166 SOILS AND MANUEES 



the land was restored after a time, owing to the re-accumu- 

 lation of available plant food, it would be again put under 

 cultivation. This is the fundamental principle of the 

 modern system of fallowing. After several crops have 

 been taken off the land it is allowed to rest for a period, 

 in order that the available plant foods may re-accumulate. 

 It is not, however, neglected, but is vigorously tilled in 

 order to accelerate the chemical changes and to destroy 

 weeds. The land is never allowed to become completely 

 exhausted, and so a comparatively short period of fallow 

 usually one year is sufficient to restore it. 



The fallow land may be kept bare throughout the whole 

 period or it may be cropped, but the crop should not be re- 

 moved from the land. A " catch crop " is sometimes taken 

 in the autumn, and is either eaten off or ploughed in green. 

 More frequently a root crop is raised and eaten off. This 

 does not interfere with the operations of cleaning and cul- 

 tivating the land. In either case the crop adds nothing 

 to the land. If it be consumed on the spot, very little plant 

 food is actually removed from the soil. Assuming that 

 all, or nearly all, the plant foods are returned to the soil, 

 a cropped fallow is better than a bare one, because apart 

 from other advantages xwhich cannot be discussed here 

 the crops take up the plant food that is rendered avail- 

 able and preserve it from loss. If the fallow crops roots, 

 etc. be removed from the land the benefit of the fallow, 

 as a means of regenerating the supply of available plant 

 food, is entirely lost, and must be compensated in other 

 ways. In that case the only advantage is the opportunity 

 afforded of cleaning the land. 



Laying down Land in Grass. This also is a very ancient 

 device for the restoration of partly exhausted soils and 

 the maintenance of fertility. It generally forms a regular 

 part of the rotation or system of farming, and is often the 

 subject of special stipulations in leases. The total annual 



