EESEAKCH METHODS IN STUDY OF FOKEST ENVIRONMENT. 73 



TOTAL-MOISTURE DETERMINATIONS. 



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

 a given point is an exceedingly simple matter, and a vast amount of 

 such work has been done in connection with agricultural investiga- 

 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 very difficult to 

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

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

 ture condition. The next sample must, therefore, almost certainly 

 be taken a short distance away, and almost invariably this introduces 

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

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

 agricultural soils or well-mixed potting soils, these variations 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 groups 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 less 

 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 conditions which 

 occur at this point. 



SOIL-WEIXS FOB REPRESENTATIVE POINTS. 



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

 sion for establishing some standard conditions under which soil sam- 

 ple- :-li;ill be taloMi at permanent stations. The ideal method would 

 undoubtedly be to show the moisture content of a single sample of 

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

 be accomplished by the periodic weighing of a standard soil sample 

 contained in a porous cup which would be permanently located at 

 the -oil point. This plan involves a number of technical difficulties, 

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

 to the method of a single sample would seem to be in the plan of 



