Early Use of Clover 207 



after it had been grown on the same soil a number of 

 times. This was a matter of common knowledge in 

 England even in Tull's day, for he was led to say that 

 "the true cause why clover and St.-Foin do not succeed 

 so well after their own respective species, or that of each 

 other, as corn, etc., can, is that they take great part 

 of their nourishment from below the plough's reach 

 so that under-earth cannot be tilled deep enough, but 

 the upper part may be tilled deep enough for the hori- 

 zontal roots of corn, etc., towards which the rotting of 

 the clover and St.-Foin roots, when cut off by the plough, 

 do not a little contribute." 



Legumes and fertilizers. In the application of marl, 

 and, subsequently, of gypsum, the farmers found a 

 means for bringing clover back to their soils, but, in 

 .the course of time, even these ceased to be efficient. 

 It was stated about the middle of the last century that 

 "the application of gypsum to the soil now makes the 

 clover only more watery, without increasing the crop; 

 land treated with marl is more unproductive than before." 



The inability of the land to grow clover decreased 

 the resources of the farmer for producing manure, 

 practically the only important fertilizer then known. 

 This loss was felt keenly. 



The cause of the soil-enriching qualities of legumes. 

 It is evident that the peculiar value of clover and of 

 other legumes was fully appreciated in the eighteenth 

 and early in the nineteenth centuries. As to the reason 

 for the soil-enriching qualities of crops like clover, 

 opinions differed. It was thought by many that these 

 qualities were due entirely to the deep-rooting habits 



