Correction

James G. Beisel, horticulture instructor at the Longview Community College in Lees Summit, Mo., has pointed out an error in an article I wrote last month on feeding trees.

In calculating the nitrogen needs of a tree, the Ortho book ''All About Trees'' suggests feeding one-tenth of a pound of actual nitrogen for every inch of a tree's diameter. Thus, a 10-inch-diameter tree would need 10 pounds of a 10 -percent nitrogen fertilizer (a 10-8-7 analysis fertilizer, in which the first figure represents the percentage of nitrogen in the mixture), not one pound, as I suggested.