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Herbicidal Effects on the Nodulation of Glycine Max (L.) Merrill¹

Nodulation of legumes is one of the processes in the soil that is liable to be adversely affected by the application of herbicides. This investigation was conducted in a greenhouse and in the field to determine what effects selected pre- and post-emergence herbicides had on total number, dry weight, fresh volume, and Fe content of nodules formed on soybeans [Glycine max (L.) Merrill]. Five soils were employed in greenhouse experiments. Several rates of seven herbicides were surface-applied to the air-dried, soils in pots at planting and each pot was watered immediately. After 5 to 7 weeks of growth the roots were carefully isolated from the soil, the nodules were removed, and the total number and dry weight of the nodules were determined. Analyses of the results indicated that different rates of several of the herbicides had detrimental effects on the nodulation process in four of the five soils used. Dry weight was more readily affected than was total number of nodules. With three of the soils, analyses were made to determine the effects of the herbicides on tap-root and lateral-root nodulation. Adverse effects were found at both sites with the greater sensitivity being noted on the tap-root nodules. Field studies were conducted for 3 years on an Olivier silt loam soil using both pre- and post-emergence herbicides. Plants were excavated from the soil after 8 to 12 weeks of growth and the nodules were removed from the roots. Analyses of the data obtained from determining both the dry weight and the Fe content of the nodules did not reveal any detrimental effects from any of the herbicides used.

Key Words: Herbicide • Soybean nodulation • Nitrogen fixation

² Assistant Professor and Former Graduate Students, respectively, Dept. of Agronomy, Louisiana State Univ., Baton Rouge 70803.

Received for publication March 22, 1972.