Leonardite applications increased the specific gravity compared to control plots, but there was no statistically significant differences observed between different leonardite doses for specific gravity (Table 4). However significant differences were detected between potato cultivars for their specific gravity. The highest specific gravity was observed in Lady Olympia (1.091 g cm3 -1) followed by Van Gogh (1.089 g cm3 -1), Milva (1.080 g cm3 -1) and Agata (1.078 g cm3 -1).