**5. Conclusions**

The extensive use of PE mulching materials owes to their lower market prices compared to biodegradable materials. However, our results show that the inclusion of the costs of waste managemen<sup>t</sup> and recycling is crucial for a proper evaluation of the economic profitability of di fferent options in the short-term. The inclusion of such costs under the current Spanish legislation only increases the costs by 9.5 € ha−<sup>1</sup> with respect to the no waste managemen<sup>t</sup> scenario and 15.5 € ha−<sup>1</sup> if total recycling cost is considered. These increases represent a reduction in the final net margin of 0.1%. This is supporting the mandatory measures for farmers to assume the costs of waste managemen<sup>t</sup> and recycling.

Economic consideration of current Spanish governmen<sup>t</sup> support of biodegradable mulching materials allows us to a ffirm that only two materials (Ecovio ® and Sphere ®) are profitable alternatives to PE when the same yield is considered. Despite the saving in costs of field conditioning with regard to PE, the high market prices of biodegradable and paper materials are not compensated with the current level of subsidies, thus impeding their adoption in fields. An increase in subsidies rates of up to 50.1% would allow all biodegradable films to be better alternatives than PE.

Although no fully conclusive evidence has been found on the environmental e ffects of long-term use of the specific materials analyzed, the consideration of soil quality e ffects supports measures towards mandatory full recycling of waste and for the use of biodegradable and paper materials. Correct assessment of environmental damages of materials would require other types of field experiments than those conducted here. These data could be included in a long-term economic model based on the analysis of the net present value of discounted future social costs (economic plus environmental damages) and benefits (yield gains and reduced environmental damages). In addition, an adequate evaluation must take into account that subsidies provide an economic incentive for the adoption of bio-materials, but also an opportunity cost to society, thus a proper design must be ensured.

Finally, although this study refers to field trials with pepper crops, the results may be representative of the open-air growing conditions for other summer horticultural crops under similar climatic conditions, mainly in the Ebro Valley, where mulches are often used.

**Author Contributions:** A.I.M., G.P. and A.C. conceived and designed the field experiments; A.I.M., G.P. and A.C. performed the field experiments; A.I.M. compiled and analyzed the field data; Y.M. analyzed the economic results; All the authors wrote the paper.

**Funding:** This work has been financed by the INIA Projects RTA2011-00104-C04-00 and RTA2017-00082-00-00 funded by the Spanish Ministry of Agriculture and Fisheries, Food and Environment, and ECO2016-75927-R funded by the Spanish Ministry of Economics, Industry and Competitiveness.

**Acknowledgments:** We thank JA Alins, F Arrieta, and D Redondo for their help and valuable contribution. We thank Verso Paper Corporation, Fábrica de papeles crepados Arrosi S.A. Fábrica de papeles crepados, BASF S.E., FKuR Kunststo ff GmbH, Mimcord S.A., Novamont S.p.A., Oerlemans Plastics BV, Stora-EnsoFinland and Sphere Group Spain S.L. for generously providing the materials and the market prices.

**Conflicts of Interest:** The authors declare no conflict of interest and the founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
