University of Idaho farm researchers are looking at soil conditions as the possible answer to the "dark end" problem that plagues potato processors.

Dark ends are the bane of processing plants. The problem also is called translucent end or sugar end. It's caused by an accumulation of sugar in one end of the potato, mainly during the early stages of development.French fries made from potatoes with sugar end turn dark when they are cooked because the sugar turns into caramel and burns.

John Hammel, University of Idaho soil scientist, and Brad Brown, scientist at the school's Southwest Idaho Research and Extension Center at Parma, have been cooperating in a two-year study to find out how "white" soils contribute to the condition that causes dark end.

White soils, high in calcium carbonate, are soils immediately under topsoil in the potato-growing regions of southwestern Idaho and eastern Oregon. They often replace topsoil as a result of land-leveling operations or erosion. Potatoes grown in white soils have a higher incidence and severity of translucent end than potatoes grown in darker topsoil.

The research was started because farmers and processors in southwestern end is especially bad.

Hammel presented a report on his research at the American Society of Agronomy's annual meeting at Anaheim, Calif. He said plant stress, caused by hot, dry weather, increases the incidence of dark end.

He said Brown is looking into the chemical composition of white soils, and he is looking at physical properties, such as water retention and permeability.

For two years, the scientists have been collecting data and core samples from 20 farmers' fields in Idaho and Oregon. They are comparing data from white soils with data from adjacent, darker topsoils to see if the differences can be connected to the sugar end problem.

They also are comparing results from furrow and sprinkler irrigation systems.