STATEMENT OF SOIL MOISTURE CONTENT 139 



The second method -that based on the wet weight 

 of the soil is unsatisfactory, because it is not only- 

 open to the objections made to the first method, but 

 also because figures on moisture content of the same 

 sample of soil are not comparable. They do not repre- 

 sent the same degree of wetness indicated by the per- 

 centages. For example, 100 grams of wet clay contain- 

 ing 10 per cent of water would consist of 10 grams of 

 water in 90 grams of soil, and 100 grams of wet clay 

 containing 20 per cent would consist of 20 grams of 

 water in 80 grams of soil. In the first case, the ratio 

 of water to soil is as 1 to 9; while, in the second, case 

 the ratio is 1 to 4, instead of 1 to 4.5, as the percentage 

 comparison would indicate. The difficulty in deriving 

 other figures from percentages based on wet weight 

 makes its use undesirable. 



The third method, statement of percentage of water 

 by volume, is the most rational of the first three. It 

 gives a direct practical basis of comparison for all soils. 

 It shows the volume of water held by the soil, which 

 is really the important consideration from the point 

 of view of the plant. For purposes of comparing the 

 moisture content of different soils in the field, it is 

 probably the most satisfactory method. Derivation 

 of these quantities involves considerable calculation, 

 and often the determination of some quantities not 

 readily obtainable. 



The fourth method of statement is really a variation 

 in detail from the third method by which specific quan- 

 titive statements are made. One hundred seventy-two 

 and ei.;ht-tenths cubic inches of water in one cubic 



