Influence of irrigation regimes on alfalfa dry matter yield and water productivity in a semiarid subtropical environment*

Abstract Managing water in alfalfa ( Medicago sativa L.) production is crucial for sustaining the limited surface and groundwater resources. A 3‐year study in eastern New Mexico, USA, compared nine irrigation strategies that included various combinations of in‐season irrigations for six harvests (1–2–3–4–5–6, 1–2–3–4–5, 1–2–3–5, 1–2–3, 2–3–5, 1–2–5, 1–5, and 2–3) plus unirrigated control (none) to evaluate the dry matter (DM) yield production capability and irrigation efficiency. The number in each treatment structure represents irrigation provided for each cutting. For example, number ‘1’ represents irrigation provided for the first cutting; number ‘2’ represents irrigation provided for the second cutting, and so on. The results suggested that terminating irrigation for the last harvest (1–2–3–4–5), equivalent to 96 mm water saving, had no significant negative impact on annual DM yield of established alfalfa compared to season‐long full irrigation (1–2–3–4–5–6) (14.4 vs 13.3 t ha −1 ; P > 0.05) during the 3‐year study period. Irrigation water productivity was doubled when alfalfa was irrigated during the first three harvests (1–2–3), compared to 1–2–3–4–5–6 (0.050 vs 0.027 t ha −1 mm −1 ). The second and third harvests provided the greatest DM yields in alfalfa. The DM yields declined drastically after the third harvest, with the exception of the third year. Therefore, irrigating alfalfa early in the season during the initial three harvests is an important strategy when water is limited.