MICROMORPHOLOGICAL CHARACTERISTICS OF LONG-TERM NO-TILL AND CONVENTIONALLY TILLED SOILS

Conservation tillage practices have been shown to affect a number of soil physical properties, but less is known about their effect on the size, shape, and arrangement of soil constituents. To evaluate soil structural differences between tillage treatments, six paired conventionally tilled and no-tilled plots of Maury silt loam soil (fine, mixed, mesic Typic Paleudalf) were analyzed. Oriented undisturbed samples (16 by 9.5 by 5.5 cm) were taken from each plot at depths of 0 to 5, 10 to 15, and 20 to 25 cm. The samples were impregnated with polyester resin and two vertical thin sections were prepared from each sample. The micromorphic features were described, and the size (equivalent spherical diameter), shape, and orientation of pores and aggregates were measured using an interactive image analysis system. The no-tilled plots had platy structure near the surface and interconnection of fine pores (50-100 mum) throughout the profile. Earthworm channels with excrement infillings were abundant in the no-till plots at all depths, but absent in conventionally tilled plots. The conventionally-tilled soil was composed of granular and fragmented structural units with no evidence of earthworm activity. The no-till plots contained about 11% pore area >50 mum, compared with about 16% for conventional tillage management. However, the no-till plots have an average pore size (0.18-0.26-mm diam.) that is greater than the conventionally filled plots (0.12-0.17-mm diam.). The finer aggregate size of the conventionally tilled plots (0.25-0.39-mm diam.) compared with the no-till plots (0.41-1.08-mm diam.) is probably due to plowing and disking.