April 15, 2011

With precipitation levels significantly below normal in some areas of the state, alfalfa growers may want to initiate a preseason irrigation.

While it's unusual to irrigate before the first cutting, you may need to this year. Check your soil moisture profile to determine how much water is available for early season growth. Actually, early spring often is the best time to irrigate alfalfa. It's about the only time you can actually build a reserve water source for summer use.

Alfalfa can develop roots more than 8 feet deep, but this only occurs when surface moisture doesn't meet crop needs and moisture is available at a lower level. Deep roots and deep moisture will make your summer irrigating much easier by providing extra moisture when plants are using as much as ½ inch per day. Typical shallow watering during summer encourages shallow rooting.

The biggest advantage to having a water reserve comes after each summer cutting. Alfalfa roots need oxygen in the soil if plants are to regrow rapidly.

Watering right after cutting suffocates roots, slowing regrowth. Immediate watering also stimulates shallow rooted or sprouting weeds, especially at a time when alfalfa plants are not very competitive. Both problems are reduced when water is available for deep alfalfa roots while the top several inches of soil remain dry.

Early spring irrigation also tends to help warm up the soil since irrigation water usually is about 55°F. This can help speed early alfalfa growth.

Bruce Anderson
Extension Forage Specialist