Reimagining alfalfa as a flexible crop for water security in the Southwestern USA.

Alfalfa has been vilified as one of the thirstiest crops in the semi-arid southwestern USA and partially responsible for decreased water security in the Colorado, Rio Grande and San Joaquin River basins. We demonstrate that adoption of summer deficit irrigation in alfalfa production can yield large water savings and flexibility to adapt to changing water supplies with minimal on-field economic impact. We estimate that deficit irrigation of alfalfa can save 1333 to 4157 million cubic meters of water annually (16-50 % of total alfalfa water use) over 926,000 ha in the southwestern USA if summer deficit irrigation (suspended after July 1) were implemented. Cash-flow analyses, assuming a producer sells conserved irrigation water and forfeits revenue from alfalfa sales beyond August 1, indicate a possible win-win net benefit at a price point of greater than $71 (Tulare, CA) or $44 (Imperial, CA) per 1000 m of irrigation water. We document the benefits of summer deficit irrigation for water conservation and farm and regional agricultural economic viability in rural communities. We acknowledge its practical challenges and risks as it will require infrastructure for water trading, support systems and mechanisms for producer decision-making, and improvements to field-level water accounting. These findings underscore the need to reassess the role of alfalfa in water management, not just as a water-intensive crop but also as a flexible one that may be a key instrument in achieving agricultural resilience against the backdrop of climate variability and recurring droughts.