PYROLYSIS OF AGRICULTURAL WASTE PLASTIC INTO ...

ABSTRACT

PYROLYSIS OF AGRICULTURAL WASTE PLASTIC INTO DIESEL AND EVALUATION OF THE CARBONACEOUS BYPRODUCT

AS A SOIL AMENDMENT

High density polyethylene[HDPE] from used drip irrigation tubing was

thermochemically broken down through pyrolysis at 500 °C for 20 minutes in the

presence of a clinoptilolite zeolite catalyst to produce pyrolysis oil and a carbonaceous

byproduct. The pyrolysis oil produced had a melting point of 50 °C, a boiling point of 80

°C, and a flash point of 89 °F. The melting point is higher than that of diesel fuel and the

boiling point and flash point are lower than that of diesel fuel. The high melting point

necessitates preheating before use as a fuel and prevents the pyrolysis oil from being a

direct substitute for diesel fuel. The carbonaceous byproduct, when used as a soil

amendment, increased soil water holding capacity and microbial respiration but had not

effect on cation exchange capacity. Two-percent by weight of carbonaceous byproduct

reduced soil hydraulic conductivity and increased nitrate leaching but lower treatment

levels did not affect soil hydraulic conductivity or nitrate leaching. Amended soil had a

slightly increased pH compared to the control. The properties of the pyrolysis oil can

potentially be improved by using a different catalyst or increasing the pyrolysis reaction

time from 20 minutes to several hours. The carbonaceous byproduct can be used as an

effective soil amendment that improves several important soil characteristics.

Alexis Jackson May 2019

PYROLYSIS OF AGRICULTURAL WASTE PLASTIC INTO DIESEL

AND EVALUATION OF THE CARBONACEOUS BYPRODUCT

AS A SOIL AMENDMENT

by

Alexis Jackson

A thesis

submitted in partial

fulfillment of the requirements for the degree of

Master of Science in Plant Science

in the Jordan College of Agricultural Sciences and Technology

California State University, Fresno

May 2019

APPROVED

For the Department of Plant Science:

We, the undersigned, certify that the thesis of the following student meets the required standards of scholarship, format, and style of the university and the student's graduate degree program for the awarding of the master's degree. Alexis Jackson

Thesis Author

Dave Goorahoo (Chair) Plant Science

John Bushoven Plant Science

William Wright Civil and Geomatics Engineering

For the University Graduate Committee:

Dean, Division of Graduate Studies

AUTHORIZATION FOR REPRODUCTION

OF MASTER’S THESIS

X I grant permission for the reproduction of this thesis in part or in its

entirety without further authorization from me, on the condition that

the person or agency requesting reproduction absorbs the cost and

provides proper acknowledgment of authorship.

Permission to reproduce this thesis in part or in its entirety must be

obtained from me.

Signature of thesis author:

ACKNOWLEDGMENTS

Funding for this thesis was provided in part by a Fresno State Graduate Net

Initiative Graduate Research Grant and a Fresno State Graduate Net Initiative Graduate

Research and Creative Studies Support Award.

I would like to thank my committee members Dr. Dave Goorahoo, Dr. John

Bushoven, and Dr. William Wright for providing their support and lending their expertise

during this journey.

TABLE OF CONTENTS

Page

LIST OF FIGURES ........................................................................................................... vi

STATEMENT OF THE PROBLEM .................................................................................. 1

INTRODUCTION .............................................................................................................. 3

SIGNIFICANCE OF THE PROJECT ................................................................................ 9

OBJECTIVES ................................................................................................................... 10

MATERIALS & METHODS ........................................................................................... 12

Pyrolysis of Agricultural Waste Plastic .................................................................... 12

Evaluation of the Carbonaceous Byproduct as a Soil Amendment .......................... 12

STATISTICAL ANALYSIS ............................................................................................ 15

RESULTS & DISCUSSION ............................................................................................ 16

CONCLUSIONS............................................................................................................... 25

REFERENCES ................................................................................................................. 27

LIST OF FIGURES

Page

Figure 1. Disc infiltrometer used to determine soil hydraulic conductivity. .................... 14

Figure 2a. Melting points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE. ..... 17

Figure 2b. Boiling points of #1 diesel fuel, #2 diesel fuel and pyrolysis oil. ................... 17

Figure 2c. Flash points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE. ......... 18

Figure 3. Mass water holding capacity of soils amended with carbonaceous byproduct ......................................................................................................... 19

Figure 4. pH of fluid vacuum extracted from saturated soil paste made with amended soil. ................................................................................................................... 20

Figure 5. ppm CO2 detected in 100 mL sample taken from respiration chamber. ........... 21

Figure 6. Hydraulic conductivity in cm/s of soils amended with carbonaceous byproduct. ........................................................................................................ 22

Figure 7. mg nitrate that leached through soils amended with carbonaceous byproduct ......................................................................................................... 23

Figure 8. mg NH4 N /L in leachate produced by the ammonium replacement method of determining cation exchange capacity. ........................................................ 24

