INTRODUCTION 



Knowledge of the water retention properties of soils is an important facet of the 

 hydrologic data necessary for wise management of forested lands. Management decisions 

 that are based on soil water retention data include: types and expected rates of 

 timber regeneration; potential for erosion and sediment production; changes in water 

 yields following vegetative manipulation; design and location of roads; and a myriad of 

 ecological factors. 



Land managers have become increasingly aware of the importance of hydrologic in- 

 puts to forest land management in the Idaho Batholith in the last decade as a result of 

 the contrasting values of a timber resource, fishery resource, and the inherent high 

 erosion potential of the Batholith soils (Bethlahmy and Kidd 1966; Gonsior and Gardner 

 1971; Haupt and Kidd 1965; Megahan and Kidd 1972a and 1972b). 



We have attempted in this study to provide a more complete understanding of the 

 interacting effects of percent soil organic matter (OM) , bulk density (Pb) , and percent 

 fines (diameter <50iim, F) on water retention. The water retention models developed 

 appear to have regional applicability throughout the Idaho Batholith. 



The prediction of soil water storage has practical value only when either the 

 parameters used for this prediction are more easily determined than water retention 

 determined by conventional laboratory techniques, or the soil parameters other than 

 water retention are available. Experienced field soil scientists can make reasonably 

 accurate estimates of texture, organic matter content, and bulk density (Visser 1966), 

 particularly after some training and familiarity with the soils involved. 



