The influence of method of inoculation and certain herbicides on nodulation and seed yield of soybeans

Field trials were conducted on soybeans (Glycine max (L.) Merr.) in a hot, dry environment under irrigation and a warm, moist environment on soils on which the crop had not previously been grown. The aim was to assess the effectiveness of the method of inoculation with Bradyrhizobium japonicum (no inoculation, seed dressing, spraying the planting furrow, and placement of inoculant 50 mm below seed depth) and the effect of two herbicides (metolachlor and trifluralin) on nodulation. Seed dressing and deep placement of inoculum achieved satisfactory nodulation and seed yield, with deep placement appearing to be marginally better under hot, dry conditions. Nodule proliferation on secondary roots was enhanced by deep placement of inoculum as opposed to seed dressing, which led to larger and greater numbers of nodules on the primary root. Herbicide application had no effect on nodule numbers or mass per plant. Satisfactory herbicide weed control significantly depressed soybean yield by 10% when compared with complete hand-weeding.