PhD

The study entitled “Management of blood grass (Isachne miliacea Roth ex Roem et
Schult) in wetland rice ecosystem” was carried out at College of Agriculture, Vellayani
during the period 2016 - 2018. The objectives were to study the eco-biology and habitat
affinity of blood grass, to develop an effective strategy for managing the weed, to study
the influence of the management practices on
weed dynamics,
to work out the
economics of the weed management practices and also to assess the impact of the
herbicides on the soil microorganisms.
The weed biology was studied by observing sample plants for a period of one
year. The results revealed that blood grass which propagated through both seeds and
rooted stem bits flourished in the rice field all throughout the year. The seeds showed no
dormancy and could germinate soon after shedding. However direct sunlight was found
essential for germination of the weed seeds. The stored seeds retained > 80 per cent
viability upto six months and after that there was a sharp decline in germination
percentage.
Effect of water regime and soil depth on weed propagation was assessed by
conducting two separate lab studies by subjecting the seeds and stem cuttings to varying
soil and water depth. The design was CRD and there were 5 x5 treatments (Factor I.
Water depth (W): 0, 2.5, 5.0, 7.5, 10.0 cm and Factor II. Soil depth (S): 0, 2.5, 5.0 ,7.5,
10.0 cm ) and three replications. From the results, it was inferred that soil depth was the
major factor that determined the germination and establishment of blood grass which
emphasized the significance of land preparation in managing blood grass.
Plant and soil samples from heavily
infested rice field sites in four agro
ecological units (AEU 10-North central laterite; AEU 4- Kuttanad; AEU 9- South central
laterite; AEU 8- Southern laterite) were collected and analysed and correlated with weed
dry weight to assess the habitat affinity of the weed. The results indicated that the
biomass production of blood grass has significant positive correlation with soil organic
carbon and available nitrogen while EC was negatively correlated. Water level also had
significant negative correlation with plant dry weight.
.
The field experiments to develop an effective
strategy for managing the weed
were conducted during the first and second crop seasons of 2016 at the State seed farm,
Kottarakkara, Kerala. the initial infestation intensity of blood grass was 84 per cent.
The experiment was laid out in split plot design with three replications and the crop
variety used was
Sreyas released from Rice Research station Moncombu, Kerala.
Combinations of tillage (P) and water regimes (W) were the main plot treatments and
weed management practices (M) were the subplot treatments. The tillage practices
included were: P1- intensive tillage (three ploughings fb puddling) and P2
-
farmers‟
practice (two ploughings fb puddling). The water regimes tried were W1-continuous
deep water ponding i.e., > 7.5 cm from 7 days after transplanting (DAT) till grain filling
stage, W2- >7.5 cm water from 7 DAT
till panicle initiation stage and W 3-
maintaining about 5cm water level with intermittent drainage (KAU, 2011). The weed
management practices in the subplots were M1 - oxyflourfen @ 0.15 kg ha-1 fb one hand
weeding (HW), M2 - azimsulfuron @ 35 g ha-1 , M3- (bispyribac sodium + metamifop)
70 g ha-1 , M4- fenoxaprop- p-ethyl @ 60 g ha-1 , M5- hand weeding twice at 20 and 40
DAT and M6 - unweeded control. Oxyflourfen was applied as pre- plant three days
before transplanting and the post emergence herbicides were applied at 15 days after
transplanting (DAT). The second crop of rice was taken immediately after the first crop
without disturbing the field layout.
The results of the field experiments revealed that an integrated strategy involving
intensive tillage (three ploughings fb puddling), deep water ponding (ie., > 7.5 cm upto
panicle initiation and saturation thereafter ) and application of azimsulfuron @ 35 g ha-1
at 3-5 leaf stage of the weed was the most efficient treatment for managing the weed in
terms of weed control efficiency (WCE), crop performance and net income. Preplant
application of oxyflourfen @ 0.15 kg ha-1 fb hand weeding when combined with deep
water ponding and intensive tillage recorded high WCE but was inferior in terms of
economics. Combinations of these modified cultural practices with manual weeding
though uneconomic, was efficient in managing the weed and recorded high yield also and
hence could be an option for organic rice cultivation.
The results from soil seed bank studies revealed that the density of blood grass
propagules in the soil could be significantly reduced through intensive tillage and
continuous maintenance of > 7.5 cm water level in the field. Among the weed
management practices, application of azimsulfuron recorded the lowest weed seed
density in the soil. When compared to the weedy check combinations, the soil seed bank
was considerably lower in all the other treatments.
The response of the microbial community to varying concentrations of the
herbicides included in the study was assessed by conducting a separate field experiment
which was laid out in RBD with 3 replications. The treatments were : oxyflourfen @
150, 300, 450 g ha-1, azimsulfuron 35, 70, 105 g ha-1, bispyribac sodium +metamifop @
70 , 140, 210 g ha-1, fenoxyprop- p-ethyl @ 60, 120, 180 g ha-1 and untreated control.
The results showed that the bacterial population was stimulated with each increment of
the herbicide concentrations. The fungal and actinomyctes
population declined
significantly immediately after the herbicide application but the negative impact was
only transient and in most of the treatments the population recovered within two weeks.
The soil enzyme activity was also found positively influenced by the herbicide
application.
From the results it was concluded that an integrated strategy involving intensive
tillage (three ploughings fb puddling), deep water ponding (ie., > 7.5 cm upto panicle
initiation and saturation thereafter ) and application of azimsulfuron @ 35 g ha-1 at 3-5
leaf stage of the weed
was very effective for
managing
blood grass. Similarly
application of oxyflourfen, bispyribac sodium + metamifop and fenoxyprop- p-ethyl at
the recommended dose did not show any negative impact on the microbial community
in the wetland rice ecosystem.