Stress/strain processes in a structured unsaturated silty loam Luvisol under different tillage treatments in Germany

Abstract

In agriculture, the degradation of soil structure by tillage and field traffic is an adverse process causing a reduction in productivity of arable land. In order to manage this problem, various kinds of traffic and tillage systems have been developed. Relatively few studies have examined changes of soil mechanical properties induced by conservation tillage systems. The objectives of this study were to determine the effect of long term reduced tillage on soil strength properties. A field experiment was conducted in Germany on a silty loam Luvisol derived from loess, tilled differently by conventional (ploughed) and conservation (rotary) tillage systems for more than 25 years. In the spring of 1995, plots were compacted by increasing dynamic loads (number of passes × wheel load: 2 × 2.5, 2 × 5 and 6 × 5 Mg) and the soil physical, and mechanical properties were determined by field and laboratory techniques. The repeated deep impact of tillage tools in conventionally treated plots resulted in a permanent destruction of newly formed soil aggregates. This led to a relatively weak soil structure of the tilled horizons as dynamic loads as low as 2.5 Mg induced structural degradation. In the conservation tillage plots, in contrast, a single wheeling event with 2.5 Mg was compensated by a robust aggregate system and did not lead to structural degradation. Thus a higher soil strength due to the robust aggregate system was provided by reduced tillage. Increasing wheel loads and repeated tire passes resulted in an increasing structural degradation of the subsoil in both tillage systems. Since preserved fragments of channels were observed in depth greater than 30 cm in conservation tillage plots, trafficked by 6 × 5 Mg, the conditions for structural recovery are expected to be more favourable with this tillage system than conventional tillage.