Effects of Humic Acid Applications along with Reduced Nitrogen Fertilization on Potato Tuber Yield and Quality

This research was conducted in 2020 to determine the effects of leonardite-derived humic acids (Humas-15, Liquid Humus and Humico Maximix-K) with different properties, along with reduced nitrogen fertilization, on tuber yield and quality in potatoes (cv. Van Gogh). In the study, chemical fertilizer applications were made as basic fertilization (20 N 10 P 10 K), reduced fertilization I (15 N 10 P 10 K) and reduced fertilization II (10 N 10 P 10 K). Humic acids were applied twice with irrigation water, at the beginning of the flowering period and 15 days later. Humas-15 and Liquid Humus were applied at 1.0 and 2.0 lt/da doses, and Humico Maximix-K was applied at 400 and 800 g/da doses. A total of seven traits (tuber number per plant, tuber yield per plant, marketable tuber yield, total tuber yield, dry matter content, reducing sugar content and total sugar content) were measured. Reducing nitrogen applications with humic acid applications significantly affected all the traits studied. Humic acid applications combined with reduced nitrogen fertilization increased the number of tubers per plant by up to 13%, marketable tuber yield by up to 18% and total tuber yield by up to 16% compared with the control. Total and reducing sugar contents varied between 1.27-1.58% and 159-389 mg/100g fw, respectively depending on the applications. In the study, the highest tuber yield was obtained from 1.0 and 2.0 L/da Humas-15 and 2.0 L/da Liquid Humus applications applied together with reducing nitrogen applications which have close values to the recommended fertilization applications.