3 Reasons Your Legume Cover Crop Nodulation May Have Failed

nitrogen fixing nodules in the roots of legumes

Legumes are inoculated with bacteria of the genus Rhizobium which induce nitrogen-fixing nodules in the roots of legumes. The fixated atmospheric nitrogen is then used by grasses what makes the overall system self-sufficient in terms of nitrogen. Photo: Terraprima, Wikimedia Commons

By Emilie Ritter Saunders, NCAT Communications Director

Legumes make for great cover crops thanks to an important partnership between the plant roots and bacteria. When this biological partnership is thriving, nitrogen is being pumped back into the soil for future crops to benefit from.

It can sometimes appear like your cover crop is thriving above ground, but if bright pink nodules on the roots below ground aren’t visible around 30 days after germinating, there might be a problem.

As Stephanie Kasper, a biology research associate at University of Texas at Rio Grande Valley explains in Voices from the Field Episode 205: Inoculating Legume Cover Crops, there are three common reasons your legume cover crop may have failed.

  1. Rhizobia inoculant may have expired or overheated.
  2. Pre-inoculated seeds don’t always work well; inoculate your own.
  3. Wet seeds that have been inoculated might not work. Make sure your seeds are dry before planting.

Listen to Kasper’s full conversation with National Center for Appropriate Technology Sustainable Agriculture Specialist Colin Mitchell in Voices from the Field Episode 205: Inoculating Legume Cover Crops to learn how to troubleshoot and diagnose nodulation problems and avoid legume cover crop pitfalls.

Related Resources:

Cover Crop Options for Hot and Humid Areas

Blog 65. The Two Best Legume Cover Crops for Hot and Humid Climates

Blog 68. How to Make Sure Your Leguminous Cover Crop is Doing its Job

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