Central Rice Research Institute Annual report...2011-12

grain yield varied from 2.95 to 8.20 t ha -1 , straw yield
from 3.45 to 7.75 t ha -1 , effective tillers from 139 to 388
and panicle weight from 1.68 to 3.64 g whereas during
the wet season grain yield varied from 9.10 to 17.70 t
ha -1 , straw yield from 12.95 to 31.50 t ha -1 , effective tillers
from 255 to 457 and panicle weight from 2.90 to 7.13 g.
The soil samples were collected from the same grid
point, processed and analysed for soil pH, OC, P and
K. The geo-spatial maps for yield and nutrient status
were developed using GIS software. It was found that
the low fertility loops in the map is matching with low
rice yield indicating a yield improvement if variable
fertilizer application is made matching with low and
high fertility zones.
Ecologically based integrated weed management
in rice
Population dynamics, biology and management of weeds
through low-dose high-efficacy novel herbicides, bio-agents
and allelopathic effects
In direct-sown rainfed lowlands, the grassy weed,
Echinochloa colona was prevalent (63% of total weed
population) at early vegetative stage i.e., at 30 days after
sowing (DAS) while at 60 DAS, the Leptochloa
chinensis along with sedges viz., Cyperus iria and
Fimbristylis miliacea and broad leaf weeds viz., Ludwigia
octovalvis and Cleome viscosa were predominant (89%
of total weed population). In medium deep (intermediate)
lowlands, the major weed species at 30 DAS were
Echinochloa colona, Cyperus iria and Fimbristylis miliacea
(81% of total population). However, at 90 DAS, there
was prevalence of Leersia hexandra, Cyperus haspan,
Ludwigia octovalvis and Commelina benghalensis (87% of
total population). The predominant weed floras in
transplanted rice were Echinochloa colona, Fimbristylis
miliacea, Ludwigia octovalvis , Marsilea quadrifolia and
Sphenoclea zeylanica. The mean relative density of major
weed species in wet direct-sown summer rice were
Echinochloa colona (8.7%), Cyperus difformis (26.1%),
Fimbristylis miliacea (14.5%), Sphenoclea zeylanica
(27.5%), Marsilea quadrifolia(23.2%) at 30 days after sowing
(DAS). In case of transplanted rice, it was observed
that Cyperus difformis was the most prevalent weed species
(33% of total weed population) followed by
Sphenoclea zeylanica (25%) at early vegetative stage (30
DAT). But the dominance of Leptochloa chinensis (21%)
was recorded maximum at tillering stage (60 DAT).
An experiment was conducted to study the allelopathic
effect of Lantana camara leaf extract on germination
and seedling growth of three predominant weeds
of irrigated rice field viz.,Echinochloa colona, Cyperus
difformis and Sphenoclea zeylanica. It was found that the
aqueous extract suppressed seed germination in all the
three associated weeds and the suppressive effect increased
with an increase in percentage of extract. The
effect was more pronounced in Cyperus difformis (43%
germination in 10% extract against 73% under normal
condition). In case of seedling growth, it was found
that the root elongation was affected more than shoot
elongation in all the weeds after one week of germination,
with the suppressive effect being most pronounced
in Cyperus difformis followed by Echinochloa colona and
Sphenoclea zeylanica. Shoot growth was significantly
suppressed at higher concentration in Cyperus diformis.
It was also observed that there was inhibition of total
biomass in all the three weeds after three weeks of germination
and the inhibition effect was highest in 10%
of extract. The reduction was highest (86%) for Cyperus
difformis followed by Echinochloa colona (81%) and
Sphenoclea zeylanica (70%) by application of 10% aqueous
extract of Lantana camara leaves.
The efficacy of two new low-dose high-efficacy herbicides
viz., Bispyribac sodium and Penoxulam and
herbicide mixture, Penoxulam + Cyhalofop in conjunction
with recommended herbicides were tested in wet
direct- sown rice. Bispyribac sodium (at 30 g ha -1 ) was
found effective for controlling Echinochloa colona with
weed control efficiency (WCE) 83% and Penoxulam +
Cyhalofop (at 135 g ha -1 ) found effective for contolling
major weeds with WCE 86%. Except Azimsulfuron,
other herbicides could not be found effective against
Leptochloa chinensis. Azimsulfuron at 35 g ha -1 and
Azimsulfuron + Metsulfuron methyl (30 + 2 g ha -1 )
found most effective in controlling weeds (WCE 88 and
90%, respectively) and produced comparable yield with
recommended practice of hand weeding twice at 20 and
40 DAS. There was 45% reduction in the grain yield of
rice due to competition with weeds in the weedy plots.
Integrated weed management in upland rice
A field experiment was conducted at CRRI Regional
Station, Hazaribag to study integrated weed management
in rainfed upland rice during wet season, 2011 in
factorial randomized complete block design combining
weed management practices with different intercrop
row ratios of rice and black gram (BG). Four row
ratios of rice and BG (1:1, 2:1, 3:1 and 4:1) were sown
using uniform base and intercrop spacings of 15, 20
and 25 cm. Pendimethalin alone or in combination with
72 CRRI ANNUAL REPORT 2011-12