Series: Potato production in a
changing climate. III. What is in
store for the Eastern Free State?
Dr Linus Franke, Prof Martin Steyn and Prof Anton Haverkort
In the previous two issues of CHIPS we reported on how
we expect climate change to affect the future climate of
South Africa and how that will affect potato production
in Limpopo (May / June 2014) and the Sandveld (July /
August 2014).
Climate Risks
In brief, climate forecasts suggest that between 1960
Page 36 •
CHIPS • September/Oktober 2014
and 2050 average air temperatures of South Africa are
expected to increase on by 2oC, while atmospheric CO2
levels are expected to increase by about 235 ppm from
315 to 550 ppm. These higher temperatures will likely
increase crop heat stress and evapotranspiration demand,
while the higher atmospheric CO2 levels are expected
to have a strong positive effect on potato yields and
at the same time reduce crop transpiration rate (water
requirements).
Tegniese Nuus • Technical News
In this last article in the series of three,
we report on how climatic conditions
are expected to change in the Eastern
Free State, how that will affect potato
crops and how growers can adjust their
practices to utilise the available growing
season best. We again investigated
how optimal planting dates for potato
may shift as a result of climate change
by looking at the forecasts for yields
and water use efficiencies (WUE) in
a theoretical situation where potato is
planted each month of the year with a
fixed growing period of 120 days.
Suitable growing periods
In the Eastern Free State the number of
hot days (maximum daily temperature
> 35oC) in the growing season will
increase more than threefold between
2010 and 2050 if the crop is planted
in November (Figure 1). Nevertheless,
there will still only be about 15 hot days
in the growing season if planting occurs
in late spring / early summer, compared
with over 40 days in the Sandveld
summer growing season.
No. of days with Tmax>35oC
Eastern Free State
20
1961-1970
18
2001-2010
16
2040-2049
14
12
10
8
6
4
2
0
Jan Feb
Mardays
Apr(maximum
May Jun temperature
Jul Aug Sep>35°C)
Oct Nov
Dec a 120-day
Figure 1. Number
of hot
during
growing period following planting
on the
15th of each month during three periMonth
of planting
ods (1961-1970, 2001-2010 and 2040-2049) in the Eastern Free State.
Figure 1. Number of hot days (maximum temperature >35 °C) during a 120-day growing
period following planting on the 15th of each month in the Eastern Free State.
Eastern Free State
Dec
Oct
Sep
Month
The net effect of climate change on
potato production in South Africa
will depend strongly on the specific
production region and the ability of
farmers to adapt production practices to
changing conditions. We have shown
that in both the Limpopo and Sandveld
regions, summer growing seasons are
expected to become less favourable
for potato production due to heat
stress. As a result, the suitable summer
growing period for potatoes without
excessive heat stress will become shorter.
In Limpopo the risk of winter frost is
expected to disappear and as a result,
potato growers will probably be able
to advance their main potato planting
date to late autumn in order to best
utilise the heat and frost free growing
period. Similarly, early spring planting
dates will give best potato yields in the
Sandveld. Yields for summer plantings
in both these regions are expected to
drop drastically, while winter yields will
increase substantially.
Jul
May
Apr
Feb
Jan
1960
Last day with frost
First day with frost
1970
1980
1990
2000
2010
2020
2030
2040
2050
Year
Figure 2. Changes in the length of the suitable potato growing season in the Eastern
Free State between 1961 and 2050: Dates with the first (x) and last (▲) frost are
Figureindicated.
2. Changes
in the
length
the suitable
potato
growing
season
the EastThe lines
indicate
theof
approximate
planting
(dotted
upper line)
and in
harvest
ern Free
State
between
1961
2050:
Datesthe
with
the
first towards
(x) and2050,
last (s) frost
dates
(solid
lower line).
Theand
distance
between
lines
decline
indicatingThe
that the
frost
free period
for crop
growth is(dotted
getting shorter
are indicated.
lines
indicate
theunsuitable
approximate
planting
upperwith
line) and
time.
harvest dates (solid lower line). The vertical distance between the lines decline
towards 2050, indicating that the cold period unsuitable for potato production is
getting shorter with time.
The increase in temperatures (especially in early spring) is generally
expected to benefit potato production in this region, as the suitable
period during which potato can be grown without substantial risk of frost
is expected to lengthen considerably over time. The cold winter period
(unsuitable for potato production) will become shorter by some 50 days
between now and 2050 and as a result farmers will be able to start planting
earlier and/or harvest later (Figure 2).
CHIPS • September/October 2014
• Page 37
The Eastern Free State is predominantly a dry land
potato production area and therefore crop performance
is highly dependent on total rainfall and seasonal
rainfall distribution. Climate change forecasts of rainfall
are associated with a high degree of uncertainty, but
indications are that the number of dry spells (>10 days
without rain) in the Free State will not change substantially
in future.
