Nitrogen fertilizer in the form of ammonium nitrate was applied to two 40-year-old stands of black walnut growing in southern Wisconsin. The stands--one upland and one bottomland--were fertilized in 1965, 1969, and 1972 with 1,500 pounds per acre of ammonium nitrate. On the upland site, fertilized trees increased in diameter growth, but not significantly. On the bottomland site, fertilized trees had significantly lower diameter growth. Upland fertilized trees had significantly fewer new sprouts than did control trees, and bottom trees had no new sprouts. No loss of net log quality resulted from fertilization. Wood anatomy differences due to fertilizing should not affect wood machining or drying properties. It is recommended that both soil and foliar analyses be made prior to fertilizing black walnut. Sites with high levels of phosphorus and potassium should not be fertilized with nitrogen. (Author).