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Desember 2017
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Delayed planting
impacts sunflower yield
S
unflower is classified as the third
largest grain crop produced in
South Africa after maize and wheat.
According to the Crop Estimates
Committee 2016/2017, the production fore-
cast for sunflower is 821 970 tons. Sunflow-
er is primarily used for the manufacturing
of sunflower oil for human consumption and
oil cake for animal feed.
Over the years, sunflowers have received
the status of an ideal crop to grow in South
Africa under conditions of low-input farm-
ing and marginal cropping conditions. It
produces relatively consistent yields un-
der adverse weather conditions and their
overall characteristic of drought-tolerance
makes it an attractive crop for producers in
dryland production regions.
Sunflower is particularly efficient in extract-
ing water from the soil profile, especially in
sandy loam soils. Accordingly, it tolerates
drier conditions better than other crops and
explains the surprising yields achieved by
producers in the drought stricken regions
during the 2014/2015 growing season.
Unlike other grain crop alternatives, sun-
flower has a relatively long period, or ‘win-
dow,’ of possible planting dates, extending
from the first of November to late January.
The yield components of sunflower, heads
per hectare, seeds per head, and weight per
seed, are determined during different peri-
ods of growth.
The prevailing environmental conditions
during these growth stages thus ultimately
determine yield. To better understand the
effect of planting date on yield, however,
sunflower development can be simplified
into three growth stages:
Planting to floral initiation (GS1)
Floral initiation to bloom (GS2)
Bloom to physiological maturity (GS3)
Growth stage 1 (GS1)
This growth stage begins when the seed
is planted and ends when floral parts of
the sunflower are initiated. Floral initiation
cannot be directly observed, but occurs be-
tween the ten to 14 leaf stage or approxi-
mately two-thirds of the way through the
period from planting to bloom.
Comparing the three growth stages, sun-
flower in GS1 is the most delicate and sen-
sitive to stress, yet if stress occurs it has
the least effect upon yield. The plant must
only remain alive to maintain the yield com-
ponent of heads per hectare.
Growth stage 2 (GS2)
Although the beginning of this growth stage
is not readily recognisable, it represents an
important event determining the final yield.
The floral parts, which later become the har-
vested seeds, are formed during this stage.
After the seeds are initiated, they expand to
form the visible bud and eventually the sun-
flower head, which blooms and completes
GS2. The head size, or the number of seeds
per head is established during this stage.
Any stress that limits the growth rate during
GS2 will be reflected in a reduced number of
seeds per head. Drought stress during this
stage reduces yield more than any other
phase of sunflower development.
ON FARM LEVEL
Sunflower / Planting date / Yield
Management practices
DR SAFIAH MA’ALI,
ARC-Grain Crops, Potchefstroom
Graph 1: Rainfall (mm) and sunflower seed yield (t/ha) data from 2007/2008 till 2015/2016 growing
season at Potchefstroom.
Graph 2: Sunflower seed yield (t/ha) at different planting dates over 38 trials planted at
Potchefstroom during 2007 to 2016 growing seasons.
Graph 3: Probability (%) exceeding different yield potentials for three planting dates over
38 sunflower trials planted at Potchefstroom from 2007 to 2016 growing seasons.