INDIRECT DETERMINATION OF THE WILTING COEFFICIENT. 



67 



with water. The moisture-holding capacity is the percentage of water 

 a soil can retain in opposition to the force of gravity when free drain- 

 age is provided. This is dependent on the height of the soil column 

 employed, diminishing as the height of the column is increased. 1 

 When the soil column is made very short — for example, 1 centimeter 

 in height — the two determinations are practically identical. Both 

 are greatly influenced by the packing and the granulation of the soil, 

 so that determinations are subject to wide variation in the hands of 

 different observers. 



In Table XXI the wilting coefficients of a series of soils 2 are com- 

 pared' with their moisture-holding capacity. Following Hilgard, 3 

 determinations of moisture-holding capacity were made with a soil 

 column 1 centimeter in height, with free drainage. 



Table XXI. — Relation of the wilting coefficient to the moisture-holding capacity of 



different soils. 



Soil. 



Types of soil. 



Moisture- 

 holding 

 capacity. 



Wilting 

 coefficient. 



Ratio of 

 moisture- 

 holding 

 capacity 

 -21 to 

 wilting 

 coefficient. 



7 





23.2 

 29.9 

 28.5 

 31.4 

 44.9 

 50.1 

 55.9 

 58.6 

 59.8 

 54.2 

 58.2 

 63.2 

 71.3 

 67.2 

 69.5 



0.9 



2.6 



3.3 



3.6 



8.3 



9.5 



11.0 



11.6 



11.7 



13.8 



14.7 



14.9 



15.0 



15.7 



16.7 



2.44 



2 





3.40 



8 



do 



2,27 



9 



do 



2.84 



F 





2.88 



G 



do 



3.06 



H 





3. 17 



I 



do 



3.24 



J 



do 



3.30 



86 





2.40 



K 



do 



2.52 



L 



...do 



2.83 



M 



do.. 



3.35 



N 



do 



2.94 







do 



2.90 





Mean 











2.90 





Probable error of mean ratio 







± .06 













The moisture-holding capacity of the soils used in the comparison 

 ranged from about 23 to about 71 per cent. In this case the ratio 

 between the moisture-holding capacity and the wilting coefficient is 

 not constant. However, an approximately constant relationship is 

 obtained if the moisture-holding capacity (expressed as a percentage) 

 is first reduced by 21. The ratio of the moisture-holding capacity 

 less 21 to the wilting coefficient is shown in the last column of the 

 table. The mean ratio for the 15 soils examined is 2.90±0.06. The 



1 Loughridge, R. H. Investigations in Soil Physics. Report, California Agricultural Experiment Sta- 

 tion, 1892-1894, p. 99. 



Briggs, L. J. The Mechanics of Soil Moisture. Bulletin 10, Division of Soils, XT. S. Dept. of Agricul 

 ture, 1897. 



2 In this work it was not possible to obtain samples of all the soils used in the preceding experiments. 



3 Hilgard, E. W. Soils, New York, 1906, p. 209. 



230 



