Irrigated alfalfa growers shouldn’t be in much of a hurry to turn off their watering systems this fall, given the severity of drought in many parts of the country this growing season, says University of Nebraska Extension forage specialist Bruce Anderson.
“We need some surface soil moisture to prevent alfalfa roots from drying out and dying over winter,” he says. “Soil moisture also helps keep soil temperatures from dropping too low for alfalfa plants to survive.”
For top yields next year, subsoil water also will be needed. “During the peak water-use period in summer, it can be impossible to keep up with the water demand of alfalfa with irrigation alone – unless a water reserve is available in the deeper portion of the root and soil profile. Irrigating in October and into November until soils freeze can protect plants and improve yields.”
Water usually doesn’t penetrate past 4’ deep on most irrigated alfalfa fields, yet alfalfa can develop roots 8’ or more deep. “You waste some of the water-collection ability of alfalfa by not building water reserves below 4’. That water reserve will keep your alfalfa growing rapidly during next summer's heat and allow you to irrigate on a more timely basis.”
With a deep-water reserve, growers also won't have to worry much about winter survival or getting water immediately on their alfalfa after each harvest. “Since many alfalfa soils have low water infiltration rates, irrigating now might be the only time you actually can build that water reserve,” says Anderson.