DISTINCTIVE! CSAHACTfiUlSTICS Oi^ CROP^ ^5 



nitrates which would be lost by drainage during cereal 

 cultivation is thus assimilated and retained by a root 

 crop, and such crops are found to stand in less need of 

 nitrogenous manure than cereals. By consuming the 

 roots on the land the nitrates collected by the crop are 

 returned to the soil in the form of animal manure, and 

 the land thus prepared to carry a cereal crop. Similar 

 remarks might be made respecting other green crops 

 whose active growth extends into the autumn.^ 



Another important difference between crops lies in 

 their range of roots. Deeply-rooted crops, as lucerne, 

 sainfoin, red clover, rape, and mangel, and among the 

 cereals, wheat and rye, are to a considerable extent sub- 

 soil feeders, and have a greater power of obtaining ash 

 constituents from the soil than shallow-rooted crops, as 

 white clover, potatoes, turnips and barley. In accor- 

 dance with this we find that superphosphate is a very 

 effective manure for the last-named crops, but is much 

 less required by such crops as mangel or wheat. By 

 growing deeply-rooted crops as part of a rotation the 

 subsoil is made to contribute to the general fertihty. 

 Shallow-rooted crops, on the other hand, have generally 

 a special faculty for appropriating food accumulated at 

 the surface, and are often of great use in this respect, 

 as when barley is made to follow turnips fed off on 

 the land. 



Very little is definitely known as to the different 

 capacity of different crops for assimilating various 

 forms of plant food, but there can be no doubt that 

 this forms one of the most important distinctions 



' The writer was indebted to Sir J. B. Lawes for the important ideas 

 contained in the two preceding paragraphs. 



