"Infiltration Test Clearly Shows Benefits of Good Soil Health Management"Wed, 29 Jul 2020 07:30:45 CDT
Most people have heard the old cliché, "The root of the problem."
However, an infiltration test being conducted by the Oklahoma Conservation Commission (OCC), the Natural Resources Conservation Service (NRCS) and the Oklahoma Association of Conservation Districts (OACD) is using color dyed water to focus in part on the root of the solution how water follows old root paths and other channels.
"We know that when soils heal, they build preferential flow paths that move large volumes of water deeply into the soil in a short time," said Greg Scott, OCC Soil Scientist. "The ability of a soil to move water rapidly into the subsoil saves that water from being at risk for evaporation from sun, wind, and heat."
With few exceptions, producers often view rain as a gift. Conservation practices strive to make sure that gift is not wasted. These particular fields in Dewey County in western Oklahoma have been in a soil health management system for several years. One of those fields had just been planted to double-crop corn, the other was planted to soybeans.
"The test is merely a demonstration to show that water infiltration in the soil follows preferred pathways that are created by biological activity in the soil," said Steve Alspach, NRCS State Soil Scientist. "Water follows old plant root paths or earthworm burrows to rapidly enter the soil."
The test is conducted by a simulated rainfall event using color dyed water then digging in the site to show the distribution pattern of the dyed water. Scott and Alspach are hoping to develop a demonstration they can use at future field days to show producers how water distribution really works in a soil profile.
Why take this approach?
"It is sometimes difficult to visualize those paths," Scott said. "Again, we are experimenting with several different tracer dyes to try to trace those flow paths into the soil. Earthworm burrows, ant hills, root channels, and structural cracks all contribute to the rapid movement of water into soil. This technique has been used to trace water flow in rock formations. Since it can be difficult to see those flow paths, we are trying to use dye to illustrate those paths."
So they took a 4.5 feet diameter by 5 inch steel ring and hammered it into the surface about two inches. Then they poured concentrated dye onto the surface and turned on the irrigation system to add "rainfall." They put a rain gauge out to measure the water and waited.
"After some rain fell, we took shovels and dug into the application area to trace the dye," Scott said.
The tests are continuing. Scott said they plan to perform the test again with a different dye and concentration.
"However, what we did find and learn is very significant," Scott said of the test on the land of Jimmy Emmons, a former Leopold Conservation Award Recipient and a Regional Director for USDA's Farm Production and Conservation (FPAC). "Before Jimmy began applying soil health management, he could only apply a 1/2 inch of water before water would start running off the field. The infiltration was so poor he couldn't apply enough water for a crop."
Since that time, Emmons has been applying no-till, crop rotation, cover crops, and strategic grazing. The soil has healed dramatically.
"On our test day we applied 6.5 inches of water in about 4 hours," Scott said. "There was zero runoff from the irrigated strip that was about 1/4 mile long and 30 feet wide. The irrigation system stayed in place during our test."
The soil was uniformly wetted throughout the profile to at least 44 inches deep. There was no standing water within a few minutes of turning off the irrigation.
"The soil was a Westola fine sandy loam," Scott said. "In 2005 the organic matter content was 0.3 percent. Since that time, the organic matter has risen, by visual estimates, to between 1 and 2 percent, and the high organic matter layer (topsoil) is about 15 inches thick."
Scott explained that the large amount of organic matter breaks surface tension and helps infiltration. It also increases the water holding capacity by adding high surface-area residue to the soil.
"The ability of the soil to take in a large rainfall event is crucial to resilience in agricultural production," he said. "Formerly, this soil would lose any rain over about 1/2 inch as runoff and associated losses soil erosion, nutrient runoff, and chemical runoff. Now, this soil has healed and can infiltrate the largest storm that is likely to occur. We noticed that the results on the soybean field were the same as the corn field."
Much of that 6.5 inches of water will be held in the root zone. Some will make its way back to the river as base flow, and another portion will contribute to aquifer recharge.
That's how you get to the root of the solution.
Photo Caption Left : Greg Scott, Oklahoma Conservation Commission Soil Scientist , is seen during an infiltration test in which 6.5 inches of water was applied to a field that has been in a soil health management system for several years. On the ground is a steel ring where they placed a rain gauge to measure the water. To the right: Scott is shown next to the ring a few minutes after the irrigation was turned off and there is no standing water because the water was able to be distributed into the healthy soil's profile. Photos courtesy of the Oklahoma Natural Resources Conservation Service.
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