CHAPTER XXIV 

 GREEN-MAN URING 



Modern research on the nitrogen-gathering power 

 of legumes has led to their systematic use as green- 

 manures. They have become, to a great extent, the 

 present-day fallow crops, the successors of the bare 

 fallows. Green-manuring, which is, essentially, the 

 turning under of green crops for the benefit of succeeding 

 crops, has b,een developed into a system. The crops used 

 for green-manuring purposes need not necessarily belong 

 to the legume family. Crops Hke rye, wheat, oats, 

 buckwheat, mustard, rape, and even turnips have been 

 used more or less extensively as green-manures. All of 

 these may benefit the soil by preventing the loss of 

 soluble constituents, and particularly nitrates, during 

 a part of the year when the main crops are not occupying 

 the land. Furthermore, they supply organic material 

 which, when plowed under, helps to maintain the store 

 of humus in the soil. 



Green-manures and humus in the soil. — The impor- 

 tance of this latter function will be readily recognized 

 when we remember that the humus combines with a 

 part of the phosphoric acid, potash, and hme of the soil. 

 These combinations, known as humates, are extremely 

 important as available sources of the mineral constitu- 



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