Polysulphate fertilization – the effect of calcium on skin quality of tuber and root crops

Dr. Idit Ginzburg and Dr. Uri Yermiyahu
Start: Mar 2016 –  End: Mar 2019

Root and tuber crops provide a substantial part of the world’s food supply (http://faostat.fao.org). Among these are the potato (Solanum tuberosum) and sweetpotato (Ipomoea batatas) and to a lesser extent, carrot (Daucus carota). The protective peel of potato tuber and the sweetpotato and carrot storage roots is made of periderm tissue, whose outmost cell layers contain corky cell walls and is named ‘skin’. The skin protects the crop form water loss and pathogen invasion, and its appearance is a highly important marketable factor. Skin physiological blemishes (that are not caused by pathogens) are of great concern, mainly russeting phenomenon and skinning injuries (Ginzberg et al. 2005, 2009, 2012). In potato, russeting refers to dark-brown patches on the surface of the tubers characterized by dead skin cells that remain adhered to the newly formed skin layers below them – during normal skin development, these cells are sloughed off, rendering the skin smooth and shiny. Skinning injuries refers to mechanical wounding of the skin during harvest that detach the skin from the tuber flesh due to problems in skin maturation (skin-set). Potato skin is the accepted model to study the composition and development of corky cells as well as skin blemishes, although sweetpotato and carrot share similar problems (Villavicencio et al. 2007).

Previously we showed that application of CaCl₂ reduced the rate and the severity of skin russeting (Ginzberg et al. 2012). The effect of Ca on the skin could originate from transport of the mineral with the transpiration stream via the xylem into the tuber, or from direct interaction of the skin with the soil solution that surround the tuber. Being surrounded by moist soil, potato tubers are considered to be low-transpiring organs which may therefore suffer from Ca deficiency (Kratzke and Palta 1985; Palta 1996), accordingly skin-Ca interaction at tuber-soil interphase may be the favored cause for the effect of Ca on the skin. Accordingly, the formula with which the Ca is applied to the soil may affect its availability to the plant and its interaction with the skin at the surface of the tuber.

The exact effect of Ca on the skin of root and tuber crops is not clear – Ca has been implicated in maintaining the structural integrity of cell walls and intracellular adhesion (Jarvis et al. 2003; Vincken 2000), for that reason it would be also interesting to decipher the role of Ca on skin quality.

There are various formula and mode of application of Ca fertilization. The present proposal tests Ca-fertilization by Polysulphate, a fertilizer produced from polyhalite mineral. The mineral is a hydrated sulfate of potassium, calcium and magnesium, K₂Ca₂Mg(SO₄)₄•2H2O, of relative proportions: 48% SO₃, 14% K₂O, 6% MgO and 17% CaO.