Soil sorptivity is one of the most important soil hydraulic parameters, representing the capacity of soil to absorb and release the soil solution by capillary force. Quantifying soil sorptivity is essential for describing and modeling hydrological and biological processes, and promoting the theoretical research of the unsaturated soil water movement processes, as well as for the determination of rational irrigation and drainage technology parameters. However, obtaining sufficient and reliable soil sorptivity data is expensive and time consuming. Since the measurement is fast and good for the in-site measurement in fields, the disc infiltration method has been paid more attention gradually. The objective of this study was to assess the feasibility of using a disc infiltrometer to determine soil sorptivity in 3 soils with different land uses (vegetable field, grass land and tea garden) and contrasting soil textures. For this purpose, a series of 3-D infiltration experiments were conducted using 2 sizes (in diameter of 10 and 20 cm) of disc infiltrometer under 4 pressure heads (-9, -6, -3, and 0 cm). The performances of Philip, Haverkamp 3-D infiltration and modified Haverkamp 3-D infiltration method were assessed by setting the Vandervaere method as the control. The results showed that the optimum infiltration time (OIT) for sorptivity calculation differed with methods. Among the 4 methods, the optimum infiltration time for Philip method was the shortest, being 30 s. The OIT for the modified Haverkamp 3-D infiltration method was about 240 s, but the whole infiltration process was required to get a reasonable sorptivity value for the Haverkamp 3-D infiltration method. The Haverkamp method was better than the other 2 methods because that the Haverkamp 3-D infiltration method resulted in sorptivity values closest to that of the Vandervaere method. No significant difference in the soil sorptivity determined by infiltrometers was found between different diameter discs. This may indicate that sorptivity measurement is not affected by the disc size. Small disc is thus recommended for the field application considering that small disc is in better contact with soil surface and a smaller quantity of water is required for the measurement. Pressure heads and land use types had interaction on sorptivity rate. The sorptivity rate under 4 pressure heads was not significant at vegetable field (P>0.05), but significant at tea garden and grass land (P<0.05). Except for the pressure head of 0 cm, soil sorptivity was significantly different in the 3 land use types (P<0.05), and the order of measured soil sorptivity among the 3 land uses differed with pressure heads. The soil sorptivity of vegetable field was highest under lower pressure heads (-9 and -6 cm), while that of tea garden and grass land was higher than that of vegetable field under higher pressure heads (-3 cm). This indicated that the difference of soil pore distribution is obvious in different land use types. This study may be instructive in estimating soil hydraulic parameters by disc infiltrometer in hilly area of South China.
