5 2 SCIENTIFIC AGRICULTURE. 



which must be supplied before particular plants can 

 grow. The food may be in the soil, but not in a 

 condition to be appropriated by the plant. 



112. Soils may be naturally deficient in impor- 

 tant constituents, or they may have become so by 

 long-continued cultivation and removal of crops. 

 In such cases, improvement is effected by the addi- 

 tion of a suitable fertilizer, or manure. 



113. The continued removal of crops is sure to 

 produce exhaustion. The following table. shows the 

 quantity and composition of the ash contained in 

 one English ton (2,240 pounds) of hay of different 

 kinds, and which is carried off when the hay is taken 

 from the farm (the numbers represent pounds) : 



114. Animal products also remove valuable con- 

 stituents, and in large quantities, as can be seen from 

 the following table, which is based upon the experi- 

 ence of Messrs. Lawes and Gilbert, two noted Eng- 

 lish agriculturists : 



