EFFECTS OF MICRONUTRIENTS ON BIOLOGICAL NITROGEN-FIXATION AND SOYBEANPRODUCTIVITY

The effects of micronutrients on biological nitrogen fixation (BNF) an d on soyabean yield were studied in two sets of field experiments. The effects of Zn, Co, B and Mo were tested at three sites (soils LRe, LE a and, LRd) where soyabean had been cultivated for more than eight yea rs. In the other set, the effects of Mo (9.0 g) were tested at two sit es of acid soils (LBd and LRa), in a first-year soyabean crop producti on, at different levels of lime. The micronutrients were applied on th e seeds,just before inoculation with Bradyrhizobium elkanii, using 80 kg of seeds by hectare: 15 g of Zn, 0.75 g of Co, 4.5 and 9.0 g of Mo and 3.0 g of B. In soils already cultivated with soyabean, Zn, Co and B did not increase BNF and soyabean yield, but Mo increased BNF and so yabean yield in two of these soils. Mo did not increase BNF and soyabe an yield in LBd soil. In the other soil (LRa soil), Mo increased BNF a nd soyabean yield, but only without lime.