348 



SYSTEMS OF FARMING 



It isclearthat the above system tends toward rapid soil depletion. 



The Balance Shown in a Grain Rotation. On the other hand, 

 if a rotation like that mentioned in the Ohio trial were practiced, 

 the following would represent the exchange of the elements on one 

 acre during the four-year period (when the composition table 

 in Chapter VI is used in computing). 



Exchange of Fertilizer Elements in Grain Rotation 



Removed 



Added 



*The nineteen bushels of soybeans will carry about sixty-six pounds of nitrogen, and 

 the straw about thirty-five pounds, or 101 pounds in the seed and straw. There is also 

 some nitrogen to be accounted for in the roots and stubble, which, according to experiments, 

 amounts to about one-tenth of the total amount in the whole soybean plant, or about ten 

 pounds. In the soybeans on one acre there are contained, therefore, 111 pounds of nitrogen, 

 of which two-thirds, or seventy-four pounds, are taken from the air. Since sixty-six pounds 

 are sold in the grain, there are left eight pounds of gain per acre (all straw returned). 



The balance in this case shows a gain per acre of about thirty- 

 four pounds of nitrogen, twenty-eight pounds of phosphorus, and 

 a loss of forty-two pounds of potassium for each rotation period. 



The above system tends to increase soil fertility, as it has been 

 demonstrated. The loss of ten and one-half pounds of potassium 

 per acre is small, and can be easily restored, when necessary, by 

 a little potash fertilizer. No account was taken of the leaching of 

 nitrogen from the soil. 



Increase of Fertility on a Dairy Farm. The following repre- 

 sents the losses and gains of nitrogen and phosphorus on one acre 

 on a dairy farm. A three-year rotation is practiced, manure is 



