Effect of pre-emergence application of some herbicides on nodulation, nitrogen fixation and growth of soybean

Abstract

Aretit at the recommended rate (XI) and treflan, especially at high concentration (x 5 folds), stimulated nodulation of soybean 'Clark', while planavin, cobex or linuron, especially at high concentration inhibited nodule formation and even, in some instances, prevented plant growth. In all herbicidal treatments, the dry matter content of whole plant on the second harvest (92 days or pod filling) was lower, even those which showed stimulation at the first harvest (49 days or full bloom) than the control; the yields of pods obtained on maturity were also lower. In general, total-N contents of shoots, roots and pods as well as yield of total-N seemed to be affected by the application of herbicides. The effect differed according to herbicides concentration and growth stages of the plant. Nitrogenase activity as a measure of biological fixation of atmospheric nitrogen using the acetylene-reduction technique was also carried out for root nodules to investigate effect of aretit or treflan on the symbiotic N-fixation processes. The dehydrogenase (DHA) activity in nodule homogenate was also determined in presence or absence of succinate, citrate or ethanol to investigate the effect of herbicidal treatments on respiratory chain of bacteroids. This was claimed to thraw light on effect of herbicidal treatments on capacity of the legume plant (soybean 'Clark') to supply the symbiont (R. japonicum) in the root nodules with some products (hydrogen doners) of the Kreb's cycle and consequently thus affects nitrogen fixation efficiency of root nodules.