RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 129 



Considering only that which is particularly relevant to the prob- 

 lem, it was found by Buckingham that considerably different types 

 of soil show about the same capillary flow under the same condi- 

 tions. A moist and a dry layer of soil were, in these experiments, 

 placed one above the other in direct contact. The amount transferred 

 from the moister to the drier soil in a given time was found to depend 

 almost wholly on their original difference in moisture content; fur- 

 thermore, the greater part of this transfer was accomplished in a 

 very short time. 



A great many methods have been devised for showing the rate of 

 movement of water in soils; but none of these, so far as known, is 

 readily standardized or will produce closely comparable results on 

 duplication with the same soil. This is because the granulation of 

 soil has an important influence on the capillary forces set up. In 

 view of this difficulty, no procedure can be suggested which is more 

 likely to produce reliable comparative data than the following: 



After the completion of the moisture equivalent determination on 

 the centrifugal machine, all water having been extracted which is 

 subject to the force employed (whether this be 100 gravity or 3,000 

 gravity), and the soil being then in a state of compactness which is 

 somewhat close to a standard, add to the unit volume of soil a small 

 standard amount of water, say 10 cubic centimeters; as soon as this 

 has been absorbed in the surface centrifuge again for short periods 

 until the amount added has been extracted, determining the time for 

 this unit process. This should be a measure of the resistance offered 

 by the soil to the passage of a unit amount of water through a unit 

 distance (the distance may be somewhat variable, but correction may 

 be made directly) . 



It would be unwise to leave this very open subject without refer- 

 ence to the possibilities of the electrical conductivity method; for, 

 as Buckingham (116) has shown, there is a close correlation between 

 the conditions affecting electrical conductivity and those affecting 

 water conductivity in a given soil. It would seem that there is also 

 a chance for correlation between heat conductivity and water con- 

 ductivity. 



CHEMICAL ANALYSIS FOR NUTRIENTS. 



It may be said that almost nothing is known as to the quantitative 

 requirements of most plants for the nutrient materials obtainable 

 from the soil with the soil water, and little enough as to the elements 

 which in greater or less quantity are essential for growth. The lack 

 of knowledge with respect to trees is especially glaring, 20 little atten- 

 tion having been paid to the subject because of the almost universal 

 belief that the requirements of trees are satisfied by almost any soil. 



20 The writers do not consider the evidence obtained by the examination of leaf ash and other similarly 

 crude methods even as convincing evidence of qualitative requirements. 



