Impact of Winter Irrigation and Summer Irrigation Termination on Alfalfa Dry Matter Yields.

Producers are interested in the feasibility of winter irrigation on alfalfa yields. Therefore, an area of alfalfa established in late summer 2012 under a center pivot irrigation system was divided into sections irrigated according to one of these four regimes beginning after the last harvest of 2013: irrigated throughout the winter and growing season, winter-irrigated and terminated after the 4^th harvest, irrigated from mid-April when canal water typically becomes available and throughout the growing season, or typically-irrigated until the 4^th harvest. Three replications were harvested for yield from each area on May 29, June 25, July 17, Aug. 14, Sep. 16, and Oct. 27 in 2014 and May 14, 2015. Individual harvest and total yield data were subjected to SAS Mixed procedures as a strip-plot for tests of significance and means separation (P < 0.05). Rep x treatment was considered random and used as the denominator for tests of significance. Harvests within 2014 were evaluated as repeated measurements. The main effect of irrigation schedule (winter vs. typical) was significant for season total yield in 2014 (4.20 vs. 2.48 tons/ac, respectively) and the irrigation timing effect (seasonlong vs. terminated) was significant (3.60 vs. 3.08 tons/ac, respectively), but the interaction between the two main effects was not. The irrigation schedule x harvest date interaction was significant because irrigating in winter increased yields over typical irrigation for every harvest except the final one. Hence, it is beneficial to irrigate whenever possible and feasible throughout the winter using sprinkler irrigation.