Volume XII JULY, 1922 Part III 



tJOTANiCAR, 



SOME INVESTIGATIONS ON THE ELECTRICAL 

 METHOD OF SOIL MOISTURE DETERMINATION. 



By THOMAS DEIGHTON, M.A., B.Sc. 



(School of Agriculture, Cambridge.) 



(With Six Text-Figures.) 



The investigations described in the following pages had their origin in 

 a desire to find some method of moisture determination in the soil 

 which would not require the taking of samples, with a view to some 

 further experiments on the cultivation of the soil in root-crop pro- 

 duction. 



Tentative work on these hues was commenced in America in 1887 

 by Professor Milton Whitney (i) who employed an earth battery con- 

 sisting of alternate copper and zinc plates buried in the soil, connected 

 through a galvanometer. Later in Bull. No. 6, "Division of Soils," 

 U.S. Dept. Agriculture the same author further develops this method 

 of moisture determination. 



In 1897 M. Whitney and T. H. Means (2) published an accoimt of 

 some experiments in which they determined the specific resistance of 

 various soils, making a correction for packing error, and showed that 

 this varied considerably for different soils. The authors plotted the 

 resistance against the moisture in various soils and found that the curves 

 obtained "agree in the main with an hyperbolic curve except that they 

 are more or less rotated," and they discovered that "it requires from 



1 to 3 per cent, more water to produce the same change in the resistance 

 of some soils than in others." To this paper is appended a table for the 

 reduction of soil resistances to a standard temperature. In the experi- 



;ments a compensating temperature cell was used. 

 C2 The following year F. D. Gardner (3) dealt with the use of under- 

 ground cables on ploughed land and gave results of an extended series 

 ^ of measurements of soil moisture by the electrical method compared 

 c.Jwith determinations by drying on the same plots. The results, though 

 J.-J considered satisfactory by the author, show a mean difference of about 



2 per cent, in the moisture content between the two methods of working. 

 The maximum difference was as high as 4-3 per cent. 



Journ. of Agrio. Soi. xil 15 



