Mpumalanga cultivar trial under irrigation at Davel/Bethal in 2024/25
Estimated reading time: 7 minutes
Approximately 2.11% of the total hectares under potatoes in South Africa are planted by 37 potato producers in the Mpumalanga production area.
Potatoes in this region are planted under irrigation and are destined mostly for fresh markets and processing (1 082 ha in the 2024 season). The main cultivars produced in this region are Mondial and FL2108.
The cultivar trial was conducted near Davel in Mpumalanga’s moderate summer rainfall region.
Over the past six years, the closest Agricultural Research Council (ARC) weather station recorded an average annual rainfall of approximately 537 mm for the broader area surrounding Davel and Bethal. This region is characterised by hot summers and very cold winters, with frost that can occur late into spring.
Trial design and details
The cultivar trial was laid out in a randomised block design with three replications per cultivar. Table 1 contains relevant technical information regarding the trial. Soil samples were taken prior to planting to determine the soil’s nutritional profile at the trial site (Table 2).
The cultivar trial includes cultivars with short and long growing periods. Hence, growing periods can influence certain cultivars’ eventual yield. The length of growing periods is subject to the nature of the seasons but are generally regarded as the time that passed from emergence to natural leaf senescence. Table 3 sets out how these growing periods differ among cultivars.
Table 3 contains the plant readiness of tubers at the time of planting, as well as the haulm count later in the growing season.
The evaluation of new cultivars, as in the case of the Davel cultivar trial, provides results relating to yield and marketing index. The marketing index of the cultivars involved are calculated by classing and sorting each cultivar based on quality and size groups (for example Class 1 large or Class 2 large-medium).
Prices are then compared to market prices obtained at the time of harvest.
However, the performance of cultivars cannot be based solely on the results of a single season, as climate differs from one year to the next. Therefore, cultivars are preferably tested across several seasons.
Climate and weather conditions
As with any crop, factors such as temperature, water availability (whether through good irrigation scheduling or rainfall), and heat units have a significant influence on the potato plant during its growth period.
These factors are considered when evaluating cultivar performance.
Applicable daily weather data for the season is obtained from a weather station located on the farm where the trial was conducted. The long-term data, however, comprises data from the past six years generated by the nearest ARC weather station, located 21 km south of the trial.
The 2024/25 season (Figure 2) commenced under very dry weather conditions, with widespread concerns regarding dam levels amid the hot conditions. Somewhat below-average rainfall was recorded during the first month of the active growing season.
Thereafter, above-average rainfall prevailed, with well-distributed showers occurring.
Figure 3 illustrates the minimum and maximum temperatures. The relevant season was consistently characterised by above-average maximum and minimum temperatures, as reflected by the accumulated heat units. A total of 41 days with temperatures above 30°C were recorded, particularly during the first two months after planting and at the end of the active growing period.
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 this season’s Davel cultivar trial appears to be higher than the long-term data trend of heat units (Figure 4). The available temperature data also indicates that it was an exceptionally warm season.
Yield and cultivar effect
Yield data recorded during harvesting day are subjected to statistical processing 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 5) was statistically significant (p<0.05) and the coefficient of variation (CV) was low (13.2%). These factors indicate that the trial was well executed, and the results are therefore reliable.
The yield of each of the cultivars is divided by the trial average, with the average of all the cultivars taken as 100%. This is used to determine a yield index and each cultivar’s performance in terms of yield is read as a percentage of the trial average.
The average yield of the trial for the 2024/25 season was 74.9 t/ha.
The higher yield could be attributed to coincidence and good management practices, such as high plant density, good soil, and efficient irrigation scheduling. Lilly and Lanorma achieved the highest marketing index. A good marketing index can be ascribed to a higher yield of large potatoes and/or potatoes of good quality.
Size group distribution and grading evaluations in potatoes are essential for determining a cultivar’s marketability (Figures 6 and 7).
The main reasons for downgrading are indicated in Table 4. Greening and insect damage were the major reasons for downgrading potatoes to Class 2 and 3.
Lastly, processing characteristics can also be evaluated by studying the internal quality of potatoes. To adhere to processing requirements, cultivars must meet a specific gravity (SG) of ≥1.075 (Table 5). No cultivar met the desired SG requirement, but almost all had the correct chip colour. – Enrike Verster, Potatoes SA
Special thanks to the collaborators at Fremax Farms, participants GWK, RSA and Provision Agri, as well as Damien da Cal and Dikgetho Mokoena of Potatoes SA.