Soil mechanical properties of a partly-reloosened (split plough system) and a conventionally-tilled overconsolidated gleyic luvisol derived from glacial till

In the Eastern states of Germany, there are many arable soils which have been compacted and overconsolidated as a result of intensive wheeling. These require mechanical loosening in order to improve the structure of the deeper layers of these originally very fertile soils. Repeated wheeling of highly-overconsolidated soils results in a further stress distribution to greater soil depths, because the hard plough pan layer serves as an elastic pressure plate provided that the deeper soil horizons are not strong enough to carry the load applied. Furthermore, the types of stresses induced during wheeling differ depending on the original soil strength and the number of loading events. The slit-ploughed soil volume is subjected to further changes of the pore system and of the soil strength induced by shear stresses, because during wheeling additional soil material is pressed in the weaker slit-ploughed soil volume. The hydraulic properties also change very significantly. In order to preserve the improved soil conditions, two further aspects have to be considered: 1.Wheeling should be carried out only at right angles to the slits which has the benefit of using the adjacent, stronger, unslotted soil to attenuate the stresses applied. 2.Under drier soil conditions, slotted soils can be wheeled. Wheeling must be avoided if the soil is moist in order to prevent the re loosened soil volume from additional soil compaction due to slip-induced transport of adjacent, previously-undisturbed soil into the slit itself.