Summer Irrigation Termination Effects On Furrow-Irrigated Alfalfa In New Mexico.

Alfalfa (Medicago sativa) growers in the irrigated western USA seek ways to continue production despite declining or inconsistent water supplies. In a randomized complete block study by New Mexico State University’s Agricultural Science Center at Tucumcari, various cuttings were not furrow-irrigated in a six-cut system. The test was sown in 2005 and fully irrigated in 2006. Irrigation termination treatments were imposed from 2007 through 2009, after which full irrigation was applied to the last four cuttings in 2010. Irrigation treatments were grouped by the number of cuttings irrigated as 6, 5, 4, 3, 2, and 0 for analysis by SAS PROC MIXED. From 2007 through 2009, there were differences among treatments (14.39a, 13.20ab, 10.88bc, 10.33c, 9.08c, and 6.55d Mg ha^-1 for 6, 5, 4, 3, 2, and 0 cuttings irrigated, respectively, based on SAS MIXED PDIFF analysis; means followed by the same letter are not different at P < 0.05). Any cutting not irrigated after early July yielded <0.22 Mg ha^-1. Whenever water is limited, alfalfa should be fully irrigated early in the season until the water is depleted to maximize yields through greater water use efficiency. In 2010, the first irrigation was delayed until early July and no harvest or total yield differences existed among treatments, including the 0 irrigation treatment that had not been irrigated since 2006. Consequently, even if water does not become available until later in the season, alfalfa can be fully irrigated to achieve maximum yields. Finally, when stands are <3 or 4 years old, producers should consider that it may be more economical and less risky to maintain an intact stand producing lower yields for 2-3 years in anticipation of plentiful irrigation water than to risk establishing annual crops with or without irrigation for two years before replanting alfalfa.