The amount of moisture held in the soil varies depending on the type of soil and the amount of time between watering events. When you’re using a sensor-based watering methodology, you should have a general understanding of the water holding capacity of various types of soil. We’ve included a brief description of the standard soil moisture content levels in this document. You can learn more about soil moisture content, soil classification, infiltration, and water movement in Baseline’s document titled Watering with Soil Moisture Sensors.
Soil moisture content is identified by the following levels:
Saturation: At the saturation level, nearly all of the spaces between soil particles are filled with water. As a rule, irrigators do not want to saturate the soil because it cuts off the plant’s supply of oxygen, which, in effect, drowns the plant.
Field Capacity: When soil is at the field capacity level, it means that all excess moisture has drained freely from that soil. The amount of remaining moisture is the field capacity. To irrigate properly, you would turn off the water when the soil in the root zone of the plants reaches field capacity. A Baseline biSensor measures field capacity in the calibration process and uses this value as the basis for other settings.
Maximum Allowed Depletion (MAD): In most cases, the maximum allowed depletion level is just before the plants begin to show visible signs of stress. Irrigators typically start watering at or before MAD is reached because they don’t want their landscapes to show signs of stress. MAD is not measured because it is based on observation and opinion. The biSensor can automatically set a MAD threshold for you based on the measurement of field capacity; however, keep in mind, this setting is based on a calculation, and we encourage our customers to fine-tune their thresholds.
Permanent Wilting Point: At the permanent wilting point, the level of water in the soil is not sufficient to meet the plant’s needs.