Infiltration rate is a measure of how fast water enters the soil. Water entering too slowly may lead to ponding on level fields or to erosion from surface runoff on sloping fields.
If the soil is saturated, infiltration will not occur. Wait for one or two days to allow for some drying. Make sure the sampling area is free of residue and weeds or vegetation is trimmed to the soil surface before inserting the ring.
Materials needed to measure infiltration:
- 6-inch diameter ring
- Plastic wrap
- 500 ml plastic bottle or graduated cylinder
- Distilled water
- Stopwatch or times
- Firm soil
With the 6-inch diameter ring in place, use your finger to gently firm the soil surface only around the inside edges of the ring to prevent extra seepage. Minimize disturbance to the rest of the soil surface inside the ring.
- Line ring with plastic wrap
Line the soil surface inside the ring with a sheet of plastic wrap to completely cover the soil and ring as shown in the figure. This procedure prevents disturbance to the soil surface when adding water.
- Add water
Fill the plastic bottle or graduated cylinder to the 444 mL mark with distilled water. Pour the 444 mL of water (1″ of water) into the ring lined with plastic wrap as shown in the figure.
- Remove wrap and record time
Remove the plastic wrap by gently pulling it out, leaving the water in the ring. Note the time. Record the amount of time (in minutes) it takes for the 1″ of water to infiltrate the soil. Stop timing when the surface is just glistening.
If the soil surface is uneven inside the ring, count the time until half of the surface is exposed and just glistening. Record the time in minutes.
- Repeat infiltration test
In the same ring, perform Steps 2, 3, & 4 with a second inch of water. Record the number of minutes elapsed for the second infiltration measurement. If soil moisture is at or near field capacity, the second test is not necessary.
The moisture content of the soil will affect the rate of infiltration; therefore, two infiltration tests are usually performed (if soil is dry). The first inch of water wets the soil, and the second inch gives a better estimate of the infiltration rate of the soil.