*v 



86 THE SOILS AND CKOPS OF THE FARM. 



are reasons for the high esteem in which clover is held 

 as a valuable crop in any system of rotation. Another 

 important reason is found in the fact that the clovers 

 and other leguminous crops, such as peas and beans, are 

 able to assimilate greater quantities of nitrogen than 

 are the cereal, grass, or root crops. In recent years 

 it has been shown that leguminous plants have the 

 power, not possessed by other plants, of assimilating 

 the free nitrogen of the air. It is believed that this 

 power is the result of the action of minute organisms 

 which cause the formation of tubercles on the roots 

 of plants of this order.. It is a remarkable fact that, 

 although a crop of clover hay will often contain twice 

 as much nitrogen as will a crop of wheat, oats, corn or 

 grass, it leaves so much nitrogen in its roots and stems 

 that the soil contains more of this especially valuable 

 element than it had before the clover was grown. A 

 good crop of clover may be grown on soil which, 

 because of lack of nitrogen, would not produce a good 

 crop of wheat. After removing the hay, the soil may 

 be fitted to give a good grain crop the next year by 

 plowing under the stubble. 



It has already been stated that there is a loss of 

 nitrogen from the soil in drainage water or by its be- 

 ing washed into an open subsoil. In wet weather, 

 especially where there are warm and wet winters, the 

 loss in this way may be considerable. The loss is 

 greater on soils free from vegetation than on those on 

 which a crop is growing. The roots of the growing 

 plants take up and make use of nitrogen which other- 

 wise might be lost. Especially is this true of deep- 

 rooted plants. The roots of red clover have been 

 called "nitrogen traps." Obviously crops like pasture 



