How we use a handheld soil moisture probe to supplement in situ plant ecology sampling

It is best to deploy loggers with appropriate sensors to capture an environmental signal within a set of study sites. Nonetheless, when actively sampling for plant-plant interactions dynamics,  an estimate of soil moisture at that particular point in time and space precisely is useful (at least as a covariate). We use the Delta-T SM-150 handheld unit to complement our long-term logging arrays.

Here is a brief summary of the settings/methodology we use.

Method

  1. Push right button to activate unit.
  2. Repeatedly depress right button to cycle through modes until you reach ‘organic’.
  3. Insert probe into ground and ensure that metal conductors are fully embedded in ground with ceramic/plastic unit flush with ground surface.
  4. Left button to measure. Typically, it should take only 1-2 seconds.
  5. Avoid rocks and voids in the ground when inserting probe.

Comments: Ranges you can expect at least in arid and semi-arid systems we have tested within California are between 1-40% but most frequently < 10%.  The unit is durable, and the control unit is ‘water resistant’. However, when the controller gets wet in the rain, it stops working until it drys out again (typically at least a day later). The cable is not that robust, and to be safe, we insert/push the sensors into the ground using the ceramic casing.