Estimating Soil Moisture by Feel and Appearance - USDA NRCS
DOWNLOADSeptember 1, 1997 - U.S. Department of Agriculture Natural Resources Conservation Service
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EmailIrrigation Water Management (IWM) is applying water according to crop needs in an amount that can be stored in the plant zone of the soil.
The feel and appearance method is one of several irrigation scheduling methods used in IWM. It is a way of monitoring soil moisture to determine when to irrigate and how much water to apply. Applying too much water may cause excessive runoff and/or deep percolation. As a result, nutrients and chemicals may be lost or leached into the ground water.
In applying this method, you determine the amount of irrigation water needed by subtracting water in soil storage (estimated using the feel and appearance method) from the available water capacity (AWC) of the soil. (See the example computation below.)
The feel and appearance of soil varies with texture and moisture content. Water available for plant use can be estimated, with experience, to an accuracy of about 5 percent. Soil moisture is typically sampled in 1-foot increments to the root depth of the crop at three or more sites per field. You vary the number of sample sites and depths according to: crop, field size, soil texture, and soil stratification. For each sample the feel and appearance method involves:
- Obtaining a soil sample at the selected depth using a probe, auger, or shovel;
- Squeezing the soil sample firmly in your hand several times to form an irregularly shaped ball;
- Observing soil texture, ability to ribbon, firmness and surface roughness of ball, water glistening, loose soil particles, soil/water staining on fingers, and soil color;
- Comparing observations with photographs and/or chart to estimate percent water available. (Note: A very weak ball disintegrates with one bounce of the hand. A weak ball disintegrates with 2 to 3 bounces.)
