Poster presented at BioEnergy '98: Expanding Bioenergy Partnerships, Madison, Wisconsin, October 4-8, 1998.

POSTER ABSTRACT

Short-rotation, intensive-culture (SRIC) poplars have been proposed as biofuels, but relatively little is known about their productivity in densely planted stands in Wisconsin. The objective of this study is to quantify yield from a prototype high-density, short-rotation hybrid poplar plantation on a high quality site located near Arlington, WI. Spacing and harvest intervals are similar to those used for willow biofuel production in Sweden. Two clones and two weed control practices are being compared.

Methods: There are ten replicate plots for each of the two clones and two weed control practices (40 plots total). Each plot consists of three 4.6-m-long (15-ft-long) double rows, with 1.5 m (5 ft) between double rows. Individual rows in the double row pair are 46 cm (18 inches) apart with a cutting planted every 30 cm (12 inches) within the row. Clones DN34 (Eugenei) and NM6 were established from 20-cm-long (8-inch-long) cuttings planted the second week of May 1995. The field (Plano silt loam soil) previously was in alfalfa that was plowed under that spring (no chemical preparation). Weeds have been mechanically and chemically controlled in half the plots. In the remaining plots, each double row was planted through 1.2-m-wide (4-ft-wide) AL-OR plastic, laid with edges buried. Shoots were thinned to one per cutting early in the first season of growth. No additional weed control was performed between plastic mulch strips. Data are being collected from a subsample of trees located near the center of each plot. Survival, stem numbers, and their heights and diameters were obtained after the first growing season. Stems then were harvested, and both the biomass and the number of cuttings with top diameters in the range of 0.95 to 1.90 cm (3/8 to 3/4 inch) that could have been produced were estimated. Sprouting occurred in spring 1996 and regrowth has continued for two years with annual stem counts and measurements of heights and diameters.

Preliminary results: Heavy weed competition developed between the plastic mulch strips, especially velvet leaf, which overtopped trees in the plastic mulch plots for much of the 1995 growing season. However, survival was excellent (averaging > 98% for each clone/treatment combination). Mean stem heights and diameters, respectively, ranged from 1.8 m (5.9 ft) and 1.2 cm (0.47 inch) for DN34 in plastic mulch plots to 2.7 m (8.9 ft) and 1.9 cm (0.75 inch) for NM6 in mechanically and chemically treated plots. Estimated cutting yield was greatest for NM6 in mechanically and chemically treated plots (>247,000 per hectare or >100,000 per acre). Estimated dry biomass was greatest for DN34 in mechanically and chemically treated plots (approximately 5,700 kg per hectare or 2.6 tons per acre). After two years of regrowth, the mean numbers of stems per clump range from 2.25 for DN34 in plastic mulch plots to 6.30 for NM6 in mechanically and chemically treated plots. Mean stem heights and diameters, respectively, ranged from 1.7 m (5.6 ft) and 1.2 cm (0.47 inch) for NM6 in mechanically and chemically treated plots to 2.2 m (7.2 ft) and 1.6 cm (0.63 inch) for DN34 in plastic mulch plots. Estimates of stem dry biomass for 2-year-old regrowth (branches not considered) range from approximately 6,700 to 11,200 kg per hectare (3 to 5 tons per acre). Additional measurements and destructive sampling for biomass determination are planned following the third season of growth.

Keywords: intensive culture, poplar, Populus, short rotation, SRIC