166 



NATURE AND PROPERTIES OF SOILS 



or vice versa as tiie 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 Always 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 yevj shortly after irrigation. 



Table XXXI 



THE MAXIMUM V5^ATER CAPACITY OF VARIOUS SURFACE SOILS AS 



DETERMINED IN THE LABORATORY AND UNDER FIELD 



CONDITIONS, RESPECTIVELY ^ 











Maximum 





Organic 



Matter 

 % 



Hygeo- 



Field 



Water 



Soils 



scopic Co- 

 efficient 



Water 

 Capacity 



Capacity, 

 Laboratory 





% 



% 



Method 











% 



Sand 



1l,ci2i 



1.1 

 1.7 

 3.3 



11.7 

 12.8 

 19.6 



37,0 



Sand 



27.1 



Sandy soil, residual. 



34.2 



Red loam, residual . . 



1.07 



10.0 



31.5 



49.0 



Silt loam, loess 



1.55 



10.1 



31.3 



56.8 



Silt loam, loess 



4.93 



10.2 



39.2 



60.9 



Black adobe 



2.22 



12.9 



47.6 



60.3 



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 



"•Alway, F. J., and McDolej G. E., The delation of Movement of 

 Water m a Soil to its Eygroscopicity and Initial Moistnes^; Jour. 

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



*Not« again that moisture percentages are always expressed on diy- 

 soil weight. 



