208 DRY FARMING 



an intertilled crop, such as corn, at frequent intervals, 

 while one in a short season in humid regions need have 

 no fallow if mixed grass and legume crops are grown 

 occasionally and the sod plowed immediately after har- 

 vesting the hay. 



The difficulty in applying these practices to western 

 conditions lies in the delayed returns and relatively low 

 yields from the crops classed as grass, legume or hoed 

 crops. In proportion as each is unprofitable in any 

 community it will, of course, have to be omitted from 

 the rotation, and some other measures taken for meet- 

 ing the soil conditions the rotation is designed to correct. 



166. The Effect of Rotations on Soil Fertility. It is 

 sometimes stated that a good crop rotation will main- 

 tain the fertility of the soil. This is quite erroneous. 

 A good rotation will result in keeping up the produc- 

 tiveness of land much longer than continuous crop- 

 ping either with or without fallowing, but it will main- 

 tain the plant food content of only one element, viz., 

 nitrogen, and this only if legumes are grown frequently 

 enough and a portion of the crop turned under occa- 

 sionally. It is generally considered that the nitrogen 

 can be maintained without fertilizers' if about one- 

 fourth of the land is kept in legume crops and a part of 

 the crop or an occasional catch crop of some other 

 legume plowed under and the crop residues returned 

 to the land. The other important elements of plant food 

 are, of course, used up faster in a rotation than in con- 

 tinuous cropping and eventually they will have to be 

 kept up by using manure or commercial fertilizers or 

 both. The value of a good crop rotation is not in its 

 maintaining the plant food content of the soil (except 

 nitrogen) but in its other beneficial effects. To per- 



