Crop Rotation — Its Purpose and Practice 149 



for a large percentage of potash, and in the series of years 

 they had been grown on the land they had so reduced the 

 content of potash in it that potatoes could no longer be 

 made, but there was still enough left to make a fine crop 

 of barley, the food requirements of which are very different. 

 In our native forests we find that there is usually a very 

 great diversity of plants, and a great difference in their 

 root development. The pine tree sends a deep tap root 

 into the soil and gets food below where the spreading roots 

 of the oak feed, and it takes food of a different composition 

 from the oak, and the leaves of all the trees fall and decay 

 and furnish each with what it wants, so that in the forest 

 there is really a rotation of crops going on all the time. 



We have seen that humus, or organic de- 

 Economical ^^y^ jg a^ ygj-y important constituent in a 

 a RoJLuon'o/ fertile soil. Long clean cultivation of the 

 Crops land in a hoed crop exposes the soil to the 



sun in summer and the winter rains till 

 the humus is used up and the plant food is leached away 

 from the soil. This can readily be seen in the cotton belt 

 of the South, where this continuous clean cultivation has 

 been the rule for many years imtil the land refuses to give 

 a fair crop and only makes a moderate one by the use of 

 commercial fertilizers. 



This has been the result of an impression that cotton 

 was the only crop it paid the farmers to grow, and that 

 they could buy com and hay cheaper than they could grow 

 it. But they overlooked the fact that the crops that should 

 properly form their rotation would, if properly arranged, 

 tend continually to increase the productiveness of the 

 land in cotton. 



