Plants need water. It is essential for them. However, just how much is too much and how much is just right? Of course, you can perform the touch test. Simply stick your finger into the soil. That would give you a relative idea on soil moisture. But you probably want to be more exact. There are tools that can make a more exact reading. Moreover, there are different elements of soil moisture to measure.
The three things you are determining when you measure garden soil moisture content include:
- Garden Soil water content
- Garden Soil water potential/soil moisture tension
- Plant available water (PAW)
Soil water content is the amount of water present in a given quantity of garden soil. It is measured as a percent of water in the soil or inches of water per volume of soil.
Soil water potential/soil moisture tension measures how firmly the water molecules are attached to the soil. If this measurement is high, then the water has a firmer grip on the soil and it is therefore harder for it to get to the plants.
Plant available water is the range of water in the garden soil that is between the saturation point and the point at which plant roots can no longer extract moisture from the soil. This point is known as the “Permanent Wilting Point.”
Tools Available To Measure Garden Soil Moisture
There are four tools that are used to measure various levels of soil moisture. They include:
- Electrical Resistance Blocks
- Tension Meters
- Time Domain Reflecto meter
- Gravimetric Measuring
Electrical Resistance Blocks are also known as gypsum blocks and are used to measure soil moisture tension. The blocks are installed permanently at a site and permit a quick monitoring of soil moisture throughout the year. They measure the electrical resistance between two electrodes attached to a small, cast block of gypsum buried in the soil. The tool features wires of various lengths that lead from the blocks to the soil surface. The electrical resistance is read using a portable conductance meter. Measuring conductance requires alternating current (AC) that is produced by the meter from direct current (DC) from a battery.
Tension meters also measure soil moisture tension and are very effective at measuring very wet soil. They are water-filled tubes that include a porous ceramic tip that is placed into the soil and airtight containers that have a vacuum gauge. They work best in coarse soils between 0 and 80 centibars. The vacuum gauge displays the water tension measurement in centibars.
Time Domain Reflecto meter is a tool that sends electrical signals through the soil to measure soil water content. A specialist in this type of measurement is needed to adequately read the results.
Gravimetric Measuring is a method of measuring soil water content and involves weighing a sample of soil, heating it to cause the water to evaporate, and then weighing it again.