Whole-biomass Ulva lactuca-derived soil-degradable mulch films for sustainable agriculture

Biodegradable agricultural mulches that can replace conventional plastics are essential for improving the sustainability of crop production. In this study, mulch films were produced from whole Ulva lactuca biomass through mild alkaline hydrolysis and solution casting, avoiding biomass extraction and purification steps. Film formulations were optimized by varying the content of diglycerol (DG) as a bio-based plasticizer and natural rubber latex (LX) as a hydrophobic phase. The optimal formulation contained 60 wt.% Ulva lactuca , 20 wt.% DG, and 20 wt.% LX, providing a balance between mechanical performance, water resistance, and soil degradability. The films were characterized in terms of chemical structure, morphology, thermal stability, optical properties, mechanical behavior, and water interactions. Incorporation of LX improved flexibility and reduced water sensitivity, while maintaining the high biomass content of the material. Soil burial tests showed approximately 65% mass loss after two months, indicating progressive disintegration under soil conditions. Greenhouse experiments using Italian red chicory ( Cichorium intybus L .) showed greater leaf area and biomass accumulation in plants grown with the seaweed-derived mulch than in the polyethylene mulch and bare-soil controls under the tested greenhouse conditions. These results demonstrate that whole- Ulva lactuca -based mulch films can provide agronomic performance while functioning as biodegradable soil covers. Overall, this proof-of-concept study demonstrates the feasibility of converting whole Ulva lactuca biomass into soil-degradable mulch films without extraction or purification steps, providing a promising bio-based alternative to conventional agricultural plastics.