CROP ROTATION 247 



soil particularly favorable to the production of any one crop, 

 like tobacco, cotton, hay, corn or wheat, it will seldom be ad- 

 visable to raise one crop to the exclusion of others, but the 

 most rational practice will generally provide for some system 

 of crop rotation. 



There are three classes of crops that should, so far as possi- 

 ble, have a place in any rotation. These are legumes, sod 

 crops or grasses and intertilled crops. The value of legumes 

 as nitrogen gatherers has already been discussed. It is partic- ' 

 ularly on poor land that legumes are of most benefit, and if 

 some of the tops, as for instance, the second growth of clover, 

 be plowed under, their value will be greater. 



Sod crops are of great value in furnishing organic matter 

 to the soil. The larger the hay crop, the more sod produced, 

 which is a double incentive to the use of fertilizers and 

 farm manure on this crop (see § 204). Sod also forms 

 a favorable condition for the fixation of nitrogen. Legumes 

 appear to have one advantage over sod crops as nitrogen 

 gatherers, in that the nitrogenous matter remaining in the soil 

 is more available to some crops, at least, and is more readily 

 converted into nitrates. 



In each course of a rotation there should be, if possible, one 

 intertilled crop, like corn, cotton, potatoes or cabbage. The 

 intertilled crop should follow the sod crop, or the legume, 

 because the cultivation given the soil throughout the summer 

 produces a condition favorable to the decomposition of the 

 organic matter furnished by the sod. Except where the con- 

 servation of moisture is an important factor, the use of an 

 intertilled crop is preferable to a clean fallow, as it is more 

 economical of the nitrogen and lime supply, and appears to 

 result in better crops the year following. 



Other crops to be used in the rotation will be determined by 

 the climate, soil, market and convenience in handling. 



Fertilization of the rotation is discussed in section 271. 



