60 



WILTING COEFFICIENT FOE DIFFEEENT PLANTS. 



The wuting-coefficient determinations given in Tables XI and 

 XIII also provide an opportunity for testing this relationship. 

 For this purpose use is made of the mean wilting coefficient as deter- 

 mined from all the plants tested in each soil, which is given at the 

 end of the measurement for each soil in Table XI (except No. 30, 

 which is given in Table XIII). For convenient reference, these 

 mean wilting coefficients have been collected in Table XIX, to- 

 gether with the moisture equivalent for each sample, and the ratio 

 determined as before. The mean value of all the ratios is 1.85, 

 with a probable error of ±0.02. This ratio also agrees, within the 

 probable error, with the mean ratio obtained from the results in 

 Table XVII. In the results given in Tables XVII and XVIII, 

 Kubanka wheat alone was used as an indicator plant. From the 

 results given in Table XIX, it is seen that the same ratio between the 

 moisture equivalent and the wilting coefficient is obtained when many 

 different plants are used as indicators. This result accords with the 

 idea already advanced that the difference resulting from using differ- 

 ent varieties or different crops as indicator plants is slight. The 

 agreement obtained through a wide range of soils and with different 

 plants as indicators leads to the belief that the relationship given is 

 quite general in its application and sufficiently accurate to meet field 

 requirements in determining the wilting coefficient. 



Table XIX. — Ratio of the moisture equivalent of the soils covered by Tables XI and 

 XIII to the mean ivilting-coefficient determinations of those soils. 





Types of soil. 



Moisture 

 equivalent. 



Wilting coefficient. 



Ratio of 



moisture 

 equivalent, 

 to coeffi- 

 cient. 



Soil. 



Number of 

 determina- 

 tions. 



Mean. 



1 



Coarse sand 



1.55 



1.55 



2.48 



4.66 



5.5 



6.74 



11 

 59 



8 

 18 

 42 

 44 

 15 

 14 

 45 

 11 

 36 

 418 

 64 

 45 



9 

 34 

 13 

 55 

 33 

 16 



0.86 

 1.03 

 1.23 

 2.6 

 3.03 

 3.76 

 4.2 

 4.8 

 6.3 

 7.8 

 9.3 

 9.7 

 8.84 

 10.4 

 13.4 

 12.7 

 13.9 

 14.8 

 17.1 

 16.3 



1.81 



7 



do 



1.51 



87 



Sand 



2.01 



2 





1.79 



8 



...do 



1.82 



9 



do 



1.79 



80 







3 



....do 



9.7 

 12.0 

 14.5 

 18.1 

 18.5 

 18.6 

 18.9 

 23.3 

 23.8 

 25.0 

 27.4 

 29.3 

 30.2 



2.02 



10 



..do 



1.91 



82 



...do 



1.86 



4 



Fine sandy loam 



1.95 



30 



do 



1.91 



26 





2.10 



12 





1.82 



86 



Clay loam 



1.74 



78 





1.87 



5 



.. ..do 



1.80 



13 





1.85 



14 



do 



1.71 



6 



....do 



1.85 





Mean 













1.85 





Probable error of mean 









± .02 















The results given in Tables XVII and XVIII are combined 

 graphically in figure 7, in which the wilting coefficients are given 



230 



