Abstract:
A series of outdoor experiments were conducted to
determine the nature of the competitive relationships between the perennial grass-weed torpedograss
( Panicum reDens L.) and two broad-leaf vegetable
crops, mungbean Phaseolus aureus Roxb. ) and
tomato ( LvcoDersicon esculentum Mill.).
Increasing weed density significantly reduced the
growth and yield of both mungbean and tomato, but
the overall adverse effects on tomato were greater
than on mungbean. A weed density of 8 plants/ pot
did not significantly reduce the mean shoot dry
weight or Leaf area Index of mungbean, but this
density reduced the mean root dry weight significantly, by 52%, indicating that significantly
'below-ground' competition had occurred. Tomato was
much more sensitive to competition both below- and
above-ground. Even the presence of a single weed
39.6\ and 69.7% respectively, compared with the
"weed-free" condition.
plant (density I weed plant/ pot) significantly
reduced the mean shoot dry weight, mean root dry
weight and Leaf Area Index of tomato by 56.7\,
".
The presence of torpedograss upto 4 weeks after
transplanting of mungbean, did not alter any of the
crop growth parameters significantly, but the
presence of weed competition beyond 6 weeks reduced
yield parameter significantly. The whole-season
'unweeded' mungbean gave 54% of the yield of the
whole-season 'weed-free' check. In the case of
tomato, the 'unweeded' crop gave only 13.8% of the
yield of the 'weed-free' crop, indicating that
tomato was more sensitive to competition by
torpedograss.
When tomato was kept 'weed-free' from week.- 4
onwards at least, a yield similar to that of wholeseason 'weed- free' check was obtained. Similarly,
the presence of the weed beyond the first 4 weeks
reduced tomato yields significantly to a level
comparable with the whole-season 'weedy' check.
Both these results strongly indicated the sensitivity of tomato to the presence of the weed dur ing
the 'critical' first four - six weeks after transplanting. Mungbean was found to have significantly
greater Leaf Area Index and initial growth rate
compared to tomato and hence appeared to withstand
competition from the grass-weed better. When the
nature of the competitive relationship was further
investigated with the 'replacement series'
approach, evidence was obtained that mungbean and
torpedograss were not vigorously 'excluding' each
other. The relative yields of mungbean was not
significantly affected by the weed, based on any
parameter such as shoot, root, or total plant and
leaf area, and the relative yield totals of the
association did not differ from unity, significantly. On the other hand, the relative yields of
tomato (based on above parameters) were significantly depressed in the presence of torpedograss
compared to monoculture yields. Torpedograss also
showed significantly greater "gains" in this
association,
I,
based on the yield of a number of
growth parameters. The relative yield totals of
the torpedograss and tomato association however,
did not deviate significantly from unity, probably
indicating that the "gains" made by the weed, were
balanced by the "losses" of the crop.
The overall results of the study indicated that
unlike with the less sensitive mungbean, the growth
and yields of tomato were significantly reduced by
torpedograss. The basis of the competitive
advantage mungbean has over the weed, appeared to
be due to the rapid and relatively extensive leaf
area production.