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Soil-Water Hysteresis: the Domain Theory Extended to Pore Interaction Conditions¹

ABSTRACT

Some inadequacies of the independent domain theory of hysteresis were overcome by modifying an extension to the theory to include two types of pore interactions. In the independent domain theory only the shapes of the pores determined the draining and filling characteristics of each pore. In this extension to the theory the draining and filling of each pore was assumed to depend on the state of neighboring pores as well as the pore geometry. The ratios of changes in water content of the soil during drying and rewetting over a given pressure head range were used to determine the importance of pore interactions and to separate the two types of pore blockage. Primary scanning curve data for porous materials ranging from glass beads to clay loam soil showed that pore blockage against air-entry during drying of a soil near saturation and pore blockage against water-entry during rewetting of a relatively dry soil were the two major types of pore interactions. The curves showing the degree of pore blockage appeared to be dependent only on the water content of the soil. This information in conjunction with a set of scanning curves was used to make satisfactory predictions of the other set of scanning curves.

¹ Contribution no. 342, Soil Research Institute, Canada Dept. of Agriculture, Ottawa, Ontario. Presented before Div. S-1, Soil Science Society of America, Aug. 24, 1970, at Tucson, Ariz.

² Soil Physicist, Soil Research Inst., CDA, Ottawa.

Received for publication September 23, 1970. Accepted for publication December 14, 1970.