Determining Soil Infiltration Rate

By Christina Curell

Water is one of the most important nutrients, and many producers agree can be the difference between a good and a bad year. We watch the skies religiously looking for rain. Some years, we want to see dark clouds overhead while other years they are our enemy. For those years that the clouds are few and far between, some of us turn to irrigation while others hope and pray for just another inch of water. There is one place where all producers should look, and that is down.

Soil has the capacity to store water for crop use. Soil and organic matter act like a sponge collecting and holding water for crop use. Determining the rate at which water can move through the soil filling up the soil reservoir can be done with an infiltration test. The faster water moves through the soil profile without pending or running off the surface, generally the less organic matter is in the soil absorbing and holding water. Soils that are fine-textured such as clay and clay loam have poor infiltration. The steps to determine water infiltration are easy and with a few basic tools, farmers can periodically test their fields.

Before an infiltration test is conducted, clear a small area, a square foot, of all debris and weeds and vegetation that is present clipped to the soil surface. The testing area should not be saturated so if it has rained wait until the area is dry.

Material to conduct an infiltration test:

• six inch diameter ring that has a mark around the outside that is three inches from the bottom of the ring
• plastic wrap
• 500 mL plastic bottle or graduated cylinder
• water
• stopwatch or timer

Step 1: Drive the ring into the ground up to the three inch mark. The best way to do this is to pound a small block of wood laying across the ring with a mallet. Firm the soil around the inside of the ring.

Step 2: Cover the soil and inside of the ring with plastic wrap completely

Step 3: Pour 444 mL, 1” of water, into the ring lined with plastic wrap.

Step 4: Gently remove the plastic wrap allowing the water to pour into the ring. Record in minutes how long it takes the water to infiltrate through the soil until there is only a glistening sheen on the soil.

Step 5: If the soil is dry repeat steps 2-4 to get a better estimate of soil infiltration rate. Infiltration  rate is influenced by soil moisture so to get an accurate rate soil should be wet. Recording in minutes how long it takes 1” of water to move through the soil.

Source: msu.edu