June 21, 2002

LINCOLN, Neb. — As producers gear up for another hot Nebraska summer, some simple tips for managing irrigation will improve chances of maximizing pasture and alfalfa production.

Low prices for row crops and more promising livestock markets in recent years convinced more Nebraska producers to convert center pivot-irrigated cropland to irrigated pasture. Success with irrigated pasture requires proper management, said Bruce Anderson, University of Nebraska forage specialist.

"With row crops, irrigation generally is used to supply moisture to a 4-foot root zone," he said. "Many plants in irrigated pastures, though, tend to be more shallow rooted and may have 95 percent of their roots in the first 2 or 3 feet of soil. They become moisture stressed more quickly, and soil moisture at the 4-foot level may not be very useful."

For pastures, water use will average about a quarter-inch per day, the Institute of Agriculture and Natural Resources specialist said. Water use starts much earlier in the season for pastures than for row crops, too.

"Start irrigating early for pastures if the rain isn't doing its job," Anderson said.

Pastures need to be irrigated more frequently than crops. Ideally, producers should apply one-half to three-fourths of an inch at least twice a week.

To minimize compaction, producers should avoid irrigating where animals are grazing or will soon graze before the surface dries.

Alfalfa irrigation is very different from pasture irrigation. In alfalfa fields, improper irrigation can stimulate weeds and weaken the stand, Anderson said.

"Alfalfa can require up to 40 inches of water a year and sometimes over four-tenths of an inch a day," he said. "It's no wonder irrigators find it difficult to keep up with these demands. As a result, alfalfa is often irrigated as soon as the hay is removed from the field until the next cutting."

Constant watering, though, can hurt alfalfa because it increases the chance that grassy weeds like foxtail and perennial grasses like bluegrass will invade the alfalfa. Constant watering also encourages rood disease in alfalfa and reduces the soil oxygen content.

Since alfalfa roots can penetrate below 6 feet, the best irrigation strategy encourages deep rooting of alfalfa and dry surface soils during harvest, Anderson said. He suggested that producers stop irrigating a few days before harvest to allow the soil surface to dry and become firm. They also should not irrigate after harvest until regrowth is 3 to 4 inches tall.

By holding off on irrigation, Anderson said, "shallow-rooted weeds like foxtail and bluegrass won't be able to grow until alfalfa already has a head start."

"Your alfalfa will regrow more rapidly because the roots will find more oxygen they need in soil that has not been saturated with water," he said. "Of course, this assumes that you have been deep watering when you do irrigate so there is deep water available for alfalfa roots that weeds can't reach."

06/21/02-HC

Bruce Anderson - Ph.D
Agronomy
Professor
(402) 472-6237

Heather Corley
IANR News and Publishing
(402) 472-3030

Department: Agronomy & Horticulture