Lab Infiltration Rate

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Lab Infiltration Test:

Purpose: To evaluate soil porosity due to soil texture and the presence of water stable aggregates. Water stable aggregates form in soil as a result of biological processes. The smallest aggregates (not much larger than dust particles) are formed as clay clumps around the sticky microbial debris, and larger (2 mm - the size of large grains of sand, or bread crumbs) aggregates form when fungal hyphae and plant roots "knit" or tie the smaller clumps together. These aggregates are very beneficial, and allow water to soak in, and also help hold onto water longer than non-aggregated, low organic matter soils.

Tools: Assemble these before starting.

soil samples from the field; the soil should be moist, not too dry or too wet/muddy

cup measuring scoop (1/8 cup)

distilled water

filter paper (in kit, or coffee filter would work)

small funnel

jar to set the funnel on

stopwatch, or clock or watch with second hand

Procedure:

Put funnel on top or jar or container that is sturdy and will keep the funnel level. Place a folded filter paper inside the funnel.

Place 1/8 cup level scoop of either fresh or air-dry soil in the filter paper. Do not pack, but level it with a slight tap or by jiggling the funnel.

Gently pour 1/8 cup of distilled water onto the surface of the soil, and start the stopwatch.

Once the water has disappeared beneath the surface, stop the stopwatch and record the time.

Repeat steps 3 and 4 with a second cup of water, but with the same soil. You will have two times written on the data sheet - time 1, and time 2 (in minutes:seconds). Convert the seconds to fractions of minutes (for example, 30 seconds = 0.5 minutes).


 

Figure XX.  Lab Infiltration Test with Funnel.

   

 

Interpretation of Lab Infiltration Rate: Like the field infiltration test, the following numbers are based simply on experience. This is a relatively new test, so there is little to no published literature. However, these guidelines should help you in the evaluation of the quality of your soil.

Time for:

4

3

2

1

1st scoop of water 0-30 seconds. 30 seconds to 2 minutes. 2-10 minutes. 10 minutes or more.
2nd scoop of water 0-3 minutes. 3-10 minutes. 10-20 minutes. 20 minutes or more.

Note: a "scoop" 1/8 cup size was used for development of these tests and guidelines. A larger scoop (1/4 cup or larger) would also work, as long as equal parts of soil and water were used.