Abstract

Sorptivity (S) is one of the important soil hydraulic parameters, which can be estimated by disc infiltration data at the early stage with one dimensional infiltration theory. With the purpose of understanding the effects of infiltration time (IT) on the estimated S, two sizes (radius of 5 and 2.5 cm) of disc infiltrometer were used to perform disc infiltration under five pressure heads (0, -3, -6, -9, -15 cm) using a packed sandy loam soil. S values for different IT were estimated with White method. Results showed that the estimated S was in general overestimated and it increased with the increase of IT. The relative measurement error as compared with the Parlange method increased with the increase of IT, a behavior that could be well fitted by a logarithmic function. There was a tendency that the relative measurement error decreased with the decrease of pressure head, and the optimized value of IT (IT_OP) in general increased exponentially with decreasing pressure head, ranging from 20 to 75 s for disc radius of 5 cm and 8 to 26 s for disc radius of 2.5 cm. The estimated S values and relative measurement errors for smaller disc were greater than those of larger disc. Attentions should be given to the suitable IT for determining S by White method. Furthermore, the relatively larger disc size should be preferred under the premise of a good hydraulic contact between disc and soil surface.

Key words: Disc infiltrometer, Philip, sorptivity, sandy loam soil.