University of California

Thermodynamics of soil moisture


N. E. Edlefsen
Alfred B. C. Anderson

Authors Affiliations

N. E. Edlefsen was Associate Professor of Irrigation and Associate Irrigation Engineer in the Experiment Station; Alfred B. C. Anderson was Junior Irrigation Physicist in the Experiment Station.

Publication Information

Hilgardia 15(2):31-298. DOI:10.3733/hilg.v15n02p031. February 1943.

PDF of full article, Cite this article


Abstract does not appear. First page follows.


The worker who attempts to study the basic principles of thermodynamics with reference to soil moisture has considerable difficulty because both the nomenclature and the method of treatment in existing literature vary greatly. Writers on thermodynamics have usually had in mind specific purposes quite foreign to soil-moisture studies; their conclusions and equations, being adapted to some other particular field, are not easily applied to soil moisture. This paper aims to eliminate at least part of the difficulty and also to make certain helpful original applications. It applies the well-grounded principles of thermodynamics to a study of the soil-moisture system. The first part includes, for the convenience of the reader, some material that can be found scattered in numerous published reports and books. Such material, it is hoped, is here presented in such a way as to be more readily available.

Probably the most useful thermodynamic function, as far as the student of soil moisture is concerned, is free energy. The following treatment has been built, accordingly, around that function. The chief purpose of this paper, aside from the presentation of the basic thermodynamic principles, is to develop quantitative expressions for the dependence of the free energy of soil moisture on such factors as the adsorptive force field that surrounds a soil particle, the hydrostatic pressure on the soil moisture, the dissolved material present, and the temperature.

In mathematical treatments of physical systems, the inexperienced student cannot always distinguish clearly between the parts that result from pure mathematical manipulation and the parts that can be deduced, either directly or indirectly, from experimental measurements.


[1] Adam Neil Kensington. The physics and chemistry of surfaces. 1930. London, England: Oxford University Press. 332p.

[2] Alexander Lyle T., Haring M. M. Vapor pressure—water content relations for certain typical soil colloids. Jour. Phys. Chem. 1936. 40:195-205. DOI: 10.1021/j150371a005 [CrossRef]

[3] Alway F. J. Studies on the relation of the non-available water of the soil to the hygroscopic coefficient. Univ. Nebraska Res. Bul. 1913. 3:1-122.

[4] Alway F. J., Clark V. L. Use of two indirect methods for the determination of the hygroscopic coefficients of soils. Jour. Agr. Res. 1916. 7:345-59.

[5] Alway F. J., Kline M. A., McDole Guy R. Some notes on the direct determination of the hygroscopic coefficient. Jour. Agr. Res. 1917. 11:147-66.

[6] Alway F. J., McDole G. R. Relation of the water retaining capacity of a soil to its hygroscopic coefficient. Jour. Agr. Res. 1917. 9:27-71.

[7] Alway F. J., McDole G. R., Trumbull R. S. Interpretation of field observations on the moistness of the subsoil. Amer. Soc. Agron. Jour. 1918. 10:265-78. DOI: 10.2134/agronj1918.00021962001007-80001x [CrossRef]

[8] Anderson M. S. The heat of wetting of soil colloids. Jour. Agr. Res. 1924. 28:927-35.

[9] Anderson M. S., Fry W. H., Gile P. L., Middleton H. E., Robinson W. O. Absorption by colloidal and non-colloidal soil constituents. U. S. Dept. Agr. Bul. 1922. 1122:1-20.

[10] Anderson M. S., Mattson Sante. Properties of the colloidal soil material. U. S. Dept. Agr. Dept. Bul. 1926. 1452:1-46.

[11] Baver L. D. The relation of exchangeable cations to the physical properties of soils. Amer. Soc. Agron. Jour. 1928. 20:921-41. DOI: 10.2134/agronj1928.00021962002000090005x [CrossRef]

[12] Baver L. D. The effect of the amount and nature of exchangeable cations on the structure of a colloidal clay. Missouri Agr. Exp. Sta. Res. Bul. 1929. 129:1-48.

[13] Baver L. D., Horner G. M. Water content of soil colloids as related to their chemical composition. Soil Sci. 1933. 36:329-53. DOI: 10.1097/00010694-193311000-00001 [CrossRef]

[14] Baver L. D., Winterkorn H. F. Sorption of liquids by soil colloids: II. Surface behavior in the hydration of clays. Soil Sci. 1935. 40:403-19.

