The aim of three-year-long field trials was to determine an optimal nutritional status of potato plants with nitrogen in a growing season using a Minolta optical measuring Camera SPAD 502, called the N-Tester. The research was carried out on three potato cultivars (Gwiazda - early, Etiuda - medium early, and Gustaw - medium late) grown under conditions of different levels of mineral fertilization with nitrogen (0, 50, 100, 150 and 200 kg ha-1 N). Nitrogen fertilization on plots under 100 kg ha-1 N was applied directly before planting tubers and on plots above 100 kg ha-1 N in two doses before planting and before the emergence of potato plants. During the growing season, three dates (28, 42 and 56 DAE - BBCH 30-70 phase) were selected for determination of the total yield of dry matter of potato plants (leaves, stems, roots, tubers) and the nitrogen content. Three plants were harvested from each plot to make 30 measurements of SPAD in total on their leaves. It was found that as the potato plants grew, the yield of the plants’ dry matter increased and the nitrogen content decreased. Under the influence of nitrogen fertilization, a significant increase in the yield of dry matter of plants in response to a dose of 100 kg N ha-1 was obtained and the nitrogen content in the yield increased under a dose of 200 kg N ha-1. With the increased nitrogen fertilization dose, the NNI index and SPAD indicators increased as well. In order to calibrate the SPAD test, its dependence with the values of the NNI test was determined. A linear regression model was implemented to describe the relationship between SPAD measurements and NNI indices. It was found that the critical values of leaf greenness indices evaluated using an N-Tester on a scale of 0-80 from the phase from crop cover in inter rows to fruit setting on plants amounted to 43.9 for the early cultivar Gwiazda and the medium early cv. Etiuda, and to 43.7 SPAD units for the medium late cultivar Gustaw. With these SPAD unit values, the potato plants were optimally nourished with nitrogen.  

24.2.2019