NITROGEN-FIXATION IN SOYBEAN TREATED WITH NITROGEN-DIOXIDE AND MOLYBDENUM

Soybean plants were treated with Mo (0.0 or 2.0 mg kg-1, soil dry wt.) and exposed to NO2 (0.0, 0.05, or 0.1-mu-mol mol-1) at flowering stage. Specific root nodule activity (SNA), chlorophyll-a (Ch-a), chlorophyll-b (Ch-b), leaf N, number of pods, seeds per pod, weight of seeds, and shoot dry weight were measured. Compared with control, SNA did not change on the addition of 2 mg Mo to the soil, but increased by 65% on exposure to 0.1-mu-mol mol-1 NO2 and by 106% on treatment with both NO2 and Mo. Both Ch-a and Ch-b increased significantly on exposure to 0.1-mu-mol mol-1 NO2 and the amount of this increase with 0.05-mu-mol mol-1 NO2 and 2 mg MO was almost the same as with 0.1-mu-mol mol-1 NO2 alone. Leaf-N increased by 46% on exposure to NO2 but did not change on the addition of Mo. Pod number, seed number and weight, and shoot dry weights showed significantly higher values on exposure to 0.1-mu-mol mol-1 NO2 and 2 mg Mo.