MSc

Weed control is the most expensive operation In nee culture in Kerala. An
understanding of the association of different weeds and their adaptive mechanisms to
different rice ecosystems in Kerala is essential for planning effective weed management
practices. Therefore an investigation focusing on the influence of soil conditions and
methods of rice growing, on the di.stribution, biology and ecology of weeds of rice in
Kerala was carried out in the Department of Agronomy, College of Horticulture, K.A.U.
during 2000-2002.
Results of the Permanent Manurial Trial at RRS, Kayamkulam, revealed the
dominance of Aeschynomene indica to low N , Scirpus juncoides to low P soils. The
number of weed species was more in plots receiving all the fertilizers compared to those
receiving no nutrients. The fungal, bacterial and actinomycete population was higher in
plots supplied with nitrogen and phosphorus and or organic matter.
The influence of soil conditions on weed flora was studied by conducting surveys
across the various rice ecosystems. The data from the surveys were analyzed statistically
and diversity indices such as Simpson's diversity index, Shannon's diversity index,
Evenness index and the dissimilarity coefficient were worked out. Cluster analysis was
also done and dendrograms were prepared grouping the different regions based on the
similarity of weed flora. Striking dissimilarities were noticed in the distribution of grass
weeds while it was lesser in the case of sedges, total weed flora and ferns and least in the
case of broad leaf weeds. Kole, Pokkali, Kayal, Kari and Palakkad (Rabi season) regions
showed much similarity in the flora of grass weeds, while there was 75 % dissimilarity for
these regions to Chittur- and Karappadam lands.
Investigations on the mechanisms of survival of some of the indicator weeds
showed that Aeschynomene indica thrive in low N soils by fixing atmospheric N in its
aerial nodules. Diplachne fusca adapt to the saline habitats by excreting the excess salt

through the micro hairs. ThL: luxuriant vegetative growth of" Ecliinochloa crusgalli and
other weeds in Pokkali region seems to be an adaptation for diluting the salts absorbed.
Based on the surveys as well as the data from PMT, a few weeds were identified
as indicators of soil conditions which are listed below.



Aeschynomene indica
Scirpus juncoides
Monochoria vaginalis
Ludwigia parviflora
Eleocharis dulcis
Leptochola chinensis
Diplachne Jusca
Acrostichum aureum
Acanthus ilicifolius
Sphaeranthus africanus -
Spehnoclea zeylanica
Echinochloa stagnina
Cyperus rotundus
Echinochloa colona
Cyperus pangorei
Ipomoea aquatica
Sacciolepis interrupta


LowN
LowP
High organic matter and high P
. High organic matter
High Acidity
High Alkalinity
High Salinity
High Salinity
High Salinity
High Salinity
High Salinity
Low Salinity
Upland rice
Upland rice
Low land rice
Low land rice
Sernidry rice



The study revealed that weed flora can be used as an indicator of the soil conditions and
offers scope for ameliorative management for better weed control and crop growth.