Agroforestry and Grass Buffer Influences on Macropores Measured by Computed Tomography under Grazed Pasture Systems

Abstract

Agroforestry buffers, which include trees, grass, and shrubs, have been proposed for improving water quality in watersheds. The objectives of the study were to compare differences in macropore (>1000‐μm diam.) and coarse mesopore (200–1000‐μm diam.) parameters measured by computed tomography (CT) within agroforestry buffer (AgB) and grass buffer (GB) systems associated with rotationally grazed pasture (RG) and continuously grazed pasture (CG) systems, and to examine relationships between CT‐measured pore parameters and saturated hydraulic conductivity (Ksat). Pasture and GB areas included red clover (Trifolium pratense L.) and Korean lespedeza [Kummerowia stipulacea (Maxim.) Makino] planted into fescue (Festuca arundinacea Schreb.), while AgB included eastern cottonwood trees (Populus deltoides W. Bartram ex Marshall ssp. deltoides) planted into fescue. Soils at the site were Menfro silt loam (fine‐silty, mixed, superactive, mesic Typic Hapludalf). Intact soil cores were collected from the four treatments at five soil depths. Five equally spaced images were acquired from each core and were analyzed with Image‐J software. The CT‐measured soil macroporosity was 13 times higher (0.053 m3 m−3) for the buffer treatments than the pasture treatments (0.004 m3 m−3) for the surface 0‐ to 10‐cm soil depth. Buffer treatments had greater macroporosity (0.02 m3 m−3) than RG (0.005 m3 m−3) or CG (0.004 m3 m−3) treatments. The Ksat values for buffer treatments were five times higher than pasture treatments. Soil bulk density was 5.6% lower for the buffer treatments than the pasture treatments. The CT‐measured pore parameters (except macropore circularity) were positively correlated with Ksat This study illustrates the benefits of agroforestry and grass buffers for maintaining soil pore parameters critical for soil water transport.