170 



SOIL PHYSICS AND MANAGEMENT 



lost. These spots are still visible in oats after 25 years 011 a 1'arin 

 in the vicinity of the University of Illinois. 



8. Organic Residues of the farm are of two kinds, those that 

 form no part of the crop, as weeds, and those that are part of the 

 crop or harvested with the crop, such as corn stalks, straw and 

 stubble. Heretofore it has been believed by many farmers that 

 most crop residues have little or no value and the easiest way of 

 disposing of them was the best; consequently much material wa--' 

 burned and the practice has by no means ceased. It is estimated 



Fio. 85. Burning corn stalks In addition to the organic matter destroyed in burning the 

 stalks some organic matter in the soil is burned. 



that in the western part of the United States the straw from 20,000,- 

 000 to 30,000,000 acres of grain is burned every year, while in the 

 corn belt the practice of burning stalks is still somewhat prevalent in 

 certain sections (Fig. 85). This enormous waste of organic mat- 

 ter and nitrogen is to be regretted very much. Crop residues of 

 all kinds have great value. Chemists tell us that straw has a 

 manurial value of $2 to $3 per ton, over half of which is due to 

 the plant food which it contains, while the rest is due to the physical 

 effect upon the soil. Corn stalks contain Ifi pounds of nitrogen per 

 ton, and even after exposure during the winter the amount is re- 



