Study: Radish Cover Crop Biomass Doesn’t Share Nitrogen

Radish-cover-cropWhile a radish cover crop does trap nitrogen in the fall, it does not supply nitrogen (N) to subsequent crops, a study published in Agronomy Journal Abstract shows.

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The study team, lead by University of Wisconsin’s Matthew Ruark, confirmed that radish cover crops can have substantial nitrogen uptake in the fall. The team planted the radish cover crop in the fall for this study.

“It remains unclear if the N in the radish biomass can supply N to a subsequent corn (Zea mays L.) crop,” the team wrote in its abstract for the study.

The study had three main objectives:

  1. Measure both radish growth and nitrogren uptake.
  2. Determine what effect radish growth had on the folllowing season’s available nitrogen soil content.
  3. See if the radish cover crop had an effect on the following season’s corn yields and response to nitrogen fertilizer.

The study was conducted across several sites across Wisconsin.

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Results of the Study

As expected, the radish cover crop’s nitrogen uptake ranged from 17.6 to 180.2 pounds/acre-1. But in-season, plant-available nitrogen content differed across the growing seasons. And the cover crop mostly had no or a neutral effect on corn yields, although there were some increases and decreases.

“This research supports the use of radish as a trap crop for fall nitrogen,” the study team writes in its abstract.

But do not expect the cover crop’s biomass to fertilize future crops.

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This story seems incomplete. If the radish takes up the nitrogen, then where does it go? Why is it not available to subsequent crop growth? This story leaves more questions than it answers.

Avatar for Carol Miller Carol Miller says:

Hi, Thomas
Tracing where the nitrogen went outside of subsequent crops wasn’t part of this particular study. But the study’s lead, Matthew Ruark, has this say:
“We have some theories here about why there wasn’t an N credit from the radish. I think it was that the decomposition happened too quickly. The N in the radish is split between the leafy biomass and the tap root, which are probably decomposing at different rates. The tap root decomposes quickly (turns to ooze) and then probably moves down through the hole made by the tap root.”

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