Resistance to water flow in soil and plant. I. Soil resistance in relation to amounts of root: theoretical estimates.
Abstract
The mathematical models of Gardner (1960) and Cowan (1965) are developed to show that the soil matric potential at which rhizosphere resistance becomes appreciable compared with plant resistance depends in particular on the length of root under unit surface area of ground (LA). Known values of LA under field conditions range from about 5-100 cm/cm2 for woody plants, and 50-4000 cm/cm2 for herbaceous plants. According to the relationship between rhizosphere resistance and LA derived from the Gardner and Cowan models, for most herbaceous and some woody species the rhizosphere resistance will remain smaller than the plant resistance (and for some species will not even become appreciable) until near or beyond the permanent wilting point.