Winter barley grown in a long-term field trial with a large variation in N supply: Grain yield, yield components, protein concentration and their trends

Information on the responsiveness of winter barley to nitrogen (N) is scarce. Based on a long-term field trial (1978-2015) with different winter barley varieties in northern Germany combined with 64 N fertilizer treatments differing in amount (0-360 kg N ha(-1)) and distribution, the effects of N fertilizer amount and variety on the grain yield and its components, grain protein concentration (GPC), N use efficiency (NUE), and apparent fertilizer N recovery (AFR) were determined. In addition, quadratic N response curves and linear trends over the experimental period (parameters derived from annual N response curves) were estimated. N fertilization increased grain yield in all varieties, mainly due to a larger number of grains m(-2) rather than to an improved thousand grain weight (TGW). The newer varieties released since the late 1990s outyielded the older ones, especially at higher N supply, revealing a clear breeding progress, which in turn resulted in an improved NUE and AFR. Only if exceeding 190 kg N ha(-1) AFR started to decrease. During the trial, GPC in the unfertilized control significantly decreased, while the yield slightly, but non-significantly increased. In contrast, at economic optimum N supply, a significant increase in grain yield and number of grains m(-2) occurred while TGW and GPC remained stable over time. From the practical view of barley growing in humid climates, our results suggest to provide sufficient grains per area (sinks) in order to tap the full yield potential, especially against the background of climate change with its predicted temperature increase in spring and summer impairing grain filling.