Abstract
The growing demand for sustainable agricultural practices necessitates innovative solutions that enhance crop productivity while minimizing environmental impact. This doctoral research explores the potential of seaweed-derived biomaterials as versatile, eco-friendly resources for agriculture. Seaweeds, rich in bioactive compounds such as polysaccharides, proteins, minerals, and phytohormones, offer promising applications in improving soil health, stimulating plant growth, and mitigating biotic and abiotic stress. The study focuses on three key areas: (1) the extraction and processing of seaweed-based compounds, (2) the formulation of functional agricultural products, and (3) their evaluation in controlled laboratory and greenhouse settings. The research emphasizes the development of seaweed-based biostimulants, biofertilizers, and soil conditioners to promote sustainable farming practices by showing three different applications. The efficacy of these materials was assessed through their effects on seed germination, root elongation, and crop yield across two different plant species, demonstrating significant improvements in plant vigor and biomass. The first phase of the research involved the development of hydrogels for soilless cultivation, polymeric blends combining carrageenan (a red seaweed-derived polysaccharide) and hydrolyzed seaweed extracts in varying ratios. These hydrogels were evaluated for chemical composition, mechanical properties, water interaction, and plant growth performance using Arabidopsis thaliana in a controlled growth chamber. The second phase investigated the formulation of a biodegradable bioplastic for mulching derived from hydrolyzed Ulva lactuca (green seaweed), blended with diglycerol as a plasticizer and latex for improved flexibility. The films were extensively characterized using mechanical testing (Young’s modulus, elongation at break, tensile strength), thermal stability (TGA), chemical composition (FT-IR), morphology (SEM), transparency (UV-Vis), and water interaction tests (solubility, moisture content, vapor transmission rate). A selected bioplastic formulation was tested in a greenhouse with red chicory plants, comparing its biostimulant effects to commercial black plastic mulch and uncovered soil. Results demonstrated that the green bioplastic enhanced chicory plant growth. As a proof of concept, a third material was developed: a microparticle-based fertilizer in which a brown seaweed extract was encapsulated in zein microparticles using a spray-drying technique. Different seaweed-to-zein ratios were tested, and the microparticles were analyzed using SEM, FT-IR, and electrochemical stability testing showing a weak interaction between the two components. Overall, this research demonstrates the potential of seaweed-based biomaterials to enhance sustainable agriculture through improved plant growth, soil conditioning, and biodegradable alternatives to synthetic inputs. The biostimulant effect, evaluated using Arabidopsis thaliana and red chicory, resulted in significant enhancements in root and shoot growth, as well as an overall increase in plant biomass in both species. This study underscores the multifunctionality of these materials, representing a novel contribution to the existing literature in this research area.