RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 



sary to subtract 21 from the percentage of capillary moisture 

 obtain a quantity having a fairly constant ratio to the wilting 

 efficient. 



r™ . • • r Capillarity — 21 „ 



This is given by W i ltin(y Q oeff = 2.90 ± 0.06, or±2.1 per cent. 



The probable error of a single determination by this means was 

 found to be 8.3 per cent of the wilting coefficient. 



In the treatment of forest soils Bates (105), at the Fremont Ex- 

 periment Station, has found it necessary to use much larger cans 

 than those employed by Hilgard, and has also reversed the pro< 

 so that the result is rather a measure of the ability <«f the soil to 

 hold the water- of saturation than to lift water from below. A gal- 

 vanized can 5§ inches deep and 4 inches in diameter, is filled to a 

 depth of 5 inches with air-dried soil, which is jarred and tampered 

 until no appreciable settling occurs. This can is perforated in the 

 bottom and a filter paper is used to keep the soil from sifting out. 

 The can is immersed to its full depth in water, but no water is al- 

 lowed to flow on the top of the soil. As the water rises from the 

 bottom by its own pressure, the air is pushed out, so that lew. if 

 any, air spaces are left. The samples are allowed to soak at Last 

 24 hours to insure complete absorption by the larger, permeahle rock 



fragments. 



The weight attained at the end of this period, or a longer period 

 if it appears necessary, is an index to the saturation capacity. 



The cans are now placed on a drain board, covered, and allowed to 

 stand for 48 hours. In rehandling the cans care must be used to 

 avoid jarring, as some of the water is held in a very delicate balance. 

 The amount of water held at this time is a measure of the capillary 

 moisture. In the vast majority of soils that have been treated, the 

 capillary moisture is about 90 per cent of the saturation capacity. 

 Clay does not affect this ratio appreciably, but humus increases 



The same cans are now used for the centrifugal test or moisture 

 equivalent determination, which will shortly be described. After 

 they are oven-dried, to give the basis for dry-weighl calculation* 

 The apparent density is also computed from the weight and volume 



after this treatment. 



In Table 2, there is presented a comparison of the capillary moi 

 tures and wdting coefficients of 10 soils of one general type granil 

 from an Engelmann spruce forest, bnt varying widely m state rt 

 decomposition, clay content, and humus content. Each aoU repre- 

 sents a sample extending from the surface to a depth of I l- • 

 wilting coefficients for Douglas fir and Engelmann f™- 

 carefully determined, the only objection that nngh e ■ 

 against the treatment being that the seedlings were given n b» 



