Agriculture Reference
In-Depth Information
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Varieties
Fig. 5.5.
Stem diameter as a function of plant variety (FDGEDA de l'Aube, 1999).
5.4 Agronomics
harvest and this can affect the quality of the
seed crop adversely.
5.4.1
Date of sowing
Effect of sowing date on yields
Emergence takes place at 85 GDD
2
after sow-
ing (the temperature is recorded from the
ground at the level of the bed where the
seed is sown). When rainfall is abundant after
planting, emergence may be delayed and poor.
Even if plants emerge precisely 90 GDD after
sowing, the density at emergence declines
when soil temperature is low (FNPC, 2000).
Whatever the date of sowing, flowering
will only begin once 800-900 GDD have
accumulated. The start of flowering varies from
May to August, depending on the date of sow-
ing. This stage is primarily thermophotoperi-
odic (FNPC, 2000, 2002).
For both early planted (February and
March) and late planted (end May, June and
July) seeds, the total accumulated GDD require-
ment is close to 900. For planting in April and
May, the requirement approaches 1100 GDD.
Regardless of the date of sowing, full flow-
ering and termination of flowering will occur
on an identical date for a given latitude and
variety, with the following exception: planting
after mid-June may not achieve the tempera-
ture accumulation required for flowering. In
this case, flowering is determined solely by
photoperiod. The duration of flowering is thus
largely dependent on sowing date, that is, flow-
ering will be longer with early sown crops and
more restricted for late sown crops.
The effect of an extended flowering period
is non-uniformity of plants in the stand at
Hurd yield is determined by the duration of the
vegetative growth phase, which ceases at
flowering; hence, yield is diminished the later
the planting date (Fig. 5.6). However, planting
date does not appear to affect the
percentage
of fibre in the hurds (assuming the stand is well
established). The best grain yields are obtained
from crops sown in April, when the climatic
conditions are the most favourable. If sown too
early, flowering will be too spread out and will
result in a large proportion of unripened seeds
at harvest.
5.4.2
Density of sowing
Density of plants at emergence
and density at harvest
A positive correlation exists between the den-
sity of seeds sown and the population at har-
vest, as well as between the density sown and
the density at emergence (Fig. 5.7).
In all the trials, loss of population density
in the stand was recorded between sowing and
emergence and averaged around 10%. Higher
losses were found where the seeding rate was
elevated, reflecting the fact that at low density
there is less competition between plants.
Losses in density between emergence and
harvest were more important (up to 50% in
