CROPS TO SUPPLY NITROGEN 515 



ing if no fertility is brought to the farm from outside sources. 

 Among the crops which may be grown for live stock feeding 

 are corn, grass, clover, alfalfa, oats, and barley. 



674. A Crop to Supply Vegetable Matter and Nitrogen. 

 It is necessary to conserve the supply of vegetable matter in 

 the soil, in order to maintain profitable crop yields. The 

 exhaustion of the vegetable matter makes the soil "hard to 

 work;" it becomes stiff and lifeless, bakes and'clods badly, 

 and dries out very quickly. Vegetable matter improves 

 the physical condition of the land and increases its moisture- 

 holding capacity. The acids formed through the decay 

 of this organic matter also help to unlock the unavailable 

 supply of some of the elements of plant food by changing 

 the nature of the compounds and by acting as a stronger 

 solvent than water. Nitrogen, the most expensive of the 

 three elements of plant food usually purchased in the form of 

 commercial fertilizers, can be added to the soil very cheaply 

 through the medium of leguminous crops. The grasses 

 increase the supply of vegetable matter; the legumes increase 

 the supply of both vegetable matter and nitrogen. Vege- 

 table matter is also added to the soil in corn and cotton 

 stalks, straw, stubble, and manure. The more important 

 crops to supply vegetable matter are clover, alfalfa, the 

 perennial grasses, cowpeas, soy beans, field peas, and green 

 manure crops such as rye, vetch, and rape. 



675. What Crops to Grow. The crops which are included 

 in the rotation depend entirely on the kind of farming which is 

 followed, the crops which succeed best in the locality, and 

 the individual preferences of the farmer. All the farm 

 need not necessarily be included in a single rotation. It may 

 be advisable to have a primary rotation for the greater part 

 of the land, and a secondary one for a smaller portion of it 

 which is different in texture or fertility, or to supply crops 