Changing yields and water use efficiencies
Crop growth model simulations suggest that potential yields
(highest theoretical yields in any region if no limitations
occur) in the Eastern Free State will increase by 15 to 20%,
but the best planting dates that give highest potential yields
will move earlier from October-November to SeptemberOctober (Figure 3). The reduced risk of frosts and higher
temperatures will allow earlier planting in spring but at
similar temperatures than currently. This benefit will only
materialise in practice if sufficient rainfall occurs early
in spring to allow for earlier planting, or if supplemental
irrigation will be possible. When planting occurs after
October, the increase in warm and hot days will reduce
photosynthetic rate and cancel out the benefit of higher
CO2 levels.
Advancement in the planting date to optimise yield and
avoid hot temperatures will also bring the optimal planting
time closer to the time that gives the highest water use
efficiencies (WUE) for this region. WUE is currently highest
for September plantings and is expected to remain the
month with highest WUE in future (Figure 3).
Conclusions
• The length of the growing season suitable for potato
production during the Eastern Free State summer will
increase substantially due to higher temperatures in
early spring and late autumn.
• Potato producers in the Eastern Free State region can
reap the benefits of increased CO2 levels and
increasing photosynthetic rate through higher expected
yields and lower water requirements by the crop.
• When the crop is grown in mid-summer, however, these
benefits will be counteracted by an increased incidence
of heat stress and increased evapotranspiration
demand.
• Producers can respond to climate change by advancing
planting dates to early spring, provided that sufficient
rainfall will occur to allow for earlier planting.
• These cooler periods of the year (early spring plantings)
are expected to increase potato yields and water use
efficiencies due to higher photosynthetic rate, less cold
stress and more rapid early canopy development.
Page 38 •
CHIPS • September/Oktober 2014
Opsomming
• Die lengte van die geskikte aartappel groeiseisoen in die Oos-Vrystaat gaan in die
toekoms na verwagting aansienlik verleng
weens hoër temperature in die lente en laat
herfs.
• Aartappelprodusente in die streek sal
suksesvol by klimaatsverandering kan
aanpas deur vroeër in die lente te plant, met
die veronderstelling dat genoeg reën reeds
vroeg in die lente sal val.
• Produsente gaan verder voordeel trek uit
die verhoogde CO2 vlakke en
gepaardgaande verhoogde fotosintesetempo,
aangesien opbrengs na verwagting gaan
verhoog en waterbehoeftes gaan afneem.
• Indien aartappels egter gedurende
die warm somermaande verbou word, sal
hierdie voordelige effek teengewerk word
deur ’n verhoging in hittestremming en hoër
evapotranspirasie aanvraag.
• Aanplantings gedurende die koeler tye van
die jaar (vroeë lente) sal na verwagting lei tot
hoër opbrengs en waterverbruiksdoel treffendheid vanweë hoër fotosintesetempo,
minder koue stremming en vinniger vroeë
loofontwikkeling.
• Om die voordele wat klimaatveranderinge
gaan meebring ten volle te benut, sal
produsente buiten planttye ook addisionele
aanpassings moet oorweeg. Byvoorbeeld
Oos-Vrystaatse produsente kan oorweeg om
in die toekoms langer groeiseisoen kultivars
aan te plant om die langer groeiseisoen
optimaal te benut.
• Om voorsiening te maak vir die verwagte
hoër opbrengspotensiaal, sal aanpassings in
bemesting waarskynlik ook gemaak moet
word.
• Siekte- en pesdruk gaan waarskynlik toeneem
met die verwagte styging in temperature, wat
die koste van gewasbeskerming sal laat styg.
Tegniese Nuus • Technical News
• To capitalise on the opportunities
offered by climate change to increase
yields and lower water use in potato
production systems, not only
adaptation in planting time, but also
in other aspects of the cropping
system is needed. For instance, in
future, longer duration cultivars may
enable Eastern Free State farmers to
take advantage of the longer
growing season.
• Yields can also increase substantially
if supplemental irrigation is applied
during critically dry spells.
• To realise higher yields with
increasing potential yields, changes
in nutrient levels are also likely to be
required.
• The pressure of pests and diseases in
general is likely to increase with
higher temperatures and this may
require additional investment in crop
protection measures.
The Authors
A.C. Franke1,3, J.M. Steyn2, A.J.
Haverkort1,2
1) Wageningen University and Research
Center, P.O. Box 430, 6700 AK,
Wageningen, the Netherlands
2) Department of Plant Production and Soil
Science, University of Pretoria, Private
Bag X20, Hatfield 0028, South Africa
3) Current address: Department of Soil,
Crop and Climate Sciences, University of
the Free State, P.O. Box 339,
Bloemfontein 9300, South Africa C
Figure 3. Calculated potential fresh tuber yield (top) and water use efficiency
(WUE) (bottom) of a 120 day crop planted on the 15th of each month during
three periods (1961-1970, 2001-2010 and 2040-2049) in the Eastern Free State.
CHIPS • September/October 2014
• Page 39