SOIL MULCH IN CONSERVING MOISTURE 105 



crop represents an enormous loss of moisture which should go to 

 the crop (see first table in this chapter). The killing of weeds, 

 therefore, is an important factor in moisture conservation. 



Demonstrations. Material Needed. One balance; a baking-powder can; 

 a piece of cheese cloth; 6 student lamp chimneys, or j^-inch glass tubes 12 to 

 16 inches long; a few pieces of lump sugar (cubes); a few teaspoonfuls of 

 powdered sugar; red ink; a saucer; a few fine needles; some road dust; a piece 

 of dusty board; 2 one-gallon crocks; about a quart each of air-dried loam, 

 fine gravel, coarse sand, fine sand, silt loam; and 8 quarts of loam or silt loam. 



To Make Clear the Meaning of the Three Forms of Soil Water. 

 Procedure. A. Allow the plants in the crock that was kept in the greenhouse 

 (Demonstration No. 4, Chapter V) to dry up and die. Now take out of the 

 crock 100 grams, or about 4 ounces of soil, and dry it at 105 C. or 221 F. 

 (to prevent burning of organic matter) for 3 to 5 hours. Weigh again and deter- 

 mine the per cent of water contained in the air-dried soil. Most of this water 

 is hygroscopic water. 



Plants are wilted and dying in a sand and a clay loam. Which soil contains 

 the more hygroscopic water? 



B. Over the perforated bottom of a baking-powder can, or over the open- 

 ing in a funnel, place a piece of cheese cloth. Fill the can or funnel nearly 

 full of air-dried loam. Pour on the soil a measured amount of water and 

 allow to drain. 



Questions. (a) Did all the water drain through the soil? 



(6) What is the water called that drained through? 



(c) Name the water that was retained by the soil. 



To Observe the Rise of Capillary Water in Soils and to Study Some of 

 the Factors Which Influence This Process. Procedure. Tie some cloth over 

 the lower end of student lamp chimneys, or %-inch glass tubes (Fig. 41). 

 (Tubes should be at least 12 to 18 inches long.) Fill student lamp chimneys 

 or tubes with dry soil as follows: 



No. 1. Fill with dry gravel; tamp well. 



No. 2. Fill with dry coarse sand; tamp well. 



No. 3. Fill with dry fine sand; tamp well. 



No. 4. Fill with dry silt loam; tamp well. 



No. 5. Fill as in No. 3 to within one inch of the top; tamp well. Fill to 

 top with dry, crummy silt loam do not tamp. (This top layer of loose, dry 

 crummy soil serves as a soil mulch.) 



No. 6. Fill as in No. 3 to within 6 inches of the top; tamp well. Now 

 place on top of this soil column half an inch of cut up straw, dry grass, or hay; 

 then fill to top with dry fine sand tamp well (see Fig. 40). 



Place soil columns in a pan in a vertical position, then pour about half 

 an inch of water into the pan. Observe results at end of 5 minutes; after 

 1, 2, 3, 4 and 5 days, respectively. 



Questions. (a) Why is it necessary to have good contact between the 

 soil particles within the seed bed. Between the soil and subsoil? 



(6) What is a droughty soil? 



(c) What effect has texture on the capillary rise of water in soils? 



To Demonstrate the Principle of Soil Mulch in Conserving Moisture. 

 Procedure. A. Observe results in tube No. 5, previous experiment. 



B. Sprinkle as much powdered sugar on top of a lump (do not press down 

 the powdered sugar) as it will hold, and place the lump in a pool of about 12 

 drops of red ink poured out on a white dish. Observe results. 



The lump of sugar represents soil, and the powdered sugar a soil mulch. 



C. Fill a saucer with water; place a perfectly dry, fine needle carefully 

 on the surface film of the water. The needle will float. Why? Take a pinch 



