Agroforestry and Grass Buffer Influence on Macropore Characteristics

Although agroforestry and grass filter strips have been identified as possible land management practices to reduce nonpoint-source pollution from row-crop agriculture, their effects on detailed soil pore characteristics are rare. 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 and to examine relationships between CT-measured pore parameters and saturated hydraulic conductivity (K sat ). Samples were collected from a no-till corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotational watershed with pin oak (Quercus palustris Muenchch.) and cool season grass-legume buffers established in 1997. Soils in the sampling region are mapped as Putnam silt loam (fine, smectitic, mesic Vertic Albaqualf). Undisturbed soil cores (76 by 76 mm) from tree buffer, grass buffer, and row crop areas were collected with six replicates. Five CT images were acquired from each soil core using a hospital CT scanner with 0.2 by 0.2 mm pixel resolution with 0.5-mm slice thickness. Computed tomography images were compared by depth -within and among treatments. Soil from the tree and grass buffer treatments had significantly (p ≤ 0.01) greater number of pores, number of macropores, area for the largest pore, macroporosity, mesoporosity and significantly lower circularity than soil from the row crop treatment. Soil under trees, grass, and crop areas on average had 207, 87, and 44 CT-measured pores on a 3632 mm 2 area, respectively. Soil under the trees had 2.5 and 3.6 times greater number of macropores than grass and crop areas, respectively. Computed tomography-measured number of macropores explained 64% of the variation for K sat . Computed tomography-measured parameters that were correlated with saturated hydraulic conductivity included macroporosity, mesoporosity, area of the largest pore, macropore circularity, and number of pores. Results showed that CT-measured pore parameters can be used to predict saturated hydraulic conductivity as affected by land management practices. The study also showed that buffer practices improve soil pore parameters related to soil water infiltration.

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