RESULTS 



Description of the Models 



Evaluations of the dependent and independent variables show the means, standard 

 deviations, and ranges for the data used in developing the two water retention models 

 (table 1). The water retention values appear typical for coarse-textured soils. Values 

 nublished by Broadfoot and Burke (1958, p. 5) can be compared by dividing Batholith 

 ^oil values by the mean Pb value to express retention on a weight basis. The retentions 

 at both energy levels fall between their published values for loamy sand and sandy loam 

 textures. A similar comparison of bulk densities by textural classes can be made with 

 Broadfoot and Burke's data (1958, p. 13) and shows our bulk densities to be similar. 



The water retention surfaces incorporating the effects of all independent variables 

 for 1/3 bar and 15 bars tension are presented in figures 6 and 7, along with the 

 indices of determination (R^) , and the standard errors of estimate (s ) . The equa- 

 tions for these models are specified in the Appendix. ^ ^ 



Basically these surfaces fit expectation and can be described as follows: 



The most significant feature of the 1/3-bar model is that retention increases 

 strongly (15 to 20 percent) as OM increases from to 8 or 10 percent, regardless of 

 Pb and F values. At low OM, only small to modest positive effects can be seen over 

 Pb and F. And, at high OM, the expected interaction materializes except that the left 

 front third of the figure has been arbitrarily brought to a lower asymptote for each 

 F-level. Data are either scant or absent there. A sharp retention increase in the 

 range 1.3 < Pb < 1.5 occurs in the lower range of F, 10 to 20 percent. 



Table 1. Univariate descriptions of the data. (N = 47 for all variables) 



: : Standard : : : 



^^^"^ : Mean : deviation : Lowest : Highest • Range 



1/3 atm. Pv 15.11 4.14 6.5 27.0 20.5 



15 atm. Pv 6.20 1.73 3.7 11.1 7.4 



OM 4.26 1.97 1.6 11.7 10.1 



°^ F 22.80 8.46 7.4 53.0 45.6 



Bulk density g/cc 1.30 .19 .94 1.7 .76 



