Chapter 2. Gravimetric and volumetric direct measurements of soil water content

Equipment for direct soil water content measurements varies widely, and is available from many manufacturers. Ordinarily such equipment consists of devices for taking soil samples, devices for determining the volume of soil excavated (if volume is not determined directly by using a volumetric sampling device), containers for retaining and transporting the samples without loss of water, ovens for drying the samples, and scales for weighing the samples. Sampling equipment for mass basis water contents (θm, g g-1) may be as simple as a shovel, scoop or tube to be thrust into the soil. Since volume is not a consideration for θm, the exact volume of the sampling equipment is not a concern, nor is any sample compaction or dilation. Equipment for volumetric water content (θv, m3 m-3) determination is of known dimensions, and typically consists of tubes or cylinders with a bevelled cutting edge to ease insertion of the sampler into the soil. There are many different samplers, each with its own advantages and disadvantages