INDIRECT DETERMINATION OF THE WILTING COEFFICIENT. 



65 



Table XX. — Relation of the wilting coefficient to the hygroscopic coefficient of soils 



ranging from sand to clay. 



Soil. 



Types of soil. 



Hygro- 

 scopic 

 coefficient. 



Wilting coefficient. 



Number of 

 determi- 

 nations. 



Average. 



Ratio of 

 hygro- 

 scopic 

 coefficient 

 to wilting 

 coefficient. 



Coarse sand 



Fine sand 



do 



do 



Sandy loam 



do 



Fine sandy loam . 



Loam 



Sandy loam 



Fine sandy loam. 



do 



Loam 



do 



Clay loam 



do 



do 



do 



0.5 

 1.5 



2.3 

 2.3 

 3.5 

 4.4 

 6.5 

 7.8 

 6.3 

 6.6 

 7.5 

 9.8 

 9.6 

 11.8 

 13.2 

 11.2 

 11.4 



Mean 



Probable error of mean . 



0.9 

 2.6 

 3.3 

 3.6 

 4.8 

 6.3 

 9.7 

 10.3 

 9.9 

 10.8 

 11.6 

 13.9 

 15.2 

 14.6 

 16.2 

 16.5 

 16.3 



0.556 

 .577 



.729 

 ,699 

 ,670 

 ,757 

 .636 

 ,611 

 ,646 

 ,705 

 ,631 

 .808 

 .815 

 .679 

 .700 



± .012 



The hygroscopic determinations given in the table are the mean 

 of duplicate measurements. The determinations range from 0.5 per 

 cent in sand to 13.2 per cent in clay loam. The corresponding 

 wilting coefficients have been discussed in connection with Table 

 XVII. 



The ratio of the hygroscopic coefficient to the wilting coefficient 

 is given for each soil in the last column of Table XX. The mean of 

 this ratio is 0.68, with a probable error of ±0.012. This ratio 

 presents a second method of deterrnining the wilting coefficient when 

 the hygroscopic coefficient is known, as follows : 



Hygroscopic coefficient ., . „, . 



■ 68-h0 01? = Wlltin § coefficient. 



Heinrich * determined the nonavailable moisture in six types of 

 soil, using corn and oats for indicator plants. He also measured the 

 hygroscopic coefficient of each soil used in his experiments. Com- 

 puted from his measurements, the mean ratio of the hygroscopic 

 coefficient to the wilting coefficient, together with the probable error 

 of the mean, gives the value 0.696 ±0.03, as compared with the ratio 

 0.68 ±0.01 obtained from our experiments. While Heinrich's deter- 

 mination show more variation than our own, the ratio obtained from 

 his results agrees within the limits of his probable error with the 



i Heinrich, R. Zweiter Bericht iiber die Verhaltnisse und 

 Versuchs-Stationen zu Rostock, 1894, pp. 28-32. 



8477°— Bul. 230—12 5 



Wirksamkeit der landwirtschaftlichen 



