Wednesday, November 7, 2007
305-1

Soil Hydraulic Properties Influenced by Agroforestry and Grass Buffers for Grazed Pasture Systems.

Sandeep Kumar, Stephen H. Anderson, Laura G. Bricknell, Ranjith P. Udawatta, and Clark J. Gantzer. University of Missouri, 302 ABNR Building, Department of Soil, Environmental & Atmospheric Sciences, Columbia, MO 65211

Agroforestry buffers have been recently introduced in temperate climates to improve water quality and diversify farm income. The objective of this study was to evaluate saturated hydraulic conductivity and water retention for soils managed under normal rotationally-grazed pasture (P), high animal traffic grazed pasture (TP), grass buffers (GB), and agroforestry buffers (AgB). 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. Water retention was measured at -0.4, -1.0, -2.5, -5.0, -10, -20, and -30 kPa soil water pressures using 76 mm diam. by 76 mm long cores from the 0-10, 10-20, 20-30, and 30-40 cm depths. Soil bulk density was 12.6% higher for the P and TP treatments (1.41 and 1.45 g cm-3) than the GB and AgB treatments (1.25 and 1.29 g cm-3). Soil water content at high soil water potentials (0 and -0.4 kPa) was greater in the buffer treatments relative to the other treatments for the 0-10 cm soil depth. Soil macroporosity (> 1000 μm diam.) was 5.7, 4.5, and 3.9 times higher, respectively, for the AgB, GB, and P treatments compared to the TP treatment for the 0-10 cm soil depth. Buffer treatments had greater macroporosity, coarse mesoporosity (60 to 1000 μm diam.) and fine mesoporosity (10 to 60 μm diam.) but lower microporosity (< 10 μm diam.) compared to P and TP treatments. Saturated hydraulic conductivity values for GB and AgB treatments were 16.7 times higher (56.95 vs.61.33 mm hr-1) compared with P and TP (3.98 vs. 3.11 mm hr-1). This study illustrates the benefits of agroforestry and grass buffers for improving hydraulic properties compared to grazed pasture systems.