There are certain signs to look for when tracking pulse crop growth and development through vegetative stages. Formation of nodules typically takes two to four weeks for pulse crops, depending on growing conditions, pulse nutrition, and rate of nitrogen fixation. To monitor nodulation, carefully dig up pulse plants from different areas of the field. Brush off the dirt from the roots in order to look for nodules, which appear in clumps along the primary and/or secondary roots.
To check for successful fixation in nodules, cut them open and look closely at the interior color. Active nitrogen fixation is indicated by a pink or red color caused by the iron-containing substance called leg-hemoglobin, which is necessary for fixation. If the inside of your pulse crop nodule is white, green or brown, then fixation isn’t active. Poor nitrogen fixation also leads to yellowed leaves toward the base of the plant prior to flowering. Conversely, pulse crops with nodules greater in size and number is a clear sign of successful nitrogen fixation.