CULTIVATION OF THE SOIL. 87 



soon become dissolved and leach down beyond the 

 reach of the plants and so become useless. 



From the above illustration we understand that 

 the fertility of the soil depends largely upon the 

 amount and quality of vegetable matter it contains. 



When we speak of worn-out land we do not mean Worn-out 

 the quality of the subsoil, as that undergoes little Lack of 

 or no change. The whole difficulty is in the lack of Humus - 



46. LAND ROLLER. 



vegetable matter on the surface. When this is 

 destroyed by deep plowing and lack of a proper 

 system of rotation, the soil will become hard and 

 crack open unless there is rain every few days 

 throughout the summer months. Soil which lacks 

 decomposed vegetable matter is of a light color, 

 while a rich soil, filled with humus, is dark. 



In adopting a system of rotation of crops, a bare Bare Summer 

 summer fallow need not be included, because plow- 

 ing, harrowing and cultivating the land several times 



Fallow. 



