OREEN CROPS 93 



of hay removed, the greater part of this increase of 

 nitrogen in the soil could not be accounted for by the 

 quantity applied as manure ; it was, in fact, to a large 

 extent derived from the atmosphere. 



Leguminous crops, as already mentioned, have a 

 special power of acquiring nitrogen from the atmo- 

 sphere by means of their root-tubercles, and are hence 

 of the greatest value in a rotation. The accumulation 

 of nitrogen in the surface soil in the form of roots, 

 stubble, and decayed vegetable matter is, in the case 

 of a good crop of clover, so considerable, that the 

 whole of the above-ground growth may be removed as 

 hay, and the land yet remain greatly enriched with 

 nitrogen and in an excellent condition for producing a 

 crop of wheat. The growth of leguminous crops is 

 the most important means which a farmer possesses 

 for enriching his arable land with nitrogen. 



The ploughing in of green crops has some advan- 

 tages over the feeding of crops on the land. By 

 this mode of proceeding the whole of the crop is re- 

 turned to the soil, whereas in feeding a small part of 

 the nitrogen and ash constituents is retained by the 

 animal. The characteristic advantage of green manur- 

 ing lies, however, in the large amount of humus 

 which the soil acquires. All the carbon which the 

 crop has obtained from the atmosphere is in this case 

 incorporated with the soil, instead of being consumed 

 by the animal. Green manuring is thus especially 

 adapted for light, sandy soils, which need humus to 

 increase their retentive power. It is employed with 

 great advantage to fertilise barren soils in hot climates. 

 Leguminous crops are clearly to be preferred before 

 all others for the purpose of green manuring, as in 

 their case nitrogen is obtained from the atmosphere. 