[15] Beckett S. H., Blaney H. F., Taylor C. A. Irrigation water requirement studies of citrus and avocado trees in San Diego County, California, 1926 and 1927. California Agr. Exp. Sta. Bul. 1930. 489:1-51. (Out of print.) http://archive.org/details/irrigationwaterr489beck

[16] Beckett S. H., Dunshee C. F. Water requirements of cotton on sandy loam soils in southern San Joaquin Valley. California Agr. Exp. Sta. Bul. 1932. 537:1-48. http://archive.org/details/waterrequirement537beck

[17] Blanck E. Handbuch der Bodenlehre. VI. Die physikalische Beschaffenheit des Bodens. 1930. Berlin, Germany: J. Springer. 423p.

[18] Bodman G. B., Day P. R. Thermoelectric method of determining the freezing points of soils. Soil Sci. Soc. Amer. Proc. 1937. 2:65-71. DOI: 10.2136/sssaj1938.036159950002000C0009x [CrossRef]

[19] Bodman G. B., Edlefsen N. E. Field measurement of the permeability to water of a silt loam soil at University Farm, Davis, California. Science. 1933. 78:355 DOI: 10.1126/science.78.2025.355 [CrossRef]

[20] Bodman G. B., Edlefsen N. E. The soil-moisture system. Soil Sci. 1934. 38:425-44. DOI: 10.1097/00010694-193412000-00001 [CrossRef]

[21] Bodman G. B., Mahmud A. J. The use of the moisture equivalent in the textural classification of soils. Soil Sci. 1932. 33:363-74. DOI: 10.1097/00010694-193205000-00003 [CrossRef]

[22] Bordas J., Mathieu G. Recherches sur le force de succion des sols et l’irrigation souterraine. Ann. Agron. 1930. 47:192-235.

[23] Bouyoucos George J. Classification and measurement of the different forms of water in the soil by means of the dilatometer method. Michigan Agr. Exp. Sta. Tech. Bul. 1917. 36:1-48.

[24] Bouyoucos George J., McCool M. M. The freezing point method as a new means of measuring the concentration of the soil solution directly in the soil. Michigan Agr. Exp. Sta. Tech. Bul. 1916. 24:1-44.

[25] Boynton Damon. Capillary tension as a measure of the pore space unoccupied by water in some dense orchard subsoils. Soil Sci. 1939. 47:347-52. DOI: 10.1097/00010694-193905000-00001 [CrossRef]

[26] Bradfield R. The chemical nature of colloidal clay. Amer. Soc. Agron. Jour. 1925. 17:253-70. DOI: 10.2134/agronj1925.00021962001700050001x [CrossRef]

[27] Briggs L. J. The mechanics of soil moisture. U. S. Dept. Agr. Bur. Soils. Bul. 1897. 10:1-24.

[28] Briggs L. J., McLane J. W. The moisture equivalent of soils. U. S. Dept. Agr. Bur. Soils Bul. 1907. 45:1-23.

[29] Briggs L. J., Shantz H. L. The wilting coefficient for different plants and its indirect determination. U. S. Dept. Agr. Bur. Plant Indus. Bul. 1912. 230:1-83.

[30] Buckingham E. Studies on the movement of soil moisture. U. S. Dept. Agr. Bur. Soils Bul. 1907. 38:1-61.

[31] Burd J. S., Martin J. C. Secular and seasonal changes in soils. Hilgardia. 1931. 5(15):455-509. DOI: 10.3733/hilg.v05n15p455 [CrossRef]

[32] Burr W. W. Storing moisture in the soil. Nebraska Agr. Exp. Sta. Bul. 1910. 114:1-51.

[33] Caldwell Joseph Stuart. The relation of environmental conditions to the phenomenon of permanent wilting in plants. Physiol. Res. 1913. 1:1-56.

[34] Cameron F. K. The soil solution. 1911. Easton, Pa.: Chem. Pub. Co. 136p.

[35] Cameron F. K., Gallagher F. E. Moisture content and physical condition of soils. U. S. Dept. Agr. Bur. Soils Bul. 1908. 50:1-70.

[36] Coke J. E., Doneen L. D. Irrigation of sugar beets. Pacific Rural Press. 1937. 133:370-71.

[37] Conrad J. P., Veihmeyer F. J. Root development and soil moisture. Hilgardia. 1929. 4(4):113-34. (Out of print.) DOI: 10.3733/hilg.v04n04p113 [CrossRef]

[38] Coutts J. R. H. “Single-value” soil constants: a study of the significance of certain soil constants. Jour. Agr. Sci. 1932. 22:200-2. DOI: 10.1017/S0021859600053181 [CrossRef]

[39] Crowther E. M., Puri A. N. The indirect measurement of the aqueous vapour pressure of capillary systems by the freezing-point depression of benzene. Roy. Soc. London Proc. ser. A. 1924. 106:232-42. DOI: 10.1098/rspa.1924.0065 [CrossRef]

[40] Doneen L. D., Porter D. R., MacGillivray J. H. Irrigation studies with watermelons. Amer. Soc. Hort. Sci. Proc. 1939. 37:821-24.

