LOSSES DURING ROTATION 97 



good account, is the production of a maximum total 

 yield of produce with a minimum amount of manure. 



Losses to the Land during Rotation.— The table 

 showing the composition of ordinary farm crops will 

 supply the requisite information as to the loss which 

 a farm may suffer by the sale of individual crops. We 

 will now consider briefly the losses during a rotation. 



The conservation of plant food on a farm is generally 

 effected by confining the exports to corn and meat, 

 the rest of the produce being consumed on the farm, 

 and the manure returned to the land. Let us assume 

 that a farm is managed on the four-course system, and 

 that the average crops obtained per acre are — swedes, 

 14 tons ; barley, 40 bushels ; seeds (half clover, half 

 grass), 3 tons of hay ; and wheat, 30 bushels. Further 

 that two bushels both of wheat and barley are returned 

 to the land as seed. If the whole of this produce were 

 removed from the land, the average annual loss would 

 amount to 73 lbs. of nitrogen, 22 lbs. of phosphoric 

 acid, and 61 lbs. of potash per acre. If, on the other 

 hand, only corn and meat are sold ; if we assume that 

 700 lbs. of linseed cake are fed with each acre of 

 swedes ; that 110 lbs. of oats are purchased per acre 

 per annum for the horses ; that half a ton of straw is 

 fed per acre in the course of the rotation, and the 

 rest used as litter ; and that the whole of the manure 

 annually produced is returned without loss to the land ; 

 then the quantities of nitrogen, phosphoric acid and 

 potash lost to the farm per acre during the four years' 

 rotation, as the excess of exports over imports, will be 

 as follows : — 



