Two diameters of disc infiltrometer (5 cm and 10 cm) and two distinctly textured soil (Yangling caly soil and Shenmu sandy loam soil) were used to carry out dis c 3D laboratory infiltration experiment under five pressure heads(-1,-3,-6,-9 ,-12 cm H2O). Vandervaere formula was chosen as standard model, and then the time scales of determining soil sorptivety by Philip formula were analyzed accor ding to Vandervaere equation. The results are as followed, for the two textured soil, soil sorptivety reduces as pressure heads decrease at the same disc diame ter; soil sorptivety becomes bigger as the disc diameter gets smaller. The soil sorptivety of Shenmu soil is obviously bigger than that of Yangling. The soil so rptivety of the two kinds of soil is nearly overrated. The overrated values of s oil sorptivety decrease as pressure heads reduce. That is to say, the veracity o f estimating soil sorptivety is higher as pressure heads become smaller within t he chosen time. For Yangling soil, the proper time scales of determining soil so rptivety by Philip equation under the situation that the disc diameter is 5cm wi th -12 cm H2O and the disc diameter is 10 cm with -9 cm H2O and -12 cm H2O are 30～40 s and 40～50 s respectively, while the proper time scales in other s ituation should be less than 30 s. For Shenmu soil, the proper time scales of de termining soil sorptivety by Philip equation under the situation that the disc d iameter is 10 cm with -9 cm H2O and -12 cm H2O are 30～40 s and 40～50 s res pectively, while the proper time scales in other situation should be less than 3 0 s too. The bigger diameter of disc infiltometer is recommended to determine so il sorptivety for the light soil.%选用直径5 cm和10 cm的盘式吸渗仪,对杨凌土(粘土 )和神木砂黄土(砂壤土)两种质地的土壤在1 cm、3 cm、6 cm、9 cm和12 cm水头5种负压下进行了室内盘式吸渗仪三维吸渗实验,选取Vandervaere公式作为参考模型,对Philip 公式确定吸渗率的时间尺度选取进行了分析.结果表明,对两种质地的土壤,在相同盘径下 ,随着负压的降低,吸渗率随之减小;在相同负压下,盘径越小,吸渗率越大;质地较砂的砂黄土吸渗率明显大于质地较粘的土的吸渗率.从相对误差来看,两种质地土壤吸渗率均被高估;在同一盘径下,随着负压的减小,误差值逐渐降低;即在选取的时间范围内,负压越低,计算吸渗率的准确性越高.对土而言,5 cm盘径下-12 cm水头、10 cm盘径下-9 cm水头和-12 cm水头时确定吸渗率的适宜时间分别为30～40 s和40～50 s;其余确定吸渗率的适宜时间均应小于30 s ;对砂黄土而言,10 cm盘径下-9 cm水头和-12 cm水头时确定吸渗率的适宜时间分别为30～ 40 s和40～50 s,其余确定吸渗率的适宜时间也均应小于30 s.对于质地较砂的土壤推荐使用大盘径进行盘式吸渗仪实验.
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