The article from the November/December 2023 issue of the South African CHIPS magazine, titled “Low magnesium content in potato tubers associated with mass loss during storage,” focuses on research conducted by Stellenbosch University with funding from Potatoes South Africa.
The study, led by R Gericke from the Department of Agronomy at Stellenbosch University, NJJ Combrink, a doctor of crop physiology and plant nutrition, and Marieta van der Rijst, a senior biometrician at the Agricultural Research Council, addresses a significant issue faced by potato growers in the Sandveld and Koue Bokkeveld regions: moisture loss during marketing.
Key findings of the research include:
- Moisture Loss Issue: Potatoes grown in these regions, which have sandy soil with less than 3% clay, were experiencing moisture loss during marketing.
- Study Methodology: The study, conducted from January 2016 to July 2017, involved collecting tuber samples by hand a day or two before mechanical harvesting. Soil and irrigation water samples were also collected for analysis.
- Evaluation of Tubers: The study evaluated skinning potential, chemical composition, and specific gravity of the tubers. After storing undamaged tubers at room temperature for 42 days, their mass loss and firmness were assessed.
- Magnesium’s Role: A key finding was the high positive correlation between tuber firmness after storage and magnesium (Mg) levels in the tubers. Higher Mg levels in tubers resulted in firmer skins and better moisture retention, as indicated by lower mass loss percentages after storage.
- Impact of Low Mg Levels: Tubers with Mg levels lower than 0.13% not only had easily removable skins but also failed to retain moisture, leading to more than 4.5% mass loss during storage.
- Factors Affecting Mg Levels: The study noted that practices like applying gypsum to prevent internal brown fleck should be done cautiously, as high calcium levels may reduce Mg uptake. The balance of cations (K+, Ca++, and Mg++) is crucial, as indicated in fertilizer guidelines for potatoes.
- Ammonium’s Influence: High levels of ammonium may restrict potato yield and quality, especially in biologically inactive substrates like those in Sandveld and Koue Bokkeveld, where ammonium cannot be converted to nitrate. Ammonium at high levels may compete with the uptake of potassium, calcium, and magnesium.
This research highlights the importance of magnesium in maintaining the post-harvest quality of potatoes and sheds light on the complex interactions between soil composition, nutrient uptake, and tuber quality. The findings are particularly relevant for potato growers in regions with similar soil characteristics, providing valuable insights for improving storage and marketing outcomes.