Responses of Winter Barley Genotypes to Low Nitrogen Supply Under Rainfed Conditions

Reducing nitrogen inputs while maintaining grain yield and quality is an important objective for sustainable barley production. This study evaluated 39 winter barley genotypes (20 six-row and 19 two-row) under two N management treatments following pea as the preceding crop during two contrasting growing seasons (2021–2022 and 2022–2023) under rainfed conditions. Both treatments received the same basal fertilization, while the fertilized treatment received an additional 46 kg N ha−1 as urea. Yield response to additional N differed between barley types and growing seasons. In six-row barley, grain yield increased by 5.9% in 2021–2022 but decreased by 4.8% in 2022–2023, whereas two-row barley maintained positive responses of 7.9% and 5.9%, respectively. Additional N consistently increased grain protein content by 17.2–21.7% in six-row and 17.1–19.0% in two-row barley, while starch content decreased in both barley types. NDVI generally increased following additional N application. GGE biplot analysis revealed substantial genotypic variation in performance and response across the four year × nitrogen combinations evaluated at the experimental location. Overall, two-row barley showed a more consistent yield response to additional N across the two growing seasons, while the identified genotypic variation provides useful material for selecting winter barley adapted to reduced N inputs following a legume preceding crop.