Hydroponics, the practice of growing plants without soil, can substantially increase the sustainability in agriculture by reducing the need for large amounts of land, water and pesticides. This process requires a suitable growth medium with sufficient water holding capacity and durability, and ideally this medium would also be produced or obtained through sustainable means. Hemp fibers offer a promising foundation for biocomposite growth media, but current methods for strengthening these materials produce harmful volatile organic compounds (VOCs). Now, a research team at the University of Nebraska-Lincoln have produced a sturdy hemp-based biocomposite growth medium with great water holding capacity and without harmful byproducts.
The researchers managed to increase the mechanical strength of the hemp fibers by coupling the lignin from the fibers to linker molecules. This process uses only water as a solvent, with the only byproducts being inorganic salts instead of VOCs. This pairing of lignin with linker molecules fortifies the biocomposite, and mechanical testing showed the composite was able to hold its shape well when subjected to compressive forces.
The new hemp-based growth medium can also hold roughly twice as much water as pure hemp fiber, making its capacity nearly on par with commercial peat moss. The research team further tested the abilities of the growth medium by planting Daikon radishes and green peas, and successfully grew the plants over a 14-day period. This study was published in ACS Agricultural Science & Technology.
The researchers said applying their fortifying technique to other lignin-containing fibers, like flax, jute and coconut husk, could produce other sustainable biocomposites for use in growth media, bioplastics and packaging materials. Hydroponic growing using sustainable media could provide a solution for farmers as water resources become scarcer and erosion of topsoil makes conventional farming more difficult.
Photo: The hydroponic growth of a Daikon radish plant from day 8 to 14, using a hemp-based biocomposite as the growth medium. Credit: American Chemical Society/Agricultural Science and Technology