Mitigation of subsoil recompaction by light traffic and on-land ploughing. I. Soil response

Summary

Mechanically loosened subsoil has been shown to be prone to recompaction. We evaluated the degree of recompaction of a sandy loam mechanically loosened to a depth of 35 cm in 1997 and again in 1998. Perennial grass/clover was grown with limited traffic intensity in 1999 and 2000. The recompaction experiment was conducted in 2001 and 2002 when the soil was grown with oat and winter wheat, respectively. On-land ploughing was compared with traditional mouldboard ploughing with the tractor wheels in the furrow. In addition, the loosened plots were either light trafficked (<6 Mg axle load and <100 kPa inflation pressure) or heavy trafficked (10-18 Mg axle load and ~200 kPa inflation pressure), respectively. The soils loosened by non-inversion deep tillage (NINV) were referenced by a conventional ploughing-harrowing tillage system (CONV). The CONV treatment was modified in 2001, i.e. on-land ploughing and light traffic was applied instead of traditional ploughing and traffic. Penetration resistance and bulk density was recorded in the field. Undisturbed soil cores were taken in 1998, 1999 and 2002 from the 7-14 cm, 18-27 cm and 25-30 cm layer and used for measuring total porosity, macropores >30 μm and air permeability at –100 hPa matric potential. The results showed that on-land ploughing mitigated recompaction of the upper part of the subsoil. In contrast, only small differences between heavy and light traffic were observed. Mitigation of subsoil recompaction by primarily on-land ploughing was needed for the loosened NINV soil to produce an upper subsoil with similar – not better – pore characteristics than the non-loosened CONV soil 4 years after loosening. The structural conditions in the transition layer between plough layer and subsoil improved for the CONV soil from 1998 to 2002 as indicated by an almost doubling in air permeability. This was interpreted as being related to the growing of grass/clover ley in 1999 and 2000 combined with a shift from traditional tillage and traffic to on-land ploughing and light traffic when growing cereals in 2001 and 2002. Results on root growth and crop yield are reported in an adjoining paper.