Willing or complying? The delicate interplay between voluntary and mandatory interventions to promote farmers' environmental behavior.

• Framed field experiment to test impact of varying income and mandatory contributions to the environment on voluntary ones. • Variations of mandatory contributions to the environment affect voluntary contributions more than income. • Increased income leads to higher total environmental contributions than increased mandatory contributions. • Environmental concern of farmers does not affect voluntary or total contributions to the environment. • Reactance increases crowding out of mandatory contributions to voluntary ones. Agri-environmental policies generally build around two complementary approaches: mandatory requirements and (compensated) voluntary measures. One of the challenges of the future EU Common Agricultural Policy is precisely to find the right balance between these two types of interventions. We conducted an experiment with farmers in three EU Member States to assess the impact of (1) increasing mandatory contributions to the environment, and of (2) decreasing unconditional income support. We also assess the effect of two key behavioural factors: environmental concern and trait reactance. Results show that both interventions reduce voluntary contributions to the environment, but the reduction is higher when mandatory contributions increase than when income decreases.. However, when mandatory contribution increases substantially, this more than offsets the reduction of voluntary contributions, leading to higher total contributions. [ABSTRACT FROM AUTHOR]