J01N£ OF AGRICDLTIAL ISEARCfl 



DEPARTMENT OF AGRICULTURE 



Washington, D. C, October 25, 1915 



Vol. V 



No. 4 



EFFECT OF TEMPERATURE ON MOVEMENT OF WATER 

 VAPOR AND CAPILLARY MOISTURE IN SOILS 



By G. J. BouYOUCOS, 

 Research Soil Physicist, Michigan Agricultural Experiment Station 



INTRODUCTION 

 An investigation of the influence of temperature on the various physi- 

 cal processes in the soil was undertaken by the writer at the Michigan 

 Agricultural Experiment Station. One of the phases of this investi- 

 gation, the effect of temperature on the movement of water vapor and 

 capillary moisture in soils, will be considered in the present paper. 



MOVEMENT OF MOISTURE FROM WARM TO COLD COLUMN OF SOIL OF 

 UNIFORM MOISTURE CONTENT 



A rise of temperature decreases both the surface tension and the vis- 

 cosity of water to the extent shown by the data in Table I. 



Table I. — Relation of temperature to the surface tension and viscosity of water 



It will be noted that the degree of diminution with rise in tempera- 

 ture is considerably greater in the case of viscosity than in that of sur- 

 face tension. 



During the warm part of the year the soil at the upper depths main- 

 tains a rather marked temperature gradient which reverses itself be- 

 tween day and night to the depth that the diurnal amplitude of tem- 

 perature oscillation extends. This diurnal change of temperature 

 gradient occasions an alteration in surface tension and viscosity of the 

 soil moisture, the amount depending upon its variation at the different 

 depths. Since capillary action is said to depend upon surface tension 

 and facility of movement upon viscosity, there should occur an up- 



Joumal of Agriailtural Research. 

 Dept. of Agriculture, Washington, D. C. 

 af 



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Vol. V, No. 4 

 Oct. 25, 191S 

 Mich.— I 



