The power of soil amendments to restore degraded grassland soil: A combined approach using physical indicators and X-ray computed tomography

The impact of organic and inorganic amendments on soil physical properties under varying moisture conditions remains unclear. This study uniquely integrates X-ray Computed Tomography (CT) and soil physical measurements to assess structure changes following amendment application in degraded soil under different moisture conditions. In this study i) soil resilience, defined as soil ability to naturally restore physical structure and functionality after disturbance, was evaluated in soils physically degraded by traffic under dry (D), moist (M), and waterlogged (W) conditions, as well as in unmanaged soils; ii) soil recovery capacity was evaluated when slurry (SL), farmyard manure (FYM), and agricultural gypsum (AG) were applied as soil amendments. Key soil physical properties, including soil bulk density, pore volume (measured using X-ray CT scan), water-stable aggregates, and herbage dry matter, were evaluated at time intervals of: Prior-amendments application, six- and 12-months post–amendments application. In the short term (6 months), FYM was the most effective amendment across all three soil moisture conditions, with AG and SL showing notable performance in D and M soils. In W soils, FYM remained the top performer, followed by SL. Over the long term (12 months), FYM and AG provided comparable remediation benefits in D soils, while SL proved to be the most effective in moist conditions. The results indicate that amendment effectiveness is influenced by initial soil conditions. In the short term (6 months), FYM reduced bulk density by up to 12 % in D and M soils, while SL showed the same reduction after 12 months in M plots only. However, all the tested amendments did have a significant increase in soil water stable aggregates. Overall, under waterlogged conditions, amendment effects were significantly reduced, with no measurable improvement in bulk density across treatments (p > 0.05). For future management advice, understanding the interactions between compaction, amendment type and time will be critical as these determine how different amendments like FYM, SL and AG can be strategically used to remediate soil compaction and restore soil physical structure and help to improve aspects of soil health.