PhD

An experiment was conducted to assess the performance of system of rice
intensification (SRI) vis-à-vis conventional system with special emphasis on weed
problems under SRI and to develop an economic weed management strategy.
Aiming at reducing drudgery while using manual cono weeder, it was also
envisaged to develop the prototype of a self propelled cono weeder.
The field studies laid out in randomized block design with 16 treatments in
three replications were conducted at RARS, Pattambi in Palakkad district and in
farmers’ fields at Alappad Kole in Thrissur district, during the Mundakan seasons
of 2007 and 2008. The soil at Pattambi was lateritic sandy clay loam with pH 4.96
and medium fertility, and that at Alappad Kole was clayey in texture with pH 5.0
and of high fertility.
At both locations, the density and dry weight of weeds at 45 and 60 days
after transplanting (DAT) were higher in all the SRI treatments especially when
weed control was done through repeated cono weeding.
At Pattambi, weed density and weed dry weight were the lowest in
conventional system with post emergence herbicides, which recorded lower
nutrient removal by the weeds and the lowest weed index and also higher gross
return, net return and B:C ratio. The weed density and dry weight in the SRI fields
were the lowest with pre emergence herbicide followed by hand weeding at 30
DAT, but the use of post emergence herbicides showed higher B:C ratio.
At Alappad Kole, the weed density and dry weight, both at 45 and 60
DAT, were the lowest in conventional system with cono weeding at 10 DAT
followed by post emergence herbicides. Cono weeding followed by hand
weeding, pre emergence herbicides followed by hand weeding as well as the use
of post emergence herbicides were also equally effective in controlling the weeds
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in the conventional system, and were on par in the B:C ratios. In the SRI plots
cono weeding at 10 DAT followed by post emergence herbicides recorded the
lowest weed density and dry weight, however, use of post emergence herbicides
recorded the highest net return and B:C ratio among the SRI treatments.
Thus, considering the acute shortage and high wages for the labourers in
Kerala, weed management through post emergence herbicides will be the
preferable option for the farmers in both conventional and SRI systems of rice
cultivation.
Comparison between the two systems of rice cultivation at two different
rice growing ecosystems showed that SRI improved the performance of individual
hills through higher number of tillers hill-1, root length and root dry weight hill-1.
On the other hand, the tiller number, dry matter production, root dry weight and
productive tillers per unit area were higher in the conventional treatments. Owing
to higher number of productive tillers per unit area the grain yield of conventional
treatments was significantly higher than that of the typical SRI.
At Pattambi, conventional system with post emergence herbicides
recorded higher number of productive tillers m-2, panicle length, number of filled
grains panicle-1, 1000 grain weight and grain yield (2877 kg ha-1), which was 33
per cent higher than the grain yield in the typical SRI. This treatment also
recorded significantly higher B:C ratio (1.27) compared to that (0.91) of the
typical SRI. However, the highest straw yield (2510 kg ha-1) at Pattambi was
observed in ‘SRI with cono weeding at 10 DAT followed by post emergence
herbicides’, which was on par with the typical SRI treatment.
At Alappad Kole, higher number of productive tillers m-2, more filled
grain percentage, highest 1000 grain weight, highest grain yield (6073 kg ha-1)
and highest straw yield (5109 kg ha-1) were recorded by conventional system with
cono weeding followed by hand weeding, which showed an increase of 93 per
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cent in grain yield, with an additional yield of 2934 kg ha-1, and 109 per cent in
straw yield over the typical SRI and recorded the highest gross return, net return
and B:C ratio (2.46).
Thus, the study showed the superiority of conventional system of rice
cultivation at a spacing of 20 cm x 10 cm over the SRI system at a spacing of 30
cm x 30 cm at both the two different rice growing ecosystems studied viz., the
sandy loam soils at Pattambi and the clayey soils at Alappad Kole.
Prototype of the self propelled cono weeder was developed and field
tested. It works satisfactorily in a single forward pass, and covers an area of 0.1 ha
h-1. The field study showed that the self propelled cono weeder is effective for
inter row weeding in rice, however, further refinement is needed to improve its
weeding efficiency.