How to influence potato tuber numbers

The numbers of potato tubers produced by each potato plant is influenced by agronomy and varietal potential. The nutrients phosphate, potassium, and calcium all influence tuber number.

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

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.

Phosphate increases maximum tuber set

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).Phosphorus and potato yield

This study from Wales shows the effect of phosphorus on increasing total tuber numbers and overall yield.

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.

Foliar phosphorus - effect on potato tuber number

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.

Distances roots can uptake nutrients

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 on soil P availability

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 affects the number of tubers set

Potassium form and rate applied can also influence the numbers of tubers which are set.

Potassium form and tuber number

This study from shows the effect of potassium form on increasing total tuber numbers.

Potassium and Potato Yield

These trials demonstrate the yield increase due to potassium and also the benefit from potassium sulphate (sulphat of potash - SOP) rather than potassium chloride (muriate of potash - MOP).

Other crop management practices influencing potato tuber numbers

  • Selecting the right variety
  • Minimising 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

Recommended Yara fertilisers for potatoes

How to make better informed nutrient decisions

Our collection of tools help you to make better nutrient decisions in making the right fertiliser choice and applying the right amount of nutrients at the right time and in the right place so that the crop yield and quality can be maximised whilst still keeping costs in check, avoiding over-fertilisation and protecting the environment.