322 SYSTEMS OF MANURING CROPS [chap. 



The Leguminous Crops. — It has already been 

 explained that the leguminous plants are able to obtain 

 nitrogen from the atmosphere by the agency of the 

 bacteria in their nodules and can in this way satisfy 

 their requirements for nitrogen : it should, however, 

 not be forgotten that they also feed upon combined 

 nitrogen like all other plants, and as a rule derive their 

 nitrogen both from the air and from the soil. To 

 obtain the biggest crops rich soil and certain nitro- 

 genous manures are necessary, but to secure the greatest 

 profit out of a leguminous crop, it should be left as 

 far as possible to derive its nitrogen from the atmo- 

 sphere. All leguminous plants are particularly sensitive 

 to any trace of acidity in the soil, so alkaline fertilisers 

 like basic slag or nitrate of soda should be selected. 

 Lime is also desirable, both for its basic properties and 

 as a liberator of insoluble potash in the soil, because all 

 leguminous crops are specially dependent upon an 

 abundant supply of potash. 



Beans. — Beans no longer play the important part in 

 British agriculture that they once possessed ; essentially 

 a heavy land crop, the cultivation has declined since so 

 much of the strong clay land has been laid down to 

 grass. In the rotation beans generally come between 

 two white straw crops. They will follow oats or barley, 

 for example, and precede wheat, and as a rule they do 

 not receive any manure. A little farmyard manure 

 may be spread on the stubble before it is ploughed, 

 but other nitrogenous manures have little beneficial 

 effect upon the crop. The Rothamsted experiments 

 show that beans, like other leguminous plants, respond 

 chiefly to phosphates and potash, to the latter especially, 

 and are able to derive most of the nitrogen they require 

 from the atmosphere. For example, the average results 

 for eight years at Rothamsted were — 



