Trial on three South African cultivars links water, potassium to tuber quality
Researchers tested how irrigation at 40%, 70% and 100% of crop evapotranspiration and potassium at 0 to 200 kg per hectare shape tuber quality in Mondial, Markies and Panamera, three cultivars sold in South Africa. Deficit irrigation raised dry matter and ascorbic acid, while sucrose responded to both water and potassium, a paper published 11 Nov 2026 reports.
Why it matters
Dry matter and sugar levels decide fry and chip color, texture and oil uptake, so growers who cut water or adjust potassium change what reaches the plant. The results suggest that, where water is short, deficit irrigation may not harm solids, but sugar behavior depends on the cultivar and on how water and potassium are managed together.
A study published online on 11 Nov 2026 in the American Journal of Potato Research looks at how water supply and potassium fertilizer together affect the quality of the tuber, rather than the leaf, where most earlier drought work has focused. The authors are Xola Sigenu, Samson Z. Tesfay, Lembe S. Magwaza, Alistair Clulow, Vivek Naiken and Asanda Mditshwa. The work was funded by Sol Plaatje University (American Journal of Potato Research).
How was the trial set up?
The trial was grown in a tunnel using a split-split plot design. It compared three irrigation regimes, set at 40%, 70% and 100% of crop evapotranspiration (ETc), with four potassium rates of 0, 100, 150 and 200 kg K per hectare. The three cultivars, Mondial, Markies and Panamera, are all sold commercially in South Africa.
What changed in the tubers?
- Dry matter: deficit irrigation raised dry matter content.
- Phenolics: full irrigation gave the highest total phenolic content, 0.15 mg gallic acid equivalent per gram of dry weight at 100% ETc. This compared with 0.118 mg at 70% ETc and 0.113 mg at 40% ETc.
- Ascorbic acid: vitamin C rose by 5% at 40% ETc and by 17% at 70% ETc compared with full irrigation.
- Sugars: sucrose responded to both irrigation and potassium. Glucose and fructose differed mainly between cultivars.
What does it mean for processors?
The authors conclude that irrigation, potassium supply and cultivar interact to shape tuber quality, which is relevant to growing potatoes where water is limited. For processing buyers, the findings tie field water and fertilizer choices to solids and sugar profiles. Reducing sugars such as glucose and fructose drive browning and acrylamide formation in frying. This trial found that those sugars varied mainly with cultivar choice.
Key numbers
| Figure | Value | Date | Source |
|---|---|---|---|
| Irrigation regimes tested | 40, 70 and 100 % of crop evapotranspiration | 11 Nov 2026 | Source |
| Potassium rates tested | 0, 100, 150 and 200 kg K per hectare | 11 Nov 2026 | Source |
| Total phenolic content at full irrigation | 0.15 mg GAE per g dry weight | 11 Nov 2026 | Source |
| Ascorbic acid increase at 70% ETc vs full irrigation | 17 % | 11 Nov 2026 | Source |
Sources
- Effect of Different Water Regimes and Potassium Fertilisation on Tuber Quality and Bioactive Compounds in Three Potato Cultivars · American Journal of Potato Research (Springer) (primary source)