Influence of Establishing Short-Rotation Woody Crops on Short-Term Net Ecosystem Productivity on Sharkey Shrink-Swell Clay Soils.

INFLUENCE OF ESTABLISHING SHORT-ROTATION WOODY CROPS ON SHORT-TERM NET ECOSYSTEM PRODUCTIVITY ON SHARKEY SHRINK-SWELL CLAY SOILS Wilson G. Hood1, Michael C. Tyree1, Ray Souter2, Emile S. Gardiner2, Theodor D. Leininger2 1School of Forestry, Louisiana Tech University, Ruston, LA 71272 2Center for Bottomland Hardwoods Research, U.S. Forest Service, SRS, Stoneville, MS 38776 The Lower Mississippi Alluvial Valley (LMAV) offers an opportunity for short-rotation woody crop (SRWC) production by pairing underutilized, marginal agricultural land with optimal climate for plant growth. Shrink-swell clay soils (e.g., Sharkey, Perry, and Alligator series) comprise approximately 1.7 million hectares within the LMAV, and while their hydric nature makes much of this resource unsuitable for traditional agriculture; when planted with native, well-adapted species, they are ideal for SRWC production. This work seeks to quantify: 1.) the immediate impact of SRWC management on net ecosystem productivity (NEP) throughout stand establishment, and 2.) whether differences in NEP occur among species or management intensity treatments. Seasonal estimates of soil respiration, soil temperature and moisture were taken with a portable infra-red gas analyzer (LiCor 8100A) using PVC root exclusion zones to partition autotrophic and heterotrophic components. Soil respiration, which was modeled using continuously monitored meteorological data, crop net primary productivity (NPP), and non-crop NPP, was used to calculate NEP for each treatment. We found that soil temperature and total biomass explained 84% of the seasonal variation in soil respiration (r2=0.84), however, there were no treatment differences detected at this early stage of stand development. Non-crop biomass made up 94.2% of total aboveground biomass and varied significantly (p=0.04) between our two species. Overall, NEP was negative (-4.9 Mg C ha-1) across all treatments and differed marginally between species (p<0.10), but not management intensities (p=0.45), which is likely due to the domination of non-crop biomass that invaded the site.