EXERCISE A-25. TO SHOW THE EFFECT OF PLOW- 

 ING UNDER COARSE MATERIAL SUCH AS MANURE, 

 GREEN COVER CROPS, OR CLODS. 



Equipment: Three lamp chimneys; rack to support 

 chimneys; tray 1'X4"X12''; cheese cloth; scissors; twine; 

 sample of sandy loam soil; cut straw; soil lumps or clocls. 



Method: Cover the small end of each lamp chimney 

 with a piece of cloth and tie it on with the twine. Number 

 and fill the tubes as follows: (1) when about two-thirds 

 full add enough cut straw to make a layer one inch thick, 

 and complete filling; (2) when two-thirds full add enough 

 round hard clods to make a layer about one inch thick, and 

 complete filhng; (3) fill with fine soil. Hang the tubes in 

 the rack with their lower ends resting lightly on the bottom 

 of the tray and fill the pan with water. At the end of four 

 days note the height of the water in each tube. Since the 

 same kind of soil was used in each tube would you not ex- 

 pect the water to rise to the same height in each? Explain 

 the cause for what you find. 



Discussion: When capillary water rises in the soil it 

 passes from one tiny particle to another which lies next to 

 it. If the particles are separated by a very wide space or 

 by some loose substance the rise of water is stopped. This 

 may happen when a heavy growth of green material like 

 rye is plowed under. Harm will be prevented if the green 

 material is thoroughly cut with a disc before being turned 



under and the furrows turned so as to lap and not lie flat. 



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