Soil compaction - evaluating effects of remediation strategies on soil, nutrients, plants and water

Soil physical quality is a critical requirement for ecosystem services essential for meeting global food demands. As agricultural intensification must become sustainable, effective soil management strategies are urgently required to reduce soil degradation while maintaining productivity. In Ireland’s grassland systems, machinery operations often occur under sub-optimal field conditions due to Atlantic weather, leading to high soil water contents. This creates challenges for farmers in predicting soil water status, scheduling sustainable field operations due to the inherent spatial and temporal variability of soil moisture. Machinery trafficking, combined with soil water content, is a key driver of soil compaction and structural damage. Understanding how to prevent soil compaction during field activities remains critical for achieving sustainable agricultural intensification. Furthermore, evaluating the potential of farm byproducts as soil amendments to restore soil structure and functionality following compaction is an area requiring further investigation. This thesis investigates the physical aspects of soil quality, focusing on the interplay between soil water content, machinery trafficking, and the application of organic and inorganic amendments to prevent and mitigate soil compaction. Results highlight the utility of the Soil Moisture Deficit (SMD) tool in predicting soil water status, with an SMD of +10 mm or higher identified as a threshold for safe machinery traffic. Under wetter conditions (SMD below +10 mm), soil bulk density alone proved insufficient to assess structural status, necessitating complementary indicators such as aggregate stability. When compaction occurred, amendments such as farmyard manure (FYM) and agricultural gypsum (AG) demonstrated the potential to mitigate compaction and enhance soil recovery, depending on soil moisture conditions. FYM was most effective across all conditions in the short term, while AG showed comparable benefits in dry soils over the long term. Using novel Soil Water Retention Curve analysis and X-ray CT imaging, the study revealed how these amendments influenced pore structure and water dynamics, with AG improving macroporosity and hydraulic conductivity and FYM enhancing microporosity and water retention. The results presented have relevance to current and future soil protection and agri-environmental policy, informing the development of sustainable intensification practices to support resilient agricultural systems.