Ireland's State of the Environment Report 2024

152 Chapter 6: Soil For Irish soils, Bondi et al. (2021) developed a soil trafficking intensity index that considers the effect of geo-climatic variability or differences in drainage classes on soil compaction risk. 4 In general, poorly drained sites were more vulnerable to machinery trafficking than grazing trafficking pressure, being more prone to damage. At a national scale, this index can be used to identify soils at risk of compaction and to underpin targeted management advice for supporting sustainable grassland production. Acidification (soil acidity in pH). Chemical indicators yield substantial information on nutrient cycling, primary production and carbon sequestration functions in soils. Notably, soil pH and soil organic matter have been recognised as key elements in regulating nutrient availability in soils and influencing various soil functions, including carbon sequestration and nutrient cycling. Loss of soil biodiversity. Soil biology is often referred to as the ‘engine of the soil’, with soil biodiversity and the soil microbiome positioned at the core of soil functioning. Biological indicators provide insights into the impact of past and current management practices on soil health. For instance, the abundance and presence of earthworms serve as practical and easily recognisable soil health indicators (Figure 6.10). Nevertheless, a considerable portion of soil biology necessitates more advanced analysis, which may not always be feasible for routine in-field soil health assessments. Figure 6.10  Photo of soil biodiversity (earthworm) Credit: Olaf Schmidt, UCD 4 The index can detect changes in direct indicators of soil structural quality, such as bulk density, total porosity, water holding capacity, water conductivity and visual soil appearance, but also indirect indicators, such as soil carbon content, earthworm abundance and microbial biomass. The soil biome is an ecosystem and provides essential services to support soil formation, soil structure and plant growth. The EU Soil Observatory modelled a set of 13 factors, such as habitat fragmentation, land use change, soil pollution and soil sealing, that negatively affect soil biological functions. The model differentiates between soils that have a higher than moderate risk of loss of soil biological functions. The assessment identified that 36.73% of the EU’s soil area has potential threats to its biological functions that are moderate or worse than moderate. Two-thirds of Ireland’s soil area falls within these categories (62.98%). The EU Soil Observatory assessment is based on modelled data. A national assessment to understand the status of Ireland’s soil biome would be important to validate this assessment. Intensive exploitation and soil organic matter decline are the highest potential threats to soil biodiversity in the EU (Orgiazzi et al. , 2016). Agricultural practices with high levels of mechanisation and use of pesticides strongly affect soil biodiversity. To counteract such threats, Orgiazzi et al. (2016) recommend that agri- environmental schemes include measures to protect and enhance soil biodiversity. The EU Soil Observatory assessment also identifies soil areas under threat within protected area boundaries; Orgiazzi et al. (2016) recommend considering soil biodiversity as a criterion for protected area designation and planning. Further research highlights the links between farming practices, soil biodiversity health and terrestrial ecosystem health. The research suggests a strong link between pesticide and fertiliser use and declines in bird populations across Europe (Rigal et al. , 2023). This is attributed in part to the known impact of pesticide use on invertebrates, a crucial food source for many birds. Such assessment of soil organisms is an important part of measuring soil health, but these data are currently sparse in both the EU (Orgiazzi et al. , 2016) and Ireland (Bondi et al. , 2019). Given the importance of the soil biome, and the impact of soil biological functions on plant growth and terrestrial ecosystems, measures to collect data and to protect soil biodiversity functions against potential threats should be prioritised (Orgiazzi et al. , 2016). The ability of soils to absorb and sequester carbon has a relationship with plant diversity. Studies of agriculturally degraded and abandoned lands found that the carbon sequestration rate was greatly enhanced when the plant diversity of these lands was restored (Yang et al. , 2019).