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Compaction Characteristics of a Soil Cropped to Corn and Bromegrass¹

ABSTRACT

This study was initiated in order to determine if the compaction characteristics of soils are modified by cropping history. Uniaxial compression tests were made on cores of aggregated soil. The tensile strength of individual aggregates was also measured. Four different cropping histories ranging from 15 yr of continuous corn (Zea mays L.), C₁₅, to 15 yr of continuous bromegrass (Bromus inermis Leyss.), B₁₅, were investigated. The bulk density of soil cores under standard compaction conditions (100 kPa load and 50% water saturation) did not vary with cropping history. However, interaggregate porosity under standard compaction conditions was 18% larger in B₁₅ than in C₁₅, and the aggregate strength, which was positively correlated with interaggregate porosity, was 50% larger. The compression index was 12% larger in B₁₅ than C₁₅ and was positively correlated with interaggregate porosity under standard compaction conditions. This suggests that the loss of porosity on compaction was strongly influenced by collapse of interaggregate pores. Soils with a recent history of bromegrass had a greater proportion of interaggregate pores and this benefit persisted across a range of pressures that would normally be encountered in the field (<500 kPa). Changes in the compression index, tensile strength and interaggregate porosity appeared to occur rapidly when cropping practices changed.

¹ Contribution from the Dep. of Land Resource Science, Univ. of Guelph, Guelph, Ontario, Canada. N1G 2W1.

² Graduate Student and Professors, respectively. The senior author is now at the Agric. Canada Res. Stn., 2560 Hochelaga Blvd., Ste. Foy, Quebec, Canada G1V 2J3.

Received for publication December 16, 1985.