STATEMENT OF THE PROBLEM

Enormous amounts of plastic are used annually in the United States due to the

affordability and versatility of plastic resins. A total of 34.5 million tons of plastic waste

was generated in the United States in 2015 (U.S. EPA, 2018). 75.4% of those 34.5

million tons were landfilled (U.S. EPA, 2018). Plastic is used extensively in agriculture

due to a wide range of benefits and low cost of plastic resins. The use of plastic in

agriculture experienced a 3-fold increase from 1994-2002, increasing from 521 million

pounds annually in 1994 to 1.678 billion pounds annually in 2002 (Hurley, 2008). Plastic

is typically used for drip irrigation tubing, plastic mulch, fertilizer and pesticide

containers, nursery seedling trays, silage covers, fruit bins, grain storage bags, and baling

twine. A survey of 215 California farms with gross incomes exceeding $100,000 annually

found a total of 2.57 million pounds of plastic was used on a yearly basis (Hurley, 2008).

The global market for agricultural plastic film alone was worth $5.87 billion in 2012 with

mulching and greenhouse use accounting for 85% of the market (Transparency Market

Research, 2013).

A large majority of this plastic is not recycled due to a myriad of obstacles

including high transportation costs, tonnage and cleanliness requirements imposed by

recycling centers, and lack of nearby recycling centers willing to accept agricultural

waste plastics (Hurley, 2008). The difficulty of transporting waste plastics is exacerbated

by the bulky nature of the plastics and the challenge of compressing plastics into a form

that is easier to transport (Goldy, 2005). Commercial balers experience difficulty when

baling waste plastics; plastic frequently becomes caught on any protrusions and belts

break under the weight of the plastic (Goldy, 2005). Additionally, the supply of

agricultural waste plastics is irregular with a majority of plastics disposed of during

narrow periods of time (Hurley, 2008). Farmers in areas where recycling facilities are

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available frequently must wait in long lines to drop off their plastics (Hurley, 2008).

Recycling of agricultural waste plastics in California ranged from 13% among melon

growers to 46% among nurseries (Hurley, 2008).

Agricultural plastic waste currently is economically unfeasible to recycle for a

majority of farmers. It was economically unfeasible to mix agricultural waste plastics

with recycled juniper to make fuel cubes (Jaeger, 2006). It was also economically

unfeasible to use baling twine as a fuel source, as a component of rubber composite

shingle, or as a reinforcing agent in concrete (Randall Conrad and Assoc. Ltd., 2000).

Disposal in landfills remains the most common way of handling agricultural plastic waste

(Hurley, 2008).

INTRODUCTION

Plastics are derived from petroleum which is the same material that gasoline and

diesel fuels are derived from. Plastics and fuels like diesel are both composed of

hydrocarbons. The primary difference between plastic and diesel is the length of those

hydrocarbons. Diesel hydrocarbons are 12-25 carbons in length (Auxilio et al., 2017)

whereas hydrocarbons found in plastics can be thousands of carbon atoms in length.

Pyrolysis is a thermolytic breakdown of organic matter in the presence of high

temperatures and an anaerobic environment. Pyrolysis can be used to break hydrocarbons

down into hydrocarbons with shorter molecule lengths. This process can convert the

hydrocarbons found in plastic into shorter chain hydrocarbons mimicking those found in

gasoline and diesel fuel (Wongkhorsub and Chindaprasert, 2013). There are several

methods of pyrolysis including thermal reactors (Auxilio et. al., 2017), microwave

induced pyrolysis (Khaghanikavkani et al., 2013), and plasma arc pyrolysis (Puncochar et

al. 2012). Pyrolysis of plastic produces fluid products (oil vapor and gas) and a solid

residue. The products of pyrolysis vary greatly depending on the type of plastic used as

feedstock, the type of catalyst used, and the temperatures the plastic was exposed to

during pyrolysis (Hamidi et al., 2013). Kumar et al. (2015) found that pyrolysis of linear

thermoplastic polymers produced straight chain hydrocarbons. Pyrolysis oil can contain

hydrocarbons ranging from C5-C80 (Almeida and Marques, 2016). Pyrolysis of low

density polyethylene [LDPE] and high density polyethylene [HDPE] in a batch reactor

with the catalyst HZSM-5 produced 70.7% and 72.6% gas respectively (Marcilla,

Beltran, and Navarro, 2009). Pyrolysis of HDPE in a fixed bed reactor for 2 hours and 40

minutes produced 38.5% pyrolysis oil at 330 °C and 76% pyrolysis oil at 425 °C (Khan et

al., 2016). This liquid fuel oil produced from pyrolysis of HDPE at 330 °C-490 °C was

within all ASTM D975 diesel fuel specifications (Khan et al., 2016). Pyrolysis of

polyethylene and polypropylene in an autoclave pyrolysis reactor at 300 °C – 500 °C for

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3 hours produced 60%-80% pyrolysis oil and 5%-10% carbonaceous residue

(Wongkhorsub and Chindaprasert, 2013). This pyrolysis oil contained a mixture of C10-

