300 SOILS 



one part being in spring-sown grain, another in 

 fall-sown grain, the other third being summer- 

 fallowed. In more recent years farmers have 

 noticed that it not only benefits some crops to follow 

 different crops, but also that it often makes a de- 

 cided difference what crops are associated in the 

 rotation. 



The practice of growing different crops in suc- 

 cession, instead of one crop continuously, did not 

 originate with man. Crop rotation is almost 

 universal in Nature. The oak forest is cut off and 

 soon the land is shadowed with pines. The pines 

 grow lusty, fall before the woodman's ax, and oaks 

 or white birches take their place. The low-bush 

 blueberry and the arbutus flourish in the hardwood 

 clearings. Everywhere we may see that Nature 

 rarely follows one of her crops with another of the 

 same kind of plant. The wise economy of her 

 rotations we may study with profit. 



WHY A ROTATION IS BENEFICIAL 



A rotation is usually beneficial in several ways; 

 sometimes one benefit is most pronounced, some- 

 times another. The explanation that one naturally 

 thinks of first is that it affects the relative supply 

 of the different plant foods in the soil. Every 

 farmer knows that some crops are "harder upon 

 the soil" than others. The chemist, also, says 

 that some plants use more plant food than others. 

 Different crops take from the soil, not different 

 kinds of plant food, as some suppose, but different 

 amounts of the same plant foods. Thus wheat 

 needs more phosphoric acid and less potash than 

 fruits. Oats require more potash than corn. Cro]> 

 ping a soil continuously with corn, for example, is 



