Fall harvest management for irrigated alfalfa in southern Saskatchewan

Abstract

Three trials were conducted under irrigation at Swift Current, Saskatchewan to examine the interaction of fall harvest date and alfalfa cultivar. The treatments were five fall harvest dates, 15 Aug., 1 Sept., 15 Sept., 30 Sept. (two harvests per season) and 15 Aug. + 15 Oct. (three harvests per season), on three or four alfalfa cultivars. Trials were seeded on irrigated alluvial clay loam soil in 1979, 1981 and 1987. Low-temperature injury occurred in 1982, 1985, and 1989 in these three experiments, respectively. In Trial I, the effect of fall harvest date on stand and yield loss was greatest for the least winterhardy cultivar, Anchor, and least for the most winterhardy cultivar, Rambler. Forage yield recovered the year after injury, in spite of an apparent permanent reduction in stand density. In Trial II, low temperature injury was extensive in all treatments and the cultivar × date interaction was not significant. In Trial III, Anchor alfalfa harvested on 15 Oct. exhibited the lowest percent survival and shoot density. Heinrichs and Rambler were less affected by winterkill at all dates than Anchor but did exhibit severe yield reduction when harvested three times per season compared to two times. Anchor exhibited greater stand loss and lower first harvest forage yield in 1989 for both treatments that were cut on Oct. 15. There was no significant fall harvest date effect among the four two-harvest regimes in this trial. The observed date effect was due to the three-harvest regime compared to the rest. A fourth experiment was located at Outlook, Saskatchewan, where alfalfa, cv. Beaver, was harvested on 19 Sept., 24 Sept., 2 Oct. and 10 Oct. in 1989. Low-temperature injury was evident in 1990. First harvest forage yield in 1990 was significantly reduced for the third harvest dates compared to two harvests per season. These results do not provide categorical evidence of a "critical fall harvest period" for these two sites. The low-temperature tolerance of the cultivar determines to a large extent its sensitivity to fall harvest management.Key words: Medicago sativa L., winter survival, autumn management