The Daily Dirt

Runoff Got You Run Down? NRCS Rainfall Simulator Showcases Soil Care Best Practices

The National Resource Conservation Service (NRCS) introduced their famous rainfall simulator at our food safety and soil health workshop at  Mayflor Farms. The rainfall simulator consists of a sprinkler mounted over four trays with four different soil samples in them. The soil samples were all taken recently from farms in Georgia. They contained continuously grazed pasture, rotationally grazed pasture (in which the grass is given year-long rest periods from grazing), tilled soil, and soil with a multi-species cover crop.

In front of the soil sample is a chute for the “rainwater” from the sprinkler to flow into a jar, simulating runoff.  The farmers and gardeners gathered around and Dan Wallace, a soil health instructor from the NRCS, as he turned the sprinkler on and started the simulated downpour.

After about 10 minutes, Dan turned the sprinkler off and showed us the runoff results. The runoff from the cover cropped soil was nearly non-existent, and what little there was in the jar was crystal clear. The tilled soil runoff jar, however, was overflowing and full of dirt.

“You can see that the soil here is what we call cracked and compact,” notes Dan, pointing to the cracked tilled soil. “Bare soil like this forms a hard crust after it rains and compacts the soil beneath it, preventing it from absorbing water which creates more runoff. Then, your soil is compacted so you have to re-till after every heavy rain, creating more work for yourself. Plus any fertilizers or inputs you put in the ground are washed away and you have to reapply them over and over again.” Dan stressed the importance of cover cropping to keep the soil protected and to enable more rainwater to be absorbed. He notes that a multi-species mix of cover crop plants like red clover, peas, and barley is best since the different plants create a more robust mini-ecosystem that is more resistant to disease and more nurturing to the soil.

“This one is what really surprises people,” says Dan, moving onto the rotationally grazed grass sample. He points to the jars which show significantly more soil and water runoff from the continuously grazed grass than from the rotationally grazed grass.

“There’s a huge difference between the continuously grazed grass and the grass that you allow to rest. When you continuously stress a plant through activities like grazing, it prevents it from forming a strong root system that helps the soil absorb rainwater. ”

“So the takeaways here are to use cover crops, preferably a multispecies mix, and to let your pasture rest!” summarizes Dan. The workshop attendees took note and will hopefully bring these best practices back to their own farms.

Want more information about soil health, cover-cropping, or rotational grazing? Check out the Soil Health page on the NRCS website for a wealth of great resources, our article on cover cropping with Julia Gaskin, and be sure to attend the 2019 Georgia Organics conference for a whole track of soil health sessions!

A big thanks to Dan Wallace from the NRCS for this demonstration, and thank you to Mayflor Farms for hosting this workshop!



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