348 



SYSTEMS OF FARMING 



Crop 



Yield 



Nitrogen 



Phosphorus 



• 

 Potassium 





Bu. 



Lbs. 



Lhs. 



Lhs 



Corn 



60 



54 



8 



11 



Corn 



50 



45 



7 



9 



Wheat 



25 



43 



7 



23 



Oats 



60 



56 



9 



46 



Total amount ren 



loved by crops 



198 



31 



89 



It isclear that 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 Fertilizing Elements in Grain Rotation 



Removed 



Added 



Crop 



Average 

 yield 



Nitro- 

 gen 

 Lbs. 



Phos- 

 phorus 

 Lbs. 



Potas- 

 sium 

 Lbs. 





Nitro- 

 gen 

 Lbs. 



Phos- 

 phorus 

 Lbs. 



Corn 



Soybeans. . . . 



Wheat 



Clover 



58.6 bu. 



19.0 bu. 



28.7 bu. 

 2.75 tons 



53 

 34 



8 



7 

 6 



11 



24 



7 



Acid Phosphate 

 (700 lbs.) (7% P) 



Clover 

 Soybeans * 





49 



113 



S 



. . 



Total for 4-ye 



ar period. 



87 



21 



42 



Total added 



121 



49 



*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 



