224 THE PRINCIPLES OF SOIL MANAGEMENT 



101. Factors affecting the duty of water. Eleven 

 factors, as follows, affect the duty of water in irriga- 

 tion: 



(1) The peculiarities of the crop (see page 134). 

 Some crops require much more water than others for 

 their growth and maturity. Even certain varieties 

 may require much more water than others of the same 

 species. 



(2) The physical character of the soil. If the applica- 

 tion of water is such that leaching may take place, 

 more water will be lost through sand than through clay. 

 The character of the soil also determines the effective- 

 ness of the mulch, which may be maintained. 



(3) The character of the subsoil. 



(4) The frequency of irrigation. 



(5) Amount and distribution of the rainfall. These 

 last two factors are closely related in their effect on the 

 duty of irrigation water. Their frequency determines 

 the proportion of the water which will be lost by surface 

 evaporation. (See page 198.) 



(6) The amount and time of applying water. Water 

 applied in the evening will be more efficient than when 

 applied in the morning, because during the cool night 

 it will have opportunity to diffuse deeply into the soil, 

 where the hot sun of the following day will have less 

 effect upon it than if the water were applied in the 

 morning. 



(7) The climate. Other things being equal, more 

 water will be required in a warm, windy climate than in 

 one of a cool, quiet atmosphere. This factor, of course, 

 largely determines the rate of evaporation. 



