114 



IRRIGATION PRACTICE 



80. Distribution of water in the soil. The distribu- 

 tion of water in the soil is likewise important in determi- 

 ning the rate at which plants use water. 



As shown in the above table, two soils may each con- 

 tain approximately an average of 17 per cent of water to 

 a depth of 8 feet, but in the first the percentage of mois- 

 ture in the first foot is over 23 per cent, while in the second 

 the percentage of moisture in the first foot is about 17 

 per cent. That is, the distribution of water is not the 

 same in the two soils. In such a case, more water is lost 

 from the soil in which the water is heaped up near the 

 surface. The more evenly the water is distributed to 

 the full depth of root-action, the more slowly does the 

 plant consume the water during any given period of time. 

 The data in the table show that during a period of ten 

 days, where the top soil was wettest, 4.69 pounds more 

 were lost to the square foot than where the water was 

 more evenly distributed throughout the soil. 



The greater water loss from soils, otherwise alike, that 

 contain a large proportion of water in the first foot, may 

 be explained in part by the greater root-development in 

 the upper layers of the soil. Roots are well developed in 

 arid soils to a depth of 10 or more feet, but the larger part 

 of the small roots are developed within the upper 3 or 4 

 feet. Moreover, when the top soil is abundantly rich in 



