Alfalfa is a tough perennial with established rooting depths down 8 feet or more. Depending on deep soil profile moisture, some varieties can extend spring dormancy and survive up to 45 days without rainfall. However, forage yields drop dramatically, since alfalfa requires about 6 inches of root available water to produce one ton of forage per acre.
So, what irrigation strategy is recommended for alfalfa during the early spring season prior to the first cutting? Remember that once perennial alfalfa plants experience moisture deficiency, soil moisture storage catch-up through irrigation is difficult especially during the hot summer season due to high evapotranspiration water needs. Also, stressed plants may drop leaves prematurely, even if the alfalfa cutting is harvested before the recommended one-tenth bloom alfalfa development stage to salvage yield. This timing disruption may impact target irrigation just prior to the first cutting to increase regrowth tonnage for the succeeding crop.
Early season irrigation linked with first cutting alfalfa can potentially lower water use sharply because transpiration is lower when the leaf foliage is removed. Following the first cutting, irrigation might be delayed slightly in fields where weeds could respond quicker to the moisture than alfalfa regrowth.
Otherwise, full water irrigation or rainfall target amounts will be typically 6-7 inches of water for each subsequent cutting. Spring water usage may only be one-fourth inch per day but will rapidly increase as summer temperatures rise. Peak water alfalfa usage in July and August can extend beyond the normal one-third inch per day (or two inches per week) to a half inch per day during extreme stress times. — Todd Whitney, Nebraska Extension
