An Iowa Demonstration of Agroforestry: Short-Rotation Woody Crops

Abstract

Results of a "wood-for-energy" demonstration and research study are presented. Three short-rotation woody crop (SRWC) systems were planted in 1986 on an old agriculture field. One system has a one-year rotation and a 0.3 × 0.3 m spacing. The second has a 3-5 year rotation and a 1.8 × 0.9 m spacing, and the last has a 7-10 year rotation and a 1.8 × 1.8 m spacing. Three different Populus clones and sliver maple (Acer saccharinum L.) were used for the systems. All plantings, except the annual system, were 0.2 ha in size. Site preparation included discing, rototilling, and application of pre-emergent herbicides. Planting was done with a conventional single row tree planter, with the exception of the wood grass, which was hand planted. Early growth and yield varied by system and were affected by severe drought conditions in 1988 and 1989. Average height and diameter growth for the first three years were significantly greater for the two Populus clones than for the silver maple. For the annually harvested 0.3 × 0.3 m system, the average yields were 7.2, 9.2, 9.4, and 6.6 dry metric tons per ha (dmt ha−1 yr−1) from 1986 to 1989. Populus clones NC-5326 and NC-5328 in the 1.8 × 0.9 m system produced similar yields since establishment in 1986. After the first four growing seasons, there was a moderate difference in growth and yield between the Populus clones in the 1.8 × 1.8 m system. The NC-5326 produced 50% more than NC-5328. The annual system was costly to establish, with costs exceeding $7,069 ha−1 The 1986 establishment costs were $1,648 ha−1 or the Populus clones and $1,665 ha−1 for silver maple, both included in the 1.8 × 0.9 m system. In comparison, a 1987 planting of this system had a 18% reduction in costs. The 1986 establishment costs for the 18 × 1 8 m system were $1,023 ha−1for the Populus clones and $1,038 ha−1for silver maple, with a 23% cost savings in a 1987 planting. Pest problems were limited to a cottonwood leaf beetle infestation in the summer of 1987, which was easily controlled with a pesticide. Early growth and yields are encouraging given the severe drought conditions of 1988 and 1989. Moreover, the cost reductions from subsequent plantings (1987) indicate a trend towards cost-efficient short-rotation woody crop systems producing biomass for energy in the Iowa agricultural landscape.