🌱 What Is Biodegradable Mulch and Why Is It Used in Agriculture?

Biodegradable mulch refers to thin films made from materials designed to break down naturally in soil through the action of microorganisms, turning into water, carbon dioxide, and biomass over time. Unlike traditional polyethylene (PE) plastic mulches, which persist for years and require mechanical removal, biodegradable versions promise convenience for farmers by eliminating disposal hassles. Common materials include poly(butylene adipate-co-terephthalate) (PBAT), a flexible bioplastic derived from fossil fuels but engineered for soil degradation, often blended with starch or polylactic acid (PLA) from renewable sources like corn.

In the United States, plastic mulches cover millions of acres annually, particularly in vegetable production in states like California, Florida, and Georgia. These films suppress weeds, retain soil moisture, regulate temperature, and reduce pesticide needs, boosting yields by up to 20-50% for crops like tomatoes, strawberries, and peppers. The U.S. Department of Agriculture (USDA) estimates that agricultural plastic use exceeds 100,000 tons yearly, with biodegradable options gaining traction amid growing concerns over microplastic pollution from conventional films.

However, certification standards like ASTM D6400 focus on industrial composting conditions—high heat, moisture, and oxygen—rather than real-world soil environments. This gap has led to questions about true field performance, setting the stage for recent revelations.

📊 Breakthrough Findings from the Latest Research

A study published on February 22, 2026, in Environmental Science and Ecotechnology (DOI: 10.1016/j.ese.2026.100678) has exposed critical flaws in biodegradable mulch degradation. Researchers from East China University of Science and Technology conducted a 70-day pot experiment with soybean plants, testing PBAT microplastics in two sizes: large (1 mm) and small (150 micrometers) at realistic and high concentrations.

Using a mesh barrier to isolate rhizosphere soil—the microbe-rich zone around roots—from bulk soil, they employed quantitative proton nuclear magnetic resonance (q-¹H NMR), microbial DNA sequencing, metabolomics, and aggregate analysis. Results were stark: in bulk soil, polymer loss was minimal at 1.4-3.7%. In the rhizosphere, large particles degraded faster due to root-exuded nutrients fueling specialized bacteria like Bradyrhizobium and Ramlibacter (Proteobacteria), which ramp up esterase enzymes for surface erosion.

Yet, small particles hunkered down in soil microaggregates, evading microbes. Worse, breakdown products—adipic acid and terephthalic acid from PBAT's adipate units—piled up higher in root zones, potentially phytotoxic (harmful to plants) by disrupting growth or nutrient uptake. The corresponding author noted, “The rhizosphere is a conditional hotspot... This challenges the assumption that biodegradability automatically equates to ecological safety.”

Details from the study summary underscore particle size as a key variable, with implications rippling to U.S. farms where fragmented mulch becomes microplastics.

Photo by Markus Spiske on Unsplash

🔬 How Plant Roots Influence Plastic Breakdown

The rhizosphere transforms soil into a dynamic ecosystem. Plant roots release sugars, amino acids, and organic acids—exudates—that feed microbes, shifting communities toward plastic-degraders. In the study, esterase activity surged on particle surfaces, forming a "plastisphere" biofilm. Large particles, with more exposed area, eroded quickly, but this funneled toxins toward roots.

• Particle Size Effect: >500 μm degrade via microbes; <150 μm shelter in aggregates.
• Microbial Shift: Proteobacteria dominate, hydrolyzing ester bonds.
• Byproduct Buildup: Adipic acid (soluble, mobile) and terephthalic acid (less soluble) concentrate near crops.

Prior U.S. research from the University of Georgia's New Materials Institute echoes this, showing variable field degradation influenced by soil type, temperature, and tillage. One trial found only 26-83% breakdown after 36 months, far from the 90% promised in two years.

🌍 Environmental and Agricultural Impacts in the U.S.

For American growers, this means potential long-term soil contamination. Microplastics from mulch already detected in U.S. farmlands could alter microbial diversity, nutrient cycling, and crop health. Phytotoxic monomers might stunt roots, reduce yields, or enter food chains—concerns amplified in high-value organic sectors eyeing biodegradables for compliance.

Economically, U.S. biodegradable mulch market nears $3 billion by 2026, but slow breakdown risks clogs in machinery and persistent weed havens. Environmentally, incomplete mineralization contributes to soil carbon imbalance and water pollution via runoff. Policymakers note California's bans on non-biodegradable films, yet without rhizosphere-tested standards, solutions fall short.

Photo by Maarten van den Heuvel on Unsplash

💡 Sustainable Alternatives and Best Practices

Farmers aren't powerless. Transition to proven options:

• Organic Mulches: Straw, wood chips, or compost (4-6 inches thick) mimic benefits without plastics, improving soil organic matter.
• Paper/Cardboard Mulches: Biodegradable, affordable; enhanced with starch for durability.
• Cover Crops: Living mulches like clover suppress weeds, fix nitrogen; roll-kill for no-till.
• Improved Biodegradables: Seek films tested under ASTM D5988 (soil burial); avoid unverified PBAT blends.

Actionable advice: Test soil pH/moisture pre-mulching, till lightly post-season to expose fragments, and monitor via extension services. For research careers advancing these solutions, explore research jobs or faculty positions in agronomy.

🔮 Looking Ahead: Policy, Research, and Solutions

Experts urge rhizosphere-inclusive certifications and monomer monitoring. U.S. collaborations, like USDA-funded trials, could refine materials. Meanwhile, integrated pest management and precision irrigation reduce mulch reliance.

In summary, while biodegradable mulch offers promise, this study warns of hidden pitfalls. U.S. agriculture must prioritize verified sustainability. Stay informed via higher education news, pursue higher ed jobs in environmental science, rate professors at Rate My Professor, or advance your career with higher ed career advice. Share your experiences in the comments—your insights drive change. For university positions, visit university jobs or post a job.