[41] Duclaux J. The osmotic pressure of colloidal solutions. Colloid. Chem. 1926. 1:515-24.

[42] Edlefsen N. E. Forces acting on soil moisture in relation to other fundamental functions. Amer. Geophys. Union Trans. 1932. 13:328-30. DOI: 10.1029/TR013i001p00328 [CrossRef]

[43] Edlefsen N. E. A glass wool cell for measuring aqueous vapor pressure of soils. Rev. Sci. Instruments. 1933. 4:345-46. DOI: 10.1063/1.1749138 [CrossRef]

[44] Edlefsen N. E. A review of results of dielectric methods of measuring moisture present in materials. Agr. Engin. 1933. 14:243-44.

[45] Edlefsen N. E. Capillary potential theory of flow in soils 1934. pp.22-34. Amer. Soc. Mech. Engin., Aeronautics and Hydraulics Div., Preprinted Papers, Summer Meeting

[46] Edlefsen N. E. A new method of measuring the aqueous vapor pressure of soils. Soil Sci. 1934. 38:29-35. DOI: 10.1097/00010694-193407000-00003 [CrossRef]

[47] Edlefsen N. E. Effect of soil moisture characteristics on irrigation requirements. Agr. Engin. 1937. 18:247-50.

[48] Ewing Dwight T., Spurway C. H. The density of water adsorbed on silica gel. Amer. Chem. Soc. Jour. 1930. 52:4635-41. DOI: 10.1021/ja01375a002 [CrossRef]

[49] Ewing Scott. The movement of saturated water vapor through quartz flour. Soil Sci. 1922. 13:57-61. DOI: 10.1097/00010694-192201000-00006 [CrossRef]

[50] Fisher E. A. The phenomena of adsorption in soils: a critical discussion of the hypotheses put forward. Faraday Soc. Trans. 1922. 17(2):305-16. DOI: 10.1039/tf9221700305 [CrossRef]

[51] Fisher E. A. Some moisture relations of colloids. I. A comparative study of the rates of evaporation of water from wool, sand and clay. Roy. Soc. London Proc., ser. A. 1923. 103:139-61. DOI: 10.1098/rspa.1923.0046 [CrossRef]

[52] Fisher E. A. The freezing of water in capillary systems: a critical discussion. Jour. Phys. Chem. 1924. 28:36-67.

[53] Fisher R. A. On the capillary forces in an ideal soil. Jour. Agr. Sci. 1926. 16:492-505. DOI: 10.1017/S0021859600007838 [CrossRef]

[54] Fisher R. A. Further note on the capillary forces in an ideal soil. Jour. Agr. Sci. 1928. 18:406-10. DOI: 10.1017/S0021859600019432 [CrossRef]

[55] Gardner W. The capillary potential and its relation to soil-moisture constants. Soil Sci. 1920. 10:357-59. DOI: 10.1097/00010694-192011000-00003 [CrossRef]

[56] Gardner Willard. A capillary transmission constant and methods of determining it experimentally. Soil Sci. 1920. 10:103-26. DOI: 10.1097/00010694-192008000-00002 [CrossRef]

[57] Gardner W. Note on the dynamics of capillary flow. Physiol. Revs., ser. 2. 1921. 18:206-9. DOI: 10.1103/PhysRev.18.206 [CrossRef]

[58] Gardner W., Israelsen O. W., Edlefsen N. E., Clyde H. S. The capillary potential function and its relation to irrigation practice. Physiol. Revs., ser. 2. 1922. 20:196

[59] Gardner W., Widtsoe J. A. The movement of soil moisture. Soil Sci. 1921. 11:215-32. DOI: 10.1097/00010694-192103000-00003 [CrossRef]

[60] Glasstone Samuel. Recent advances in physical chemistry. 1933. 2d ed. Philadelphia, Pa.: P. Blakiston’s Son &; Co. 498p.

[61] Gortner R. A., Gortner W. A. The cryoscopic method for the determination of “bound water.”. Jour. Gen. Physiol. 1934. 17:327-39. DOI: 10.1085/jgp.17.3.327 [CrossRef]

[62] Greathouse Glenn A. Unfreezable and freezable water equilibrium in plant tissues as influenced by sub-zero temperatures. Plant Physiol. 1935. 10:781-88. DOI: 10.1104/pp.10.4.781 [CrossRef]

[63] Greaves J. E., Hirst C. T. Composition of the irrigation waters of Utah. Utah Agr. Exp. Sta. Bul. 1918. 163:1-43.

