Studies in Prairie and Woodland 37 



Even a casual examination of these data reveals a higher water 

 content of the soil in the thicket than in the prairie, or in the 

 forest than in the shrub. Although wilting coefficient determina- 

 tions were not made for all the soils at these depths, it seems 

 probable that water was available for plant growth at all times in 

 the forest. In the shrub it was exhausted to a depth of 3 feet in 

 September, beyond which depth the roots of hazel, sumac, grape 

 coral berry and other shrubs in this community were found to 

 extend. No water was available to prairie plants in the 6-24 

 inch soil stratum on August 6 nor again on August 25, while on 

 September 26 all available moisture had been used to a depth of 

 3 feet. Whether prairie vegetation occupying a unit area of soil 

 surface gives off more water by transpiration than is lost in a 

 similar manner from woody plants occupying an equal soil area, 

 or whether the greater water content of forest soils is due entirely 

 to their greater water-holding capacity and lower soil surface 

 evaporation remains to be determined. The writers are inclined 

 strongly toward the view that increased transpiration from grass- 

 land plays an important role. 



A comparison of the soil moisture conditions at Lincoln with 

 those at Peru may be found interesting. The following table 

 shows the number of times during the growing season during 

 which the soil moisture had reached the non-available point at 

 the various depths. 



TABLE 5 



A Comparison of the Periods during which Water was Non-available 

 FOR Plant Growth in the Prairies at Lincoln and at Peru 



* Assuming that the wilting coefficients which were not determined at 

 these depths are no greater than at a depth of i or 2 feet. 



43 



