This material is based on work supported by the National Institute of Food and Agriculture, under award number 

2014-51181-22382. Any opinions, findings, conclusions or recommendations expressed in this presentation are 

those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. 

Douglas Hayes (PD), Annette Wszelaki, Jennifer DeBruyn, Markus Flury, Eric Belasco, Sean Schaeffer, Arnold Saxton, Susan Schexnayder, 

Margarita Velandia, Larry Wadsworth, Mark Fly, Carol Miles, Debra Inglis, Thomas Marsh, Jessica Goldberger, Suzette Galinato, Chris 

Benedict, Jeremy Cowan, Peter Tozer, Andy Bary, Lydia Tymon, Courtney Lyons, Jennifer Moore, Amy Salamone, Babette Gunderson, Ed 

Scheenstra, Jacky King, Marie English, Sreejata Bandopadhyay, Nurul Farhana Omar, Shuresh Ghimire, Henry Sintim, Kuan Chen

USDA	SCRI	Project	No.	2014-51181-22382

www.biodegradablemulch.org

Biodegradable Plastic Mulch
Sociology Economics

Material

Science

Overall Research Project

Horticulture

Plant Pathology

Soil 

Ecology
Sociology Economics

Material

Science

Overall Research Project

Horticulture

Plant Pathology

Soil 

Ecology
Mount Vernon, Washington 

Knoxville, Tennessee 

Field Experiment
Field Experiment
Field Experiment
Field Experiment

Paper

No mulch Polyethylene

BDM 2

BDM 1 BDM 3

BDM 4 BDM 5
Biodegradable Plastic

1. Does biodegradable plastic affect soil health?

2. Does biodegradable plastic degrade 

completely in soil?

3. Are residues released during degradation?

Questions:
Soil Health Assessment

Aggregate Stability

−50

0

50

100

Change in agg. stability (%)

b

a

a

a

a

a a a

a

a a a a

Knoxville,TN Mount Vernon, WA

No−mulch

Paper

BioAgri

Naturecycle

Organix

PLA/PHA

Polyethylene

b a

b

2015-2017
Soil Health Assessment

Microbial Communities

2015-2017

Tennessee Washington

Spring 2015

Spring 2015

Spring 2017

Spring 2017

Fall 2015 Fall 2015

Fall 2017

Fall 2017
Biodegradable Plastic Mulches

1. Similar agronomic benefits

2. No short-term effects of mulches on soil health

3. Seasonal changes more pronounced than mulch effects

4. Soil health is a slow changing process

 long-term study needed
Ramani Narayan (narayan@msu.edu)

MSU University Distinguished Professor

Biodegradable Mulch Film Basics

If you use any of the slides/materials, please reference authorship and affiliation (Ramani Narayan, 

Michigan State University) – thank you -- Copyright Ramani Narayan
Narayan

QUESTIONS

1. What is the effect on overall soil health, including soil biology, when this material 

biodegrades

2. What is the cumulative effect of the continued use of this biodegradable biobased 

mulch film, on soil nutrient balance, soil biological life, and soil tilth, when used in the 

same area of the field for 3-5-10 years?

3. What effect does the breakdown of these polymers have on soil and plant life as well 

as livestock that would graze either crop residues or forages grown the subsequent 

year after this mulch film was used?

4. Are there different cropping systems, climate, soil types or other factors that affect 

the decomposition rate (Examples would be long cold winters, or exceptionally dry 

conditions, such as found in a desert)?

5. Are there metabolites of these mulches that do not fully decompose, and if so, is 

there an effect upon soil health or biological life?

6. Can you provide information on the existence or development of biobased 

biodegradable mulch films that would meet the requirements of NOP policy 

memorandum 15-1?
What does “Biodegradable” Mean?

Can the microorganisms in the target disposal system (composting, soil, anaerobic 

digestor) assimilate/utilize the carbon substrate as food source completely and in a 

short defined time period?

Oligomers & polymer fragments

Hydrolytic

Polymer chains with 

susceptible linkages

Enzymatic

Oxidative

Environment – soil, compost, 

waste water plant, marine

STEP 1

Biodegradation(Step 2): Only if all fragmented 

residues consumed by microorganisms as a food 

& energy source as measured by evolved CO2 in 

defined time and disposal environment

CO2 + H2O + Cell biomass

Complete

microbial 

assimilaton

defined time 

frame, no residues STEP 2
Carbon footprint reduction strategy using bio content

Basics of microbial utilization -- biodegradability

4

 Microorganisms utilize carbon substrates as “food” to extract chemical energy for 

their life processes. 

 They do so by transporting the C-substrate inside their cells and:

 Under aerobic conditions, the carbon is biologically oxidized to CO2 releasing 

energy that is harnessed by the microorganisms for its life processes. Under 

anaerobic conditions, CO2+CH4 are produced. 

