How to influence potato dry matter content
Dry matter content is important for both fresh markets and processing. Tubers with dry matter above 18-20% tend to be more susceptible to bruising and tubers disintegrate more readily when cooked. However, for processing high dry matter content is required to achieve a good fry colour and often 20-25% is specified. Nitrogen, potassium and magnesium can all have influences on tuber dry matter content.
Nitrogen excess may reduce dry matter content
Nitrogen is an essential nutrient to fuel canopy growth, however in temperate climates, an excess supply of nitrogen at later stages of growth will keep the crop growing, delaying maturity and may reduce starch and dry matter content, reducing processing potato crop quality.
This trial in Norway demonstrate that too much late nitrogen can reduce tuber dry matter.
Too much late growth in cool climate crops can also result in a crop with many 'oversize' potatoes and cause internal cracking.
Potassium form has an effect on dry matter content
The form of potassium has an effect on dry matter. Sulphate of potash - SOP (potassium sulphate) can achieve higher dry matters than muriate of potash - MOP (potassium chloride) and therefore is frequently the preferred form for processing potatoes. This is due to the chloride in the muriate of potash having a negative effect on tuber dry matter content.
This study from Denmark demonstrates the higher dry matter content achieved with SOP (potassium sulphate) rather than MOP (potassium chloride).
Magnesium deficiency will reduce potato dry matter content
Low levels of magnesium will reduce the starch content of tubers and trials have confirmed the positive benefits of magnesium on tuber dry matter and specific gravity.
Manganese deficiency will reduce potato dry matter content
Low levels of manganese also reduces the starch content of tubers and so reduces tuber dry matter.
![Manganese and potato tuber dry matter content]()
Other crop management practices influencing dry matter content
- Selecting the right variety to meet dry matter production needs
- Selecting quality seed with less risk of disease
- Avoiding fields, with adverse factors such poor drainage or low water holding capabilities
- Ensuring blight spray programs are effective
- Scheduling irrigation to maximize quality characteristics
- Harvesting early, thereby minimizing late disease ingress or tuber deterioration
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