Infiltration Rate

Knowing how easily water infiltrates into your soil tells you how well it is soaking up rain. You want water to be stored in the soil profile, and not to run off into water courses.

If your infiltration rate is quick, it indicates your top soil structure is good, with stable aggregates, around which water can percolate down into the soil profile. If your infiltration rate is slow, it indicates your top soil structure is poor. The top soil has unstable aggregates and is compact, blocking water from percolating downwards. Instead water runs off taking topsoil and nutrients with it!

Infiltration rate testing (from the 2nd pour) is included for benchmarking & analysis in the Soilmentor Regen Platform.

The testing area should not be saturated so if it has rained heavily, wait until the area is a bit drier. Learn how to make an infiltration rate tube here.

What to record


  • The number of minutes it takes for 25mm/1 inch of water to infiltrate into the soil. Record two pours separately – ‘1st inch’ & ‘2nd inch’
  • Photos

Equipment


  •  150mm (6″) downpipe / tube (with 75mm / 3″ depth marked)
  • Ruler – to measure 25mm / 1″ water poured into tube
  • 2 litres (1/2 gal) of water per sample site (so you can do multiple pours)
  • Mallet – for driving tube into soil (optional)
  • Wood block – to protect from damage when hammering in (optional)
  • Stopwatch (on phone)

How to do the test

1. Locate your chosen sample site – you can use the GPS mapping feature on the app to do this if you’ve recorded the sample locations previously

2. Remove all debris, weeds and vegetation where you aim to set the tube – either trim down or cut through with a knife.

3. Insert the cylinder/tube into the bare ground, to 75mm (3″) depth

4. Firm soil gently on the inside of the tube. If using plastic wrap, cover soil and inside of tube with wrap to protect soil surface

5. Either measure out 450ml of water, or insert ruler into the cylinder, ready to record 25mm / 1″ of water added

6. Pour water into cylinder and start timer (if using one, gently pull away the plastic sheet before starting the timer)

7. Stop timer when all the water has disappeared into the ground and the surface is just glistening. Record the time in Soilmentor to the nearest half minute under ‘Infiltration rate – 1st inch (mins)’

8. Repeat steps 5-7. Record this second time in Soilmentor under ‘Infiltration rate – (2nd inch) mins’. Only this 2nd inch reading will be used on the Regen Platform, as it gives a better indication of your soil’s ‘real’ infiltration rate, less affected by recent weather – the first test may be just wetting the soil. If the soil is already saturated you may find there is little difference between the times.

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

If desired you can use the below formula to work out your infiltration rate in inches/hr.

Infiltration inches/hr = 60 / minutes taken to infiltrate 1 inch or 25mm

E.G. 8 minutes to infiltrate 1 inch would be 7.5 inches/hr (60 / 8)

Read this article to learn how many times to do the each test on each field.