Maclean et al. - 2002 - Rice almanac source book for the most important e

Amount of growth
Ineffective
tillers
Tiller number
Grain weight
Plant height
Panicle
number
0 30 60 90 120
Days after germination
Germination
Emergence
Seedling growth
Active tillering
End of effective tillering
Maximum tiller number
Panicle primordia initiation
Booting
Heading/anthesis
Milky
Dough
Yellow-ripe
Maturity
Vegetative Reproductive Ripening
Fig. 5. Schematic of growth of a 120-d rice variety
in the tropics.
leaf emergence at regular intervals. Tillers that
do not bear panicles are called ineffective tillers.
The number of ineffective tillers is a closely
examined trait in plant breeding since it is
undesirable in irrigated varieties, but sometimes
an advantage in rainfed lowland varieties in
which productive tillers or panicles may be lost
because of unfavorable conditions.
Reproductive phase
The reproductive growth phase is characterized
by culm elongation (which increases plant
height), a decline in tiller number, emergence of
the flag leaf (the last leaf), booting, heading, and
flowering of the spikelets. Panicle initiation is
the stage about 25 d before heading when the
panicle has grown to about 1 mm long and can
be recognized visually or under magnification
following stem dissection.
Spikelet anthesis (or flowering) begins with
panicle exsertion (heading) or on the following
day. Consequently, heading is considered a synonym
for anthesis in rice. It takes 10–14 d for a
rice crop to complete heading because there is
variation in panicle exsertion among tillers of the
same plant and among plants in the same field.
Agronomically, heading is usually defined as the
time when 50% of the panicles have exserted.
Anthesis normally occurs from 1000 to 1300
hours in tropical environments and fertilization is
completed within 6 h. Very few spikelets have
anthesis in the afternoon, usually when the
temperature is low. Within the same plant, it
takes 7–10 d for all the panicles to complete
anthesis; the spikelets themselves complete
anthesis within 5 d.
Ripening follows fertilization and can be
subdivided into milky, dough, yellow-ripe, and
maturity stages. These terms are primarily based
on the texture and color of the growing grains.
The length of ripening varies among varieties
from about 15 to 40 d. Ripening is also affected
by temperature, with a range from about 30 d in
the tropics to 65 d in cool temperate regions,
such as Hokkaido, Japan, and Yanco, Australia.
Soils
Rice soils are wetland soils that are grown to
rice. Wetlands are defined as having free water at
or near the surface for at least the major part of
the growing season of arable crops, or for at least
2 mo of the growing season of perennial crops,
grasslands, forests, or other vegetation. The
floodwater is sufficiently shallow to allow the
growth of a crop or of natural vegetation rooted
in the soil. Free surface water may occur
naturally, or rainfall, runoff, or irrigation water
may be retained by field bunds, puddled plow
layers, or traffic pans.
Wetlands have at least one wet growing
season, but may be dry, moist, or without surface
water in other seasons. Wetland soils may
therefore alternately support wetland and upland
crops when cultivated.
The transition from wetlands to uplands is
often gradual. It may fluctuate from year to year,
depending on variations in precipitation, runoff,
or irrigation. If water (both drainage and irrigation)
can be fully controlled, farmers can choose
to establish wetlands or uplands. But, in most
wetlands, drainage capacities are insufficient to
prevent soil submergence during the rainy season,
particularly in the lowlands of the humid tropics.
The presence of “aquic” soil conditions is
indicated by redoximorphic features, such as
zones of accumulation and depletion of Fe and
14 Rice almanac