Skip

Estimating Soil Moisture Content by Feel and Appearance

Irrigation Water Management (IWM) is applying water according to crop needs in an amount that can be stored in the plant root 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 causes excessive runoff and/or deep percolation. As a result, valuable water is lost along with nutrients and chemicals, which may leach into the ground water.

The feel and appearance of soil vary with texture and moisture content. Soil moisture conditions can be estimated, with experience, to an accuracy of about 5 percent. Soil moisture is typically sampled in I-foot increments to the root depth of the crop at three or more sites per field. It is best to 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:

I. Obtaining a soil sample at the selected depth using a probe, auger, or shovel;

2. Squeezing the soil sample firmly in your hand several times to form an irregularly shaped "ball";

3. Squeezing the soil sample out of your hand between thumb and forefinger to form a ribbon;

4. 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. [Note: A very weak ball will disintegrate with one bounce of the hand. A weak ball disintegrates with two to three bounces;

5. Comparing observations with photographs and/or charts to estimate percent water available and the inches depleted below field capacity.

Example
Sample
Depth
Zone
USDA
Texture
AWC for
Zone
Soil Moisture
Depletion
Percent
Depletion
6"
0-12"
Sandy Loam
1.4"
1.0"
70
18"
12-24"
Sandy Loam
1.4"
0.8"
55
30"
24-36"
Loam
2.0"
0.8"
40
42"
36-48"
Loam
2.0"
0.5"
25
Total
 
 
5.8"
3.1"
 

Results:  A 3.1" net irrigation will refill the root zone.

Available Water Capacity (AWC) is the portion of water in a soil that can be readily absorbed by plant roots of most crops.

Soil Moisture Deficit (SMD) or Depletion is the amount of water required to raise the soil-water content of the crop root zone to field capacity.

Appearance of different types of soil at various moisture conditions: