CAPILLARY WATER 



213 



which the plant wilts permanently or at which it cannot maintain 

 its rigidity is the uniting coefficient. This point does not vary a 

 great deal with different plants, not often over three per cent and 

 usually within 1.5 per cent. It, however, varies widely with different 

 soils. The work of Briggs and Shantz shows that it is approxi- 

 mately one and one-half (1.47) times that of the hygroscopic coeffi- 

 cient. It represents the lower limit of available moisture. In 

 sands and light sandy loams in which the hygroscopic coefficient is 

 very low the wilting coefficient is also low. In clay soils whose 

 hygroscopic coefficient varies from 12 to 20 per cent the wilting 

 coefficient is from 18 to 30 per cent, while in muck and peat soils 

 it may run as high as 70 per cent. The wilting coefficient of the 

 same soil is a constant that may he used in the determination of 

 other constants, such as the hygroscopic coefficient and water-hold- 

 ing capacity. 



The wilting coefficient is determined experimentally, hut may 

 also he found indirectly from other soil constants to which it sus- 

 tains a definite relation. The following formula 1 mav he used: 



(a) Wilting Coefficient = 



Moisture equivalent 

 1.84 



n \ 

 (b) 



-ur-i.- r* a- Hygroscopic Coefficient 



Wilting Coefficient = ~I\RQ~ 



(c) Wilting Coefficient = 



Moisture holding capacity 

 2.90 



(d) Wilting Coefficient = 0.01 sands + 0.12 silt + 0.57 clay 



The probable errors have been omitted from these formulae. 

 Willing Coefficients of Various Soils for Different Plants l7 



Moisture equivalent. . . . 1.55 



12.0 



1S.9 



27.4 



