134 Fertilizers 



able than the nitrogen contained in the green-manures 

 from the leguminous crops. In their growth, too, they 

 appropriate the immediately available nitrogen of the soil, 

 and convert it into the less available organic form ; hence 

 the crop that follows is frequently unable to obtain its 

 food as readily as would have been the case, provided the 

 green-manure crop had not been grown, and furthermore, 

 legumes may be the cause of too much nitrogen in organic 

 form, frequently experienced by potato growers. There- 

 fore, while the practice of using green-manures is a desir- 

 able one when properly understood, it should not be 

 regarded as a means by which soils may be directly en- 

 riched, except in the case of the plants of the legume 

 family, where nitrogen is really added to the soil. In the 

 case of all other crops, the benefit is indirect, and is in 

 proportion to the amount of minerals added. 