 Thus, a measure of the rate and amount of CO2 or CO2+CH4 evolved as a function of 

total carbon input to the process is a direct measure of the amount of carbon 

substrate being utilized by the microorganism (percent biodegradation)

Glucose/C-bioplastic + 6 O2 6 CO2 + 6 H2O; ∆G0’ = -686 kcal/mol

Glucose/C-bioplastic 2 lactate; ∆G0’ = -47 kcal/mol

CO2 + CH4
level of biodegradation needed to claim 

safe and efficacious removal of the plastic 

carbon from the environmental 

compartment

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200

Time (days)

% C conversion to CO2 (% biodegradation)

lag

phase

biodegradation phase

plateau phase

biodegradation degree 

O2

Soil & 

Test 

Materials

CO2

ASTM D5988; ISO 17556 -- Soil biodegradability test method

EN 17033 – soil biodegradability specifications for biodegradable mulch film
Unqualified use of the term “biodegradable” is wrong, misleading, and deceptive. 

It violates the law in the State of California and U.S. Federal Trade Commission (FTC) 

green guides & in Australia too

 Need to define disposal environment, time/rate and extent of biodegradation 

– qualified biodegradability claim

 Soil biodegradability (mulch films & ag products) 

 Compostable plastics -- enabler for food and organic waste diversion from 

landfills to composting

• Need complete microbial assimilation and removal from the environmental 

compartment in a short time period otherwise may have environmental and health 

consequences

• Degradable, partial biodegradable not acceptable – serious health and 

environmental consequences

• Phil. Trans. Royal. Soc. (Biology) July 27, 2009; 364

CAUTION!!!
Misleading (Green Washing) Claims -- Additive Technology

• “Plastic products with our additives at 1% levels will fully biodegrade in 9 

months to 5 years wherever they are disposed like composting, or landfills 

under both aerobic and anaerobic conditions”

The 50% Bio-Batch film did not degrade as completely or as quickly as the cellulose. 

At the end of the test, 19% of the film had degraded.

The results of the aerobic degradation tests indicate that, in time, plastics produced 

using Bio-Batch pellets will biodegrade in aerobic conditions.

DATA DOES NOT SUPPORT THE CONCLUSIONS!
Narayan

MISUSE OF BIODEGRADABILITY CLAIMS

• Chem. Commun., 2002, (23), 2884 - 2885 

– A hypothesis was developed, and successfully tested, to greatly increase the rates of 

biodegradation of polyolefins, by anchoring minute quantities of glucose, sucrose or lactose, 

onto functionalized polystyrene (polystyrene-co-maleic anhydride copolymer) and measuring 

their rates of biodegradation, which were found to be significantly improved 

• PRESS

• Sugar turns plastics biodegradable. Bacteria make a meal of sweetened polythene 

and polystyrene. 

weight loss of only 2-12%, 

Only sugar is being assimilated, PE 

chain intact – Is this a genuine 

example of biodegradable plastic?
Narayan

Aliphatic-aromatic copolyester

Copolyester

C C

O O

O CH2 O C

O

CH2 C

O

m n

x y z

Terephthalic acid Diol Aliphatic diacid

Tm ~ 110 -125 0C

Completely Biodegradable 

(microbial assimilation) under 

composting conditions

BASF

KingFa

Showa

Mitsubishi

Novamont

C-14 label on aromatic carbon – the 

most recalcitrant component
Narayan

Aliphatic-aromatic copolyester

Aromatic ring carbons, the most recalcitrant component is 

assimilated by the compost microorganisms as seen by evolution 

of the C-14 carbon dioxide 
Narayan Zumstein et al., Sci. Adv. 2018;

“Carbon from each monomer unit of PBAT was 

used by soil microorganisms, including 

filamentous fungi, to gain energy and to

form biomass”

Biomass refers to cellular biomass – PBAT 

carbons incorporated into lipid molecules
Narayan

BASICS -- TERMINOLOGY

Biobased plastics/products refers to the “beginning of life”

 Origins of the carbon in the polymer 

 Plant-biomass feedstock (biobased) vs petro-fossil feedstock

H2C CH2

n PE

C

O

C O CH2 CH2 O

O

n

PET

CH

CH3

C

O

O

PLA

n

N R' N

H

C

O

O

H

C

O

R O

n

* O

(CH2)x

O

O

(CH2)y

O

*

n

Biobased polyester

Biobased polyurethane

Cellulose
WHY BIOBASED??

What are the benefits of replacing petro/fossil 

carbon with biocarbon?

 Reduced carbon footprint

 Food security and creating value for rural agrarian economy 

 Create “wealth” in rural agriculture through value-added industrial 

products

CAUTION:

Need to still address the issue of end-of-life

mechanical, chemical, biological/organic recycling 
H2C CH2

n PE

CH

CH3

C

O

O

PLA

n

Understanding “BIOBASED & BIODEGRADABILITY” at Molecular level

BIO-PET

C

O

C O CH2 CH2 O

O n

Biobased polyeter

H

O

(CH2)x

O

O

(CH2)y

O

OH

n

H2C CH

CH3 n PP

CH3

O

O

O O

CH2 O

CH3

x y

PHBV -- poly(3-hydroxybutyrate-co-3-

hydroxyvalerate) PHAs

Biobased Plastics are NOT necessarily biodegradable/compostable

Biodegradable-Compostable Plastics are NOT necessarily Biobased
Thank You

15