[64] Green W. H., Ampt G. A. Studies on soil physics. I. The flow of air and water through soils. Jour. Agr. Sci. 1911. 4:1-24. DOI: 10.1017/S0021859600001441 [CrossRef]

[65] Green W. H., Ampt G. A. Studies on soil physics. II. The permeability of an ideal soil to air and water. Jour. Agr. Sci. 1912. 5:1-26. DOI: 10.1017/S0021859600001751 [CrossRef]

[66] Guye Ch. Eug. Considérations théoriques sur la propagation de l’imbibition. Helvetica Physica Acta. 1934. 7(fasc. 6 and 7):584-604.

[67] Guye Ch. Eug. Quelques cas particuliers de propagation de l’imbibition. Helvetica Physica Acta. 1934. 7(fasc. 8):850-55.

[68] Guye Ch. Eug., Saini H. Contribution expérimentale a l’étude énergétique des phénomènes d’imbibition. Helvetica Physica Acta. 1929. 2(fasc. 9):445-91.

[69] Hackett F. E. The rate of ascent of liquids through granular media. Faraday Soc. Trans. 1922. 17(2):260-67. DOI: 10.1039/tf9221700260 [CrossRef]

[70] Haines W. B. Studies in physical properties of soils: V. The hysteresis effect in capillary properties and the modes of moisture distribution associated therewith. Jour. Agr. Sci. 1930. 20:97-116.

[71] Heck A. F. A soil hygrometer for irrigated cane lands of Hawaii. Amer. Soc. Agron. Jour. 1934. 26:274-78. DOI: 10.2134/agronj1934.00021962002600040003x [CrossRef]

[72] Hendricks S. B., Fry W. H. The results of x-ray and microscopic examinations of soil colloids. Soil Sci. 1930. 29:457-79. DOI: 10.1097/00010694-193006000-00003 [CrossRef]

[73] Hendrickson A. H., Veihmeyer F. J. Irrigation experiments with peaches in California. California Agr. Exp. Sta. Bul. 1929. 479:1-56. (Out of print.) http://archive.org/details/irrigationexperi47995hend

[74] Hendrickson A. H., Veihmeyer F. J. Irrigation experiments with prunes. California Agr. Exp. Sta. Bul. 1934. 573:1-44. https://archive.org/details/irrigationexperi573hend

[75] Hendrickson A. H., Veihmeyer F. J. The irrigation of pears on a clay adobe soil. Amer. Soc. Hort. Sci. Proc. 1937. 34:224-26.

[76] Hilgard E. W. Soils. 1911. New York, N. Y.: The Macmillan Co. 593p.

[77] Hoagland D. R. The freezing-point method as an index of variations in the soil solution due to season and crop growth. Jour. Agr. Res. 1918. 12:369-95.

[78] Hoagland D. R. The soil solution in relation to the plant. Faraday Soc. Trans. 1922. 17(2):249-54. DOI: 10.1039/tf9221700249 [CrossRef]

[79] Hoseh Mordecai. Heat of wetting of some colloids at different moisture contents. Soil Sci. 1937. 43:257-75. DOI: 10.1097/00010694-193704000-00003 [CrossRef]

[80] Hudson C. S. The freezing of pure liquids and solutions under various kinds of positive and negative pressure and the similarity between osmotic and negative pressure. Physiol. Revs. 1906. 22:257-64.

[81] Israelsen O. W. The application of hydrodynamics to irrigation and drainage problems. Hilgardia. 1927. 2(14):479-528. DOI: 10.3733/hilg.v02n14p479 [CrossRef]

[82] Israelsen O. W., West F. L. Water holding capacity of irrigated soils. Utah Agr. Exp. Sta. Bul. 1922. 183:1-24.

[83] Janert H. Kationenaustausch und Wasseradsorption von Böden. Ztschr. f. Pflanzenernähr., Düngung u. Bodenk. 1934. 34 A:100-8. DOI: 10.1002/jpln.19340340106 [CrossRef]

[84] Jennings D. S., Gardner Willard, Israelsen O. W. Technical studies of the physical and physico-chemical properties and processes in soil. Cardon, P. V. Summary of report of progress. 1934. 250:Utah Agr. Exp. Sta. Bul. 60p.

[85] Jennings D. S., Darrel Peterson J. Drainage and irrigation, soil, economic, and social conditions, Delta area, Utah: division 2, soil conditions. Utah Agr. Exp. Sta. Bul. 1935. 256:1-67.

