EXERCISE 22 



SOIL DRAINAGE 



Statement. A soil with its pore spaces filled with water is known as a dead soil. Surplus water may 

 be disposed of in part by surface drainage if there is sufficient slope, but in such cases surface erosion 

 or washing Usually results. Underdraining, by means of tiles, lowers the water table, checks surface 

 washing, and otherwise improves the soil. 



Object. To show that drainage does not deplete usable soil moisture, but that it conserves such 

 moisture by estabhshing a lower water table and facilitating percolation. 



Materials. Two 12-inch flowerpots; wooden box, tightly constructed and 12 inches deep; any 

 common type of soil ; i-inch bit and brace ; three round wooden rods 1 inch in diameter, such as broom 

 handles; a sprinkling can. 



Directions. 1. Close the hole in the bottom of one of the 12-inch flowerpots with a cork ; fill both 

 pots with loam. Plant kernels of corn in each pot, and water both alike. Observe differences in growth 



and explain the reason for any variation that appears. 



2. Bore holes in one end of the box 3 inches, 6 inches, and 9 

 inches, respectively, from the top and equal distances from the sides. 

 On the opposite end bore three holes at the same distance from the 

 top and sides. Place the three rods through the box, leaving one 

 end of each to protrude beyond the hole, as shown in Fig. 26. Fill 

 the box with soil, tamping it firmly to represent the natural field soil. 

 When full and leveled, turn the box on end and carefully pull out 

 the rods. If the soil is tamped thoroughly and the rods are removed 





A 



3' 



(5/3" 



Fig. 26 A simple device for illustrating carefully the openings will remain. Pour coarse sand or gravel into 

 the principles of soil drainage ■" m * " ° 



the holes until they are each filled, and turn the box back to its 



proper position. Sprinkle the surface of the soil very slowly, so that all the water will be absorbed as 

 rapidly as applied, until water begins to run in a stream from one of the holes in the box. From which 

 holes does water flow first, the top ones or the bottom ones ? Plug the holes from which water is flow- 

 ing and continue to sprinkle until water runs from the second hole. Explain what happens, and why. 

 Repeat until the water runs from the top hole. Stop this hole also and water the soil until it is 

 saturated. Then open the holes in their order, beginning at the upper one, and note the lowering 

 of the water table in the box. Apply what you have observed to the soil in the field. 

 Plan a system of under drainage, 



1. To improve some field in the neighborhood. ' 



2. To reclaim a piece of wet land in the neighborhood. 



3. To stop surface washing on a farm in the community. 



In each case show location of drains, the size of tile required for each, the slope of each, and make an 

 itemized statement of the cost of the improvements and of the value of the benefits which would 

 result. 



Questions. Explain in what respects a soil filled with water differs from one which is only moist. 

 Why will not the common cultivated plants grow in one as well as the other ? May the lack of suit- 

 able drainage of a soil be detected by the kinds of plants found growing on it? Name a half dozen 

 plants the presence of which indicate poor drainage. A half dozen which indicate good drainage. 

 How may soil erosion be prevented on gentle slopes ? How may water that comes to the surface at 

 the foot of the slopes be prevented from passing over the low level ground ? 



References. Waters, H. J. Essentials of Agriculture, pp. 122-134. Ginn and Company. King, F. H. 

 Physics of Agriculture, pp. 292-329. Mrs. F. H. King. Burkett, C. W. Soils, pp. 161-164. Orange Judd 

 Company. Mosier and Gustafson. Soil Physics and Management, pp. 222-229. J. B. Lippincott Company. 



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