What's the difference between Watermark and Capacitance soil moisture probes?

What's the difference between Watermark and Capacitance soil moisture probes?

Does it matter which one I chose?

Bridge is here to answer your questions like "how many inches of water are readily available to my crop?" or "how many days do I have left before the crop starts to stress?" We do the hard work to accurately deliver these same insights to you regardless of which technology you chose for the soil moisture probe. If in doubt, we recommend going with the capacitance probe, but for those of you who need a more detailed explanation I will try to give some of the theoretical and practical differences without going over-board on the technical jargon.
 If in doubt, we recommend going with the capacitance probe

Watermark Sensors

Irrometer Watermark sensors are based on fairly old, but very well-researched principles. These sensors actually soak-in the moisture in the soil and determine how much pressure it takes to extract water from the soil. On it's own, this number is of very limited use for irrigation scheduling. When we take into account the texture of the soil, and combine the readings from several sensors at different depths, then we are able to put together the full picture of how much water your crop is going to have access to before it starts to stress. This article goes into much more detail about how these sensors work: http://extensionpublications.unl.edu/assets/pdf/ec783.pdf

Strengths:
  1. Decades of university research provide unmatched ability to interpret raw sensor readings into accurate soil moisture values.
  2. No in-season calibration required.
  3. The thing that they measure, soil water tension, is what actually affects the root's ability to take up water.

Weaknesses:
  1. Limited lifespan requires testing and replacement every few years. BUT we test each watermark sensor before installation and replace any sensor that is “worn-out”, at no cost to you!
  2. Doesn't work as well in very sandy soils.

Capacitance Probes

Aquacheck Capacitance probes operate on entirely different principles. The individual sensors inside the probe each generate an oscillating (rapidly changing) electrical field that extends a small distance into the soil, and then measure how that field interacts with material around it. The amount of moisture in the soil has the greatest effect on the sensor readings, although soil texture, compaction, salinity, temperature, and other physical and chemical properties can all have an effect on the reading. This article has more information about capacitance probes as well as several other moisture probe technologies: http://extensionpublications.unl.edu/assets/pdf/ec3002.pdf

Strengths:
  1. Works great in any type of soil.
  2. More precise sensor readings result in a cleaner-looking graph of data.
  3. More sensors in the probe give a more accurate estimation of the inch-by-inch water content of the soil.

Weaknesses:
  1. Each probe must be manually calibrated each time it is installed, BUT as soon as the probe is installed, we start monitoring the data and fine-tune the calibration values so you don't have to!


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