How to Measure Soil Water Infiltration

What is water infiltration:

Infiltration is the downward entry of water into the soil. The velocity at which water enters the soil is infiltration rate. Infiltration rate is typically expressed in inches per hour. Water from rainfall or irrigation must first enter the soil for it to be of value. 

Why is it important:

Infiltration is an indicator of the soil’s ability to allow water movement into and through the soil profile. Soil temporarily stores water, making it available for root uptake, plant growth and habitat for soil organisms. 

How to measure water infiltration:

One simple test that a farmer can do in the field to assess water infiltration properties of his soil is to take a simple 5 gallon bucket and cut out the bottom leaving the top 10” of it and recess it into the soil after dampening an area. 

1. Insert ring (top of a 5-gallon bucket will do) in the soil. Take care not to disturb the soil inside the ring.
2. Add water to the inside of the ring. Be careful not to disturb the soil surface.
3. Record the amount of time (in minutes) it takes for each inch of water to infiltrate the soil.

The initial soil water content at time of measurement affects the ability of the soil to pull additional water into the soil. So, the infiltration rate will be higher when the soil is dry than when it is wet. A good midwestern soil should be able to store about 25% by volume of available water for crop growth - in other words, in the top 12" of soil we might want to have 3" of water for root uptake after a nice rain storm.