RELATION OF MOVEMENT OF WATER IN A SOIL TO 

 ITS HYGROSCOPICITY AND INITIAL MOISTNESS ' 



By Frederick J. Alway, Chief of Division of Soils, and Guy R. McDolE, Assistant 

 in Soils, Agricultural Experiment Station of the University of Minnesota 



INTRODUCTION 



The rate and distance of the capillary rise of water in soils have been 

 determined in many laboratory investigations; but where the ground 

 water is at a considerable distance below the surface, as is generally 

 the case, these factors appear to be of little practical importance (2, 

 p. 67).^ In contrast with the capillary rise, the downward penetration 

 of definite amounts of water has received very little attention. In the 

 experiments on both subjects the soils have usually been employed in 

 an air-dry state, a condition not met with in nature at depths below 

 the surface few inches, as plant roots are not able to reduce the soil 

 moisture to any such low point. In none of the experiments has the 

 relative hygroscopicity of the soils been considered. 



In the studies reported below we have considered both the hygro- 

 scopicity of the soils as expressed by their hygroscopic coefficients and 

 their initial moistness. Most of them were employed in three moisture 

 conditions — viz, with amounts of water equal to 0.5, i, and 1.5 times 

 the hygroscopic coefficient. 



In the case of all our soils we have determined the moisture equivalents 

 also, and in the discussion considered the relation of the movement of 

 water in a soil to this value as well as to the hygroscopic coefficient. 

 However, we give chief prominence to the latter, for the reason that the 

 experiments were planned on the basis of the hygroscopic coefficients, 

 the moisture equivalents being first determined only some time after the 

 experiments had been completed, and for the additional reason that in 

 our field studies only the hygroscopic coefficients had been determined. 

 x\s the two values for any soil have been shown to bear a more or less 

 definite relation to one another (6, p. 65; 3, p. 842), it is largely a matter 

 of personal preference as to which is used as a single valued expression 

 of soil texture. 



Our viewpoint has been not that of the irrigationist nor that of the 

 humid-land farmer with sharply rolling or sloping fields or an impervious 

 soil causing losses through run-off, but that of the dry-land farmer whose 

 crop returns depend chiefly upon the amount and the distribution of the 

 precipitation. Our interest has lain not in the rate at which water can 



' The work reported in this paper was carried out in 191 2 and 1913 at the Nebraska Agricultural Experi- 

 ment Station, where the authors were, respectively. Chemist and Research Assistant in Chemistry. 

 2 Reference is made by number to " Literature cited," p. 427-428. 



Journal of Agricultural Research, Vol. X, No. 8 



Washington. D. C. Aug. 20, 1917 



jm Key No. Minn.— 18 



(391) 



