attach to them. The quantity of protein compounds 

 or flesh-forming matter in a plant may not be so influential on the 

 quantity of meat it produces, as is the indefinable influence of the 

 breed and constitution of the animal which feeds upon it ; and I 

 therefore abandon an unsuccessful attempt to determine the 

 relative value of the different green crops as food for the more 

 promising one, to ascertain the relative merits of our rotations by 

 comparing the weight per acre of green food produced by each. 



a The first, the Norfolk or four-course rotation, may be sup- 

 posed able to yield in the 



First year, 25 cwt. of wheat straw per acre. 



Second year, 19 tons of Swedish turnips. 



Third , , 20 cwt. of barley straw. 



Fourth , , 11 tons of clover and grass. 



This is equal to 30 tons of green food in four years, or 7^ tons 

 per acre per annum, a quantity which, at the rate of one for every 

 150 lbs., is able to produce about 1 cwt. of beef per annum. 



b In the second, when this rotation is extended one year by 

 keeping the grass down two years, we may suppose a somewhat 

 larger acr cable produce of green crop. Thus — 



First year, 25 cwt. of wheat straw. 

 Second year, 20 tons of swedes. 

 Third , , 20 cwt. of barley straw. 

 Fourth , , 11 tons of clover. 

 Fifth , , 7 tons of clover. 



Giving 38 tons as the produce of five years, or nearly the same 

 acreable produce per annum as in the former case. 



c We now may take the Dunbar six years' course of crops as 

 our third rotation, and here we may expect 



First year, 20 tons of Swedes. 

 Second year, 20 cwt. of barley straw. 

 Third , , 12 tons of clover. 

 Fourth , , 25 cwt. of wheat straw. 

 Fifth , , 25 cwt. of bean straw. 

 Sixth , , 25 cwt. of wheat straw — 



which will yield 32 tons of green food, or 478 lbs. of meat per 

 acre in 6 years, a quantity equal to about 80 lbs. per acre per 

 annum. 



d In our fourth instance we take the eight years' course fol- 

 lowed on the farm from which we write. It may produce 



First year, 25 cwt. of wheat straw. 



Second year, 25 cwt. of bean straw. 



Third , , 25 cwt. of wheat straw. 



Fourth , , 24 tons of mangold wurzel. 



