Series: Potato production in a
changing climate II. What are
the prospects for the Sandveld?
Dr.Linus Franke, Prof Martin Steyn and Prof Anton Haverkort
In earlier issues of CHIPS we reported on how climate
change is expected to affect future potato production in
South Africa (September / October 2012) and Limpopo
Province (May / June 2014). In short we reported that between 1960 to 2050 the air temperatures of South Africa
are expected to increase by 2°C on average, while atmospheric CO2 levels are expected to increase by about 235
ppm (from 315 to 550 ppm). The higher temperatures will
increase crop heat stress and evapotranspiration demand,
but on the other hand the increase in atmospheric CO2
levels will likely have strong beneficial effects on potato by
increasing yields and reducing crop transpiration.
The net effect of climate change on potato production will,
however, depend on the specific production region and the
ability of farmers to adapt their production practices to the
changing conditions. In Limpopo, for example, the summer
growing season is expected to become too hot for potato
production, while the risk of winter frost may disappear.
As a result, potato growers will probably advance potato
planting dates from winter / early spring to autumn to
utilise the heat and frost free growing period.
In this second article of the series of three, we report on
how conditions will change in the Sandveld and how growers can possibly adapt their practices to cope with these
expected changes. We investigated how optimal planting
dates for potato may shift as a result of climate change by
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CHIPS • Julie/Augustus 2014
looking at the 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
The Sandveld region has a Mediterranean climate, which
is characterised by cool rainy winters and hot dry summers.
Potatoes are produced under irrigation and, depending on
the specific location, usually grown throughout the year.
However, the summer period suitable for potato production
is largely determined by the heat-free period and some
inland areas of the Sandveld are considered too hot for
summer production. For this study we used the Leipoldtville
district, where potatoes can be grown throughout the year.
According to climate projections the number of hot days
with temperatures above 35°C, will more than double in
the Sandveld (from about 20 to over 40 days in the growing season) if planting takes place in November (Figure
1). As a result, the suitable growing period for potatoes
without excessive heat stress during summer (average
maximum temperatures below 28°C) will become shorter.
This is reflected by the closer vertical distance between the
horizontal lines in Figure 2.
Changing yields and water use efficiencies
Crop growth model simulations suggest that for summer
plantings photosynthesis will be negatively affected due
Tegniese Nuus • Technical News
Sandveld
No of days with Tmax>35oC
45
1961-1970
40
2001-2010
35
2040-2049
30
25
20
15
10
5
0
Jan
Feb Mar
Apr
May Jun
Jul
Aug Sep
Oct
Nov Dec
Month of planting
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 Sandveld.
Sandveld
Dec
Oct
Month
Sep
Jul
Day with first heat in spring
Day with last heat in autumn
May
Apr
Feb
Jan
1960
1980
2000
2020
2040
Figure 2. Changes in the length of the suitable potato growing season in the Sandveld
between 1961 and 2050: Dates with the last heat in autumn (x) and the first heat in
spring (▲) are indicated. The lines indicate the approximate planting (dotted lower line)
and harvest dates (solid upper line). The distance between the lines decline towards
2050, indicating that the heat free period suitable for crop growth is getting shorter with
time.
CHIPS • July/August 2014
• Page 39
to heat stress, leading to a potential yield reduction (e.g.
from 46 to 36t/ha-1 when planting in December). Currently highest yields are achieved with August-September
plantings, but Figure 2 shows that the months of planting
with the highest yields will shift about one month earlier to
July-August.
When planting occurs in winter or early spring, a substantial potential yield improvement is expected between 1960
and 2050, with an increase from 46 to 68t/ha-1 for the
June planting (Figure 3). This increase is more than proportional to the CO2 response because the rise in temperature
not only leads to more efficient photosynthesis, as there are
less cold days with suboptimal temperatures for photosynthesis, but also to a more rapid development of foliage
early in the season due to higher temperatures, increasing
the crop’s ability to intercept solar radiation.
WUE will increase for autumn and early winter plantings,
but for a crop growing in summer the WUE will remain
approximately the same. Potato growers in the Sandveld
currently face a trade-off as the planting period giving the
highest potential yield (summer) does not coincide with the
period giving the highest WUE (winter). This conflict will
become less in future as the advancement in planting time
to optimise crop yield will bring the optimal planting time
also closer to the time giving the highest WUE.
Conclusions
• Sandveld summer months will in future become less
favourable for potato production due to an increase in
the number of hot days, resulting in more heat stress.
This will result in a shorter summer growing season.
• Autumn and winter plantings will become more favoura ble for potato production. These cooler periods of
the year (autumn and winter plantings) are expected to
increase potato yields and WUE due to higher photo synthetic rate, less cold stress and more rapid early
canopy development.
• When grown in hot periods of the year these benefits
will be counteracted by an increase in the incidence of
heat stress and increased evapotranspiration, resulting
in lower yields and WUE.
• Sandveld growers can respond to climate change by
advancing planting dates in spring to avoid heat stress
in mid-summer.
• 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, shorter
growing varieties may be preferred to take advantage
of the shorter summer growing season in the Sandveld.
• The pressure of pests and diseases is in general likely
Page 40 •
CHIPS • Julie/Augustus 2014
•
to increase with higher temperatures, which may require
additional investments in crop protection measures.
To realise higher yields, changes in nutrient applications
are also likely to be required. C
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
Opsomming
• Die Sandveld se somermaande gaan in die
toekoms minder gunstig vir aartappelproduksie
word weens ’n toename in die aantal warm dae,
wat tot meer hittestremming gaan lei. Dit sal lei tot
’n verkorte beskikbare somer groeiseisoen.
• Herfs- en winteraanplantings sal meer gunstig
word vir aartappels. Gedurende laasgenoemde
koeler tye van die jaar word verwag dat
opbrengs en waterverbruiksdoeltreffendheid
(WVD) sal toeneem vanweë hoër fotosintese tempo, minder koue stres en vinniger vroeë
loofontwikkeling.
• Indien die gewas egter tydens warm tye van
die jaar geproduseer word, sal hierdie voordelige
effek teengewerk word deur verhoogde hittestres
en evapotranspirasie, wat sal lei tot laer opbrengs
en WVD.
• Sandveld aartappelprodusente sal suksesvol by
klimaatsverandering kan aanpas deur someraan plantings vroeër te skuif (plant in Julie / Augustus)
om die ongunstige toestande van laat someraan plantings te vermy.
• Die grootste verhogings in opbrengs en WVD
word vir herfs- en winter-aanplantings verwag.
• Om die voordele wat klimaatveranderinge gaan
meebring ten volle te kan benut, sal produsente
buiten planttye ook addisionele aanpassings moet
maak. ‘n Voorbeeld is om oorweging te skenk
aan die plant van korter groeiseisoen kultivars ten
einde die verkorte somerseisoen beter te benut.
• Siekte- en pesdruk gaan waarskynlik toeneem met
die verwagte styging in temperature, wat die koste
van gewasproduksie sal laat styg.
• Om voorsiening te maak vir die verwagte hoër
opbrengspotensiaal, sal aanpassings in bemesting
waarskynlik ook gemaak moet word.
Tegniese Nuus • Technical News
35
Sandveld
30
2040-2049
2001-2010
WUE (g L-1)
25
1961-1970
20
15
10
5
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Month of planting
Figure 3. Calculated potential fresh tuber yield (top) and water use efficiency (WUE) (bottom) of
a 120 day crop planted on the 15 th of each month during three periods (1961-1970, 2001-2010
and 2040-2049) in the Sandveld.
CHIPS • July/August 2014
• Page 41