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. 



Plant-food made '^^^^ availability of the mineral food constitu- 

 ., , , ents ot the soil is increased. Ihe increase is 



available. ^^^^ . 



1. To the action of the living roots which exercise 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 

 Humus increased, admixture 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 

 Subsoil mellowed, or 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 

 Desirable charac- crop for cover or green manure are the fol- 

 teristics. lowing: 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 

 Winter rye. of 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 



