Rice plant population guidelines
July 2016, Primefact 1476, first edition
Brian Dunn, Research Agronomist, NSW DPI, Yanco
Tina Dunn, Technical Officer, NSW DPI, Yanco
Lower plant population limit
Rice growers should aim to achieve a plant
2
population in the range of 100 to 300 plants/m for
all sowing methods. This provides a buffer before
grain yield declines should establishment problems
occur.
Gross margin analysis using 2015 input costs and
contractor rates reveal that yields of 4.8 t/ha for
aerial sown rice and 3.7 t/ha for drill sown rice are
required to cover the gross margin input cost of a
crop (Table 1).
No difference in grain yield was observed for plant
2
populations between 40 and 700 plants/m in
research where a direct comparison between plant
population and grain yield was measured at over
800 sites (Figure 1).
A minimum plant population of 10 plants/m can
achieve these critical yield levels; provided the
plants are uniformly distributed and best
management practice is followed.
Figure 1. Grain yield response to plant population
(red squares are average of 25 sites).
2
Table 1. Gross margin for growing a 10 t/ha rice crop
with a water cost of $16/ML variable charge
Gross margin
Aerial sown
water @ $16/ML
$/ha
t/ha
$/ha
t/ha
3500
10.0
3500
10.0
983
2.8
457
1.3
1691
4.8
1284
3.7
1809
5.2
2216
6.3
Income 10 t/ha @
$350/t
Crop establishment
costs
Total gross margin
costs
Gross margin profit
Drill sown
Measuring plant number when
establishment is poor
High grain yields can be achieved with plant
2
populations below 40 plants/m , but there is a
declining trend in yield with decreasing plant
population (Figure 1). At low plant populations it
becomes increasingly important that plants are
evenly spaced for grain yield to be maintained.
The varieties tested included Reiziq, Sherpa,
Langi, Opus, Topaz and Koshihikari. All responded
similarly to changes in plant population.
As plant population decreased, the number of tillers
each plant produced and the number of grains per
panicle increased. Both of these factors combine to
help maintain grain yield at low plant populations.
At low plant populations the distribution of plants is
often more important than the number of plants.
Therefore, a method to determine plant population
and distribution when establishment problems
occur has been devised.
In each zone in the field with different plant
population levels, ten plant counts using the rice
2
ring (0.2 m ) should be obtained.
An average of two plants per ring from the ten rings
2
counted is needed to meet the 10 plants/m
requirement.
If more than three of the rings have only one plant
or one ring has zero plants then re-sowing the poor
establishment areas in the field is recommended.
Rice plant population guidelines
Figure 2. Aerial sown rice with a plant population of
2
37 plants/m yielded 10.4 t/ha.
requires a maximum sowing rate of 150 kg/ha. If
establishment at 150 kg/ha is as low as 20% there
2
will still be 100 plants/m established, which is
sufficient to achieve maximum grain yield when
best management practice is adhered to.
Recommended sowing rates for all rice varieties
and sowing methods, based on actual seed size
and establishment percentage, are presented in
Table 2.
Table 2. Sowing rates required to meet plant
population recommendations based on seed size
and varietal establishment percentage.
Variety
Upper plant population limit
The upper plant population limit for aerial and drill
sown rice and delayed permanent water is 300
2
plant/m . The results are not conclusive that very
high plant populations are not more prone to cold
induced sterility, but there is no yield advantage in
having a plant population above this level and seed
costs will be higher.
Sowing rate
(kg/ha)
Reiziq & Topaz
150
Sherpa, Langi, Doongara, Opus,
Koshihikari & Kyeema
130
Increasing sowing rates to compensate for poor
field layout, unsatisfactory seedbed preparation or
unreliable sowing method is rarely successful at
increasing plant population and not recommended.
Summary of main points
Figure 3. A row spacing of 36 cm could not maintain
yield at low plant populations.
The recommended rice plant population range is
2
between 100 to 300 plants/m for all sowing
methods.
Rice grain yields do not decline due to plant
number until plant populations go below 40
2
plants/m .
The plant population limit required to cover the
2
input costs of production is 10 plants/m , as long as
the plants are uniformly spaced.
The rice ring should be used to determine if
resowing is required at low plant populations.
Row spacing between 18 and 27 cm are
recommended for drill sown rice.
Row spacing for drill sown rice
Row spacing between 18 and 27 cm is
recommended for drill sown rice. Grain yield is
reduced when rows are spaced wider than 27 cm
as missing rows, or gaps within rows, cannot be
compensated for by neighbouring plants.
There is no advantage in a row spacing narrower
than 18 cm. There is no potential for increased
grain yield, the equipment is more expensive to
purchase and maintain and is more prone to
blockages by trash.
Recommended sowing rates
Rice should not be sown at rates higher than 150
kg/ha for any variety or sowing method. To
2
establish 200 plants/m at 40% (the measured
average establishment percentage of rice seed)
2
NSW Department of Primary Industries, June 2016
It is not recommended to sow more than 150 kg/ha
of seed for any variety or sowing method.
Acknowledgments
This research was funded by RIRDC and NSW
Department of Primary Industries.
For updates go to www.dpi.nsw.gov.au/factsheets
© State of New South Wales through the Department of Industry, Skills
and Regional Development, 2015. You may copy, distribute and
otherwise freely deal with this publication for any purpose, provided that
you attribute the NSW Department of Primary Industries as the owner.
Disclaimer: The information contained in this publication is based on
knowledge and understanding at the time of writing (July 2016). However,
because of advances in knowledge, users are reminded of the need to
ensure that information upon which they rely is up to date and to check
currency of the information with the appropriate officer of the Department
of Primary Industries or the user’s independent advisor.
ISSN 1832 6668
INT16/73816