Characterizing Macropores that Affect Infiltration into Nontilled Soil

Abstract

Abstract A 0.5‐ha watershed of Rayne silt loam on 9% slope at Coshocton, Ohio was farmed for 20 yr in continuous no‐till corn ( Zea mays L.). With average rainfall >1 m/yr, runoff from this mulch‐covered surface averaged <2 mm/yr. Previous dye studies show that even at low rainfall rates, water moves rapidly through vertically continuous macropores (mainly earthworm burrows) in this field that hasn't been tilled since 1960. To characterize the distribution of these pores, we photographed cleaned, horizontal 30.5‐ by 30.5‐cm 2 surfaces at depths of 2.5, 7.5, 15, and 30 cm. The images were scanned with an image analyzer to count and determine the size of open pores. With eight replications at each depth, total number of pores >0.4 mm in diameter per m 2 of surface area ranged from 3369 to 21 151 in the 2.5‐cm depth and from 5673 to 28 966 at the 30‐cm depth. The overall average was 14 576 pores per m 2 , 160 of which were >5 mm in diameter. Mean pore diameter ranged from 1 to 2 mm at all depths and the number of pores was inversely proportional to pore diameter. There were more pores at the lower depth than near the surface. Pores >0.4 mm in diameter accounted for approximately 1.4% of the total area.