The field‐saturated hydraulic conductivityKfscan be obtained from measurements of the long‐time steady flow rates from ring infiltrometers by assuming either that the soil is a “Green and Ampt” soil that has a relationship between hydraulic conductivityKand soil water pressure ψ, such thatK=Kfs, 0>ψ>ψf;K→ 0, ψƒ<ψf, or that the soil is a “Gardner” soil with an exponential relationshipK=Kfsexp(αψ), where α is a constant. It is shown that infiltration into a Green and Ampt soil from a surface source with zero head is the same as that for a Gardner soil with α → ∞ (gravity dominant) and with a surface source at a head |ψfs|. The shape factorGcalculated for Gardner soils using a numerical solution of Richards's equation is used to calculateKfsand α from ring infiltrometer tests based onQ= [aH/G+a/(αG) + πa2]Kfs, whereQis the steady state flow rate,His the constant ponded head, andais the ring radius. The equivalentGfactor for Green and Ampt soils calculated using electric analogue solutions of Laplace's equation is shown to agree very well with the numerical solution. The slope of the linear relationship between the shape factor and the depth of insertion of the ring divided by the radius of the ring is shown to have a s
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