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为了查明土壤水的运动,包括由根系活动引起的水势变化,经常并准确测量土壤水势很有必要。测量土壤水势最普通的方法是用Richard等设计的多孔陶瓷杯张力计(Haise 1955)。今天多孔杯输送的速度已经很高(Klute和Gardner1962:Klute和Peters1962)。 张力计测定土壤水分的范围在零和0.85巴之间(Baver 1956),包括几乎90％的沙土的有效水(Haise,1955),美国东南部大多数的典型土壤。张力计读数一般用真空计和水银压力计。这种人工读数有几个缺点:田间试验时,读出张力计数字所需要的时间常常使每天只能得到一次结果。
In order to find out the movement of soil water, including the change of water potential caused by root activity, it is necessary to measure soil water potential regularly and accurately. The most common method of measuring soil water potential is with a porous ceramic cup tensiometer designed by Richard et al. (Haise 1955). Today’s perforated cups are already very fast (Klute and Gardner 1962: Klute and Peters 1962). Tensiometers measure soil moisture between zero and 0.85 bar (Baver 1956), including nearly 90% of the available water in the earth (Haise, 1955), and most of the typical soils in the southeastern United States. Tensiometer readings generally use vacuum gauges and mercury gauges. This manual reading has several drawbacks: In field trials, the time taken to read the tensiometer often results in only one result per day.