How can you determine that a nodule is fixing nitrogen?
When you cut open an effective nitrogen-fixing
nodule, a significant portion
of the nodule should be pink or red in color. This color is due
to the presence of a hemoglobin
similar to that found in blood, and also involved in oxygen supply,
in this case, to the bacteria. The amount of hemoglobin
present is usually closely correlated to amount of nitrogen fixed,
with white or green-colored nodules usually very limited in their
ability to fix nitrogen. Remember though that nodules have a finite
life span (in the case of soybean estimated at 50-60 days) so that
toward the end of the growing season many of the initial nodules
will have already begun to senesce,
and are brown or green in color, while the more active nitrogen-fixing
nodules may now be located on lateral roots. Levels of nitrogen
fixation achieved by legumes
are reviewed in the recent papers of Unkovich
and Pate (2000) and van
Kessel and Hartley (2000).
|
Return to: U of M Home > Department of Soil, Water, and Climate > College of Agricultural, Food, and Environmental Sciences
