Soil Moisture Profile
- - -
Understanding Optimum
and the many variations
Reference Tip
TB9003
Technical Bulletin Series
Support Info for the Garden Calculator Pro I

This Tip is presented in order
to provide a graphic illustration
of the cross-sectional soil moisture profile.


When water application rate "Matches" the soil the spread and depth of moisture are balanced. This depth creates strong and resilient root systems.




When the water application rate exceeds optimum, but less than 75% (150% = 50%) moisture depth is still decent, though less than desired.



actual moisture profile proportions

At 200% of Optimum, the spread of moisture has become excessive while the depth is less than 6 inches. This is not a good rate of application. Waste and plant stress are certain.



actual moisture profile proportions


Ponding or Puddling looks like this.
Water flows to areas not intended to be irrigated.

When the application rate of water exceeds the Optimum by more than 300% "Ponding" is likely to occur. This is when water on the surface spreads laterally or sideways without being absorbed. This wasted water is detrimental.


This upper image is distorted
in order to facilitate reading


actual moisture profile proportions

When the applpication rate is 400% of Optimum, moisture is drastically moving sideways, and failing to reach lower depths where the root system needs it.


Application flow rates faster than Optimum are mostly found where the soil Hydraulic Condivity Rate is below 0.14 inch per hour.

A different issue crops up when the soil [HCR] is over 1.4 inches per hour. When the soil offers little resistance towards the movement of moisture, there is the need to slow the feed rate, and multiply distribution in order to prevent watering too deeply; wasting water and stressing plants.


Due to less resistance to movement, gravity draws the moisture down faster than it moves laterally due to capillary action.


This results in root system soil moisture creating a profile similar to this:

There is a way to deal with this challenge. The distribution surface area per emitter is inevitably reduced, so the design should incorporate more emitters per square foot within the necessary root zone.

This will apply water at a faster rate per square foot, but the soil will have no trouble accepting moisture at that rate (when matched - to the soil [HCR].

The GG Soil-Flow Pro-I Calculator will perform all the mathematical calculations needed to know emitters spacings and run time for any plant and soil composition

Variations from Optimum

Rarely is it practical to achieve 100% optimum application rate for a particular soil type. Any rate that is within + plus or - minus 50% of optimum, will generally produce an efficient irrigation. As you can see by the images, the further the system departs from Optimum Flow Rate (Matching), the greater the moisture profile distortion, and the less efficient the system.