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This article in SSSAJ

  1. Vol. 54 No. 4, p. 1096-1101
    Received: May 10, 1989

    * Corresponding author(s):
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Macroporosity and Its Relation to Saturated Hydraulic Conductivity under Different Tillage Practices

  1. S. D. Logsdon ,
  2. R. R. Allmaras,
  3. L. Wu,
  4. J. B. Swan and
  5. G. W. Randall
  1. Dep. of Soil Science, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN 55108
    Southern Exp. Stn., Waseca, MN 56093



Tillage management influences the distribution of macropores (biopores, cracks, interpedal planes, and packing voids) that may provide pathways for rapid infiltration of water. To aid in predicting ranges of saturated hydraulic conductivity (Ksat), macropore distribution in situ was characterized by exposing selected horizontal planes and tracing macropores on clear polyethylene sheets. A methylene blue solution was used to indicate macropore continuity through the pressure pan. Sixteen undisturbed cores were taken in a grid pattern from each Ap horizon and adjacent subsoil for determination of Ksat. Field marking on plastic sheets was superior to photographic slides as a technique to characterize macropores because film noise (false pores) was eliminated, overall analysis time was reduced, and different features could be separated for analysis. Unfortunately, a bias of pore size between observers was possible. Four sites with four different soil series were examined: Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll), Rozetta (fine-silty, mixed, mesic Typic Hapludalf), Waukegan (fine-silty over sandy or sandy-skeletal, mixed, mesic Typic Hapludoll), and Normania (fine-loamy, mixed, mesic Aquic Haplustoll). Below the maximum tillage depth, macropores were present at all locations, but tillage disrupted continuity of pores from the surface. No-till had macropores throughout the upper 70 cm with continuity observed in the 0- to 35-cm range. Numbers of pores (>0.4-mm diam.) per m2 ranged from 100 to >3000, representing 0.1 to 2% of the total area. When present, horizontal crack length ranged from 1.7 to 19.3 m m−2. Measured Ksat on undisturbed detached cores ranged from 1.1 to 180 µm s−1 with CVs ranging from 44 to 197%. The Ksat could be estimated within a range (out of eight classes) from descriptions of biopore area, cracks, soil structure, and soil texture.

Joint contribution from USDA-ARS and Minnesota Agric. Exp. Stn. paper no. 17 072.

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