Sandveld cultivar trial under irrigation at Aurora in 2025/26

The Sandveld production region accounts for roughly 13.12% of South Africa’s total potato harvest, cultivated on approximately 6 967 ha across summer and winter plantings. This region supplies potatoes and seed potatoes to the entire supply chain, including export as well as table and processing potatoes. Table potatoes are primarily exported to Angola, and seed potatoes to Mozambique. The most prominent cultivars produced here for table consumption and processing are Mondial, Sifra, FL2108, and Valor.

The trial was conducted on the farm Rietfontein in the Aurora area, at the western foot of the Piketberg. The area lies within South Africa’s winter rainfall region and receives an annual average rainfall of approximately 395 mm, based on records from the past 21 years at the closest Agricultural Research Council (ARC) weather station. The region has a Mediterranean climate with hot summers and cold, wet winters. Potatoes are produced yearround in the Sandveld, which is unique to the region although most potatoes are planted in February and June.

Trial design and details

The Aurora trial was conducted in sandy soil and laid out in a randomised block design with three replications per cultivar. Table 1 contains additional technical information relating to the trial, while Table 2 sets out the fertiliser programme for the past season. Soil samples were taken before planting to determine the soil nutrient profile of the trial site (Table 3). Pivot maintenance was carried out on a rotational basis.

The cultivar trial includes cultivars with short and long growing periods, which can influence certain cultivars’ final yield. The length of growing periods depends on the nature of the seasons but is generally regarded as the time from emergence to natural leaf senescence. Table 4 sets out how these growing periods differ among cultivars. The plant readiness of tubers on the day of planting, as well as the density percentage and haulm count observed later in the growing season, are also presented in Table 4.

Marketing-related results

The evaluation of cultivars, as in the Aurora cultivar trial, provides results on yield and marketing index, as well as baking quality and processing characteristics. The marketing index of the relevant cultivars is calculated by classing and sorting each cultivar according to quality and size groups (for example, Class 1 large or Class 2 large medium).

Prices were then compared to market prices obtained at the time of harvest. However, cultivar performance cannot be based solely on a single season’s results, as climate varies from year to year. Therefore, cultivars are preferably tested across several seasons.

Climate and weather conditions

As with any crop, factors such as temperature, radiation, water availability (whether through good irrigation scheduling or rainfall), and heat units significantly influence the potato plant’s growing period. These factors are considered when evaluating cultivar performance. Applicable weather data is obtained from a nearby weather station. The 2025/26 season (Figure 2) received below-average rainfall, although Aurora falls within the winter rainfall region.

Minimum and maximum temperatures are illustrated in Figure 3. Maximum temperatures fluctuated considerably during the season. A total of 94 days with temperatures above 30°C and 32 days above 35°C were recorded during the season – more than in the previous season. Temperatures remained almost consistently high throughout the active growing period.

Heat units and radiation

The collection of heat units during a growing period is an important factor in the development of a potato plant. The trend of heat units available for the 2025/26 season’s Aurora cultivar trial shows that the units accumulated between planting and harvesting were slightly higher than over the past few seasons (Figure 4).

Another important factor to consider is the amount of daily radiation (Figure 5). This is a measurement of the solar energy reaching a horizontal surface. Higher radiation during the growing period enhances photosynthesis. The average daily radiation for the past season was lower than in previous seasons – possibly due to a higher number of misty and cloudy days – which explains the lower yields.

When long-term data is considered, the accumulation of radiation – measured daily – was 8.45% lower in the 2025/26 season than during previous seasons. Radiation, and therefore photosynthesis and ultimate yield for the entire season, was lower than in previous seasons.

Yield and cultivar effect

Yield data recorded during harvesting was processed statistically using the GenStat® program. The Tukey test of least significant differences (LSD) was used to separate the mean. The cultivar effect during this trial (Figure 6) was statistically significant (p<0.05), and the coefficient of variation (CV) was within limits (12.3%). These factors indicate that the trial was well executed, and that the results are therefore reliable.

Each cultivar’s yield is divided by the trial average, with the average across all cultivars set to 100%. This yields a yield index, with each cultivar’s performance expressed as a percentage of the trial average.

The average trial yield in the 2025/26 season was 73.8 t/ha, which is significantly lower than the previous five seasons’ average of 92.1 t/ha.

The cultivar Avalanche statistically produced the highest yield. Avalanche and Valor achieved the best marketing index. A good marketing index can be attributed to higher yields of large potatoes and/or a high percentage of good-quality potatoes. For example, a high percentage of unmarketable potatoes will negatively affect the marketing index.

Size-group distribution and grading are important aspects when assessing a potato cultivar’s marketability (Figures 7 and 8). In this trial, only Class 1 and 2 potatoes were graded, as opposed to unmarketable (discarded) potatoes.

Cultivar performance

Given the nature of the seasons, cultivar performance varies from one season to the next simply because the climate is never the same. Therefore, it is important to consider cultivar performance across multiple seasons. Figures 9 and 10 illustrate cultivar variation over the past three and five seasons. Lanorma and Sifra showed the most stability over five years, while P1 and Lanorma performed consistently over the past three seasons.

Nematode damage was the main reason for downgrading potatoes from marketable to discarded, which is why storability was not evaluated upon completion of the trial. Nematode incidence was exceptionally high and present across all cultivars. Minor to no other defects contributed to downgrading. Sound, S1, Sifra, Lilly, P1, Mondial, and 93A15 performed best under the high nematode pressure.

Lastly, processing characteristics can also be evaluated to assess internal potato quality. To meet processing requirements, cultivars must, among other criteria, have a specific gravity (SG) of ≥1.075 and a chip colour standard of >50 (Table 5). According to ARC analyses, most cultivars achieved the desired chip colour, but only Markies met the SG requirement (Table 5).

Special thanks to the Sandveld working group, all trial participants, and relevant Potatoes SA staff. – Enrike Verster, Potatoes SA, Piet Brink, Sandveld working group, and Albert de Villiers, producer

For more information, send an email to enrike@potatoes.co.za