MACROPOROSITY OF A WELL-DRAINED SOIL UNDER NO-TILL AND CONVENTIONAL TILLAGE

Conventional tillage and no-tillage have been shown to affect the hydraulic properties of soil. For this reason, a field experiment was conducted in 1987 and 1988 to determine the effect of tillage practice and cover crop on the macroporosity of a Maury silt loam (fine, mixed, mesic Typic Paleudalf). The field used for this study has been in continuous no-till and conventional-till corn (Zea mays L.) since 1970. Ponded steady-state infiltration measurements were made using double-ring infiltrometers; afterwards, a tension infiltrometer was used to measure water flux at -0.4, -0.9, and -1.4 kPa water pressure. These negative water pressures were used to calculate equivalent cylindrical pore diameters from the capillary-rise equation. Flux at a pressure of -0.06 kPa was determined from regression equations for each plot. Equivalent pore diameters of 5.0, 0.75, 0.33, and 0.21 mm correspond to -0.06, -0.4, -0.9, and -1.4 kPa, respectively. In June 1987, conventional tillage had significantly higher water flux than no-till for the 5.0- to 0.75-mm equivalent-diameter pore size range. In 1987, rye (Secale cereale L.) cover crop plots had significantly higher water-flux values than hairy vetch (Vicia villosa Roth.) plots for the same range of equivalent pore sizes. In June 1988, no-till plots had significantly higher water-flux values for all equivalent pore size ranges. In 1987, 73 and 80% of the total water flux at -0.06 kPa water pressure was transmitted through pores > 0.21-mm equivalent diameter in no-till and conventional-tillage plots, respectively. The corresponding values in 1988 were 83 and 73%.