Soil School: Does organic matter really matter?


Every conversation on soil health these days eventually comes around to the topic of organic matter.

Does it really matter? What percentage should farmers have in their soil? How do you conserve organic matter? How do you build it?

On this episode of Soil School, Bernard Tobin and University of Minnesota soil extension specialist Jodi DeJong-Hughes tackle these questions and also explore how organic matter makes soils more resilient to extreme weather events.

In the video, DeJong-Hughes discusses many of the soil management tips she shared in her presentation at the recent Ontario Certified Crop Advisor conference. She notes that any discussion of organic matter really begins with soil type — sandy soils always score the lowest for soil organic matter while silty clay loams tend to be the highest, in an overall range that vary from highs around 5% to lows of less than 1%.

DeJong-Hughes says soil research clearly indicates the important role organic matter can play in storing and conserving moisture and reducing heat stress.  For example, she notes that soils with 4% organic matter can make water available to a corn crop for up to eight days in stressful summer growing conditions, compared to four days for soils with 2% organic matter. (Story continues after the video.)

DeJong-Hughes also does the math on the value of nutrients in organic matter. USDA calculations show that the available N, P, K and S for 1% of organic matter is generally valued at US$660 per acre.

When it comes to conserving organic matter, DeJong-Hughes says farmers have to be mindful of their tillage choices. Research shows, for example, that moldboard plowing can result in organic matter loss five times higher than observed in a no-till system.

Tillage choice also plays a key role in how organic matter can contribute to water infiltration and how soils manage extreme moisture events. To illustrate this point, DeJong-Hughes points to trials from the Irrigation Research Foundation (IRF) comparing water infiltration rates for full tillage versus strip-till. Based on IRF findings, soils that were strip-tilled typically allowed 2.5 inches per hour of water infiltration compared to 0.5 for full tillage.

Click here for more Soil School episodes.


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