Macroporosity and Hydraulic Properties of Earthworm-Affected Soils as Influenced by Tillage and Residue Management
1998
Trojan, M. D. | Linden, D. R.
Macropores affect infiltration of water and solutes in soil. A field study was conducted to determine the effect of tillage-residue management on earthworm development of macropore structure and the infiltration properties of a silt loam soil cropped in continuous corn. Tillage treatments included rototilled and nontilled soils, with or without residues, and innoculated with earthworms. Infiltration properties were measured with an instantaneous infiltration test of a 1.61 cm pulse of 0.5% methylene blue solution and by measuring steady-state infiltration rates at +5, 0, −3, and −12 cm pressures. There were no significant tillage-residue effects on steady-state infiltration rates. The time required to reach steady state was 930 and 1020 s in treatments with residues, compared to 180 and 415 s in treatments without residue. Dye solution infiltrated in 22 and 217 s in no-till and tillage-with-residue treatments, respectively, compared to >544 s in the remaining treatments. Estimates of effective porosity calculated using infiltration data and by counting stained macropores with depth were 0.85 and 1.3% in no-till and 0.99 and 0.29% in tillage-with-residue treatments, respectively. In no-till treatments, large quantities of dye solution, unaccounted for by steady-state measurements, infiltrated rapidly and were stored in deep, surface-connected earthworm macropores. In tillage-with residue treatments, infiltration of dye solution, unaccounted for by macropore stained count measurements, occurred along partially incorporated residue pieces. Measurements of infiltration properties should include measurements of early infiltration and storage in macropore systems (ponded tests) and of steady-state infiltration into the soil matrix (tension infiltrometry) once the macropore system has filled with water.
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