Tillage and Irrigation 83 



thrown high or low, according to the direction and velocity 

 of the wind and how far it should carry. 



The water is turned on only between four p.m. and 

 nine a.m., or on cloudy days; if applied while the sun 

 is shining, much of it is lost by evaporation and the leaves 

 and berries are scalded. From three to seven hours are 

 needed for each sprinkling, so as to apply at least one- 

 half inch of water, preferably more. When the water is 

 turned on, the field appears to be covered with a heavy fog. 



If a town water supply under pressure is not available, it 

 is necessary to pump water from a stream, spring or well. 

 A three and one-half horsepower engine is needed to pump 

 water for a single acre, an eight horsepower for four acres 

 and a twenty-five horsepower for twenty acres. The cost 

 of installing equipment for overhead irrigation is $85 to 

 $200 an acre (not including the pumping plant and the 

 mains). After it is installed there is practically no expense 

 except for pumping, and the equipment lasts many years. 



For humid regions overhead irrigation has several 

 distinct advantages over gravity irrigation. It permits 

 the ground to be occupied completely with plants. This 

 is the main reason why it is preferred by market-gardeners 

 and truckers. Furthermore, it can be used on any type 

 of land, whether level or sloping, and no preliminary 

 grading is needed. It does not pack or puddle the soil. 

 After once installed the upkeep is much cheaper than in 

 surface irrigation and it is more convenient to operate. 

 The overhead system is economical of water; gravity 

 irrigation is quite wasteful of water. Some growers 

 have found overhead sprinkling useful for warding off 

 light frosts. On the other hand, the expense of installa- 

 tion is so heavy as to make this method impracticable 

 except on land under intensive cultivation. 



