The Impact of Common Agricultural Policy Eco-Schemes on Crop Structure Simplification and Crop Diversity in Poland: A Regional Assessment

Enhancing crop diversity is a key pillar of the EU’s 2023–2027 CAP eco-schemes, yet Poland’s long-standing crop simplification raises doubts about the policy’s effectiveness. This study assesses the determinants of crop structure and crop diversity in Poland and evaluates whether eco-schemes generate measurable improvements at farm and municipal scales. A multilevel approach integrates municipality-level saturation with ecological interventions (eco-schemes, organic farming, and agri-environment–climate measures) with longitudinal data from 192 purposively selected farms across all 16 voivodeships for 2016, 2021, and 2024. Crop diversity is measured using the Shannon–Wiener index (H′), combined with indicators of specialization, farm size, and participation in CAP instruments. Spatial and temporal comparisons reveal that farms engaged in commercial animal production maintain simplified crop structures, which is associated with specialization as a dominant factor in low diversity. Maize share increased steadily from 12.4% to 16.7%, signalling ongoing homogenization, particularly in livestock-intensive regions. Contrary to earlier assumptions, smaller farms did not exhibit higher diversity, suggesting organizational constraints. At the municipal level, greater saturation with eco-schemes and organic farming was associated with higher H′ values, while areas with strong agri-environment–climate presence—often mountainous—showed lower diversity due to biophysical limits. The findings highlight structural barriers that may limit eco-scheme impacts.