Agricultural research communication centre

3. Molybedenum: 
Micronutrients play an important role in
increasing the yield of pulse and oilseed legumes through
their effects on plant itself and on the nitrogen fixing
symbiotic pr ocess. Molybden um is on e of the key
micronutrients in the legume production since it is an
essential component of nitrate reductase and nitrogenase
enzyme which mediates the ion exchange and control the
reduction of inorganic nitrate and helps in fixation of inert
elemental nitrogen into ammonia. Bhuiyan 
et al
(2008b)
reported that inoculation with 
Rhizobium
along with
molybdenum application significantly improved the root
length as well as number of nodules per plant. These findings
are in corr obor ation with th ose of Ch atter jee an d
Bandyopadhyay (2015) in cowpea. Similarly, Poonia and
Pithia (2014) reported higher number of root nodules when
chickpea seeds were inoculated with 
Rhizobium
and seed
treated with molybdenum.
Herbicides: 
Herbicide application is one of the most
promising methods of weed control in field crops. The
application of herbicides results in the accumulation of these
herbicidal chemicals in the upper layer of soil (0-15 cm)
which is the seat for various microbiological activities and
biochemical reactions. Various researchers have reported the
adverse effect of herbicides on nodule formation, nodule
growth, nodule efficiency and activities of beneficial
microorganisms such as
Rhizobium
in soil (Bai and
Nanjappa, 2003; Ahemad and Khan, 2013).
Khan 
et al 
(2004) reported that application of
isoproturon at 10 times higher rate (20 µg a.i./g) decreased
the nodule number by 32.3% in contrast with control (no
herbicide application) while 10 times higher dose of
bentazone (11 µg a.i./g) and 2,4-D (17.5 µg a.i./g)
completely inhibited the nodule formation suggesting that
higher concentration of these herbicides is highly toxic for
Rhizobium
-legume symbiosis in chickpea. Isoproturon,
bentazone and 2,4-D at 2.0, 1.1 and 1.75 µg a.i./g recorded
39.5, 42.8 and 33.7 number of nodules/plant as compared to
40.5 in untreated control. Further, decrease in the nitrogenase
activity was also observed due to the application of these
herbicides which may be attributed to damage in the
photosynthetic apparatus as well as alteration in nodule
cortex structure. The effects of herbicides on the legume-

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AGRICULTURAL REVIEWS
rhizobia symbiosis summarized by Parsa 
et al
(2014) are as
follows:
(i) Reduction of root biomass which leads to limit the number
of available sites for rhizobia to attach to root hairs
(ii) Alteration in the carbohydrate preparation of the root
nodules
(iii) Alteration in the nitrogenase enzyme activity which is
critical for nitrogen fixation
(iv) Inhibiting or inactivating the biochemical dialogue which
takes place between host plant and microbial symbiont
(
Rhizobium
) which is essential for nodulation process.