[86] Jenny Hans. Simple kinetic theory of ionic exchange. I. Ions of equal valency. Jour. Phys. Chem. 1936. 40:501-17. DOI: 10.1021/j150373a010 [CrossRef]

[87] Joseph A. F., Martin F. J. The moisture equivalent of heavy soils. Jour. Agr. Sci. 1923. 13:49-59. DOI: 10.1017/S002185960000321X [CrossRef]

[88] Katz J. R. The laws of swelling. Faraday Soc. Trans. 1933. 29:279-300. DOI: 10.1039/tf9332900279 [CrossRef]

[89] Keen B. A. A quantitative relation between soil and the soil solution brought out by freezing-point determinations. Jour. Agr. Sci. 1919. 9:400-15. DOI: 10.1017/S0021859600005244 [CrossRef]

[90] Keen B. A. The system soil—soil moisture. Faraday Soc. Trans. 1922. 17(2):228-43. DOI: 10.1039/tf9221700228 [CrossRef]

[91] Keen Bernard A. The physical properties of the soil. 1931. New York, N. Y.: Longmans, Green and Co. 380p.

[92] Keen B. A., Raczkowski H. The relation between the clay content and certain physical properties of a soil. Jour. Agr. Sci. 1921. 11:441-49. DOI: 10.1017/S0021859600004469 [CrossRef]

[93] Kelley W. P., Dore W. H., Brown S. M. The nature of the base-exchange material of bentonite, soils, and zeolites, as revealed by chemical investigation and x-ray analysis. Soil Sci. 1931. 31:25-55. DOI: 10.1097/00010694-193101000-00003 [CrossRef]

[94] Kelley W. P., Jenny Hans. The relation of crystal structure to base exchange and its bearing on base exchange in soils. Soil Sci. 1936. 41:367-82. DOI: 10.1097/00010694-193605000-00008 [CrossRef]

[95] Kelley W. P., Jenny Hans, Brown S. M. Hydration of minerals and soil colloids in relation to crystal structure. Soil Sci. 1936. 41:259-74. DOI: 10.1097/00010694-193604000-00002 [CrossRef]

[96] King F. H. Principles and conditions of the movements of ground water. U. S. Geol. Survey Ann. Rept. 1898. 19(pt. 2):59-294.

[97] King F. H. A textbook on physics of agriculture. 1907. Madison, Wis.: Published by the author. 604p.

[98] Kuhn Alfred. Ueberblick unserer jetzigen Kenntnisse über Wasserbindung in Kolloiden. Kolloid Ztschr. 1924. 35:275-94. DOI: 10.1007/BF01423812 [CrossRef]

[99] Lamb Arthur B., Coolidge A. S. The heat of absorption of vapors on charcoal. Amer. Chem. Soc. Jour. 1920. 42:1146-70. DOI: 10.1021/ja01451a010 [CrossRef]

[100] Langmuir I. The constitution and fundamental properties of solids and liquids. Amer. Chem. Soc. Jour. 1916. 38:2221-95. DOI: 10.1021/ja02268a002 [CrossRef]

[101] Langmuir I. The adsorption of gases on plane surfaces of glass, mica and platinum. Amer. Chem. Soc. Jour. 1918. 40:1361-403. DOI: 10.1021/ja02242a004 [CrossRef]

[102] Linebarger C. E. On the heat evolved when liquids are brought in contact with powders. Phys. Rev. 1901. 13:48-54.

[103] Linford L. B. The relation of light to soil moisture phenomena. Soil Sci. 1926. 22:233-52. DOI: 10.1097/00010694-192609000-00043 [CrossRef]

[104] Linford Leon B. Soil moisture phenomena in a saturated atmosphere. Soil Sci. 1929. 29:227-37. DOI: 10.1097/00010694-193003000-00006 [CrossRef]

[105] Livingston B. E. Plant water relations. Quart. Rev. Biol. 1927. 2:494-515. DOI: 10.1086/394286 [CrossRef]

[106] Livingston B. E., Koketsu R. The water-supplying power of the soil as related to the wilting of plants. Soil Sci. 1920. 9:469-85. DOI: 10.1097/00010694-192006000-00004 [CrossRef]

[107] Loomis W. E., Ewan L. M. Hydrotropic responses of roots in soil. Bot. Gaz. 1936. 97:728-43. DOI: 10.1086/334600 [CrossRef]

[108] Lynde C. J., Dupre H. A. On a new method of measuring the capillary lift of soils. Amer. Soc. Agron. Jour. 1913. 5:107-16. DOI: 10.2134/agronj1913.00021962000500020007x [CrossRef]

[109] McGeorge W. T., Wharton M. F. The movement of salt (alkali) in lettuce and other truck beds under cultivation. Arizona Agr. Exp. Sta. Bul. 1936. 152:355-438.

