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PHYLLOCHRON CONSIDERATIONS
The length of
phyllochron (~ 4 to 8 days) depends on the number
and extent of stresses. Phyllochron length reflects the "speed"
of the rice plant's "biological clock." The rate of cell
division and specialization is affected by many factors, as different
extra-cellular variables influence various cellular processes.
Stress
refers to negative influences/constraints, whereas growth
factors, a better term, can be either favorable or unfavorable,
along a continuum from positive to negative.
- Any single
negative growth factor may be dominating, visually represented
by Liebig's concept of "barrel staves" as limiting factors.
- Stress/growth
effects are mediated or given effect through the production of
cytokinins and other hormones in cells regulating cell division
or through other processes mediated by enzymes and genes.
| POSITIVE
FACTORS
(speed up biological clock) |
NEGATIVE
FACTORS
(slow down biological clock) |
No.
of phyllochrons of growth completed before panicle initiation (PI)
| will
be GREATER |
will
be FEWER |
depending
on
I. Climate
and Temperature (soil > air):
| *WARMTH* |
*COLD* |
| SRI
keeps soils unflooded to capture solar energy |
Flooding
of soils reflects solar radiation and insulates the soil
|
| *LONGER
DAYS* |
*SHORTER
DAYS* |
| More
insolation; greater day/night temperature differential reduces
respiration at night |
Less
insolation; warmer nights favor more respiration and loss of
plant energy.
|
II. Plant Management
| *WIDE
SPACING* |
*NARROW
SPACING* |
| 25x25cm
spacing or wider and one plant per hill reduces competition
among roots |
More
plants per m2 causes more root competition and less root system
development |
| *
EXPOSURE TO SUN* |
*
SHADING* |
| Less
shading within the canopy gives more photosynthesis |
Reduced
photosynthesis;
total depends also on leaf area |
III. Water
Management
| *
SOIL MOISTURE * |
*DROUGHT* |
| Light,
intermittent irrigation provides sufficient water, while limited
water supply plant stimulates root growth |
Inadequate water from irrigation or rainfall creates serious
stress on plant
|
| *
OXYGEN * |
*
HYPOXIA* |
| Available
in unsaturated soil; weeding done with "rotating hoe"
will aerate surface horizons |
Flooding
and pan created by conventional methods keep soil continuously
saturated, which inhibits root growth |
IV. Soil Management
| *
PERMEABILITY* |
*
COMPACTION* |
| Root
growth is promoted by compost, microorganisms, and aerated soil;
also more O2 |
Flooding and any mechanization inhibit root growth; reduces
O2 |
V. Nutrient
Management
|
*
NUTRIENT SUPPLY* |
*LIMITED
NUTRIENTS* |
| Balanced
and continuous (even if small) quantity is provided through
compost and microorganism acitivity in soil |
Imbalance
and "lumpiness" of nutrients supplied with chemical
fertilizer; if no nutrient amendments, too few nutrients are
available?
|
With 60-day period
to panicle initiation (PI)
- Positive
growth factors on left speed up the "Biological Clock"
- Negative
growth factors (stress) on right slow down the "Biological
Clock"
| 8-day
phyllochron (common average) |
7.5 phyllochrons
(10 tillers) |
| 7-day
phyllochron |
8.5
phyllochrons
(17 tillers) |
| 6-day
phyllochron |
10
phyllochrons
(33 tillers) |
| 5-day
phyllochron (presently possible) |
12
phyllochrons
(84 tillers) |
| 4-day
phyllochron (presently impossible) |
15
phyllochrons
(>250 tillers) |
- More
tillers means a greater number and density of roots
-- Larger root system supports more grain filling
- Most
Important: In unflooded soil, no degeneration of roots
-- (60-80% degeneration in flooded soils)
|
Tefy
Saina