Legumes in stress will have limited nodule numbers. Severe stress after nodulation can cause nodule sloughing. Stress can be from several sources. However, drought and nutritional deficiencies are most common. 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.