Agriculture Reference
In-Depth Information
Table 5.1.
The effect of light competition from leeks or celery on the biomass of
stands of the weed groundsel,
Senecio vulgaris
, which emerged at a range of dates
(0, 10, 20, 30 and 40 days) after transplanting the crops. These weights were
recorded 90 days after crop planting and are the means of three observations
(
SEM
13) (from Baumann
et al
., 2001, Table 3).
Biomass of groundsel (g/m
2
)
Groundsel
emergence day
0
10
20
30
40
Under leek
191
137
43
39
.6
12
.. 66
Under celery
165
62
7
0.6
0.01
Groundsel only
222
-
-
-
-
Fig. 5.1.
Fraction of light (PAR) interception by stands of leek
▫
, celery
●
and a
leek-celery intercrop
, growing from late May through to August in Switzerland.
Plant populations were 18 and 9 plants/m
2
for leek and celery, respectively, and the
intercrop was alternating rows of the two species at the same within-row spacing as
in their monocrops (from Baumann
et al
., 2001. Courtesy of
Annals of Botany
).
Experiments in the UK showed that the yield of spring-sown bulb onions
exposed to competition from a natural arable weed flora on unweeded plots was
only 3% of that on weed-free plots (Roberts, 1973). In these experiments the
maximum relative growth rate recorded for onions was 0.12/day, whereas the
weeds had a maximum of 0.18/day, and this occurred at an earlier and cooler
stage of the growing season. The result of this, and the slower seedling
emergence of the onions than some weeds, was that by early June the dry weight
of weeds was 20-fold the crop dry weight.
The consequence of weed competition is, of course, low yield. Complete
crop failure will occur if weed competition is not prevented in direct-sown
