136 DRAINAGE AND IRRIGATION 



7. Cost of Drainage. Study the structure and make notes regarding the 

 items of cost of a complete drainage system in a field where the project is 

 either completed or being contemplated. 



8. An overhead irrigation system, if one is in use in the vicinity, should 

 be studied by the students and the structure of the nozzles, the location of 

 valves and other details should be well understood. Make a drawing of the 

 pipe lines and indicate the distances apart, the size of pipe, the length of each 

 line. Show location, direction and size of the supply pipe. 



9. Testing Effect of Irrigation. If possible, on two plots grow one crop 

 having all conditions for growth the same, except the supply of water. Let 

 one plot be irrigated and the other supplied only with natural rainfall. Cal- 

 culate the increased yield due to irrigation and compare this with the cost of 

 the water supply. Credit the net increase to the cost of the irrigation plant. 



QUESTIONS 



1. Give the advantages of drainage. 



2. Tell what kinds of places are likely to need drainage. 



3. How much increase in value often accompanies drainage? 



4. How can an owner figure the profits to be derived from drainage? 



5. Give the advantages of underdrains as compared with open drains. 



6. Give some idea of the area of land under irrigation in the United States. 



How much more needs irrigation? 



7. Describe the reservoir plan of water storage and irrigation. 



8. Describe the methods of applying the water to the field. 

 References. -United States Farmers' Bulletins: 138, Irrigation in Field 



and Garden; 158, How to Build Small Irrigation Ditches; 187, Drainage of 

 Farm Lands; 263, Practical Information for Beginners in Irrigation; 266, 

 Management of Soils to Conserve Moisture; 371, Drainage of Irrigated Lands; 

 373, Irrigation of Alfalfa; 392, Irrigation of Sugar Beets; 394, The Use of 

 Windmills in Irrigation in the Semi-arid West; 399, Irrigation of Grain; 404, 

 Irrigation of Orchards; 524, Tile Drainage on the Farm; 698, Trenching 

 Machinery useJ for the Construction of Trenches for Tile Drains. 



