94 THE LAND AND ITS PROBLEMS 



by means of certain bacteria, of storing up and using 

 " free " nitrogen obtained from the atmosphere. 



If the root of a clover, lucerne, bean, pea or any other 

 leguminous plant is examined, it will be seen that it 

 possesses numerous small round lumps or nodules. 



These have been formed by the bacteria which live 

 in the plant, and in return give up the nitrogen they 

 have absorbed from the atmosphere. When the plant 

 dies this store of nitrogen becomes available in the soil 

 for the succeeding crop. 



Hence the explanation of the extra heavy crops of 

 mangolds or corn which are obtained when they follow 

 lucerne that has been " down " for a few years. 



So that lucerne or white and red clover not only give a 

 rich food for live stock in the part that grows above 

 ground, but their underground growth directly enriches 

 the soil. 



Hence it is clear that it is of the greatest economic 

 importance to make full use of these plants. 



Unfortunately there is much land which will not 

 grow clovers every four years — it becomes clover- 

 sick. 



Quite apart from this, there are other soils on which 

 the clovers are by no means a certain crop. And nothing 

 is worse in farming than to have fields carrying only a 

 two-thirds crop, or it may be a half crop. 



In the United Kingdom clover, even red clover, is 

 not generally sown by itself but with rye grass and 

 sometimes two or three other temporary grasses — the 

 " seeds " crop of the rotation. Generally speaking, this 

 is a one-year crop — though the mixture can be altered 

 to " stand " for longer. But often a one-year " ley " is 

 allowed to remain down for a second year and the red 

 clover largely disappears — this treatment is not economic. 



