166 



NATURE AND PROPERTIES OF SOILS 



or vice versa as the case may be. As the capillary water in a 

 soil is reduced there is a tendency for the soil column to be 

 more nearly uniform, providing, of course, that the equi- 

 librium forces have had time to act and are not too much 

 influenced by other factors. 



While representative data regarding the moisture-holding 

 capacity of soils are difficult to give, the following figures 

 from Alway 1 indicate the general effect of texture and organic 

 matter. The maximum water capacity was determined in the 

 laboratory and the maximum field capacity was obtained by 

 sampling the soils very shortly after irrigation. 



Table XXXI 



THE MAXIMUM WATER CAPACITY OF VARIOUS SURFACE SOILS AS 



DETERMINED IN THE LABORATORY AND UNDER FIELD 



CONDITIONS, RESPECTIVELY 2 



The effect of texture on water capacity is very apparent, a 

 rough correlation existing also between the water retained and 

 the hygroscopic coefficient. The influence of organic matter 



1 Alway, F. J., and McDole, G. K., The Relation of Movement of 

 Water in a Soil to its Hygroscopicity and Initial Moistness); Jour. 

 Agr. Res., Vol. X, No. 8, pp. 391-428, 1917. 



a Note again that moisture percentages are always expressed on dry- 

 soil weight. ' 



