EQTATIQ^ OV CROPS. 209 



is not the total of the elements exhatisted, and hence 

 the importance of arranging the crops in such a man- 

 ^ner that in a minimum time .the maximum will be re- 

 turned. In years gone by, on the greater number of 

 old estates, the rotation yielding the best results was 

 a study for centuries, and, when discovered, it was 

 handed down from father to son as one of the great 

 agricultural secrets. But even then time proved that 

 this must vary, as the soil would even under these con- 

 ditions become exhausted. A farmer discovers that a 

 giyen plant will yield better results than another ; but 

 this is not sufficient, he must also know what would be 

 the best rotation for him to adopt; and even then it 

 would not be wise for him to follow the same strictly, 

 as demand must also be considered. For example, if 

 flour mills are in the neighborhood then wheat should 

 present itself in the rotation more frequently than any 

 other; if, on the contrary, dyeing or oil mills, then the 

 corresponding plants should have the preference, and 

 if beet sugar establishments exist, then this root should 

 be selected. Everything consequently varies with each 

 soil and location. 



If it were possible to calculate the amount of each 

 element which a giVen plant extracted or I'eturned to 

 the soil, a solution of this problem would be most easy ; 

 but of this but little is known. The amount of such 

 elements remaining on the land is greater when the 

 crops have been gathered green, and for that reason,^ 

 in eases where a given grain requires more manure 



