THE SOIL 



Jethro Tull centered attention on the important fact that 

 careful and thorough tillage increases the available plant food 

 in the soil. He did not know why his crops were better 

 when they were frequently and thoroughly tilled : but he 



FIG. 3. SLOPE TO WATER SHOWS SOIL WEATHERED FROM 

 FACE OF CLIFF 



knew the fact. He explained the fact by saying that " tillage 

 is manure." We have since learned the reason for the truth 

 that Tull taught, and, while his explanation was incorrect, the 

 practice that he was following was excellent. (^The stirring 



