Lucerne in wet soils — the effect of stage of regrowth, cultivar, air temperature and root temperature

Hunter River lucerne grown in pots, was subjected to either 21°C or 33°C constant temperatures for the first 10 days of regrowth. At 33°C, flooding immediately after cutting killed 85% of the plants. Flooding 5 days after cutting killed 35% of the plants. Even when plants were not killed by flooding at 33°C they were severely checked, and made negligible regrowth during the next 30 days. At 21°C no plants were killed by flooding. Plants flooded immediately after cutting were severely checked but those flooded 5 days after cutting were similar to the unflooded controls. Hunter River lucerne flooded under all combinations of 20°C and 30°C air and root temperatures for the first 5 days after cutting was more severely affected at both root temperatures than Rhizoma and Lahontan lucernes. High root temperature during flooding had a severe effect on all cultivars, but high air temperatures did not affect flooding reaction. Possible mechanisms by which flooding damage occurs are discussed.