ROTATION OF 'CROPS 481 



encourages the keeping of more live stock than single-crop 

 farming, and live stock usually requires more attention dur- 

 ing the season when the crops require least care, thus dis- 

 tributing labor throughout the year. The system of farming 

 which provides employment for the farm labor throughout 

 the greater part of the year is the one which is most likely 

 to prove stable and profitable, other things being equal. 



659. Rotations Systematize Farm Operations. A rota- 

 tion implies a definite system of operations. The following 

 of a rotation allows the farmer to plan his work more defi- 

 nitely during the season and to figure more definitely on 

 crop yields and income. Rotations tend to the division of 

 the farm into regular units of uniform size, and decrease 

 rather than increase the number of fields on most farms. By 

 effecting a more uniform distribution of farm labor through- 

 out the season, a smaller and much more permanent force is 

 required, which in itself tends to place the work of the farm 

 on a stable and systematic basis. 



660. Rotations Do Not Conserve Fertility. Many persons 

 hold that rotations conserve soil fertility. While crop yields 

 will decrease much more slowly where several crops are 

 grown in a rotation than where any one is grown continu- 

 ously, crop rotation is just as certain to exhaust the supply 

 of available fertility eventually, if no fertilizers are used, as 

 is a single cropping system. The various crop plants all use 

 the same elements of plant food, though some draw more 

 heavily on one element and some on another. The three 

 which are most largely used and most likely to become 

 depleted are nitrogen, phosphorus, and potassium. The 

 legumes take the nitrogen from the air and store it in the 

 soil in a form available for other plants, so that if a legu- 

 minous crop is grown as often as once in three years there is 

 little danger of the exhaustion of this element, but nature's 

 supply of potassium and phosphorus must eventually be 

 supplemented. 



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