Biodegradable composite hydromulches for sustainable organic horticulture

Authors: DURADO, ANDREW - Montana State University; BAJWA, DILPREET - Montana State University; GRAMIG, GRETA - North Dakota State University; Weyers, Sharon; WASKO DEVETTER, LISA - Washington State University; FORMIGA, ALICE - Oregon State University; GALINATO, SUZETTE - Washington State University

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2024
Publication Date: 8/10/2024
Citation: Durado, A., Bajwa, D., Gramig, G., Weyers, S.L., Wasko Devetter, L., Formiga, A., Galinato, S. 2024. Biodegradable composite hydromulches for sustainable organic horticulture. Industrial Crops and Products. 221. Article 119349. https://doi.org/10.1016/j.indcrop.2024.119349.
DOI: https://doi.org/10.1016/j.indcrop.2024.119349

Interpretive Summary: The most common mulch material used in many horticultural crops is low-density polyethylene (LDPE). However, LDPE mulch is typically removed at the end of the growing season and landfilled, buried, or burned, which may harm the environment. The goal of this research was to develop and assess physical and mechanical properties of soil-biodegradable, liquid-applied (i.e., hydromulch) alternatives to LDPE mulch that are acceptable for organic horticulture. Formulations of hydromulch (HM) tested were made of water mixed with paper pulp, wood fiber, or hemp hurds with or without binding agents (called tackifiers) including guar gum, psyllium husk, and camelina meal, added at various proportions. Formulations with 6% guar gum tackifier improved the tensile strength and puncture resistance by 182% and 91%, respectively, compared to control samples with no tackifiers. Formulations containing paper were 200% or more stronger than those containing wood or hemp hurds. Formulations made with two types of tackifiers decreased strength of the dried mulch product. Formulations with wood fiber or hemp hurds did not show promising results, but those made with paper had lower porosity and improved adhesion to soil. Results from the study provide a foundation on optimal formulations for expanded trials at field-scale and will benefit researchers and developers looking to enhance environmental outcomes with naturally degradable mulch replacements for LDPE.

Technical Abstract: Surface-applied mulches help retain soil moisture and optimize soil temperature while preventing weed growth and benefiting many horticultural crops. The most common mulch material is low-density polyethylene (LDPE). At the end of the growing season, LDPE mulch is typically landfilled and, in some cases, buried or burned, causing negative environmental impacts. The goal of this research was to develop soil-biodegradable, liquid-applied (i.e., hydromulch) alternatives to LDPE mulch and optimize formulations that are acceptable for organic horticulture. Hydromulch (HM) treatments contained mixtures of paper pulp, wood fiber, or hemp hurds combined with various tackifiers and water. The tackifiers were guar gum, psyllium husk, and camelina meal, included at various proportions. Hydromulch samples were tested for physical properties (density, porosity, C:N ratio, soil adhesion) and mechanical properties (tensile strength, puncture resistance). Hydromulches containing no tackifiers were included as controls to determine if the addition of tackifiers resulted in enhanced mechanical properties. The results showed addition of 6% guar gum tackifier improved the tensile strength and puncture resistance by 182% and 91% respectively compared to control sample, and HM formulations containing paper were 200% or more stronger than those containing wood or hemp hurds. Increased tackifier proportion was found to improve most mechanical properties, with guar gum performing best. Blending of tackifiers resulted in an interaction that decreased strength. Hydromulches containing wood fiber and hemp hurds did not show promising results. Paper in HM formulations helped to reduce mulch porosity and improved adhesion to soil. Results from the study provide a foundation on optimal formulations for expanded trials at field-scale.