Individual and combined effects of soil waterlogging and compaction on physiological characteristics of wheat in southwestern China

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 (WL2W) and 4 weeks (WL4w), 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 (Phi PSII) 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-o). 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.