Biomass production of short-rotation bioenergy hardwood plantations affected by cover crops.

Abstract Effects of varying strip widths of four species of cover crops on the growth of sweetgum ( Liquidambar styraciflua L.) seedlings planted as a short-rotation bioenergy woody crop were studied. Ryegrass ( Lolium multiflorum L. a winter annual grass); tall fescue ( Festuca arundinacea Schreb a cool-season perennial grass); crimson clover ( Trifolium incarnatum L. a winter annual legume); and Interstate sericea lespedeza ( Lespedeza cuneata (Dumont) G. Don. a summer growing perennial legume), were planted using two different strip widths (1.22 and 2.44 m ) between trees on a 1.5×3 m spacing. The control had no competition. Height, ground-line diameter and volume index of trees were determined on a monthly basis. Lespedeza and tall fescue significantly reduced ground line diameter, height and volume index compared to ryegrass and the control. Crimson clover significantly reduced ground line diameter compared to the control and volume index more than ryegrass and the control. During first two growing seasons, there was no benefit from legumes as a cover crop over grasses. All cover crops except rye grass significantly reduced sweetgum biomass compared to control. The results indicate that cover crops lespedeza, tall fescue, crimson clover and ryegrass reduced biomass by approximately 41%, 37%, 27% and 15%, respectively, compared to the control. The 2.44 m strip width reduced sweetgum growth 40% relative to the control vs. 20% with the 1.22 m strip width. Strip width had a greater impact on diameter and volume index than height.