[110] Middleton Howard E. Factors influencing binding power of soil colloids. Jour. Agr. Res. 1924. 28:499-513.

[111] Moore Ross E. Water conduction from shallow water tables. Hilgardia. 1939. 12(6):383-426. DOI: 10.3733/hilg.v12n06p383 [CrossRef]

[112] Odén Sven. Note on the hygroscopicity of clay and the quantity of water adsorbed per surface-unit. Faraday Soc. Trans. 1922. 17(2):244-48. DOI: 10.1039/tf9221700244 [CrossRef]

[113] Oppenheimer H. R. Kritische Betrachtungen zu den Saugkraftmessungen von Ursprung und Blum. Sonderabdruck aus den Ber. der Deut. Bot. Gesell., Jahrgang. 1930. 68:130-40.

[114] Parker F. W. The effect of finely divided material on the freezing points of water, benzene, and nitrobenzene. Amer. Chem. Soc. Jour. 1921. 43:1011-18. DOI: 10.1021/ja01438a005 [CrossRef]

[115] Parker F. W. The classification of soil moisture. Soil Sci. 1922. 13:43-54. DOI: 10.1097/00010694-192201000-00004 [CrossRef]

[116] Parks G. J. On the heat evolved or absorbed when a liquid is brought in contact with a finely divided solid. London, Edinb. and Dublin Phil. Mag. and Jour. Sci. (VI). 1902. 4:240-53.

[117] Parks G. J. On the thickess of the liquid film formed by condensation at the surface of a solid. London, Edinb. and Dublin Phil. Mag. and Jour. Sci. (VI). 1903. 5:517-23.

[118] Patrick W. A., Grimm F. V. Heat of wetting of silica gel. Amer. Chem. Soc. Jour. 1921. 43:2144-50. DOI: 10.1021/ja01443a002 [CrossRef]

[119] Patten H. E., Gallagher F. E. Absorption of vapors and gases by soils. U. S. Dept. Agr. Bur. Soils Bul. 1908. 51:1-50.

[120] Porter A. W., Rao P. A. M. The law of capillary flow in the case of colloids. Faraday Soc. Trans. 1927. 23:311-14. DOI: 10.1039/tf9272300311 [CrossRef]

[121] Proebsting E. L. Concentrations of certain constituents of the soil solution under orchard conditions. Hilgardia. 1930. 5(3):35-59. DOI: 10.3733/hilg.v05n03p035 [CrossRef]

[122] Puri A. N. A critical study of the hygroscopic coefficient of soil. Jour. Agr. Sci. 1925. 15:272-83. DOI: 10.1017/S0021859600006729 [CrossRef]

[123] Puri A. N., Crowther E. M., Keen B. A. The relation between the vapour pressure and water content of soils. Jour. Agr. Sci. 1925. 15:68-88. DOI: 10.1017/S002185960000558X [CrossRef]

[124] Puri A. N., Hoon R. C. Physical characteristics of soils: III. Heat of wetting. Soil Sci. 1939. 47:415-23. DOI: 10.1097/00010694-193905000-00010 [CrossRef]

[125] Richards L. A. The usefulness of capillary potential to soil moisture and plant investigators. Jour. Agr. Res. 1928. 37:719-42.

[126] Richards L. A. Capillary conduction of liquids through porous mediums. Physics. 1931. 1:318-33. DOI: 10.1063/1.1745010 [CrossRef]

[127] Richards L. A., Gardner W. Tensiometers for measuring the capillary tension of soil water. Amer. Soc. Agron. Jour. 1936. 28:352-58. DOI: 10.2134/agronj1936.00021962002800050002x [CrossRef]

[128] Richards Sterling J. Soil moisture content calculations from capillary tension records 1938. pp.57-64. Cornell Univ. Graduate School Diss.

[129] Rideal Eric K. An introduction to surface chemistry. 1926. London, England: Cambridge Univ. Press. 336p.

[130] Robbins W. Rei. Relation of nutrient salt concentration to growth of the tomato and to the incidence of blossom-end rot of the fruit. Plant Physiol. 1937. 12:21-50. DOI: 10.1104/pp.12.1.21 [CrossRef]

[131] Robinson Gilbert W. Soils, their origin, constitution, and classification. 1932. London, England: Thomas Murby &; Co. 390p.

