546 



NATURE AND PROPERTIES OF SOILS 



grouped under two heads, legumes and non-legumes. Some 

 of the common green-manures are as follows: 



When other conditions are equal, it is of course always bet- 

 ter to choose a leguminous green-manure in preference to a 

 non-leguminous one, because of the nitrogen that may be 

 added to the soil. However, it is so often difficult to obtain 

 a catch of some of the legumes that it is poor management to 

 turn the stand under until after a number of years. Again, 

 the seed of many legumes is very expensive, almost prohibit- 

 ing their use as green-manures. Among the legumes most 

 commonly grown as green-manures, cowpeas, soybeans, and 

 peanuts may be named. Many of the other legumes do not so 

 fit into the common rotations as to be turned under conven- 

 iently as a green-manure. 



For the reasons already cited, the non-legumes have, in 

 many cases, proved the more popular and economic as green- 

 manures. Rye and oats are much used because of their rapid, 

 abundant, and succulent growth and because they may be 

 accommodated to almost any rotation. They are hardy and 

 will start in almost any kind of a seed-bed. They are thus 

 extremely valuable on poor soils. ' Often the value of such a 

 green-manure as oats is greatly increased by sowing peas with 

 it. The advantages of a legume and a non-legume are thus 

 combined. 



It has already been shown that the nitrate production in a 



