As field pea crops advance through the vegetative stages, it’s worth taking a few minutes to dig up some plants and check for nodulation. While peas are well known for their ability to fix nitrogen, that process depends on healthy, active nodules developing on the root system. A quick field check can help confirm that your crop is capturing the nitrogen it needs to maximize yield potential.
Nodules form when Rhizobium bacteria infect pea roots and establish a beneficial relationship with the plant. In exchange for energy from the crop, the bacteria convert atmospheric nitrogen into a plant-available form. When nodulation is successful, peas become less reliant on soil nitrogen and supports strong growth throughout the season.
The best time to evaluate nodulation is between the 10th and 12th node stage or at early flowering (R1). By then, nodules should be well developed and actively supplying nitrogen to the crop.
To assess nodulation, select 5 to 10 plants from several representative areas of the field and carefully dig up the entire root system. Avoid pulling plants by hand, as this can strip nodules from the roots and lead to an inaccurate assessment. In heavier soils, soaking roots in water can help remove soil while keeping nodules intact.
Once the roots are cleaned, examine both the number and location of nodules. Healthy nodules are commonly found on both the main root and lateral roots. Because pea nodules often branch as they mature, they may appear as clusters rather than individual nodules.
To determine whether nodules are actively fixing nitrogen, slice a few open with a pocket knife. Active nodules will have a pink to reddish colour inside, indicating the presence of active nitrogen fixation. White, green, or brown nodules are generally inactive and contributing little to the crop’s nitrogen supply.
If you observe differences in nodulation across the field, inspect additional plants to determine whether the issue is localized or widespread. Variability can often be linked to factors such as soil moisture, soil conditions, inoculant performance, compaction, or other environmental stresses.
Taking the time to inspect roots provides valuable information that can’t be seen from above the canopy. A healthy root system with abundant active nodules is a strong indication that the crop is efficiently capturing nitrogen and is well positioned to achieve its yield potential.
Sometimes the best agronomic insights are found by putting a shovel in the ground.
