I 



62 MISC. PUBLICATION 4 3 4, U. S. DEPARTMENT OF AGRICULTURE 



of 25 to 50 feet. Vertical turbine pumps have from 2 to 30 impellers 

 (multistage). In deep wells the number of impellers is increased, 

 generally by one stage for each 15 or 20 feet of head, depending also 

 somewhat on size of casing, gallonage to be delivered at the surface, 

 and pressure desired. Such pumps can be used in wells up to 1,000 

 feet deep. 



The vertical centrifugal and the vertical turbine pumps are the 

 two types most used in irrigation projects and in nurseries where the 

 water table lies too deep to use a horizontal centrifugal pump. They 

 have capacities of 500 to 1,000 or more gallons per minute and develop 

 all the pressure ever needed in a nursery. Although the initial outlay 

 is considerable, they are the best and most efficient deep-well pumps 

 when costs are prorated over a period of years. 



The deep-well cylinder pump, which operates on a plunger principle, 

 is satisfactory for deep wells but generally has a capacity of not over 

 50 to 100 gallons per minute, not enough to supply the water needed 

 in most nurseries, unless used to fill a storage pond or tank of large 

 capacity from which water can be run by gravity into irrigation 

 ditches. 



Air-lift pumps are seldom used in irrigation projects because of low 

 efficiency and high installation cost. Their chief mechanical ad- 

 vantage is that they need not be set directly over the well, as is the 

 case for the other three types of deep-well pumps. 



Ditch Irrigation 13 

 planning and construction of ditches 



Ditch irrigation is the method generally used by plains nursery- 

 men in distributing the water over the nursery. To be successful, it 

 must be planned with due consideration for limitations chiefly con- 

 nected with topography, texture of soil, and size and shape of the 

 nursery. There is therefore no general plan that can be applied to all 

 conditions. 



A topographic map of the nursery site with a contour interval of one- 

 half to one foot is prerequisite to laying out main and lateral ditches 

 and deciding the direction of tree rows. These should first be plotted 

 on the map. If the slope of the land is uniform and in one direction 

 the irrigation system wul often consist of a main ditch running down 

 the slope on a fall of 0.1 to 0.25 percent, from which laterals run out 

 approximately at right angles. The laterals follow around the con- 

 tour of the slope and are spaced at intervals of 400 to 650 feet depend- 

 ing on slope of land and soil texture. Rows should not be carried 

 down slopes of more than 2.5 feet per 100 feet in very sandy soils, 1.75 

 feet in sandy loams, or 1.5 feet in heavy soils. Otherwise, erosion 

 may result during irrigation and proper penetration of the water is 

 difficult to attain. 



The distance which water may economically be carried down tree 

 rows varies with the slope, the head of water available, and the soil 

 type. For instance, when water is turned into a tree row, on sandy 

 soils, the stream will advance down the row at a uniform rate of so 



13 This section on ditch irrigation was prepared largely by I. D. Wood and R. Hilliary, formerly with the 

 Prairie States Forestry Project, Forest Service. 