[132] Robinson W. O. The absorption of water vapor by soil colloids. Jour. Phys. Chem. 1922. 26:647-53. DOI: 10.1021/j150223a005 [CrossRef]

[133] Rogers W. S. The relation of soil moisture to plant growth, illustrated by moisture meter experiments with strawberries 1935. pp.111-20. East Malling Res. Sta. Ann. Rept.

[134] Rogers W. S. A soil moisture meter. Jour. Agr. Sci. 1935. 25:326-43. DOI: 10.1017/S0021859600010005 [CrossRef]

[135] Rose Gustav. Ueber die Fehler, welche in der Bestimmung des specifischen Gewichtes der Körper entstehen, wenn man dieselben im Zustande der feinsten Vertheilung wägt. Ann. der Phys. u. Chem. ser. 2. 1848. 149(73):1-18. DOI: 10.1002/andp.18481510902 [CrossRef]

[136] Ross C. S., Shannon E. V. The minerals of bentonite and related clays and their physical properties. Amer. Ceramic Soc. Jour. 1926. 9:77-96. DOI: 10.1111/j.1151-2916.1926.tb18305.x [CrossRef]

[137] Russell E. J. A general survey of the physico-chemical problems relating to the soil. Faraday Soc. Trans. 1922. 17(2):219-23. DOI: 10.1039/tf9221700219 [CrossRef]

[138] Schofield R. K. The pF of the water in soil. Soil Sci. 3d Internatl. Cong. Trans. 1935. 2:37-48.

[139] Schofield R. K., Da Costa J. V. B. The determination of the pF at permanent wilting and at the moisture equivalent by the freezing point method. Soil Sci. 3d Internatl. Cong. Trans. 1935. 1:6-10.

[140] Schofield R. K., Rideal E. K. Kinetic theory of surface films. Pts. I and II. Roy. Soc. London, Proc., ser. A. 1925-1926. 109:57-77. 110: 167-77 DOI: 10.1098/rspa.1925.0107 [CrossRef]

[141] Scofield Carl S. The effect of absorption by plants on the concentration of the soil solution. Jour. Agr. Res. 1927. 35:745-56.

[142] Scofield Carl S., Wright Coulsen C. The water relations of Yakima Valley soil. Jour. Agr. Res. 1928. 37:65-85.

[143] Shaw C. F. The normal moisture capacity of soils. Soil Sci. 1927. 23:303-17. DOI: 10.1097/00010694-192704000-00004 [CrossRef]

[144] Shaw C. F., Smith A. Maximum height of capillary rise starting with soil at capillary saturation. Hilgardia. 1927. 2(11):399-409. (Out of print.) DOI: 10.3733/hilg.v02n11p399 [CrossRef]

[145] Shereshefsky J. Leon. Study of the vapor pressures in small capillaries. 1926. John Hopkins Univ. Diss. 16p.

[146] Shreve Forrest, Turnage W. V. The establishment of moisture equilibrium in soil. Soil Sci. 1936. 41:351-55. DOI: 10.1097/00010694-193605000-00005 [CrossRef]

[147] Shull Chas. A. Osmotic phenomena. Faraday Soc. Trans. 1922. 17(2):255-59. DOI: 10.1039/tf9221700255 [CrossRef]

[148] Simon A., Schmidt Th. Ueber Eisenoxydhydrate und Eisenoxyde (in Zsigmondy-Festschrift). Kolloid Ztschr. 1925. 36:65-80. DOI: 10.1007/BF01451941 [CrossRef]

[149] Slichter C. S. Theoretical investigations of the motion of ground water. U. S. Geol. Survey Ann. Rept. 1897-1898. 19:295-384.

[150] Smith W. O. The final distribution of retained liquid in an ideal uniform soil. Physics. 1933. 4:425-38. DOI: 10.1063/1.1745156 [CrossRef]

[151] Smith W. O., Foote P. D., Busang P. F. Capillary rise in sands of uniform spherical grains. Physics. 1931. 1:18-26. DOI: 10.1063/1.1744981 [CrossRef]

[152] Taylor C. A., Furr J. R. The effect of decreasing soil moisture supply on size of lemon fruits. Amer. Soc. Hort. Sci. Proc. 1936. 33:71-81.

[153] Thomas Moyer D. Aqueous vapor pressure of soils. Soil Sci. 1921. 11:409-34. DOI: 10.1097/00010694-192106000-00001 [CrossRef]

[154] Thomas Moyer D. Aqueous vapor pressure of soils: II. Studies in dry soils. Soil Sci. 1924. 17:1-18.

