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Recommended managerial inputs and associated outputs expected from practicing agroforestry on marginal farm lands in the central USA are discussed. Modeled management combinations are based on five timber species, three s~te indices, three timber growth rates, five agricultural crops, all common crop rotations, and three tillage systems. Black walnut (Juglans nigra L.), combined with row crop production, is used to illustrate a specific multicropping alternative. Based on net present value, modeled agroforestry systems incorporating black walnut performed better on the better sites and at the medium to high timber growth rates whereas management systems using red oak (Quercus rubra L.) with row crops performed better on the poorer sites and at the lower growth rates. For agroforestry to be competitive with traditional agriculture, medium to high timber growth rates were necessary. Also, lower interest rates and the existing U.S. income tax structure favored agroforestry versus traditional agriculture. Substantial increases in net income may be possible through incorporating other income producing activities such as nut production within the agroforestry system.

Silvicultural practices to reduce managerial inputs, increase yields, and decrease rotation age for eastern black walnut contribute substantially toward making this species more attractive as a forestry investment. Height and diameter measurements of black walnut interplanted with European black alder or autumn olive were taken at ages 14 and 18 in fifth-acre plots at a location in southern Illinois. Black walnut had been planted by USDA Forest Service scientists at a 12 x 32-ft spacing. For the interplanted plots, three black alder or autumn olive were planted within the rows between the walnut trees at a spacing of 8 ft. Based on projections of average dbh, the autumn olive and walnut mixture possessed the highest estimated black walnut yields and return on investment. Average dbh values of 11 in. were projected for the interplanted walnut at age 31. In the black alder interplanting it was estimated that similar rates of growth would require 40 years. Estimated dbh for the control plantings did not reach merchantable sawlog size within the 80-year projection period. Interplanting black walnut with nitrogen-fixing tree species also is well adapted for marginal farmland and may provide landowners with returns that match or exceed those from other more intensively managed alternatives. North. J. Appl. For. 6:129-132, September 1989.

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