For proper calcium nutrition in potatoes a combination of having adequate calcium in the soil and optimal moisture through the growing season is important for potato tuber development, skin quality and to reduce the incidence of internal potato tuber diseases. It is advisable to top up calcium levels annually with applications of agricultural lime as well as gypsum applied to the soil prior to sowing potatoes.

In potatoes, tubers develop below ground on the tips of underground plant stems called stolons. Tuber initiation and the numbers of tubers is determined on the stolon between 15 to 40 days following leaf shoot emergence from the soil.

Potatoes like calcium

During the tuber initiation stage it is necessary to have an adequate available source of calcium in the soil solution around the stolons as the potato tubers are forming. In addition, adequate soil moisture is required to maintain calcium levels in the soil solution.

Relying on calcium uptake by roots will not supply sufficient calcium for the developing tubers. This is due to the movement of calcium through root uptake being limited as this process is driven by transpiration (calcium uptake is via the xylem). A lack of calcium at this stage will reduce the number of potatoes formed and result in a lower yield.

The best way to secure adequate calcium in the soil is through regular annual applications of agricultural lime to bring the soil pH into an acceptable range, based on a recent soil test.  As the lime weathers in the soil it will provide a source of calcium over time.

Gypsum as a source of calcium

Gypsum (calcium sulphate)  can be applied as a supplementary source of available calcium during the early tuber initiation stage of potatoes. Gypsum can be applied in combination with lime or on it’s own. Gypsum supplies calcium without influencing soil pH.

Research in South Africa found applying gypsum as an additional calcium source had a beneficial effect on the amount of calcium accumulated by the tubers and on tuber quality. It was also noted that high humidity (85 %) and high temperature (day time 27°C/night time 17° C) improved calcium uptake by the tubers.

As a guide, aim to have good levels of calcium for that seasons’ potato crop and add a soluble calcium source, such as gypsum,  prior to planting or at mounding to improve potato tuber development, skin heath and tuber quality.

Chat to your fertiliser advisor about the benefits of a gypsum application for your next potato crop.

Gypsum- it all starts with healthy soil. Gypsum is BioGro certified.

References

University of Delaware, https://sites.udel.edu/weeklycropupdate/?p=13040

Fertility Considerations for Potatoes, April 2017, William Lamont, Jr., Ph.D. Penn State University

Yield and quality of potatoes as affected by calcium nutrition, temperature and humidity, P C Modisane, Feb 2007, University of Pretoria

The Biological Farmer, Gary Zimmer & L Zimmer Durrand, 2017, Publisher is Acres USA