Saturday, 15 July 2006
137-12

Agroforestry and Grass Buffer Influences on CT-Measured Pore Characteristics.

Ranjith P. Udawatta, Center for Agroforestry, Univ of Missouri-Columbia, 203 ABNR Natural Resources Building, Columbia, MO 65211, Stephen H. Anderson, Dept of Soil, Environmental and Atmospheric Sciences, Univ of Missouri-Columbia, 302 ABNR Building, Columbia, MO 65211, and Clark J. Gantzer, Dept of Soil, Environmental and Atmospheric Sciences, Univ of Missouri-Columbia, 302 ABNR Natural Resources Building, Columbia, MO 65211.

Agroforestry and grass filter buffer strips have been identified as possible land management practices to reduce nonpoint source pollution from row-crop agriculture in temperate regions. A better understanding of how these conservation practices affect soil pores and hydraulic properties is needed to improve application guidelines for these practices. The objective of this study was to test the hypothesis that CT-measured pore characteristics are influenced by agroforestry and grass buffers. Four treatments were evaluated: tree buffers, cool season grass buffers, warm season grass hedges, and row crop areas. Undisturbed soil cores (76 by 76 mm in Plexiglas cylinders) were collected from five soil depths: 0-10, 10-20, 20-30, 30-40, and 40-50 cm with six replicates per depth. Five CT images were acquired throughout each soil core with a Siemens Somatom Plus 4 Volume Zoom X-ray CT scanner and images were analyzed with public domain Image-J software. Pore characteristics by depth within and among treatments were compared and declared significant for p<0.01. Soil from the tree and grass buffer treatments and the grass hedge treatment had significantly (p °Ü 0.01) greater number of pores, number of macropores, area for the largest pore, macroporosity, mesoporosity and fractal dimensions than soil from the row crop treatment as measured by CT. Soils under tree buffers, grass buffers, grass hedges, and crop areas on average had 50, 41, 18, and 17 CT-measured pores, respectively. Soils under the tree buffers, grass buffers, and grass hedge areas had 4, 3, and 3 times greater number of macropores than for the crop areas, respectively. The largest pore area across all measured depths was 11, 7, 3 and 5 mm2 for the tree, grass, hedge and crop treatments, respectively. In general the largest pores occurred near the surface for all four treatments. However, several larger pores were detected for depths between 20 and 30 cm in the crop, cool season grass buffer and tree buffer treatments. Macropore fractal dimension was the largest for the tree buffer treatment followed by the grass buffers. The row crop treatment had the lowest macropore fractal dimension indicating a lower number of pores and pore volume as compared to the conservation buffer practices. The fractal dimension in the row crop treatment declined sharply below the 35 cm depth while the tree and grass buffer treatments had greater values throughout the profile. The distribution of macropores and total number of pores significantly declined in the row crop treatment for depths greater than 40 cm as compared to the tree and grass buffer treatments. The grass hedge treatment indicated an inverse hyperbolic sine curve for the number of pores with depth. The total porosity was highest for the tree buffer treatment across all 25 depths as compared to the other three treatments. Among the CT-measured parameters, macroporosity had the highest correlation with saturated hydraulic conductivity. CT-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 conservation buffer practices improve soil macropore parameters which are highly correlated to water infiltration.

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