90 



The Control of the Soil 



[PT. II 



the seeds ley. On heavy land it is sometimes found 

 worth whUe to spend a whole season over the fallow, 

 sacrificing rent, rates and capital charges, so as to allow 

 ample opportunity for obtaining these various effects of 

 spring and summer cultivation. 



Fig. 24. Effect of fallowing on nitrate content of soil. The vertical lines 

 show the amount of water percolating through the soil. 



Subsoiling and trenching. The object of these opera- 

 tions is to increase the root range of the plants. 



In ordinary circumstances plants do not have a great 

 deal of root room : the surface layer, which alone is well 

 suited to their requirements, is only about 5 or 6 inches 

 deep not always as much, indeed and it is usually 

 underlain by a subsoil which is not particularly suited 

 to the plant and from which its roots cannot draw much 

 nourishment. Any process that makes the subsoil a 

 better habitat for the roots increases the extent of the 

 root range and therefore enables the plant to make 

 better growth. The obvious method of improvement is 

 to make the subsoil more closely resemble the surface 



