Microbial Response to Biodegradable Mulch: Can Degradation Rate Be Accelerated by Management?

Authors

M. Benjamin Samuelson, University of Nebraska - LincolnFollow

First Advisor

Rhae Drijber

Second Advisor

Samuel Wortman

Date of this Version

8-2019

Citation

Samuelson, M. Benjamin. (2019) "Microbial Response to Biodegradable Mulch: Can Degradation Rate Be Accelerated by Management?" University of Nebraska - Lincoln

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Horticulture, Under the Supervision of Professors Rhae A. Drijber and Samuel E. Wortman. Lincoln, Nebraska: August, 2019

Copyright 2019 M. Benjamin Samuelson

Abstract

Single-use, petroleum-based polyethylene mulch is ubiquitous in certified organic mulched vegetable systems, representing a broken nutrient cycle and a waste concern. Current organic-allowable biodegradable mulches cannot match the performance of polyethylene, in part because of the requirements that they contain 100% bio-based feedstock, and biodegrade within two years after soil incorporation. It is valuable to understand whether management can influence postharvest degradation rate of mulch films. Two biodegradable mulches: a potentially organic nonwoven polylactic acid and wood particle prototype (PLA), and a widely-adopted non-organic starch/copolymer blend, Bio360® (BLK), were used in field trials in two distinct ecoregions of Nebraska, at Lincoln (LNK) and Scottsbluff (SBF). We tested degradation rate, influence on soil microbial community, and microbial recruitment of buried mulch residue under five management treatments. Mulch mass loss, tensile strength, and qualitative presence by bulk recovery were not affected by management treatments which included cover cropping and high rates of compost. Likewise, management had little impact on microbial community structure present on mulch surfaces. Instead, location and mulch type were strong drivers of degradation rate, while mulch type alone was the primary driver of mulch-associated microbial community. BLK mulch was nearly completely undetectable after 12 months of burial at LNK, but 67% of BLK mass remained at SBF. PLA mass loss was initially more rapid at SBF, but after 12 months this difference was not prominent with 33% and 37% remaining at SBF and LNK, respectively. Direct mass measurement is uncommon in field-based biodegradable mulch literature. We used a novel approach to direct mulch mass measurement: mesh bags and mass by combustion. While mesh bags are instrumental in detecting mass changes over time, we showed that they are a strong driver of microbial profiles present in soil and mulch sample fractions, so caution is warranted in interpreting mesh bag results as representative of field status of mulch.

Advisors: Rhae A. Drijber and Samuel E. Wortman