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The combined effects of soil waterlogging and compaction are important concerns in crop production. Two field experiments were performed over two seasons to examine the effects of soil waterlogging and high bulk density (BD) on the performance of winter wheat in terms of its agronomic and physiological traits. Trial 1 applied soil waterlogging at different stages (started at tillering, jointing, booting and anthesis). Trial 2 was conducted with soil waterlogging and compaction that created BD of the topsoil (1.6 g cm −3 ). Results from trial 1 showed that the tillering stage was the most waterlogging-sensitive period. A 12% lower grain yield caused by waterlogging was primarily reflected in reductions in spike numbers. Waterlogging at jointing and booting stages reduced grain weight through decreased dry matter translocation. Results from the field trial 2 showed that soil compaction decreased grain yield by 4.8%, and waterlogging aggravated this reduction by 20.7% and 22.4% when fields were waterlogged for 2 weeks (WL 2w ) and 4 weeks (WL 4w ), respectively. A reduction in spike number from fewer tillers at stem elongation stage was the main reason for grain yield loss. Soil compaction combined with waterlogging duration did not affect root weight, but soil compaction reduced above ground biomass and root weight after the jointing stage. Furthermore, waterlogging accelerated leaf senescence, especially under compacted conditions, which significantly decreased photosynthetic capacity, resulting in a lower maximal PSII photochemical efficiency (F v /F m ), apparent electron transport rate (ETR), effective quantum yield of photosystem II (ΦPSII) and photochemical quenching (qP). Root weight was positively related to the total above ground biomass; whereas the final grain yield was not linearly related to the shoot weight. SPAD value correlated positively with yield and PSII parameters (F v /F m , F v /F 0 ). The study concluded that the tillering stage was most susceptible to waterlogging, and soil compaction combined with waterlogging at tillering stage had a larger harmful effect on root and shoot growth during or after waterlogging. SPAD readings may be a good surrogate for photosynthetic activity under waterlogging and compaction conditions. [ABSTRACT FROM AUTHOR]

• N deficiency significantly affected GY and N utilization-related traits. • SDCs showed advantages over NSCs in GY, DM accumulation, and NUtE under N deficiency. • High-yielding SDCs is associated with the low GPC and high NUtE. Synthetic hexaploid wheat-derived cultivars (SDCs) show substantially improved yield potential compared with that of nonsynthetic-derived cultivars (NSCs) developed by conventional breeding. However, the relationship between the high-yielding traits of SDCs and nitrogen (N) use efficiency, especially their performance under N deficiency, is unclear. A field experiment was conducted in two successive seasons examining the responses of six genotypes (three SDCs and three NSCs) under two N treatments: N+ (N sufficiency, N nutrition index ≥ 1) and N− (N deficiency, N nutrition index < 1). N deficiency had a significantly negative effect on grain yield (GY) and yield-related traits. Compared with that of NSCs, SDCs showed 14% (N+) and 16% (N−) higher GY. This yield gain was mainly attributable to the higher total dry matter (DM) and post-anthesis DM accumulation of SDCs under both N treatments. On average, SDCs showed higher chlorophyll content than NSCs in the three upper leaves from 0 to 32 days post-anthesis, which was highly positively correlated with GY under both N treatments. Total and fertilizer N accumulation were significantly decreased under N deficiency. Compared with that of NSCs, SDCs showed lower grain protein concentrations under both N treatments, which was negatively correlated with GY. In addition, SDCs showed significantly higher N use efficiency and N utilization efficiency (NUtE) than NSCs, and a positive correlation was detected between NUtE and GY. The results indicated that SDCs show advantages over NSCs in GY, DM accumulation, and NUtE under N deficiency, and thus cultivation of SDCs shows potential to reduce N waste and environmental contamination. [ABSTRACT FROM AUTHOR]