Now that summer is in full swing, many farmers will begin checking their legume plants to see if nodules have properly formed. In this week’s edition of Growing Possibilities, we answer some basic question that may arise and what to expect when it comes to nodules in your legume crop.

First off, what are nodules and how do they form? Nodule formation starts with legume nitrogen fixation. Rhizobia are bacteria that infect the roots, creating a symbiotic relationship (1). The plant provides carbon to the rhizobia, while the bacteria supply the plant with nitrogen (2). Don’t let the term “infect” alarm you because the plant can regulate this process through specialized genes, preventing the infection from becoming parasitic (3).

How do you check for nodules on legume plants? Around six weeks after planting, carefully remove a plant along with its roots and surrounding soil. Gently clear the soil from the roots so the nodules can be observed. Applying inoculant directly to the seed encourages nodule formation near the root crown, whereas in-furrow placement leads to nodules developing along the lateral roots. To assess nodule health, slice one open. Pink colouration indicates active nitrogen fixation. A pale white interior suggests the plant is still young and fixation hasn’t begun. If the nodule appears grey or green, it means nitrogen fixation has stopped (4).

What if no nodules are found? If nodules are absent, further investigation is needed. Some possible causes are, soil pH below 6.0 or above 8.0, lack of soil moisture, non-ideal temperatures, high soil nitrogen level, compatibility issues between seed treatment and inoculant or improper inoculant handling (5). Unfortunately, mature plants cannot be inoculated. Successful nodulation requires application during or before seeding, so corrective measures will need to wait until the next growing season (6).

While nodules may form naturally in soils with a history of legume cultivation, extensive third-party research on commercial inoculants has shown greater benefits. XiteBio offers several products, including XiteBio® SoyRhizo®, XiteBio® PulseRhizo®, and XiteBio® OptiPlus®, which have demonstrated that on-seed or in-furrow application leads to, on average, higher crop yields (7). If you have any questions about nodulation in your crop or XiteBio’s inoculants, please contact one of our sales agronomists by visiting xitebio.com or calling 1-855-XITEBIO (948-3246).

References

1. https://pubs.nmsu.edu/_a/A129/#:~:text=In%20legumes%20and%20a%20few,a%20bacterium%20and%20a%20plant
2. https://www.sciencedirect.com/science/article/pii/S0022519320303994
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC7194392/pdf/kpsb-15-03-1733814.pdf
4. https://xitebio.ca/root-nodulation-what-do-i-look-for/
5. https://xitebio.ca/inoculant-and-biological-faqs/#nodulation
6. https://xitebio.ca/inoculant-and-biological-faqs/#n-application-specifications
7. https://xitebio.ca/xitebio-soyrhizo-premium-liquid-inoculant/