MS SOIL MANAGEMENT 



tion" in crops, while European farmers and the better 

 American farmers have practiced some kind of crop rota- 

 tion for a long time. Of late years nearly all farmers 

 have adopted the practice, because at last they have found 

 that it pays. And quite recently a great deal more has 

 been learned about why it pays, and what kinds of rotation 

 pay best. 



100. Five reasons why crop rotation pays will be noted here. 



a. Rotation varies the demand for soil-food from year 

 to year ; thus it enables the natural forces in the soil 

 to accumulate a new supply before it is again especially 

 demanded. This was the lirst beneficial result that men 

 learned, but it is not the most important. 



b. Rotation avoids the collection in the soil of certain 

 poisonous substances known as root excretions. Our 

 knowledge about this is very recent and rather theo- 

 retical. The roots of a plant, we now know, throw off 

 waste matters as we do in perspiring. These excretions 

 cannot escape freely from the soil; and so, if the same 

 crop is grown on a field for several years, the soil there 

 accumulates so much of the excretion of this particular 

 plant as to poison future crops of it. The roots of an- 

 other variety of plant, however, will not be injuriously 

 affected by this poison. Plants are rotated, then, to avoid 

 the effects of their own excretions. After three or four 

 years, natural forces in the soil destroy the excretion, and 

 then the first plant may be grown again. 



c. Rotation permits the use of different layers of soil 

 by alternating deep and shallow rooted crops, like corn 

 ami wheat. 



d. Rotation makes it easier to distribute farm labor 

 more evenly through the year. One of the problems of 

 the farmer is to keep his help busy at profitable work. 

 Farmers who grow wheat only, or cotton only, have little 



