Agriculture Reference
In-Depth Information
Fig. 4.20.
The recovery of elongation growth in onion shoots on sloping filter paper
following exposure to mechanical impedance in sand equivalent to 0.53 MPa
penetrometer pressure for 0 (
). The
curves shown were obtained using Eqn 4.12. Only one curve is shown for the 0
and 5 day treatments since time to germinate is 5 days at 20°C (from Whalley
et al
.,
1999. Courtesy of
Plant, Cell and Environment
).
●
), 5 (
), 9 (
), 14 (
), 19 (
) or 35 days (
▫
Table 4.4.
Explanation of symbols in Eqn 4.14.
Symbol
Value
Units
Definition
t
°C day
Thermal time since start of germination (base temperature
2.1°C)
t
g
90
°C day
Thermal time needed to germinate
b
0.01044
°C day
A fitted constant
L
mm
Shoot length
A
67
mm
Maximum shoot length in the absence of mechanical
impedance
MPa
Water potential in soil
L
1.1
MPa
Water potential that just prevents elongation
q
MPa
Mechanical impedance measured by penetrometer
(see text above)
q
L
1.111
MPa
Mechanical impedance that would just prevent extension
growth
n
Dimensionless scaling parameter
