Wet saturated soils also can reduce or eliminate nodule formation. Legumes depend on nodule growth for their nitrogen supply. Hence, stress and reduced nodulation can mean a nitrogen shortage before the crop matures. This can be seen each year somewhere in North Dakota dry bean and soybean crops. Drought and nutrient stress have the same affect, lower yields and early harvest.
Nodules develop on tender tissue of hair roots rather than corky tissue of older roots.
As a result, they can be found within two weeks after seedlings emerge. They will occur as clusters centered at the seeding depth when seed is inoculated and sparsely on the rest of the plant root system from indigenous Rhizobium present in the root mass. Active nodules, those producing nitrogen for the crop, will have a pink to rusty red interior. Inactive nodules will be white to green in color within the nodule. Plants too far apart, too close together and different sizes are common in fields of adequate average population.