Determination of nitrogen nutrition status in apple tree varieties using hyperspectral methods

In this study, different nitrogen doses were applied under controlled conditions to Granny Smith, Golden Delicious, and Pink Lady apple seedlings. Reflection measurements were taken from leaf samples collected from the seedlings to model the relationships between nitrogen contents and investigate the determinability of nitrogen nutrition status using hyperspectral techniques. The aim was to contribute to the development of infrastructure for smart farming, precision farming, digital farming, farm management software, and autonomous vehicles. Nitrogen doses of 0-50-100-200-400 ppm were applied to Granny Smith, Golden Delicious, and Pink Lady varieties. The experiment was conducted on 630 apple seedlings in two growing seasons, 14 periods, and 3 replicates, following a randomized block design in MAREM plots. For this purpose, the effects of the applied nitrogen doses were examined using descriptive statistics of plant nutrient elements, total chlorophyll content, chlorophyll-a, chlorophyll-b, carotenoid content analyses, and YSP, stomatal conductance, transpiration rate, assimilation rate, and leaf area index using Student's t-test The spectral reflectance values obtained were evaluated using various statistical and stepwise multiple regression methods to determine the relationships between nitrogen levels and spectral characteristics. A decrease in leaf nitrogen content was observed throughout the entire vegetation period in all varieties. In Granny Smith, 401 nm, 410 nm, 462 nm, and 561 nm; in Golden Delicious, 406 nm, 430 nm, 728 nm, 729 nm, and 992 nm; and in Pink Lady, 434 nm and 602 nm were determined to be effective wavelengths for determining the amount of nitrogen in the plant. The plant indices that stood out the most for all three varieties were NDVI (750, 705, 710). In conclusion, hyperspectral methods are considered to be an effective tool for determining nitrogen status in apple seedlings and can be used especially in precision agriculture applications. They provide a foundation for future technological developments in nitrogen fertilization methods in apple production, playing an important role in meeting plant nitrogen needs and reducing environmental pollution.