•The paper aims to assess the adoption of willow within a stylised CAP greening.•Proactive greening mechanisms enabling wide diffusion of willow are tested for Poland.•Small and mid-sized farm groups are the most sensitive to willow plantation.•Willow uptake is also high within livestock-oriented farm groups.•Willow is likely to be most grown in Mazowsze & Podlasie region. Synergies between the Common Agricultural Policy (CAP) and the deployment of bioeconomy that induces resource-efficient and sustainable biomass production patterns are in the core of discussion for the new CAP in Poland. Proactive greening mechanisms likely to enable a large-scale diffusion of willow plantation are investigated in this respect, including diversification schemes combined with incentives making willow plantation more attractive to farmers. A comprehensive approach to modelling farm diversification options is therefore provided by means of an integrated bioeconomic framework which relies on linking the agricultural supply model AROPAj with the crop model STICS. The economic and environmental impacts related to the gross margin, land use change, nitrogen (N) fertiliser use, and greenhouse gas emissions, i.e. methane (CH4) and nitrous oxide (N2O), are assessed at the regional scale according to the type of farming and the economic size. Under current crop diversification conditions only 9% of farm groups (FG) may opt for willow, benefiting solely from diversification support whereas subsidising willow increases this percentage up to 20% and 45%, for a received allocation amount equal to € 100 ha−1 and € 200 ha−1, respectively. The uptake of willow is particularly high within small and middle-sized FG and within those specialising in grazing activities. Regarding the environmental impacts, the higher the number of required crops, the lower the N-fertiliser use, and in most cases, a coupled support policy (when willow plantation is subsidised) further reduces N-use, and consequently N2O emissions. Unlike grazing-oriented FG, crop-oriented FG tend to significantly increase their CH4 emissions due to the intensification of grazing activities. The countrywide coverage of the findings and their economic and spatial detail can support informed policies for sustainable bio-based activities development.