[155] Thomas M. D., Harris K. The moisture equivalent of soils. Soil Sci. 1926. 21:411-24. DOI: 10.1097/00010694-192606000-00001 [CrossRef]

[156] Van Bemmelen J. M. Die Absorption. 1910. Germany: Dresden. 548p.

[157] Veihmeyer F. J. Some factors affecting the irrigation requirements of deciduous orchards. Hilgardia. 1927. 2(6):125-291. (Out of print.) DOI: 10.3733/hilg.v02n06p125 [CrossRef]

[158] Veihmeyer F. J. Annual report of Committee on Physics of Soil Moisture. (Interpretation of soil-moisture problems by means of energy changes.). Amer. Geophys. Union Trans. Pt. 1937. 2:302-18. DOI: 10.1029/TR018i002p00302 [CrossRef]

[159] Veihmeyer F. J., Edlefsen N. E. Water in soils and its movement. Union Internatl. de Géodésique et Géophys. Assoc. Internatl. d’Hydrologie Scientifique, Bul. 1936. 22:355-65.

[160] Veihmeyer F. J., Edlefsen N. E. Interpretation of soil-moisture problems by means of energy changes. Amer. Geophys. Union Trans. Pt. 1937. 2:302-8. DOI: 10.1029/TR018i002p00302 [CrossRef]

[161] Veihmeyer F. J., Hendrickson A. H. Soil moisture conditions in relation to plant growth. Plant Physiol. 1927. 2:71-82. DOI: 10.1104/pp.2.1.71 [CrossRef]

[162] Veihmeyer F. J., Hendrickson A. H. Soil moisture at permanent wilting of plants. Plant Physiol. 1928. 3:355-57. DOI: 10.1104/pp.3.3.355 [CrossRef]

[163] Veihmeyer F. J., Hendrickson A. H. The moisture equivalent as a measure of field capacity of soil. Soil Sci. 1931. 32:181-93. DOI: 10.1097/00010694-193109000-00003 [CrossRef]

[164] Veihmeyer F. J., Israelsen O. W., Conrad J. P. The moisture equivalent as influenced by the amount of soil used in its determination. California Agr. Exp. Sta. Tech. Paper. 1924. 16:1-65. (Out of print.)

[165] Veihmeyer F. J., Oserkowsky J., Tester K. B. Some factors affecting the moisture equivalent of soils. Soil Sci. Ist Internatl. Cong. Proc. and Papers. 1928. 1:512-34.

[166] Wadsworth H. A. Some factors influencing the heat of wetting of soils. Soil Sci. 1939. 47:385-90. DOI: 10.1097/00010694-193905000-00006 [CrossRef]

[167] Waele A. de. The manifestation of interfacial forces in dispersed systems. Jour. Amer. Chem. Soc. 1926. 48:2760-76. DOI: 10.1021/ja01690a002 [CrossRef]

[168] Walker Albert C. Moisture in textiles. Bell System Tech. Jour. 1937. 16:228-46. DOI: 10.1002/j.1538-7305.1937.tb03572.x [CrossRef]

[169] Washburn E. W., Heuse E. O. The measurement of vapor pressure lowering by air saturation method. Amer. Chem. Soc. Jour. 1915. 37:309-21. DOI: 10.1021/ja02271a009 [CrossRef]

[170] Widtsoe John A. Principles of irrigation practice. 1914. New York, N. Y.: The Macmillan Co. 496p.

[171] Winterkorn H. F. Studies on the surface behavior of bentonites and clays. Soil Sci. 1936. 41:25-32. DOI: 10.1097/00010694-193601000-00003 [CrossRef]

[172] Winterkorn Hans, Baver L. D. Sorption of liquids by soil colloids: I. Liquid intake and swelling by soil colloidal materials. Soil Sci. 1934. 38:291-98. DOI: 10.1097/00010694-193410000-00004 [CrossRef]

[173] Work R. A., Lewis M. R. Moisture equivalent, field capacity, and permanent wilting percentage and their ratios in heavy soils. Agr. Engin. 1934. 15:1-20.

[174] Work R. A., Lewis M. R. The relation of soil moisture to pear tree wilting in a heavy clay soil. Amer. Soc. Agron. Jour. 1936. 28:124-34. DOI: 10.2134/agronj1936.00021962002800020005x [CrossRef]

[175] Wyckoff R. D., Botset H. G., Muskat M. Flow of liquids through porous media under the action of gravity. Physics. 1932. 3:90-113. DOI: 10.1063/1.1745087 [CrossRef]

Edlefsen N, Anderson A. 1943. Thermodynamics of soil moisture. Hilgardia 15(2):31-298. DOI:10.3733/hilg.v15n02p031
Webmaster Email: wsuckow@ucanr.edu