THE PRINCIPLES OF CROP ROTATION. 



65 



What has already been said concerning the stage of growth of the 

 rye and also concerning the treatment of the field after plowing under 

 the crop will apply equally well to either field peas, cowpeas, or sweet 

 clover. 



THE PRINCIPLES OF CROP ROTATION. 



FACTORS INVOLVED. 



Crop rotation, with its concomitant features of farm organization, 

 diversification of crops, and stock raising, is destined to become the 

 most important problem in the agricultural development of the Great 

 Plains. It is therefore worthy of the most careful study by all who 

 are interested directly or indirectly in this development. It is one of 

 the most complex and difficult of agricultural problems. The prin- 

 cipal difficulties arise from the fact that the planning of a rotation 

 is a long-time proposition, the laying out of plans reaching many 

 years into the future, which makes it necessary to deal with factors 

 which are constantly changing, both absolutely and relatively. Some 

 of these changing factors are: The constantly varying absolute and 

 relative prices of all the crops grown, of the live stock to which some 

 of these crops must be fed, and of the products of this live stock; vari- 

 able weather conditions; the attacks of diseases and insect enemies, 

 where the same crop is grown too frequently on the same land; the 

 varying cost of labor; the uncertainty and, in some instances, the 

 utter impracticability of raising perennial crops for meadow or pas- 

 ture; and many others which will readily occur to the thoughtful 

 student of the problem. 



In no field of scientific investigation or of the practical application 

 of scientific principles is dogmatism more utterly out of place than 

 in the study or practice of crop rotation. The factors of the prob- 

 lem are so local and individual in their nature, so closely associated 

 with the local characteristics of each farm and its environment and 

 the individual tastes, abilities, and limitations of each farmer, that 

 no definite and specific directions can be given for establishing a 

 rotation for any farm until all the factors are carefully studied. 

 There are, however, certain general principles which are fairly well 

 established. There are others which are strongly indicated by the 

 investigations which have been described, but which may be either 

 firmly established or disproved by a continuation of these investiga- 

 tions. Among the established principles may be mentioned the 

 following : 



(1) All crops may be roughly classified under three heads: Exhaus- 

 tive, intermediate, and restorative. These terms must not be taken 

 too literally. All crops which are harvested and removed from the 

 land take from it more or less plant food and might therefore be said 

 to be " exhaustive.-' No crop " restores'' to the soil any considera- 



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