Effect of herbicides on survival of rhizobia and nodulation of peas, groundnuts and lucerne

Abstract

Thirteen herbicides were tested for toxicity against strains of Rhizobium used in South African legume inoculants for lucerne, clover, soybeans, groundnuts and lupins, respectively. Each of alachlor, bromoxynil, proprop, metolachlor, naptalam + dinoseb, and trifluralin inhibited at least two of the strains after a contact period of ca 10 s. No strain survived 42 h in contact with any of these herbicides. Atrazine and terbutryn were relatively non-toxic. The slow-growing strains of Rhizobium japonicum, Rhizobium lupini and Rhizobium sp. (groundnuts) were less affected by at least two of the herbicides tested than strains of the fast-growing R. meliloti and R. trifolii. Toxicity of a herbicide to rhizobia in vitro did not necessarily correlate with its effect on nodulation and some are considered suitable for field application.