Load Risks of Subsoil Compaction and Depths of Stress Propagation in Arable Luvisols

Abstract

The objective of the study was to investigate the effects of (i) wheel load (3.3, 6.3, and 7.5 Mg), (ii) tire inflation pressure, and (iii) tillage treatment (conventional vs. conservation) on stress propagation in Luvisols derived from loess and glacial till and to assess the compressibility risk of these soils under different stress situations. Stress and its distribution in the soil were determined with wheel track experiments using a tractor‐pulled load frame and stress‐state transducer stress sensors. The soil stability with respect to the soil mechanical parameter precompression stress (Pc, −6 kPa) was analyzed on undisturbed soil samples using the oedometer test. Wheel track experiments pointed out no significant differences in stress distribution between the two parent materials and higher stress (σ 1 ) with heavier wheel load, whereby σ 1 more than doubled with a load increase from 3.3 to 7.5 Mg. Conservation tillage showed a greater attenuation of σ 1 and lower stress in the topsoil and subsoil (∼26%). A reduction in tire inflation pressure decreased σ 1 in the topsoil for all loads. In the subsoil, σ 1 decreased for 3.3‐ and 6.3‐Mg loads, whereas the 7.5‐Mg wheel load resulted in a trend of increasing stress and propagation into depth with lower inflation pressure. The ratio Pc/σ 1 (the Pc concept ), which specifies the transition between plastic and elastic deformation behavior of the soil, indicated that regardless of the tillage treatment, the stress of wheel loads >6.3 Mg exceeded the Pc of the Luvisols down into the subsoil.