62 THE FERTILITY OF THE SOIL [ch. 



to eat in the field (sheep are the most convenient for 

 the purpose). These crops include swedes, rape, 

 kohl-rabi, thousand-headed kale, mustard and the 

 aftermath of clovers and cultivated grasses \ The 

 purchased food is supplied in troughs and the animals 

 are confined by hurdles to a particular area till the 

 crop and sufiicient additional food are consumed. 

 Then they are moved on, till finally they have 

 covered the whole field. 



5. Considerable tracts of land are laid down to 

 permanent pasture. Judicious management of graz- 

 ing, combined with dressings of basic slag, lime and 

 potassium salts if necessary, lead to the formation of 

 a dense turf of grass and clover. The land thus gains 

 considerable supplies of nitrogenous organic matter 

 and its fertility rises to the upper equilibrium level. 

 These areas of well-managed grass land constitute, 

 perhaps, the most fertile soils we have, and their 

 fertility is more permanent, and maintained at lower 

 cost, than that of any other soils. 



Thus the modern English farmer keeps up the 

 fertility of his soil by importing phosphates from the 

 United States, Tunis, Algeria, Belgium and France; 

 nitrates from Chili; potassium salts from Germany. 

 He also imports grain — maize, wheat, barley, oil 

 seeds, etc. — rich in valuable fertilising materials from 

 the United States, Russia, Roumania, Argentina, 



1 Often called "rotation grasses." 



