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Genomics and Applied Biology 2015, Vol. 6, No. 3, 1-14
http://gab.biopublisher.ca
8
fresh rhizome yield in turmeric. Ashok Jadhav and
Sanjay Pawar (2014) and Suresh Kumar
et al
. (2014)
reported that pre-emergence application of metribuzin
0.7 ka ha
-1
fb
straw mulch 10 t ha
-1
fb
one HW
recorded lower weed density and dry weight and
higher WCE and rhizome yield in turmeric.
Herbicidal Effect on Soil Microflora
When herbicides are applied, most of the spray
solution contacts the soil and may
affect soil
microorganisms that are important for sustainable
agriculture, recycling of plant
nutrients and
maintenance of soil structure (Rosana
et al.,
2007).
Initial setback of microorganisms and regrowth
thereafter with herbicide application was reported by
Kumar
et al
. (1987). According to Subbaiah
et al
.
(1994), herbicides like trifluralin, pendimethalin,
fluchloralin and alachlor at higher concentrations
drastically reduced the soil microbial population on 20
DAS as compared to lower concentrations and
reached the original status on 40 days after the
application of herbicides. Microbial populations
equaled or exceeded with controls at 50 and 60 days of
herbicide application. Voos and Groffman (1997)
reported that a relationship exists between size of the
soil microbial biomass and herbicide
degradation
capacity in an ecosystem. Ahmed and Vyas (1997)
reported that pre-emergence application of
oxyfluorfen at 0.25 kg ha
-1
or 0.5 kg ha
-1
did not affect
fungal population with respect to control in medium
black soil. In contrast to generalizations that
glyphosate is tightly bound and inactivated in soil,
numerous studies show that glyphosate is available to
soil and rhizosphere microbial communities as a
substrate for direct metabolism leading to increased
microbial biomass and activity (Haney
et al.,
2000).
Post-emergence application of oxyfluorfen at 0.12 kg
ha
-1
in rice increased the number of phosphate
solubilizing microorganisms in the rhizosphere soil
(75.8 CFU X 10
4
per gram of soil) with respect to
control (61.2 CFU X 10
4
per gram of soil) as observed
by Das
et al.
(2003).
Lupwayi
et al
. (2004) found that shifts in microbial
community structure in response to herbicides even
when microbial population was unaffected relative to
the control. Singh and Singh (2009) recorded initial
reduction in microbial counts due to inhibitory effect
of pre-emergence application of oxyfluorfen and
pendimethalin. At later stage of 20 and 40 days after
spray, these herbicides in irrigated summer groundnut
lost their potency, probably due to their degradation in
soil. Nalini (2010) noted that pre-emergence
application of pendimethalin (38.7% EC) at 4.0 kg ha
-1
three DAS followed by
HW and earthing up on 45
DAS exerted a significant detrimental effect on soil
bacteria, fungi and actinomycetes and reduced the
microbial count only up to 30 days after herbicide
spray in cotton. Sathya Priya (2011) noticed that higher
doses of oxyfluorfen and pendimethalin had initially
reduced the soil microbial population and the population
recovered within 30 days after herbicide spray. In wheat,
Sharma
et al
. (2014) reported that post-emergence
application of metsulfuron-mehyl 4 g ha
-1
followed by
one mechanical weeding at 50 DAS recorded lesser
microbial population in soil.
Soil Weed Seed Bank
Weed seed bank refers to the weed seeds in the soil
that is able to germinate under
convenient conditions
(Roberts, 1981). Monitoring the changes in weed seed
bank for
extended period enables us to have an insight
into efficiency of the applied measures of
weed
control and to predict weed occurrence in the
following period (Cavers, 1995;
Buhler
et al
., 1997
and Ambrosio
et al
., 2004). Weed seed bank
represents constant source
of weeds, which enables
their continuous occurrence in the field (Boutsalis and
Powles, 1998). It is variable in space and time and
largely depends on application of
cultural practices,
crop rotation (Vanasse and Leroux, 2000) and
herbicide choice
(Dorado
et al
., 1999; Ovaisi
et al
.,
2006).
Ramsdale
et al
. (2006) reported that under
no-till and conventional system, soil seed banks
consisted of about 87 per cent broadleaf and 13 per cent
grasses species, whereas under the mulch-till system
soil seed bank consisted of 68 per cent broadleaf and
32 per cent grasses species in spring wheat-soybean
cropping systems.
