Tillage Effects on Soil Water Retention and Pore Size Distribution of Two Mollisols

A study was conducted to determine the effects of conservation and conventional tillage on soil water retention and pore size distribution of two mollisols. Two locations were used, each having randomized complete-block designs with three replications of continuous-corn (Zea mays L.) plots under no-tillage, reduced tillage, and conventional tillage. One location, site 1, was in its 2nd yr of tillage experimentation on a Canisteo series soil (Typic Haplaquolls), and the other location, site 2, was in its 8th yr on a Nicollet series soil (Aquic Hapludolls). Undisturbed soil cores were obtained near the planted row at the 5.0- to 7.5-cm and 10.0- to 12.5-cm depths from the two sites. Soil water retention of the soil cores was measured at water matric potentials of 0 to −39.22 kPa. Pore size distribution was estimated by using a capillary model. Statistical differences in soil water retention due to tillage treatments appeared at site 1, with general means comparisons of reduced tillage > no tillage > conventional tillage in the amount of water retained at any matric potential. Reduced tilled soil generally retained a significantly (LSD 0.05) larger quantity of water than conventionally tilled soil. No-tilled soil was not significantly different from reduced tilled or conventionally tilled soil in its water retention characteristics. Differences in water retention between tillage treatments were not significant at site 2, but trends in the means comparisons similar to those of site 1, were observed. Analysis of variance failed to show significant tillage effects for the pore size distribution regardless of pore radius interval partitioning. Trends indicated that soil under conventional tillage had a larger proportion of its pore volume in pores > 15 µm radii compared with soils under conservation tillage. Conservation tilled soils appeared to have a larger portion of pores in the 15- to 0.1-µm pore radius interval. Implications are that conventionally tilled soils should drain more rapidly than conservation tilled soils and that conservation tilled soils should retain more plant available water than conventionally tilled soils. The data indicate that bulk density increases occurred at the expense of larger pores (>150-µm radii). Because conventionally tilled soils have the greater proportion of large pores, these soils seem to be more susceptible to densification than the soils under the conservation tillage systems.