CHEMICAL DIFFERENCES IN DARK BROWN CHERNOZEMIC Ap HORIZONS UNDER VARIOUS CONSERVATION TILLAGE SYSTEMS

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Abstract
The Ap horizons of two conservation tillage studies on Dark Brown Chernozemic soils in southern Alberta were sampled in 1986 following the fallow year. The first study, started in 1967, consisted of a wheat-fallow rotation under either no-till chemical fallow, blade-cultivate, or chemical fallow + blade-cultivate management. The second study, started in 1977, consisted of continuous winter wheat, winter wheat-barley-fallow, and winter wheat-fallow rotations under either no-till or conventional tillage management. Nine years of no-till continuous wheat and 19 yr of no-till in a wheat-fallow rotation both led to 40% of the dry aggregates being > 0.84 mm in diameter. The parameters selected helped to characterize differences in organic matter between soil tillage systems. Dehydrogenase and phosphatase activities were twice as high under no-till as under the blade-cultivate treatment. No-till also led to the largest monosaccharide accumulation in the soil. Carbohydrates, solvent-extractable organic matter, and chitin N were significantly higher in the > 0.84 mm diameter dry aggregates from the no-till treatment. The monosaccarides under the blade-cultivate regime were generally of microbial origin whereas those under the no-till regime were generally of plant origin. Key words: Water-stable aggregates, dry aggregates, enzyme activities, organic carbon, monosaccharides, fallow