MAINTAINING SOIL FERTILITY 313 



Hay is one of the most exhausting crops. If it 

 is sold, practically the entire crop leaves the farm, 

 carrying from it large quantities of plant food, 

 which is sold at a very low price per pound. When 

 a crop that contains a large amount of plant food, 

 as hay, sells for a low price, it is usually best to sell 

 it not as hay, but as a manufactured product as 

 milk or butter, for example. The farmer ought 

 to think of the several thousand pounds each 

 of nitrogen, potash and phosphoric acid that his 

 soil probably contains, as so much capital stock. 

 He draws a cheque upon his soil bank every time he 

 removes a crop from it. He should see to it that 

 every pound of plant food that leaves the farm as 

 raw material like grain, hay, potatoes, or as 

 manufactured products as milk, butter, beef, 

 pork, eggs, wool, brings him a profitable 

 income. 



On investigation the farmer may find that he is 

 selling plant food at a ruinous price. Then there 

 are two alternatives: to grow other crops which 

 contain less fertility and sell higher per pound of 

 plant food contained; or to sell the crops as 

 manufactured rather than as raw material. This 

 enforces the necessity of introducing stock of some 

 kind to manufacture the crop into products like 

 butter, eggs, or pork, which, when sold, do 

 not diminish the farm fertility bank account 

 to any appreciable extent. Then begins di- 

 versified farming, of which stock husbandry is 

 the backbone. 



The Minnesota Agricultural Experiment Station^ 

 has published the results of experiments on the 

 loss of fertility under different systems of farming. 

 The gain of nitrogen from growing clover is 

 considered in the following figures: 



