Fertigation with Ca and Mg to mitigate potato peel disorders in sandy soils

Introduction

Potato is popular crop with steady increase in production mainly due to increase in demand in India and China (FAOStat). In Israel, potato covers 15,000 ha, roughly 40% is exported, mainly to Europe (Gefen and Kahal, 2017). The soil and climate in the northern and western Negev are suitable for potato cultivation and therefore, about 85% of the area is found in the Negev (Erlich, 2009).

Potato peel disorders. In the recent years, the consumers repeatedly complains to potato’s-peel disorders and refuses to accept tubers with visual peel disorder. As a result, the annual economic impact of the decrease in potato export is estimated to be 50-60 million NIS. These physiological peel-disorders are merely esthetic issue and not related to plant disease. Peel-disorders come in many shapes and forms (Fig. 1). Some varieties are more susceptible than others, the peels-disorder are found mainly in varieties used for export. Since the consumer in Europe demands specific varieties, the growers have to grow susceptible varieties as well (Vivaldi, Anabel, Nikola, and Jazzy among others).

Calcium in plants. Calcium is macronutrient needed in large quantities. In plants, Ca translocation is possible in the xylem only. Therefore, transpiring organs tends to accumulate high Ca level while none-transpiring organs (Like fruits and tubers) have low Ca concentration, 10-20 times lower than in the shoot. Ca is essential for cell wall integrity and tissue rigidness. In field experiment in the northern Negev, broadcast application of 750 kg ha^-1 CaCl₂ reduced significantly “Magen” peel-disorder (Ginzberg et al., 2012). Following research indicates in importance of Ca and K at the maturation stage of potato skin development (Ginzberg, unpublished). Accordingly, in series of field trials in the US, tuber quality was increased in response Ca application (Palta, 2010; Karlsson et al., 2006). Karlsson et al. (2006) reported that Ca fertilizer application was associated with increased Ca concentration in the tuber and reduced bruises defect in five potato varieties.

Calcium and Mg in irrigation water. In the past decade, the irrigation water in Israel went through substantial changes because of increased utilization of desalinated water. Both freshwater and reclaimed wastewater (RWW) origin from desalination plant has significantly lower Ca and Mg concentrations. About 50% less Ca and 85% less Mg (from 2 and 1 mM down to 1 0.13 mM Ca and Mg respectively). Long-term leaf analysis in citrus (national RWW survey) shown that since desalinated water entered to the water system on-2008 there was continuous decrease in leaf Mg of 30% on 2016 (Raveh and Ben-Gal, 2018(. The Mg level in potato tuber is also very low: 9 mg 100 g^-1 compared to 20 mg 100 g^-1 world average according to the FAO. While most soils in Israel are rich in Ca and Mg, in sandy soils their availability is lower. Continuous depletion of Ca and Mg due to the reduction in their concentration in the irrigation water might lead to the development of nutritional disorders. Currently, field crop growers on general and specifically potatoes growers do not apply Ca and Mg.

Environmental factors. In a roundtable with key farmers, guides and researchers we pointed on several environmental conditions seems to affect peel disorder. Notably, sandy soils, wintertime and plant maturation accelerates peel disorder. Yet, we are far from understanding the environmental factors governing this phenomenon. Occasionally, two neighboring plots sharing similar agronomic practice has contrasting results.

Hypothesis. We hypothesize that in intensive agro-systems irrigated with low Ca and Mg levels is leading to gradual depletion Ca and Mg availability. Consequently, tuber-peel disorders described above are a result of this long-term process. Therefore, fertilization with these missing nutrients will allow enhanced tuber quality.

In a preliminary field-test carried out in the winter of 2018 we found that fertigation with N, K, Ca and Mg reduced peel disorder from 30% in the control (N only) to 7%. We wish to follow this promising direction in our proposal.

This research was initiated by the farmers due to the high concern and economic damage of peel disorders. Some major farms collaborate for the success of the research. We propose to test multiple potato sites in real conditions to identify the factor leading to peel disorder and to test our hypothesis that fertigation with Ca and Mg will diminish the disorders. We plan to carry out and experiment on two varieties in 10 sites varying in agronomic practices are compare two Ca+Mg fertilization managements to unfertilized control (10 x 3 x 2 = 60 plots a year^-1). This research is expected to generate practical guidelines for potato fertilization and agronomic management.

Research objectives:

1. Identification soil traits that are associate with potato peel disorder.
2. Identification of environmental conditions that associate with peel disorders.
3. Determining the effect of Ca and Mg nutrition on the development to potato peel disorder