The implementation of Payments for Environmental Services (PES) may face a financing constraint, especially when the buyer is a public regulator. An additionality-based PES can address this problem. The objective of this paper is to study the efficiency of PES based on additionality. To do so, we consider a farmer who has to choose to allocate his land between organic production, conventional production causing environmental damage, or biodiversity-generating grass strips. Using a two-period model, we introduce a PES in the final period, remunerating the additional grass strips provided by the farmer. We show that the additional PES distorts the behavior in the initial period, in order to obtain more payment in the final period. The second-best PES to limit this behavior is equal to the discounted difference of the marginal environmental benefits obtained in each period. We also establish the second-best value of environmental taxes in the presence of the additionality-based PES. They are no longer equal to the marginal damage and are amended to take into account the distortions caused by the additionality-based PES. The analysis is then extended by taking into account market power in the organic market. It turns out that market power reduces the distortion due to the additionality-based PES in the initial period but reduces the organic production quantity in the final period. The second-best PES depends on the size of these two effects and environmental taxes under market power have to be amended. Finally, this paper shows that an additionality-based PES never achieves environmental efficiency, even in a competitive market framework. Furthermore, this paper provides new insights into understanding the interactions between different environmental policies in the presence of several types of distortions.