RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 

 Total Moisture Determinations. 



The determination of the current-moisture contenl of the soil at 

 a given point is an exceedingly simple matter, and a vast amounl 

 such work has been done in connection with agricultural investiffa- 

 tions and greenhouse experiments; in fact, so much has been done 

 that citations are useless. 



On the other hand, repeated determinations at a given point to 

 show changes, minima, etc, immediately introduce complications. 

 When a sample has been taken from the ground, it is wry difficult to 

 fill the space with the same kind of soil as before, and even if tin- 

 were accomplished the new soil would not soon be in a normal mois- 

 ture condition. The next sample must, therefore, alm<»-t certainly 

 he taken a short distance away, and almost invariably this int rodua 

 a change in composition, such that equal moisture contents in two 

 successive samples may not have the same plant value. Usually m 

 agricultural soils or well-mixed potting soils, these variation- may 

 be ignored. Very often in forest soils, however, the changes in 

 composition are very abrupt; in fact there is often no such thing 

 as uniformity of'soil texture, even in a practical sense. The sampling 

 of forest soils, moreover,- is often difficult owing to the presence of 

 rocks which make it impossible to obtain a sample at the desired 

 spot, at least with borers of any description. These mechanical diffi- 

 culties may usually be overcome by the use of pick and shovel, and in 

 careful surveys of the root zones of individual trees or group- such 

 methods will undoubtedly have to be resorted to. 



In practice, it is usually impossible to examine a large number of 

 soil points with sufficient frequency to show even approximately 

 the changes in soil moisture. It is necessary to select, more or 1< 

 arbitrarily, points which seem to represent the average of conditions 

 in the plant formation or forest type under study, and to confine the 

 effort to showing as accurately as possible all the condition- which 

 occur at this point. 



SOIL-WELLS FOR REPRESENTATIVE POINT - 



In view of what has been said, it appears necessary to make provi- 

 sion for establishing some standard conditions under which soil sam- 

 ples shall be taken at permanent stations. The ideal method would 

 undoubtedly be to show the moisture content of a smgle sample o 

 soil from time to time, and it has been suggested that this mu 

 be accomplished bv the periodic weighing of a standard soil sample 

 contained in a porous cup which would be permanently ocated 

 the soil point. This plan involves a number of technical difficulties 

 and is, moreover, wholly untried. The nearest practical approach 

 to the method of a single sample would seem to be in the plat, of 



