Establishment and early productivity of perennial biomass alley cropping systems in Minnesota, USA

In May 2010, alley cropping systems consisting of switchgrass (Panicum virgatum L.), prairie cordgrass (Spartina pectinata Bosc ex Link), an alfalfa (Medicago sativa L.) and intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth and Dewey) mixture, and a native tallgrass-forb-legume polyculture, planted between multi-row strips of poplar hybrid ‘NM6’ (Populus maximowiczii x P. nigra) and willow cultivar ‘Fish Creek’ (Salix purpurea) were established at Empire and Granada, Minnesota, USA. Crop establishment and productivity were characterized for each species over two growing seasons and at two distances from the tree-crop interface. Prairie cordgrass and the native polyculture were among the most productive herbaceous crops at both sites, averaging between 7.1 and 11.9 Mg DM ha−1, and have shown no evidence of competition for resources along the tree-crop interface thus far. Basal area (BA) was similar at Empire for NM6 (1,744 mm2 tree−1) and Fish Creek (1,609 mm2 tree−1), but was greater for NM6 (1,045 mm2 tree−1) than Fish Creek (770 mm2 tree−1) at Granada. Despite this, stand basal area (SBA) was greater for Fish Creek at both sites due to greater planting density. Across species, BA and SBA were greater for trees along the alley than those in center rows at Empire, whereas no difference was observed at Granada. Results suggest that alley cropping provides suitable conditions for establishment of short-rotation woody and certain herbaceous biomass crops, and that some of these crops may be well suited to the alley cropping environment. However, continued research is needed to evaluate crop persistence and productivity as crops and trees mature and the potential for interspecies competition increases.