T02 SOILS: PROPERTIES AND MANAGEMENT 



of earth to prevent injury to the growing wood. This 

 method is used rather extensively throughout the arid 

 regions. 



In the open-field, or blind, flooding, the water is ^up- 

 plied in ditches which are carried across the contour- ;it 

 a moderate grade, and at intervals the flow is intercepted 

 by a canvas dam or other obstruction and forced to flow 

 over the lower bank, from which point it is distributed 

 down the slope and over the field in numerous small 

 trenches. Any surplus water is collected in a ditch at the 

 lower side of the field. In this method of applying water, 

 constant attention is required to guide the flow and prevent 

 erosion. One man can irrigate from five to ten acres in a 

 day. This method is used in irrigating grainfields and 

 sloping meadowland and in saturating the soil in prepa- 

 ration for a crop. 



603. Furrows. — In the furrow system of irrigation 

 the water is led out from the supply ditch on the upper 

 side of the field into small, parallel furrows extending 

 down or across the slope at a considerable grade. This 

 system is used for cultivated field and garden crops, and 

 to a large extent in orchards. The rate of flow of water 

 in the furrows should not exceed one to two feet per 

 second, depending on the nature of the soil. This permits 

 a wide range of grade, from 2 to 10 per cent, where the 

 head of water is only a fraction of a second-foot in each 

 furrow. The flow on a given slope may be regulated by 

 the head of water and is determined by the porosity of the 

 soil. On heavy soil a small head and a steep grade may be 

 employed ; on sandy soil, which washes easily, a low grade 

 and a large head of water is used. The length of furrows 

 that may be employed depends on the nature of the soil 

 and the head of water available. The water is distrib- 



