Soil Composition
One Hour Drainage "Quick Test"
Garden Tip
TB1472
Technical Bulletin Series
Almost every garden instruction guide refers to the importance of "well-draining soil." If water drains (percolates) away from plant roots too quickly, the plants will parch even if they're getting regular water.
If water doesn't drain well before the next irrigation, many plants will drown and rot from the roots up. Another complication from "wet soil" is due to low oxygen availability, the roots do not function properly. Yellowing leaves are often one of the symptoms.
A percolation test - or perc test - is a great way to measure drainage in your lawn or garden soil. Here's how to conduct an easy, DIY soil perk test in your yard.
Note: The Standard Perc test subjects the soil to saturation for 24 hours before measuring drainage rate.

At issue: When we irrigate soil in drought prone regions; we never come close to irrigating water saturated soil.
We follow appropriate off-cycle intervals (According to season or current average temps,) and moisture levels are near wilting for the plant.

That is the Goal!

The QUICK DRAINAGE TEST
has been calibrated to facilitate this!


Most landscape maintenance people find, filling a hole with water, and keeping it filled for 24 hours, then returning to complete the drainage test is not practical. Way too expensive for the homeowner if they did that.

Is the Quick Drainage Test Accurate?

After performing nearly 300 on-site consultations, doing both the Jar Test and the Quick Drainage Test; I found that the "Quick" drainage rate for a particular soil composition type was very close to 24 times the "Standard" percolation rate. Percolation rates follow a decreasing exponential curve during the first 24 hours, before they level out at the published rate for that soil type.

Formulas using published Water Holding (WH), Conventional Percolation (CP), and specific soil composition mix percentages confirmed the proximal relationship between these two testing results.

Quick and Standard Percolation rates
are proportional throughout the many soil types.

Knowing how fast moisture percolates through a particular soil type is necessary in order to Determine the correct water application rate and understand how deeply that moisture will penetrate the soil structure.

DEEP WATER IS THE GOAL
SOIL & IRRIGATION RATE MATCHING IS THE TOOL!

This "Quick Test" will get very close to accurately identifying soil type and standard percolation data. Sandy Loam and High Silt soils are an exception as their drainage rates are very close, yet soil composition (the right combination of sand and clay can simulate silt drainage) is significantly different. A Jar Test can identify which soil type, and is a good idea for improving soil knowledge.

Steps for Doing the Test
Step 1: Dig a Hole at least 12" in diameter by 12" deep, with reasonably straight sides. If you're testing your entire property, dig several holes scattered around your yard, since drainage can vary.

Step 2: Fill Hole with Water, and let it drain completely. This should take about an hour and pre-moisturizes the soil. This helps give a more accurate test reading.

Step 3: Refill Hole with Water about an hour after it first drained.


Step 4: Measure the second Drainage time. The chart below will suggest which type soil exists in that area. If possible, check drainage every 10 minutes. Measure the water level by laying a stick, pipe, or other straight edge across the top of the hole, then use a tape measure or yardstick to determine the water level. Continue to measure the water level every hour until the hole is empty, noting the number of inches the water level drops per hour.

Ideal drainage varies according to the types of plants to be located there. Vegetables require really good drainage. Some shrubs and trees are more tolerant of wet soils than others. Knowing your percolation rate AND the type of plant can be key to recognizing and resolving plant stress issues.


The "Happy Zone" for most plants will be a "Quick" drain time between 30 and 60 minutes. Faster drainage rates often create wilting issues for many plants, while slower rates create respiration issues. Before planting, there are things to do to improve oxygen access to the roots, or help to keep the soil moist longer. Try using the Calculator Pro-I for New Plantings to help.


Another technique for analyzing the composition of your soil is the Jar Test. This process actually does a better job of determining the content percentage of the various soil types than does the "Drainage Test" described above. To learn about this test, and to use the online calculator for analyzing the results of this test; CLICK HERE.

Technical Data for Quick Testing
Math and Science


The Soil's ability to hold or absorb water is the primary reason for the differing "Standard" and "Quick" drainage rates. A dry soil is naturally much more absorbent than a moist or saturated soil. When dry the soil will have a maximum of air pockets to fill. In high clay soil these pockets are much smaller, so the water flow into them is reduced proportionate to the soil composition. Once the soil has been saturated - absorption is finished. Any further moisture will need to pass through the soil as all the air pockets are filled.




The average particle size of high clay soil is much smaller and this has an exponential impact on percolation rate. Still, by taking the Percolation rates for Sand, Silt and Clay and then determining the weighted average for each soil type (based on a typical percent profile) a Soil Composition Factor [SCF] can be established: SCF = ((PR1 + PR2 + PR31.6 ) / 3).
At this point we bring in Effective Capacity (its ability to allow water flow) as well as Water Holding Capacity (water holding capacity, inches per foot). To arrive at a calculated Time to Drain.
These factors have already been worked into the Algorithms of the Garden Calculator Pro-I, and the "Drain Times" reported there are from this accelerated method. If you use the traditional method for a Drain Test and fully saturate the soil first the Garden Calculator Pro-I provides an alternative chart for cross-referencing drainage rates to identify Soil Type, but the drains times achieved do not properly reflect irrigating dry soil that NEEDS water.




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on this technical bulletin - Thanks!