MSc

An investigation entitled“ Management of greater club rush (Scirpus
grossus L.f) in wetland rice ecosystem’’was undertaken in a wetland rice
ecosystem heavily infested with the weed. The study was taken up during
February 2010 to January 2011. The main objectives of the experiment were to
develop a management strategy for recovering the wetland rice ecosystem
invaded by greater club rush, economical analysis of rice cultivation in the land
recovered from the invaded weed and study of the weed biology. Laboratory
studies conducted at College of Agriculture, Vellayani, were also included to
achieve the objectives envisaged.
The field experiment on weed management (part I) was laid out in
Randomised Block Design with nine treatments and three replications. The
treatments included farmer’s practice of tillage, application of lime at two
different doses after tillage and application of glyphosate and 2, 4 – D alone and
in combination on weed re-growth with and without tillage. Before applying the
treatments, the thick growing weed was given an initial mowing. The laboratory
studies were done to analyse the herbicide residue in the treated plots and to
study the effect of the applied herbicides on the soil microbial population. The
treatment adjudged as the most efficient was verified further in a larger plot, by
comparing it with the farmer’s practice of weed management to study the
economics of rice cultivation in the land recovered from the invasive weed (part
II). The biology of greater club rush was also studied simultaneously (part III).
The results of the weed management study indicated that all the
herbicidal treatments were significantly superior to farmer’s practice of tillage
in reducing the weed dry weight. Weed control efficiency was found to be 100
percent throughout the study, when the thick infestation was mowed once and
treated with a combination of (glyphosate @1kg ai ha-1 + 2,4-D @ 2 kg ai ha-1)
Tillage + glyphosate @1kg ai ha-1 + 2,4-D @ 2 kg ai ha-1 was also effective in
controlling the weed, but fragments of root system was found remaining in the
soil even after nine months; as a possible source of reinfestation. However,
application of lime as a means of controlling greater club rush was found to have
no effect on the weed growth. Considering all factors, T7 (glyphosate @1kg ai
ha-1 + 2,4-D @ 2 kg ai ha-1) was adjudged as the best treatment for testing
further in the farmer’s field (part II ).
There was substantial increase in the floristic diversity after the
experiment in herbicide treated fields which were completely cleared of greater
club rush within 45 days of herbicide application. The residue analysis of the soil
collected on the next day of herbicide application revealed that the residue was
below detectable limit in the case of both 2, 4 – D and glyphosate, alone as well
as in combination. The results on soil microbial population indicated that the soil
treated with any of the herbicides had a much higher microbial population than
the untreated plots. The cost worked out for the management of the thick
infestation of greater club rush was prohibitively high in all the treatments.
Economic analysis of rice cultivation in the land recovered from the
invasive weed indicated that the grain and straw yield in the treated plot was
substantially higher than that from the non treated plots. When the economics
was worked out inclusive of the cost of land recovery through eradication of
greater club rush, the net profit from rice cultivation was not very high. But the
important indication was that the farmers suffered great loss when they followed
the present practice of mowing followed by tillage.
The observations on the weed biology indicated that in greater club rush,
propagation was exclusively through vegetative means. The nutrient composition
of the weed was comparable to that of rice plant. Due to its very high biomass
production, the nutrient uptake of greater club rush was much higher than that of
rice crop.