利用圆盘入渗仪测定不同土地利用类型土壤吸渗率

探讨利用圆盘入渗仪测定不同利用类型土壤吸渗率的适用性,该文选用盘径分别为10和20 cm的圆盘入渗仪对3种利用土壤(菜地、草地和茶园)在0、-3、-6、-9 cm 4个压力水头下的吸渗过程进行测定。研究以Vandervaere法为参考方法,对Philip法、Haverkamp三维吸渗法、Haverkamp三维吸渗改进法的适用性进行比较分析。结果表明:吸渗率的不同计算公式所适应的吸渗过程时间尺度不同,且Haverkamp三维吸渗法所得吸渗率值与参考方法最接近。盘径对吸渗率测定差异的影响不显著。除0 cm压力水头外,不同利用类型土壤吸渗率差异显著,且不同压力水头下测得3种土壤吸渗率大小排序不同。当压力水头为-9和-6 cm时,菜地吸渗率(0.0104和0.0119 cm/s0.5)显著高于茶园(0.0017和0.0025 cm/s0.5)(P0.05);当压力水头为-3 cm时,茶园吸渗率(0.0370 cm/s0.5)显著高于菜地和草地(0.0147和0.0132 cm/s0.5)(P0.05)。该研究可为南方丘陵区土壤水力参数的测定提供理论依据。

Measurement of soil sorptivity rate under different land uses by disc infiltrometer

Abstract: 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.