Infiltration Rate

Infiltration rate is a good indicator of soil structure and therefore, soil health, as infiltration depends on the level of aggregation (crumb structure) that has formed in the topsoil. Better aggregated (healthy) soils allow water to percolate much faster than poor soils. It can also be an indicator of compaction or thin soils.

The testing area should not be saturated so if it has rained heavily wait until the area is a bit drier!

Equipment:

  •  150mm x 150mm metal/plastic tubes (with 85mm depth marked)
  • Water bottle with 450ml marked on it – (this equates to 1″ depth of water when poured into the cylinder)
  • Water (4L or so per field)
  • Mallet – for driving tube into soil (optional)
  • Wood block – to protect from damage when hammering in (optional)
  • Stopwatch (on phone)

Doing test:

  1. Select location.
  2. It’s very important to remove all debris, weeds and vegetation ~ 150mm x 150mm square
  3. Insert the cylinder/tin into the bare ground, to 85mm depth
  4. Firm soil gently on the inside of the tube
  5. Measure out exactly 450ml of water from your pre-marked water bottle
  6. Pour water into cylinder and start timer
  7. Stop timer when all the water has disappeared into the ground and the surface is just glistening. Record the time in the app.
  8. Repeat steps 5-7. Record this second time in the app. We do this because often the second time gives a better indication of the real infiltration rate that is less dependent on recent weather, as the first test just wets the soil. If the soil is already quite saturated you may find there is very little difference in the first and second times.
  9. You can stop here, or if you want to be very confident in your infiltration rate reading or if it has been particularly dry, then it’s worth repeating steps 5-7 again a couple more times to ensure you are getting a representative infiltration rate.

If it’s happening very slowly, carry-out other tests nearby and check back on it every few minutes.

If you want to work out your infiltration rate in inches/hr. Do 3600/no. of seconds, this gives you the number of inches/hr. If you want to know mm/hr then divide your answer by 25.4.

e.g 20 seconds. Is 3600/20 = 180 inches/hr.

180/25.4 = 7mm/hr

Record:

  • Number of seconds it takes for water to disappear.

Resources:

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052494.pdf

https://www.dropbox.com/s/hykau3m05c1g9yp/NRCS%20Soil%20Water%20Infiltration.pdf?dl=0