Leveraging Management to Speed Degradation of Bio-Based Mulches in Soil

Project Director: Sam Wortman, University of Nebraska, Lincoln

Project overview

Black polyethylene (PE) plastic film mulch greatly facilitates weed control and improves yield in organic vegetables, but its disposal creates serious environmental concerns. Bio-based mulches (biomulches) show promise as a more sustainable alternative to PE mulch, as they can be incorporated into soil and biologically degraded. However, biomulches can be slow to biodegrade, and at present, may not meet the degradation requirements set by USDA Certified Organic standards (90% within 2 years). As such, there is a need to understand the mechanisms behind biomulch decomposition, including any on-farm management practices that may boost decomposition rates.

This study analyzed how decomposition rates for two types of biomulch (bioplastic and PLA biofabric) are impacted by (1) mulch incorporation method, (2) compost application, and (3) cover cropping, with the goal of identifying ways in which farmers can speed the decomposition process.

Farmer takeaways

Common organic management practices, including use of compost, compost extract, and cover crops may have little-to-no effect on the degradation rate of biomulches.
Biomulch degradation rate is strongly influenced by local environmental conditions (site) and biomulch composition (type); as such, more studies are needed to understand best practices for biomulch use, including under which conditions/in what locations biomulches may decompose fast enough to meet current USDA decomposition requirements.

Project objectives and approach

Explore management strategies to speed the degradation of bio-based fabric mulch.

Field experiments at two sites evaluated the impacts of (1) a compost application at the time of mulch incorporation into the soil, (2) a cover crop (rye + vetch) grown after mulch incorporation, (3) an application of compost extract, and (4) combinations of these practices on biofabric mulch degradation rate.
A sample of biomulch residue was recovered after incorporation following green bell pepper harvest in Year 1, analyzed for surface area, divided into subsamples, and buried for re-analysis at subsequent sampling intervals (6, 12, 18, and 24 months). In Years 2 and 3, sweet corn and cabbage were planted, respectively.

Determine the impacts of degraded biomulch on soil properties.

Soil samples were collected to roto-tillage depth within each experimental plot at the time of biomulch soil incorporation and at every buried-residue sampling interval described earlier. Soil samples were processed and analyzed for soil microbial biomass, microbial community structure, and wet aggregate stability.

Key findings

Site location and biomulch type may be significantly stronger drivers of biomulch degradation rate than other management practices

Bioplastic mulch was nearly undetectable in soils after 12 months of burial at the Lincoln field site, whereas 50% of the original residue quantity remained in soils after the full 24 months at the Scottsbluff site.
By 24 months after soil incorporation, 30% of PLA biofabric mulch remained at both locations.

Biomulch may have little effect on crop yield and soil nutrients, relative to either compost application or cover cropping

Biomulch residues did not influence sweet corn crop yield.
Compost amendments increased sweet corn and cabbage yields, and cover crops decreased cabbage yield at the Lincoln site.

Resources

USDA - Project Report - ORG 2016-51106-25711

Reid, E.V., M.B. Samuelson, H. Blanco-Canqui, R. Drijber, I. Kadoma, and S.E. Wortman. 2022. Biodegradable and biobased mulch residues had limited impacts on soil properties but reduced yield of the following crop in a low fertility soil. Renewable Agriculture and Food Systems 1-14

Samuelson, M.B., E.V. Reid, R. Drijber, E. Jeske, H. Blanco, M. Mamo, I. Kadoma, and S.E. Wortman. 2021. Effects of compost, cover crops, and local conditions on degradation of two agricultural mulches in soil. Renewable Agriculture and Food Systems pp. 1-14

S.E. Wortman, Jeske, E., M.B. Samuelson, and R. Drijber. 2021. A new method for detecting micro-fragments of biodegradable mulch films containing poly(butylene adipate-co-terephthalate) (PBAT) in soil. Journal of Environmental Quality pp. 1-6

eOrganic - Assessing the quality and possible functions of compost extracts in organic systems

Location

Nebraska

Collaborators

Region

North Central

Topic

Weed Management, Tools and Technology

Year Published

2019