Water infiltration, the process by which water on the ground surface enters the soil, is a critical component of the water cycle. The goal is to keep infiltration rates as high as possible. Reduced infiltration has negative effects, some catastrophic.
Many factors influence infiltration, and it is important to remember that a “good” or “bad” measurement of any factor independent from the others does not indicate what the infiltration rate will be. They all work together to form a composite measurement that determines how well water is able to enter the soil profile at any given location. We can’t control some of the factors, but it’s good to know how they influence infiltration rates so we can consider them when choosing management strategies.
We know that infiltration is reduced in cities with every new building, each square foot of parking lot and every concrete drainage ditch. The drastic decrease of infiltration in urban areas leads to local drought, severe flash flooding and nearby streams full of whatever pollutant washed off the streets.
Inadequate water infiltration isn’t limited to the concrete jungles. Many crop fields and pastures have reduced infiltration, too. While the evidence isn’t as dramatic as cars floating down a street, it’s important to understand that reduced infiltration can result in increased erosion, ponding and drowned-out spots, decreased water quality in streams and ponds and, most importantly, inadequate soil moisture for optimum crop growth.
Water relies on voids in the soil to enter and move through the profile. The size and amount of voids are affected by factors such as soil particle size, amount of aggregation, earthworm tunnels and root channels. Frequent tillage is the most common reason infiltration is decreased. Every time the soil is tilled, the pore spaces are broken down and filled in, creating less space for water to enter.
We also need to be able to slow water down enough for it to infiltrate. If water is rushing across the slope in a field or pasture, most of it is not going to get into the soil, no matter how good the soil structure. Places with varied topography or little residue are at risk for poor infiltration just as they are for erosion.
Keeping tillage to a minimum is the primary management strategy to increase infiltration. That will allow for better soil aggregation, less potential for compaction and more abundant soil biology. Keeping crop residue on the surface and using cover crops will impede water flow and give it more time to infiltrate.
MFA Crop-Trak consultants will work with you to identify the best management strategies for your operation, including how to maximize infiltration and crop yields. Your local NRCS office is also a great place to get more information about the importance of infiltration and cost-share programs that are available to help pay for practices to address infiltration concerns on your farm.
This complex topic is difficult to describe without illustration. The University of Missouri has conducted research about water infiltration and drought mitigation. A video discussing the results of that study is available on YouTube at https://youtu.be/o_d18qX7VFk. NRCS staff have rainfall simulators that are another great demonstration of how different management strategies affect infiltration. If you haven’t seen one, search for “rainfall simulators” online to find several videos showing those demonstrations.