Agriculture Reference
In-Depth Information
14
12
10
8
6
4
2
0
0
50
75
100
125
Dose of nitrogen (u/ha)
nitrogen at sowing
nitrogen at the 50 cm stage
Fig. 5.12.
Hurd yield as a function of nitrogen dose (added in addition to existing soil nitrogen content)
and the date of fertilization (at sowing and at 50 cm stage) (ITC, 2003 (FNPC)).
50
45
40
35
30
25
20
0
50
75
100
125
Dose of nitrogen (u/ha)
Nitrogen at sowing
Nitrogen at the 50 cm stage
Fig. 5.13.
Fibre content as a function of applied nitrogen (in addition to nitrogen content of soil) and date
of fertilization (at planting and at 50 cm stage) (ITC, 2003 (FNPC)).
This series of trials reveals a progressive drop
in yield when hemp is grown as a monoculture
(cultivated on the same fields for 12 years).
This is a real-life example.
seed maturity so that the timing is optimized.
Harvest must be accomplished within a narrow
window of only 4-5 days around that date.
5.4.7 Retting
5.4.6 Harvesting date
When the cut crop is retted on the ground ('dew
retting'), hurd weight remains constant over the
2-3 weeks following cutting, irrespective of the
harvest date (FNPC, 2001, 2002). It then declines
rapidly, with a loss in dry matter of 30-50% in
1.2-2 months. The hemp hurd decomposes and
residue remains on the land after bailing.
Change in the fibre concentration during
the retting process appears to depend on the
date of harvest. Later harvest favours a constancy
in the fibre content, with levels remaining high
Hurd yield is higher if harvest is very early (
c
.20
August; See Fig. 5.17). At maturity, hurd
weight declines slightly but the weight of the
fibre component is relatively stable; thus, the
percentage of fibre content is slightly higher for
later harvest dates (September; See Fig. 5.18).
For seed, the later the harvest, the greater the
yield; more so for late flowering varieties (Fig. 5.19).
Seed harvest is not started until greenlighted by a
laboratory inspection of samples to determine
