Effects of single and multiple waterloggings on the growth and yield of winter wheat on a clay soil

The response of winter wheat to surface waterlogging in monoliths of clay soil in lysimeters was studied. The treatments, selected as corresponding to the most extreme likely in Britain, were: 5 days of waterlogging in October between germination and emergence; 42 days of waterlogging during tillering in January and February; and 21 days from mid‐April during stem elongation. These treatments were used singly and in all combinations and were compared with a freely‐drained control. During waterlogging, the oxygen concentration in the soil declined most rapidly when the soil was warmer (in October and April) and at the shallower depths (5, 20cm): also, a decrease in soil solution nitrate was accompanied by an increase in nitrous oxide evolution. Pre‐emergence waterlogging restricted plant population to 35 m −2 compared to 338 m −2 under free drainage. Subsequently, compensatory growth resulted from diminished interplant competition for nitrogen, water and light: a greater proportion of tillers survived and the flag leaves were larger, although ears at harvest were fewer in all treatments waterlogged before emergence. After waterlogging during tillering, grain loss was accounted for entirely by a decrease in the number of ear‐bearing tillers. After waterlogging during stem elongation, yield losses were associated primarily with fewer grains per spikelet. Grain yield was depressed by about 4–12% after single waterloggings, by 20% after any two waterloggings, and by 32% when plants were waterlogged on all three occasions.