178 IRRIGATION PRACTICE 



soil sufficiently dry to support the tools without danger 

 to the soil structure. 



Fall irrigation has been tried extensively in places 

 where the winter rainfall is light, and almost invariably 

 with great success. Wherever the winter precipitation is 

 high, it is probably unnecessary and possibly inadvisa- 

 ble to practise fall irrigation. Meanwhile, the use of the 

 water which ordinarily goes to waste in the fall may be 

 the means of making the summer flow cover a larger 

 area of land than would otherwise be possible. 



112. Winter irrigation. Winter irrigation means the 

 application of water to the soil during the winter proper. 

 It is seldom practised where the winters are closed in by 

 snow or where the top soil is frozen for weeks or months. 

 It is true that an unsaturated soil, when frozen, is of a 

 granular structure, and that through such a frozen soil 

 water penetrates to considerable depths. However, 

 water applied to frozen soils stands on the soil and often 

 freezes into sheets of ice. On bare soils this does little 

 harm and little good. A possible advantage is that when 

 the warmer weather melts the ice and opens the soils, 

 the water that has not run off soaks rapidly into the soil. 

 On lands bearing grass or lucern, great injury is done 

 when sheets of ice are formed over the surface of the fields, 

 and winter irrigation should never be practised on such 

 fields where freezing weather characterizes the winters. 



Winter irrigation is and should be practised chiefly 

 where the winters are mild and open. In such districts, 

 winter irrigation is really a later fall irrigation. All the 

 arguments in favor of fall irrigation hold for such winter 

 irrigation. 



Excellent studies have been made of the value of 

 winter or late fall irrigation in supplementing the rain- 



