Influencing Potato Tuber Numbers


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The numbers of potato tubers produced by each potato plant is influenced by agronomy and varietal potential.

A large number of tubers per hectare will produce a crop of predominately small tubers, ideal for canning, salad or seed potatoes. A relatively low tuber number provides less competition per unit area and allows the crop’s energies and resources to be used to produce larger potatoes for the fresh or processing markets.

Crop Nutrition and Potato Tuber Numbers

Correct balanced nutrition is critical to influencing tuber numbers. Phosphate, potassium and calcium have all been shown to have effects on tuber number.


Phosphorus and Yield

Phosphate availability at tuber initiation is important to ensure maximum tuber set, especially if tuber numbers need to be increased for certain varieties, or where the market demands a large number of smaller tubers (e.g. seed production).

Study from Wales showing the effect of phosphorus on increasing total tuber numbers and overall yield.

Foliar Phosphorus

While potatoes are very responsive to fresh phosphate, the economic optimum rate is often difficult to define. Rates will depend on soil type and soil test results. Where sufficient soil phosphate is not available for growth, foliar phosphate ensures rapid availability.

Study from Scotland showing the effect of foliar phosphorus on increasing total tuber numbers.

Applied just before tuber initiation foliar phosphate increases total tuber number.

Phosphorus Uptake

Because phosphorus is relatively immobile in the soil it is important that fertilizer –P is placed close to the tuber, banding the fertilizer usually works better than broadcasting, especially on soils with the potential for very high phosphorus lock-up.

Influence of soil pH

This chart shows the influence of soil pH on the availability of phosphorus due to precipitation by calcium at high pH and fixation by iron and aluminium at low pH.


Potassium can influence the numbers of tubers which are set and the form of Potassium is also important.

Potassium Form and Tuber Number

Study from England showing the effect of potassium form on increasing total tuber numbers.

Potassium and Yield

These trials from India demonstrate the yield increase due to potassium and also the benefit from potassium sulphate (SOP) rather than potassium chloride (MOP).

Other Crop Management Practices Influencing Potato Tuber Size

Selecting the right variety:

  • Minimizing growth checks at tuber initiation (e.g. drought, compaction)
  • Irrigating to maintain a good growing environment
  • Physiologically ageing seed to produce the desired number of buds per tuber
  • Spacing seed to ensure an optimum number of stems per square meter
  • Using crop protection inputs – such as herbicides and nematicides – to ensure the crop grows relatively unhindered


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