The effects of tillage systems on soil bulk density and penetrometer resistance of a sandy clay loam soil

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Abstract
Concern has been expressed that reduced tillage systems may lead to excessive soil compaction, with a negative impact on crop growth. The objectives of this study were to determine the effects of different tillage systems, namely, minimum tillage (disc and sweep), chisel plough and conventional tillage (plough) on soil bulk density, penetrometer resistance and yield. These effects were determined over a three-year period (1991/1992 and 1992/1993 seasons) on an Avalon sandy clay loam soil in the central Orange Free State. Results indicated that soil water content at planting was similar for the different tillage systems, except for slight differences in the upper soil depths. Penetration resistance and bulk density increased from a depth of 130 mm down to 290 mm of the soil using disc and sweeps compared with conventional tillage and chisel plough treatments. However, in the deeper soil zones, the tillage system did not consistently influence either bulk density or penetration resistance. At a depth of 400 mm, conventional tillage and chisel ploughing resulted in a lower bulk density than minimum tillage. The tillage operations for minimum tillage probably led to compaction in the deeper soil zone. Penetration resistance in the deeper soil zone in all tillage systems restricted rooting, but differences due to the tillage treatment were not sufficient to markedly influence the yield.