EFFECTS OF CROPPING SYSTEM ON STRUCTURE OF BROOKSTON CLAY LOAM IN LONG-TERM EXPERIMENTAL PLOTS AT WOODSLEE, ONTARIO

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Abstract
Macro- and microstructure were described and water desorption characteristics were measured for a Brookston clay loam soil under different cropping systems. The Ap horizon of the long-term corn (Zea mays L.) plots differed markedly from those of a bluegrass (Poa pratensis L.) plot and a never-cultivated plot as follows: massive as opposed to strongly structured, macroporosity (pore width > 60 μm) ≤ 6% as opposed to more than 10%, isolated pores as opposed to interconnected pores, bulk density 1.4–1.5 Mg m−3 as opposed to 1.0–1.3 Mg m−3. The Ap horizon of the rotation plots, oats (Avena sativa L.), alfalfa (Medicago sativa L.), alfalfa, corn, differed from those of the continuous corn plots in having many more biopores larger than 0.5 mm in diameter (≥ 0.2% relative to ≤ 0.02%). Below a depth of 30 cm comparable horizons of soils from all plots were similar in structure, bulk density and water characteristic curves. Key words: Porosity, biopores, compaction, macromorphology, image analysis