Tillage system effects on near-surface soil morphology: observations from the landscape to micro-scale in silt loam soils of southwestern Ontario

Changing soil management practices can affect processes occurring at multip le scales. This paper assesses the influence of no-till (NT) soil managemen t on conventionally tilled (CT) soils at scales from the soil landscape thr ough to the micromorphological in southwestern Ontario, Canada. Soil profil es were sampled in fine increments at three slope positions in agricultural transects under CT and NT management. The NT soils had been under their pr esent management system for 4, 6 and 11 years such that the changes in morp hology over time could be assessed. Cs-137 and soil organic matter content were used as indicators of recent morphological change along the landscape and within the pedon. Thin section samples were taken to determine the chan ges in soil micromorphological properties. The NT soils had increases of so il organic matter in the top 3 cm relative to lower portions of the Ap hori zon, while Cs-137 was diluted likely due to casting activity of earthworms. The accumulation of organic matter and the dilution of Cs-137 near the soi l surface was proportional to the number of years the soil had been in NT. The CT soils had indications of aggregate instability, surface crust format ion and lack of good pedality within soil thin sections. The top 3 cm of th e soil surface in the NT soils had a structure indicative of annual additio ns of organic residue and L. terrestris l. earthworm activity. The near-sur face soil layers in NT for 4 and 6 years had evidence of a platy structure which may have been due to compaction and/or freeze-thaw processes. However , the top 3-4 cm of the 11-year NT site had a fine granular structure which should favor crop emergence and growth. Results from image analysis of por e morphology indicated that it takes more than 4 years of NT to develop por es of equivalent diameter from 100 to 1000 mu m that are comparable to the pores numbers of this size in the CT counterparts. (C) 1999 Elsevier Scienc e B.V. All rights reserved.