Conditions Modifying Duty of Water 203 



depth, when developed from soils of different textures, and it is 

 plain that with equal losses by percolation from the three soils 

 here under consideration, more water would be required to bring 

 a crop to maturity on the virgin clay loam than on either of the 

 other soils, and hence, that the duty of water would be less, 

 supposing, of course, that the three soils were equally fertile. 



Where water is plentiful and is being used freely, and es- 

 pecially where irrigation by flooding is being practiced, the soils 

 having the coarsest, most open texture will waste the most water 

 by percolation through the zone of root feeding. Hence on this 

 account the duty of water would be smaller on these soils than 

 on those having finer texture. But, on the other hand, the sur- 

 face evaporation from the closer soils is so much greater than 

 from the sandy soils that the duty of water is much more nearly 

 equal on them than it could be were it not for these opposite 

 characteristics. 



Bearing upon this point E. Perels,* citing Eduard Markus, 

 gives the results of observations covering three years in northern 

 Italy 011 different kinds of soils and with different crops, from 

 which it appears that rice, meadows and field crops use water in 

 the ratio of 7 to 3 to 1, respectively, and when field crops are 

 grown upon very heavy soil, heavy soil, medium soil, or light 

 soil, they take water in the ratio of 



Very heavy soil Heavy soil Medium soil Light soil 

 100 . . to . . 115 . . to . . 168 . . to . . 230 



It is quite probable, however, that these ratios represent the 

 relations of the degree of permeability of these soils under the 

 conditions of the district, rather than the necessary amounts of 

 water required for irrigation on these soils, where simply the 

 transpiration from the crops and the evaporation from the soils 

 is considered. In the cases of the rice and meadows, it is cer- 

 tain that large percolation or surface drainage must have occurred. 



The losses of water by seepage from canals and reservoirs 



*Landwirthschaftlicher Wasserbau, p. 501. 



