Determinants of Soil <scp>pH</scp> and Nutrient Management Changes in Agricultural Catchments of Ireland

ABSTRACT Sustainable nutrient management is critical for maintaining soil fertility, improving agricultural productivity and mitigating environmental impacts. This study evaluated the impact of Ireland's Nitrates Action Programme (NAP) on soil pH, phosphorus (P) and potassium (K) dynamics over a 12‐year period across four meso‐scale agricultural catchments. Using a spatially defined field‐scale sampling approach, trends in studied chemical soil parameters were assessed in response to changing agricultural practices and policy interventions. Results indicate a notable increase in optimal soil pH levels (21%), likely as a result of recent targeted advisory efforts. While overall median soil test P (STP) levels decreased by 0.5 mg/L, variability among catchments was evident, with one catchment showing a significant increase due to intensive poultry manure applications. Additionally, the proportion of P Index 1 soils increased by 9%, suggesting uneven P distribution and highlighting challenges in on‐farm nutrient management. Median soil test K (STK) increased by 17.6 mg/L, with notable gains in tillage and dairy enterprises, indicating shifts in nutrient application strategies. The study also identifies critical source areas (CSAs) of P losses, which decreased by 2%, aligning with NAP objectives. However, nearly 80% of soils remain of suboptimal fertility, particularly for P and pH, underscoring the need for targeted advisory efforts, improved nutrient planning and region‐specific management strategies. Findings provide key insights into how regulatory measures influence soil nutrient trends, informing future policies for sustainable nutrient management and environmental protection in Irish agriculture.