Computed Tomographic Analysis of Soil Pore Characteristics for Agroforestry and Grass Buffers in a Grazed Pasture System.

Agroforestry buffers have been introduced as a conservation method to improve water quality for watersheds. The objective of this study was to compare x-ray computed tomography (CT)-measured pore parameters in soil under agroforestry (AgB) and grass buffers (GB) relative to rotationally grazed (RG) and continuously grazed (CG) pasture systems.  Pasture and GB areas included red clover (Trifolium pretense L.) and lespedeza (Kummerowia stipulacea Maxim.) planted into fescue (Festuca arundinacea Schreb.) while AgB included Eastern cottonwood trees (Populus deltoids  Bortr. ex Marsh.) planted into fescue. Soils at the site were Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs). Soil cores (76 mm diam. by 76 mm long) were collected from five soil depths (0-50 cm, 10-cm depth increments) with six replicates from the four treatments (AgB, GB, RG, CG).  Soil cores were scanned with a medical x-ray CT scanner and images were analyzed with ImageJ ver. 1.27 software. Macropore (>1000 μm diam.) and coarse mesopore (200 to 1000 μm diam.) parameters were evaluated to examine relationships between CT-measured pore parameters and saturated hydraulic conductivity (Ksat). Soil bulk density was higher for the CG and RG treatments compared to GB and AgB treatments.  Soil macroporosity (>1000 μm diam.) was higher for the AgB, GB, and RG treatments compared to the CG treatment for the 10 cm soil depth.  Buffer treatments had greater macroporosity (>1000 μm diam.) and coarse mesoporosity (200 to 1000 μm diam.) compared to RG and CG treatments.  Saturated hydraulic conductivity values for GB and AgB treatments were higher compared with RG and CG. CT-measured macropores, coarse mesopores, area of largest pore, macropore circularity and number of pores were correlated with Ksat. This study illustrates the benefits of agroforestry and grass buffers for maintaining soil pore parameters relative to grazed pastures.