Physical restoration of compacted soils: a lab experiment using rock fragment addition

In many world areas Alfisol and Entisol soils are susceptible of natural or anthropic deterioration that negatively affects crop yields.Specific geomorphological and climatic conditions can induce, for example, a massive soil structure and problems of asphyxia. Wetested an alternative physical restoration method based on the addition of rock fragments performing a lab experiment withrepacked soil samples.Five concentrations of 4-8mm rock fragments were added to an Alfisol and an Entisol from South Italy which exhibit problems ofnatural soil compaction. The mixtures were put in pots (15cm height x 15cm diameter) and after nine wet/dry cycles the sampleswere impregnated with fluorescent resin. The obtained soil blocks were examined by image analysis techniques. The directobservation and analysis of the soil pore system allowed to quantify the occurred modifications.In both soils the addition of stones improved the soil structure modifying the typical sub-horizontal pore arrangement of thecompacted soils into more complex and isotropic ones. This latter amelioration effect gradually increased with depth at increasingrock fragments concentrations.Outcomes of this work demonstrate that lab experimental studies combined with image analysis techniques have the potential toimprove the quantitative understanding of the mechanisms of soil structure restoration. Overall results showed that rock fragmentsaddition in compacted soil could be a useful technical structure restoration measure.