Soil Composition
One Hour Drainage "Quick Test"
Garden Tip
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 technique used in order to estimate drainage in various parts of your landscape. As this popular test is only an estimate for determining important data concerning your soil's composition, a Jar Test should also be performed.

Quick Drain Tests do not allow for soil saturation, and as the soil has not reached the "saturation point" there are too many variables that will likely cause moisture flow rate information to be errant by as much as 500%. A Jar Test (see TB1468) will give an accurate moisture movement rate within 10%, and only takes about ten minutes to do.

Even though considerable accuracy is sacrificed, a Perc or Drainage test will give an insight into possible soil composition problems. 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.
If we follow appropriate off-cycle intervals (According to season or current average temps,) then moisture levels are near wilting for the plant before the next irrigation.

That is the Goal!
Deep Infrequent Irrigations.

has been calibrated to facilitate
an approximation of the results when
performing the Standard 24 hour test.

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?

Accuracy is not really the focus with a One Hour test. Simplicity and a Ball Park Estimate is what it offers.

The chart at the bottom of this page will provide an estimate as to which primary category your landscape soil belongs to.

Quick and Standard Percolation rates
are reasonably 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. The tool for gaining this information is the Jar Test and instructions are available at TB-1468

Jar Test is the process!

This "Quick Test" will get very close to accurately identifying soil type and standard percolation data. Some soils like "Sandy Loam" and "High Silt" soils are an exception as their drainage rates are very close. Soil composition on these is very different. The right combination of sand and clay can simulate silt drainage. Even still this test can help you learn more about your soil, so you can improve the soil.

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.

As you can see; the Moisture movement range within each soil composition type varies, and varies a lot! In the case of Sandy Clay, the Hydraulic Conductivity (or the rate of moisture movement when the soil is saturated) varies ove 7,000%.

The range of Hydraulic Conductgivity Rate [HCR] for each soil composition type is based on the publication and chart provided by the USDA, and presented below.

Due to the very large variation in soil drain time that exists within the individual soil categories, it is really necessary to determine the actual HCR for any particular soil to be irrigated in order to set efficient irrigation run times and distribution patterns. This can easily and quickly be done by performing a Jar Test. TB-1468 will provide the information needed for this.

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on this technical bulletin - Thanks!