FARM IRRIGATION 259 



upon the nature of the soil and the demands of the 

 crop. The looser a soil is the closer they should 

 be. Water spreads slowly in heavy soils, but sandy 

 soils are leachy. They may be between every two 

 rows of potatoes, corn, sugar beets, or other row 

 crops, or between alternate rows; but in the latter 

 case the furrows for the next irrigation should 

 alternate with those of the previous watering. As 

 a rule the furrows should be from 4 to 6 feet apart. 

 Hilgard shows that water may be applied in wide 

 furrows much more efficiently than in shallow 

 furrows because there is less evaporation and the 

 surface is not wet as much. A few wide, deep 

 furrows are better than many narrow, shallow 

 furrows. The distance which it is possible to send 

 water along a furrow, and thoroughly wet all the 

 soil, depends upon the grade and the nature of the 

 soil. The more porous a soil is the shorter should 

 be the furrows. Water is commonly sent from 20 

 to 75 rods in furrow irrigation and sometimes over 

 100 rods. 



After a field has been irrigated, and the surface 

 has dried, the furrows are levelled with the culti- 

 vator. This is set to work as soon as possible, 

 so as to break up the crust, which indicates the 

 rapid loss of water by evaporation. The surface 

 mulch on an irrigated soil should be much deeper 

 than on soils in humid regions; four inches is barely 

 enough, and six inches is often necessary. 



A modified form of furrow irrigation is some- 

 times practised on grain fields by rolling the field 

 after sowing with a "marker," which is simply a 

 roller having parallel ridges upon it so that it makes 

 shallow grooves or furrows on the surface. The 

 roller is run in the direction that will give the right 

 slope for applying water. Water is turned into 



