Ireland's State of the Environment Report 2024

151 Chapter 6: Soil Figure 6.9  Area of soil moisture deficit by year (km 2 ), per tier 1 land cover in Ireland ˜ Urban ˜ Sparsely vegetated land ˜ Inland wetlands ˜ Heathland and scrub ˜ Grassland ˜ Forest and woodland ˜ Cropland 0 200 400 600 800 1000 1200 1400 0 0 0 0 0 0 0 0 0 0 0 0 0 0 25 0 0 0 1 0 26 0 19 18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 Source: EEA, 2021b Reduction of soil capacity to retain water. The ability of soil to retain adequate water is essential for plant growth. The EEA’s Copernicus service tracks soil moisture over time to detect and monitor agricultural droughts (EEA, 2021a). For the 2000-2019 period, Europe had a long-term soil moisture deficit. During that period, Ireland’s overall soil moisture profile showed a slight surplus rather than a deficit in soil moisture (Figure 6.9). The data for Ireland indicate the close relationship between drought and soil moisture deficit; the years that Ireland experienced drought conditions (such as 2004, 2006 and 2018) are clearly identifiable in their effects on soil moisture deficit (DAFM and DECC, 2023). Soil water retention is important in lessening the impact of flooding, particularly where it is because of extreme rainfall. Part C indicators: descriptors without criteria Excess nutrient content in soil (nitrates). While nitrogen is essential for plant growth, excessive nitrates in soil cause water pollution (see Chapter 8), have negative implications for human health and contribute to greenhouse gas emissions. The EU Soil Observatory used agricultural data and a European biogeochemical model framework to identify agricultural land areas where nitrogen surplus exceeds 50 kg/ha per year. Ireland has the third highest value in Europe (at 80%) of agricultural land above the 50 kg/ ha per year threshold. Nitrates can leach from soil into water; this is a greater issue in free-draining soils in the south-east where it causes a problem for water quality in estuaries along the southern seaboard (EPA, 2022). Soil acidification can be accelerated by the application of ammonium-based fertilisers. Topsoil compaction. Compaction is a decrease in soil porosity or volume due to stress from machinery or animal traffic, which compromises the capacity of soil to hold air or water. It represents one of main soils threats in Ireland. The Teagasc Soil Quality Assessment Research Project (SQUARE) examined soil health indicators (physical, chemical and biological) for Irish grassland soils (Bondi et al. , 2019). Among the array of physical indicators measured, soil structure emerges as a pivotal factor supporting all other soil functions. The deterioration in soil structural quality, leading to soil degradation and compaction, is frequently the outcome of intensive management practices (Bondi et al. , 2021). This can result in water’s diminished ability to permeate and drain through the soil, hampering water storage and purification in the landscape. Bondi et al. (2019) found that Irish grassland soils were generally healthy but that some soils were better at delivering soil functions than others. Well- and moderately drained soils such as brown earth and podzolic soils could support agricultural production but do not have the same capacity as poorly drained soils to store carbon or contribute to water purification. Poorly drained soils, such as gleys, are not as productive as well-drained soils. While poorly drained soils can store more carbon and support a more active soil microbiome, they are more susceptible to structural degradation in the form of compaction.