Please NOTE: This article has been published in Farming Monthly (UK)
Achieving adequate calcium (Ca) levels in potato tubers has always been the aim in the industry and an unmet challenge. Dr Apostolos Papadopoulos, Director and founder of Crop Intellect Ltd, summarises and discusses research findings with an aim to increase knowledge and enlighten producers.
Increased Ca content in the tubers is associated with a reduction in economically important defects such as internal brown spot, soft rots and hollow heart. Dr Apostolos Papadopoulos, Director and founder of Crop Intellect Ltd, has worked extensively on understanding the complex mechanisms involved in the uptake of calcium in plants.
Amongst fruits and vegetable crops, several years of research have been dedicated to further the knowledge of calcium uptake by potatoes. Crop Intellect has submitted a patent on selected molecules discovered to be effective in increasing the uptake of Ca in plant tissue and are incorporated in the crop nutrition product TECAL. Crop Intellect also offers PotiZon which is a unique product only for the potato crop. The research findings of their work including other researchers are summarised here to increase knowledge and enlighten producers.
Ca is an important plant nutrient and essential for strengthening the plant cell wall for cell integrity as well as acting as a second messenger involved in many physiological functions and abiotic stress tolerance. External inputs containing Ca and plant genotype can affect the Ca levels in the potato plant. Several studies have demonstrated that applications of Ca in various forms including calcium nitrate and lime have the ability to increase the above ground Ca levels but this is not the case for the potato tubers. Ca like Sulfur, Boron and Copper are considered to be phloem immobile as they don’t re-translocate from older leaves to younger when these elements are in deficiency.
Transport of Ca is therefore believed to occur in the xylem tissue and it is not re-translocated via the phloem from the aerial shoot tubers and main roots. Water absorbed by the main roots bypasses the tubers which has significant implications for field applied Ca. Research studies where Ca was radiolabeled to trace its movement within the plant, showed that the main root doesn’t provide Ca to the tubers. It is only the roots on the stolon and tuber that are able to increase the Ca internally.
Furthermore, tuber tissue closer to the stolon had higher Ca levels compared to the opposite end of the tuber. Calcium available on the vicinity of the tuber i.e. to the periderm doesn’t contribute to the Ca in tuber tissue as it is not transported across the periderm. Ca in the periderm is manyfold greater than that in the internal tissue and levels fluctuate easier in the periderm with external Ca applications. However, no direct relation exists between periderm and internal calcium levels. It is likely that due to differences in water potential between tubers and foliage, tubers don’t compete for Ca in the transpiration stream. The water potential is nearly equal mostly in the evening although leaves always have a lower water potential which explains why only roots on the stolon and tuber are able to supply Ca to the tuber tissue.
Therefore, the form, placement and timing of Ca are important when intended to increase tuber Ca. A highly soluble form such as calcium nitrate will likely leach if not supplied at regular intervals in the soil and will not provide a constant supply to the tuber. A persistent form of Ca such as present in LimeX (lime) can supply adequate levels when incorporated in the soil near the tuber. Ca solubility will be limited by the soil moisture but adequate quantities provide a constant supply during the growing season.
It is wrongly believed that foliar Ca applications will improve tuber Ca content. There is also no evidence to suggest that foliar Ca applications will reduce the removal of Ca from the tubers to the foliage as this is not a common physiological process. The foliage will typically have significantly higher calcium content than the tuber when Ca in present in the soil. It is the management of the transpiration stream and the consistent supply of Ca in the vicinity of the tuber that is directly related to the potential of increasing Ca levels in the tuber tissue through the uptake by the stolon and tuber roots.
For more information and advice on how to improve growing potatoes and to increase Ca content in the tuber please contact Crop Intellect Ltd.