The purpose of this article is to determine the content of nitrates and nitrites in potato tubers depending on genetic, agronomic and environmental factors that can modulate their levels. In addition, the goal is to identify the most favorable solutions in potato production that will contribute to reducing the content of nitrates and nitrites in tubers.
The tubers of the tested varieties were characterized by a low tendency to accumulate nitrates, generally below 150.0 mg kg f. m. (Tables 1, 2, 3, 4, 5 and 6). Edible potatoes should contain the lowest possible amount of nitrates and nitrites. In a study by Zarzecka et al., the nitrate content of tubers of eight edible varieties from market sales averaged between 152.1 and 170.1 mg kg f. m. In contrast, as reported by Simson et al. and Ebrahimi et al., the nitrate content of conventionally grown edible potatoes ranges from 31.0 to 460.0 mg kg f. m. and 35.6 to 163.0 mg kg f. m., respectively. Wszelaczyńska et al. conducting integrated and organic cultivation at different locations on seven clones and three varieties obtained nitrate contents averaging from 133.6 to 203.0 mg kg f. m. Nauman et al.after cultivating five potato varieties with a conventional system at different locations determined nitrate contents ranging from 48.0 to 137.0 mg kg f. m.
Our research also confirmed the general thesis that the accumulation of nitrates and nitrites in potatoes is closely related to the genotype, as the tested varieties significantly differed in their content.
Regardless of the year of the study, the location and the potato cultivation technology used, the Denar variety showed a higher tendency to accumulate nitrates and nitrites. On average, the Denar variety contained in the fresh mass of tubers: 85.4 nitrates and 0.71 nitrites, compared to 'Gardena' (82.3 and 0.61 mg kg) (Tables 1, 2, 3, 4, 5 and 6). This may be due to the length of the potato's growing season. Trawczyński, studying 21 potato varieties of different earliness groups, reports that varieties with a shorter growing season generally accumulate more nitrates. In addition, it was shown (Tables 1, 2, 3, 4, 5 and 6) that the tubers of both Gardena and Denar varieties in 2021 were characterized by higher concentrations of nitrates and nitrites, compared to 2020 in which more favorable weather conditions were recorded. The nitrate and nitrite contents were 98.5 and 0.75 in 2021 and 69.2 and 0.56 mg kg f. m. in 2020, respectively. This is in line with the results of Kołodziejczyk and Gwóźdź, in which the lowest nitrate accumulation was found in edible potato tubers produced under more favorable weather conditions. This indicates that the concentration of nitrates and nitrites depends not only on the potato genotype but also on meteorological conditions. Trawczyński, Zarzecka et al., Kołodziejczyk and Gwóźdź report that the magnitude and distribution of precipitation and air temperatures are the main factors affecting plant metabolism by which they determine the magnitude of nitrogen compound transformations in potatoes.
In addition, differences in the content of nitrates and nitrites in tubers, regardless of the variety, year of study and cultivation technology, were shown depending on the location of the experiments. The highest nitrate content was found in potatoes from the Jadwisin locality (Tables 1, 2, 3, 4 and 5) at an average of 130.7 mg kg f. m. after cultivation with the integrated system (three field experiments), compared to the Luchowo locality at 62.3 and Tytlewo at 41.6 mg kg f. m., where potatoes were grown with the organic system (Table 6). The effect of cultivation system on nitrate content of tubers of different potato varieties was reported by authors. This was also confirmed by the results obtained by other authors, in whose studies potato cultivation was carried out with the conventional system. This is determined by the use of high doses of nitrogen fertilizers in both conventional and integrated systems. However, Hamouz et al. showed no significant effect of cultivation technology (organic and conventional) on nitrate content in tubers of eight potato varieties. It should be noted, however, that they observed a tendency toward higher nitrate content in the conventional system (153.9 mg kg f. m.), compared to the organic system (136.9 mg kg f. m.). What should be emphasized is that in our study such a relationship was obtained only in the nitrite ratio.
Regardless of the cultivation system used, a reduction in nitrate content (Figs. 1,3-5) and a significant reduction in nitrite content (Figs. 2, 3, 4 and 5) were found after long-term storage. For the Gardena variety, the values were 3.1% for nitrates and 7.6% for nitrites, while for the Denar variety they were 2.2 and 7.4%, respectively (average values for the years of the study).
The reduction in nitrate content after storage under controlled conditions, in tubers from the crop in Jadwisin (integrated cultivation - Figs. 1, 3 and 4) was 3.3%, from the crop in Tytlewo (organic cultivation - Fig. 5) - 2.6% and from the crop in Luchowo (organic cultivation - Fig. 5) - 2.2%. In contrast, the reduction in nitrite content was 6.3, 7.3 and 11.8%, respectively (Figs. 2, 3, 4 and 5). The decrease in the content of harmful nitrogen compound after storage was confirmed by the obtained results of other authors. Typically, high nitrite content in potatoes is associated with the activity of nitrate-reducing bacteria, which leads to the reduction of nitrate to nitrite during storage.
Since the Gardena and Denar varieties belong to the group of edible varieties, the tubers were stored under conditions consistent with their direction of use, i.e. at 4 °C and RH 95%. Many authors state that the most important factors determining the chemical composition of potato tubers are temperature, relative humidity and storage time. Pobereżny et al. and Wszelaczyńska et al.studying edible varieties obtained a significant decrease in nitrate content after storing tubers at 4 °C for 6 months. In the study of Naumann et al., the decrease in nitrate content in tubers after 6 months storage averaged 15.0%. However, the authors point out that the period of three months of storage had no significant effect on their concentration.