Macroporosity and hydraulic properties of earthworm-affected soils as influenced by tillage and residue management

Macropores affect infiltration of water and solutes in soil. A field study was conducted to determine the effect of tillage-residue management on eart hworm development of macropore structure and the infiltration properties of a silt loam soil cropped in continuous corn. Tillage treatments included r ototilled and nontilled soils, with or without residues, and innoculated wi th 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 pressur es. There were no significant tillage-residue effects on steady-state infil tration rates, The time required to reach steady state was 930 and 1020 s i n 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-w ith-residue treatments, respectively, compared to >544 s in the remaining t reatments. Estimates of effective porosity calculated using infiltration da ta and by counting stained macropores with depth were 0.85 and 1.3% in no-t ill and 0.99 and 0.29% in tillage-with-residue treatments, respectively. In no-till treatments, large quantities of dye solution, unaccounted for by s teady-state measurements, infiltrated rapidly and were stored in deep, surf ace-connected earthworm macropores, In tillage-with residue treatments, inf iltration of dye solution, unaccounted for by macropore stained count measu rements, occurred along partially incorporated residue pieces, Measurements of infiltration properties should include measurements of early infiltrati on and storage in macropore systems (ponded tests) and of steady-state infi ltration into the soil matrix (tension infiltrometry) once the macropore sy stem has filled with water.