Those green manure or cover crops which 



Soil enriched in belong to the family of legumes (pod bearers) 



nitrogen. are capable, under the right conditions, of 



assimilating nitrogen from the air. They do 

 this through the agency of bacteria that live in nodules on their 

 roots. Through the cultivation of legumes it is possible, therefore, 

 to increase the sum total of nitrogen in the soil. The vegetable matter 

 produced by such crops as clover, peas, beans and vetches is rich in 

 nitrogen and when it decays, this element, in the form of ammonia or 

 nitrates, is gradually rendered available to a following crop. 



The availibility of the mineral food constituents 

 Plant-food made of the soil is increased. The increase is due: 

 availible. l. To the action of the living roots which exer- 



cise a solvent action on the mineral particles of 

 the soil. 



2. To the increased biological activity (bacteria and other micro- 

 organisms) favored by shade and the increased proportion of organic 

 matter in the soil. 



3. By the solvent action of carbonic acid and other organic acids 

 produced in the decay of the added vegetable matter. 



Improved physical condition due to the ad- 

 Humus increased, mixture of vegetable matter and the gradual 

 increase in the amount of humus. This means 

 better capacity to retain and to conduct moisture. 



In the case of the deep rooted green manure or 

 Subsoil mellowed, cover crops the subsoil is to a considerable extent 



opened and mellowed so that following crops 

 root more deeply. To some extent, also, such crops transfer material 

 gathered by their deep roots in the subsoil toward the surface. 



2. PRINCIPAL CROPS 



Among characteristics which especially fit a crop 



Desirable charac- for cover or green manure are the following: 



teristics. ability to thrive broadcast; rapid growth; deep 



and vigorous root system; freedom from injury 



by frosts. If the crop, besides possessing the characteristics named, is 



a legume it will prove most valuable because in one respect it surpasses 



all others, viz., it has the ability to gather nitrogen from the air which 



none of the others possesses. 



Non-Legumes 



None of the crops of this class have the capacity to gather nitrogen 

 from the air. 



Suited to light soils, one of the most useful of 



Winter rye. the green manure crops outside of the legumes, 



grows late in the autumn and begins growth very 



early in the spring, especially valuable for preventing waste of nitrates 



during the fall, winter and spring rains, and because it affords cover 



