Abstract
Nitrogen is one of the most essential nutrients for agricultural crops, and optimizing nitrogen fertilization enables the achievement of high yields and improved quality. In this context, the aim of this study was to identify the nitrogen form that influences wheat yield the most significantly, as well as the cultivars that respond positively to specific forms of nitrogen fertilization, in order to provide recommendations regarding cultivar selection and the appropriate technological approach for chernozem soils in southern Romania. Over a period of three agricultural years (2021-2022, 2022-2023, 2023-2024), 36 winter wheat cultivars were tested under three distinct fertilization conditions, nitrate nitrogen, ammonium nitrogen, and nitrate + ammonium nitrogen, each applied at three different rates: 120 kg·ha(-1) active substance (a.s.), 150 kg·ha(-1) a.s., and 170 kg·ha(-1) a.s. The comparative performance of each cultivar relative to the others was evaluated using the Newman-Keuls multiple-range test. The coefficient of variation (CV) of the obtained yields was used to determine yield stability, and its correlation with yield levels allowed for the identification and recommendation of cultivars that simultaneously demonstrated high yields (above average) and good or moderate stability. Sole application of ammonium nitrogen significantly reduced yield by 3.34% (from 70.66 Q/ha to 68.3 Q/ha), while the nitrate+ammonium combination showed a non-significant yield increase compared to nitrate nitrogen alone (+0.65%, p > 0.05). Among the tested cultivars, Sacramento was identified as the most productive, showing statistically significant superiority for Ct1-the most commonly grown wheat cultivar Glosa-as well as for control 2 (Ct2), which represented the average yield of all tested cultivars under all nitrogen fertilization treatments.