ROTATION OF CROPS 195 



barley crop, which also requires that the 

 land shall be friable and clean, and these 

 conditions are best secured by sowing barley 

 after a root crop which, if properly attended 

 to, leaves the ground free of weeds and in 

 good mechanical condition. With the barley 

 crop is generally also sown the seed of clovers 

 and grasses, and these fine seeds succeed 

 best under much the same conditions as suit 

 the barley crop. 



When certain crops, notably cereals, are 

 grown continuously upon the same area, it is 

 found that the land tends to become foul, 

 that is to say weeds become very abundant, 

 and are apt seriously to interfere with the 

 growth of the cereal. This is one of the 

 great difficulties experienced at Rothamsted 

 in the continuous growth of wheat. In actual 

 practice one can, of course, periodically bare- 

 fallow the land, and thus get rid of most of 

 the weeds ; but bare-fallows should be 

 avoided as much as possible, and the same 

 object will in most cases be attained by the 

 occasional cultivation of some crop that 

 permits of the land being kept clean during 

 the season of its growth. Crops like turnips, 

 mangolds, and potatoes, which are cultivated 

 in rows two to three feet apart, permit of 

 effective horse and hand hoeing ; and if these 



G 2 



