200 Irrigation and Drainage 



ence in the amount of water in the soil of a potato field where 

 the rows extended east and west, thus producing a shade on 

 the north side of each row. The samples of soil were taken 

 June 27. In this case the rows were planted 3 feet apart, and 

 the table given on page 161 shows a difference of 4.5 per 

 cent in the upper six inches on the sunny and shaded sides of 

 the row. 



Then, too, if the roots of the crop do not penetrate deeply 

 into the soil, more water will be required, for the double reason 

 that more water is liable to be lost by percolation below the root 

 zone, and because a greater frequency of water will be required 

 than if the roots went deeper ; hence, there will be more loss by 

 surface evaporation. 



2. The character of the soil. In the studies which have been 

 made regarding the amount of water required for a pound of dry 

 matter, there has been nothing to indicate that a plant growing 

 in one soil requires more water than when growing in another, 

 provided there is always an abundance of plant -food available to 

 the crop throughout its period of growth. In other words, if it 

 were possible to avoid losses by seepage, and by evaporation 

 other than that which takes place through the growing crop, it, 

 does not appear that the duty of water would vary with the 

 character of the soil. 



But, while it is true that by skillful management water may 

 be distributed, even over the soils of coarse texture, with 

 little or no waste through seepage, and while surface evaporation 

 may be very greatly reduced by suitable methods of applying the 

 water and of tillage, there will always be those living under the 

 same water supply who are less skillful than others, and who will, 

 by their lack of skill, require more water in order to secure the 

 same yields ; and, in consequence of this, the duty of water will 

 vary to some extent with the soil. 



There are really wide variations in the effectiveness of 

 mulches developed from different soils, and while these are not 

 as great as the variations in the rates of seepage, the losses of 

 water through surface evaporation are less completely under con- 

 trol than those due to percolation. The force of these statements 



