A Windbreak crop protection benefits are well- documented, yet it's the small area of stunted crops near the trees that often grabs attention and can give windbreaks a bad rap.

While windbreak benefits extend into a field a distance 10 times the tree height or more, some producers focus on the much smaller, but noticeable, competition zone. This zone extends into the field roughly one tree's height. Crops here compete with tree roots for moisture and often become stunted or die.

"It's so visible that it has a negative impact," said Jim Brandle, University of Nebraska windbreak ecologist who studied this problem area with agronomy graduate student Carlos Nieto-Cabrera.

They found that pruning tree roots improves crop yields in the zone and improves the appearance of field edges, which may be more important to some farmers and landowners, Brandle said.

Field-wide windbreak benefits more than compensate for the lowered competition zone yield, he said. Yet some producers remove windbreaks because they think the land would be better planted to crops than trees.

Windbreaks cut wind speeds up to 50 percent, which reduces soil erosion and water evaporation, leaving more yield-boosting moisture for dryland crops. Windbreaks generally increase yields 12 percent or more in soybeans, corn and wheat, and up to 10 percent in grain sorghum, Brandle said. That yield improvement can add up to $45,000 on a quarter section over a windbreak's 20- to 30-year life.

This NU research shows root pruning addresses both yield concerns and perceptions.

In 1996 and 1997 Brandle and Nieto-Cabrera compared dryland soybean yields in root-pruned and unpruned zones at NU's Agricultural Research and Development Center near Mead. Although results vary with conditions, pruning increased competition-zone yields 12 percent to 40 percent in dry years.

Researchers studied soybeans because they are more sensitive to tree competition than corn or sorghum. Corn would benefit similarly, but sorghum is so drought tolerant it would benefit less, Brandle said.

Pruning roots 24 to 30 inches below the ground surface doesn't appear to harm trees. Once cut, however, roots must be pruned every two to five years because they grow back thicker and bushier than ever.

Pruning requires an implement with a 3-foot steel blade, which can be borrowed from some Natural Resources Districts. Producers believe pruning isn't expensive, but Brandle says it is costly in time and fuel, especially when pruning needs to be repeated every few years.

"Economically, it doesn't make sense," the Institute of Agriculture and Natural Resources researcher said. "It's the perception we're trying to deal with."

Tree root pruning is common in North Dakota, where rainfall is scarcer and windbreak trees use more moisture. The idea hasn't branched much into Nebraska.

Brandle is incorporating research results into a series of windbreak brochures.

The McIntire-Stennis Cooperative Forestry Research Program and the Nebraska Sustainable Agriculture Society helped fund this project.

- Cheryl Alberts

Windbreak Ecologist Jim Brandle and graduate student Nancy Beecher measure dryland soybean yields in the windbreak competition zone.