The application of classical physics transport theory to water movement in soil: development and deficiencies

SUMMARY The development of soil‐water transport theory is essentially that of the application of classical physical theories that were originally derived for the perceived analogous transport of fluids, heat and electricity in continua. Much of soil‐water transport theory was developed by Buckingham at the turn of the century, but it took several decades for it to become well understood and established. An inability to solve partial differential equations with water‐dependent transport coefficients hampered a rigorous analysis and a proper interpretation of early experiments. The theory has been well proven in the laboratory, but application to the field has been less than successful because of hetereogeneity and macropores. More recent theories based on other principles have not yet received adequate testing. Future work should extend the established theory as well as develop and test new ones.