The results of the present investigation thus pointed out that
application of synthetic pyrethroid insecticides, in general,
decreased growth and activities of ammonifying and nitrifying
bacteria but significantly increased proliferation of non-symbiotic
N2-fixing bacteria resulting greater fixation of atmospheric N2,
more so with permethrin (7.8%) followed by cypermethrin (5.2%), in
soil. It was also revealed that application of the insecticides had a
deleterious effect on the accumulation oxidizable organic C and
total N, which was more pronounced with fenvalerate and
permethrin. Results of the present study also indicated that appli-
cation of synthetic pyrethroid insecticides significantly reduced
availability of exchangeable NH4
þ, which was more pronounced
with fenvalerate (15.6%) followed by deltamethrin (11.2%) and
permethrin (8%) respectively, while permethrin followed by
cypermethrin accentuated greater accumulation of soluble NO3
in
soil. Therefore, the effect of synthetic pyrethroid insecticides at
their field application rates on N2-fixation and its mineralization in
tea soil of West Bengal can not be generalized, however in most
cases the effects were more towards deleterious rather than a few
beneficial ones.