The number of potato tubers produced by each potato plant is influenced by agronomy and varietal potential. Correct balanced nutrition is critical in influencing number of tubers per plant. Phosphate, potassium, and calcium have all been shown to have effects on the total achievable tuber number.

A large number of tubers per hectare will produce a crop of predominately small sized tubers, ideal for gourmet fresh, 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 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).

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.

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

Potassium form and rate applied can also influence the numbers of tubers which are set. Other crop management practices influencing potato tuber numbers include selecting the right variety, minimizing growth checks at tuber initiation (e.g. drought, compaction), Irrigating to maintain a good growing environment and spacing seed to ensure an optimum number of stems per square meter. Also using crop protection inputs such as herbicides and nematicides helps to ensure the crop grows relatively unhindered.

A potato crop harvested with 18 tubers. Correct balanced nutrition is critical to influencing tuber numbers

Source: https://www.yaracanada.ca/crop-nutrition/potato/influencing-tuber-numbers/