222 SUCCESSFUL FARMING 



distance in a fine spray. By turning the pipe, the water is directed to 

 either side of the pipe line at the desired angle. 



With the pipes parallel and the supporting posts in line at right 

 angles to them, cultivation may take place in either direction beneath the 

 pipes. While this system is rather expensive to install, it is well adapted 

 to small areas intensively farmed, to truck crops and small fruits. Such 

 systems are common along the Atlantic Seaboard and in some parts of 

 the South. 



Duty of Water. This pertains to the area of land that may be irri- 

 gated with a unit of water, such as a "second foot" or a "miner's inch." 

 The wasteful methods of irrigating and lack of knowledge on the part 

 of the farmer result in a low duty. Under favorable conditions the duty 

 should be about 200 acres for each "second foot." It would seem wise 

 that the duty of water should be fixed within reasonable limits by some 

 competent authority for a particular state or irrigation district. Local 

 conditions, such as rainfall, length of growing season and the intensity of 

 agriculture, should be taken into consideration in fixing the duty of water. 



When to Irrigate. How often to irrigate and how much water to 

 apply will depend on local conditions, such as character of soil, kind of 

 crop and weather conditions. Economy in water as well as the labor of 

 irrigating, should make the intervals as long as feasible. Water should 

 be applied until the soil is wet to the full depth to which the roots of the 

 crop in question penetrate. The deeper the soil is wet, the longer may be 

 the interval between irrigations. Lighter and more frequent irrigations 

 penetrate the soil to less depth, increase the labor and result in greater 

 loss of water by direct evaporation. Water should be applied when the 

 crops need it and irrigation cease when the need is fully met. Enough 

 water is better than too much. 



Where there is a bountiful winter supply of water and a scant supply 

 during the summer, winter irrigation is recommended. It stores the soil 

 with water and lessens the need during the summer. 



Water should be applied to crops abundantly when they are growing 

 most rapidly. Irrigation may be withheld as they approach maturity. 



Irrigation Waters. Irrigation water sometimes becomes so heavily 

 charged with salts that it proves harmful to tender plants. This con- 

 dition arises either from concentration through evaporation in shallow 

 reservoirs or from passing through alkali soil. Along stream courses, the 

 reckless use of water gives rise to much seepage which returns to the 

 stream lower down. This frequently becomes so plentiful that it forms a 

 supply for another irrigation district further down the stream course. Such 

 water is frequently unsuited for irrigation purposes. 



Alkali Troubles. The rise of alkali is generally caused by over- 

 irrigation. An excess of water causes the ground water table to rise until 

 the gravitational water can reach the surface by capillary attraction. 

 This causes excessive evaporation at the surface of the soil and results 



