Loblolly Pine Age and Density Affects Switchgrass Growth and Soil Carbon in an Agroforestry System
Global interest in biomass-based fossil fuel substitutes is increasing, creating needs for new crops and cropping systems that will expand biofuel production. In the southeastern United States, an alley cropping agroforestry management system in which switchgrass is cultivated between rows of loblolly pine is being explored. Such a system could produce an annually harvested, high-yield energy crop, wood waste for biofuel production, conventional forest products, and environmental services such as soil carbon (C) sequestration. The objectives of this study were to determine the effects of loblolly pine age (juvenile, mid-rotation, and late-rotation) and loblolly pine density (no trees, low density, and high density) on switchgrass and loblolly pine growth and soil characteristics (microbial biomass C and activity, labile C, and total soil C) linked to carbon sequestration and site productivity. Switchgrass ground coverage was greater in loblolly pine alleys than in open conditions in 2 of the 3 years of this study, but switchgrass biomass was lower in loblolly pine alleys than in open conditions in the mid-rotation stand. Switchgrass in alleys was associated with greater labile C, respiration, and microbial biomass and activity in soil compared with that in loblolly pine plantations with intensive suppression of understory.
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