Grantee Research Project Results

Final Report: Eco-friendly Additives for Biodegradation of Agricultural Mulches

EPA Grant Number: SU835534
Title: Eco-friendly Additives for Biodegradation of Agricultural Mulches
Investigators: Hayes, Douglas G , Wadsworth, Larry C , Powell, Matthew Shafer , Burnham, Alana , Lee, Jaehoon , DeBruyn, Jennifer , Ji, Xiaoci
Institution: University of Tennessee
EPA Project Officer: Packard, Benjamin H
Phase: I
Project Period: August 15, 2013 through August 14, 2014
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2013) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Chemical Safety , Sustainable and Healthy Communities

Objective:

The objective of this project is to determine robust amendments that can be applied to biodegradable agricultural plastic mulches, particularly novel 100% biobased prototypes prepared by the applicants using nonwovens textile technology, near the end of their service life that will accelerate the mulches’ full microbial conversion into CO₂ and water subsequent to them being plowed into the soil. Plastic mulches, most of which are prepared from non- renewable polyethylene, although serving as important components of sustainable agriculture, due to their aid in enhancing water and soil conservation, their overall sustainability is poor due to limited and undesirable end-of-life alternatives. Commercially available biodegradable mulches undergo mechanical weakening, which accompanies the initiation of microbial activity, in an uncontrollable fashion. This project involves a novel approach that will lead to a more controlled, “triggerable,” onset of biodegradation.

Mulch samples of both a commercially available biodegradable film “BioTelo” and two experimental biobased nonwovens, namely 71%PLA-29%PHA mulch and 100%PLA mulch underwent simulated weathering to make their conditions close to their conditions at the end of 5 months service life. Then six different amendments that were expected to “open up” the supramolecular structure of the biodegradable mulches’ (BDMs’) polymer molecules and / or help establish microbiological communities capable of microbial assimilating of the mulches were applied to “biodegradable” mulches, to determine if the rate and extent of biodegradation is enhanced. The effects of the following affordable and readily-available amendments were examined: spent mushroom compost, commercial lime, commercial Black Kow® manure compost cow manure, biochar, and commercial 10:10:10 (N: P: K) fertilizer.

Summary/Accomplishments (Outputs/Outcomes):

First, among the six tested treatments, the tensile strength test result of the 21 days soil burial pretest showed that Black Kow® cow manure compost was the least effective amendment for promoting mulches degradation. It was then excluded from the 73 days larger scale soil burial experiment.

The tensile strength test results of the larger scale experiment showed that the effects of each amendment varied for the three tested mulch types. All treatment weakened the tensile strengths of BioTelo similarly. 10:10:10 (N: P: K) fertilizer and mushroom compost had effects on the 100%PLA mulch. The tensile strength values of 71%PLA-29%PHA did not show a clear trend of weakening.

The bacterial plate count results of the larger scale experiment indicate that addition of mulches and the amendments promoted cultivable soil bacteria populations. The mushroom compost amendment showed highest cultivable soil bacteria population, and this is likely due to the fact that mushroom compost is rich in microorganisms.

Conclusions:

Laboratory scale experiment showed limited result on the effects of amendments on mulches degradations. Since PLA and PHA need to be blended in the manufacturing process of the 71%PLA-29%PHA mulch, performance of each batch of product may vary. Thus, more replicates are needed in the future soil burial experiment to get more reliable results. In addition, the soil bacteria may need longer time to adapt to the addition of mulches and amendments. Thus, a longer term experiment is necessary to assess the bacteria activity changes and the mulch biodegradation rates. In this study, the commercial fertilizers were applied following manufacturer’s instructions. Since the instructions were designed primarily for field application, it is possible that the applied fertilizer concentrations were too high for the soil trays. If possible, in future researches, field study of the effects of these amendment on mulches degradation should be conducted.

Supplemental Keywords:

agricultural mulches, agricultural plastics, biodegradation, biopolymers, environmentally benign endpoints, nonwovens, organic agriculture, polyethylene (replacement for), renewable (biobased) feedstocks, sustainable agriculture;