CT-measured pore characteristics of surface and subsurface soils influenced by agroforestry and grass buffers

Permanent vegetative buffers with grass and/or trees are expected to improve soil porosity compared to row crop management, yet little is known about the extent of changes in soil properties with depth and how rapidly these changes take place. The objective of this study was to compare the effects of agroforestry and grass buffers on computed tomography (CT)-measured macropore (diam. > 1000 μm) and coarse mesopore (diam. 200–1000 μm) parameters within 0.50 m soil profiles and to examine relationships between CT-measured pore parameters and saturated hydraulic conductivity (Ksat). Undisturbed soil cores (76 mm diam. by 76 mm long) from a no-till corn (Zea mays L.)-soybean (Glycine max (L.) Merr.; RC) rotation, grass buffer (GB), and agroforestry buffer (AB) treatments were collected with six replicates from the 0- to 0.50-m depth in 0.10-m increments on a Putnam silt loam (fine, smectitic, mesic Vertic Albaqualf). Five CT images were acquired throughout each soil core using a medical CT scanner with 0.2 by 0.2 mm pixel resolution and 0.5 mm slice thickness. Soil pore parameters including number of pores, number of macropores, number of coarse mesopores, porosity, macroporosity, coarse mesoporosity, and fractal dimension were analyzed using ImageJ software. Treatment and depth effects were significant for all seven parameters. These seven pore parameters were different between row crop and buffer treatments as well as grass and agroforestry buffer treatments. The GB and AB treatments had 26 and 36 macropores per 2500-mm2 area, respectively. These numbers were 2 and 2.6 times greater than 14 macropores in the RC treatment. No macropores were detected in the 40 to 50 cm depth of the RC treatment. The fractal dimension of macroporosity for the agroforestry treatment was 1.2 and 1.1 times greater than row crop and grass buffer treatments, respectively. Soil bulk density and saturated hydraulic conductivity were significantly different among the treatments. The fractal dimension accounted for 76% of the variability in Ksat. This study concludes that establishment of permanent vegetative buffers improves CT-measured soil parameters and these CT-measured parameters may be used to quantify the effects of management relative to environmental benefits and improved water transport and retention models.