Species pairing and edge effects on biomass yield and nutrient uptake in perennial alley cropping systems

Perennial biomass production in agroforestry systems has been promoted as a strategy to increase productivity and ecosystem services from marginal agricultural lands. However, little is known about appropriate species combinations and production potential for such systems. We measured biomass yield, nutrient uptake, and edge eff ects on productivity in alley cropping agroforestry systems consisting of four herbaceous perennial crops and two short-rotation woody crops (SRWC) at three sites in Minnesota. Aft er 4 yr, we found that alley system yield was 23 and 35% greater for NM6 poplar (Populus maximowiczii A. Henry × P. nigra L. ‘NM6’) than Fish Creek willow (Salix purpurea L.‘Fish Creek‘) alley cropping systems at Empire and Granada, irrespective of herbaceous crop type. Nutrient uptake was consistently among the highest in NM6 poplar–native polyculture and prairie cordgrass (Spartina pectinata Bosc ex Link) systems at these sites, though at Empire the NM6 poplar– intermediate wheatgrass (Th inopyrum intermedium [Host] Barkworth and Dewey ‘Rush’) system was similar. Yields were similar for all systems at Fairmont, but nutrient uptake was highest in Fish Creek willow alley systems at this site. Crop yields were similar in poplar and willow alleys, and were greatest for prairie cordgrass and the native polyculture. At Empire, yield of all herbaceous crops declined with proximity to SRWC rows. Edge effects on SRWC productivity were not consistent across sites and species, but were an important consideration for accurately quantifying yield. Appropriate species combinations for maximizing yield and nutrient uptake vary based on site characteristics.