What is Used to Measure Moisture in Soil

Posted by Tom Laurenzi on Apr 20, 2018 11:00:00 AM

For farmers, there are few things as important as the quality of soil. If the soil they’re trying to grow crops in is depleted of nutrients, then crops will not grow well. Additionally, the amount of moisture in soil can have a major effect on crop quality: Too little water can stunt plant growth and reduce quality, while too much water can wash away fertilizer and soil nutrients.

To maintain soil health and quality, farmers need to not only rotate crops and use fertilizer to replenish lost nutrients, they also need to closely monitor and control the moisture content of their soil as well. The question is, how can farmers measure soil moisture?

One of the most accurate and reliable ways to measure the amount of water in soil is to use a soil moisture meter.

What is a Soil Moisture Meter?

The short answer is that it is a type of agriculture moisture meter designed specifically to monitor the amount of available moisture in soil at a specific depth. However, these devices are a bit different from the typical moisture meter.

The pins on a normal moisture meter would not penetrate deep enough into soil to provide any kind of useful estimate of available moisture. Also, because soil composition can vary so much from one region to the next, there is no standardized soil “scale” that could reliably give a precise moisture content (%MC) measurement in soil.

Since moisture meters use electrical resistance to measure moisture content, slight differences in electrical conductivity caused by soil having different contents can throw off moisture measurements.

So, How Do Soil Moisture Meters Work?

To get a measurement of the available moisture in soil, soil moisture meters use a specially-designed sensor block that is buried deep in the soil. The exact depth for installing the sensor block will vary based on the active root zone of the crop. For best results, most farmers install two sensor blocks, one at a “shallow” depth and one at a “deep” depth.

By using sensor blocks at two different depths, farmers can better gauge the effectiveness of their irrigation techniques and avoid wasting water.

The sensor blocks that are used with Delmhorst’s KS-D1 moisture meter are made of gypsum, a water-absorbent material. When buried in the soil, the gypsum blocks will slowly reach a state of equilibrium with the moisture content of the surrounding soil.

The electrode inside the sensor block measures the amount of moisture the block has absorbed—and, because the block itself is made of a specific material (gypsum), it is easier to accurately gauge the available moisture in the soil that a crop’s roots could absorb.

Once the sensor blocks are installed and have reached equilibrium with the surrounding soil, farmers can plug the electrode into their soil moisture meter and take a reading whenever they want.

Using a Moisture Meter for Soil

Some general tips for using a soil moisture meter include:

  • Using a 1-inch soil auger to dig the initial hole.
  • Creating a creamy slurry, consisting of soil and water, to place into the bottom of the hole prior to installing the sensor block.
  • Using two sensor blocks—a “deep” block and a “shallow” block—and marking their electrode leads off so you know which is which.
  • Lightly tamping down the soil little by little as you backfill each hole after installing the sensor blocks.
  • Tying the electrodes to a stake so they aren’t lying in the dirt.
  • Installing other stations of electrodes about 10 inches – 20 inches away from the first.
  • Avoid installing electrodes directly next to sprinkler systems or in areas that are significantly higher or lower than the rest of the field.

Want to learn more about using moisture meters for soil? Or, do you need help finding the right kind of meter to use? If you have any questions, please contact Delmhorst, or leave a comment below!

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Topics: moisture meters