C30 hydrocarbons (Wongkhorsub and Chindaprasert, 2013). Pyrolysis can be carried out

at temperatures ranging from 300 °C – 900 °C with higher temperatures decreasing the

formation of hydrogen, methane, aromatic compounds, and acetylene (Donaj et al.,

2012). However, higher pyrolysis temperatures increase the proportion non-condensable

gas produced (Scheirs, 2006). Catalysts can exert substantial influence on the

composition of the final product of pyrolysis of waste plastic. A large array of catalysts

have been used including silica-alumina, zeolites, AlCl3, alumina and FCC catalysts,

nanocrystalline zeolites, mesostructured catalysts like MCM-41, and fused metal

tetracloroaluminatos (Almeida and Marques, 2016). Zeolitic and clay based catalysts with

higher acidity and surface area were selective for gasoline fraction hydrocarbons (Auxilio

et al., 2017). Catalysts with higher acidity and surface area produced lower levels of

olefins and higher levels of aromatics (Auxilio et al., 2017).

A carbonaceous residue is a byproduct of pyrolysis (Hamidi et al., 2013) and this

carbonaceous residue may have properties similar to biochar, a carbon-rich product

produced from pyrolysis of biomass that is often used as a soil amendment. Biochar is a

material produced through thermal degradation of organic matter in the absence of

oxygen. Biochar can be produced from any organic material including corn stover, rice

hulls, woodchips, and biosolids. Biochar is differentiated from charcoal by application to

soil. Charcoal is not typically used as a soil amendment and is instead used as a fuel.

Biochar improves many aspects of soil and has a variety of other benefits besides

improving soil. Biochar reduces nitrous oxide and ammonia emissions from soil,

improves plant productivity, improves soil structure, and improves nutrient retention

(Mandal et al., 2016).

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Terra preta is an anthropogenic deposit of dark soil created by indigenous farmers

in the Amazonian basin. Terra preta is much more fertile than the surrounding soils

which are typically infertile Arenosols, Ferralsols, Acrisols, and Lixisols (Glaser, 2006).

Terra preta is created through large additions of charcoal, broken pottery, plant material,

manure, and bones (Glaser, 2006). Organic carbon in terra preta is very stable. Terra

preta deposits were created in pre-Columbian times with some deposits reaching 7,000

years of age (Glaser, 2006). Terra preta contains seventy times more charcoal than

surrounding soils and three times more organic matter, nitrogen, and phosphorus than

untreated soils (Glaser, 2006). Terra preta soils on average yield twice as much as

untreated soils (Glaser, 2006). The high productivity of terra preta soils is due to the very

high content of biochar in the soil that averages 50 Mg ha−1 m−1 (Glaser, 2006).

Approximately 1,824 billion tons of organic carbon are stored in the first meter of

soil and about 3,012 billion tons within the first two meters (Sanderman et al., 2017).

Loss of organic carbon from the top 2 m of soil due to human activities is estimated at

about 133 billion tons with the rate of loss accelerating over the last two centuries

(Sanderman et al., 2017). Loss of organic carbon leads to problems like degraded soil

structure and yield loss. Adding biochar to soil sequesters carbon from the atmosphere in

a stable form that does not readily mineralize back into CO2. Carbon dioxide levels in the

atmosphere have been rising and the rate of increase in those carbon dioxide levels has

also been rising. Global carbon dioxide emissions for 2018 increased 2.7% over global

carbon dioxide emissions for 2017 and reached a record high (Le Quere et al., 2018). The

concentration of carbon dioxide in the atmosphere has increased from 277 parts per

million in 1750 to 405 parts per million in 2017 (Le Quere et al., 2018). This rapid

increase in the carbon dioxide content of the atmosphere is believed to be causing

harmful climate change that could potentially cause enormous economic losses and

trigger mass human migration as regional rainfall patterns shift and sea levels rise.

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Biochar could be used to sequester carbon while reversing a centuries-long trend of

carbon loss from soil due to human activities.

Soils amended with biochar have an increase in surface area due to high levels of

micropores in biochar (Lone et al., 2015). Amendment with biochar also improves cation

exchange capacity, water holding capacity, and hydraulic conductivity while

simultaneously reducing soil tensile strength (Lone et al., 2015). This reduction in soil

tensile strength allows better root penetration though soil. Biochar produced from poultry

manure increased the availability of Mn, P, Cu, and Zn when added to soil (Inal et al.,

2015). Beans grown in soil amended with biochar and processed poultry manure had

higher concentrations of Ca, Fe, Zn, N, P, K, Cu and Mn (Inal et al., 2015). Soil amended

with the same processed poultry manure and biochar increased the Zn, Cu, Mn, N, P, and

K levels of corn (Inal et al., 2015). Shoot dry weight and plant uptake of K and N

increased after biochar application in komatsuna, a Japanese leaf vegetable in the

Brassicaceae family (Zang Oo et al., 2018). Biochar drastically increases the availability

of certain nutrients critical to plant growth and this results in better uptake by plants and

higher yields.

Amendment with biochar reduces nitrous oxide (N2O) emissions from soil (Zang

Oo et al., 2018). Biochar reduces N2O emissions by decreasing the relative abundance of

nitrate-oxidizing and ammonia-oxidizing bacteria in soil (Liu et al., 2014). Biochar also

has an alkalizing effect on soil which increases the production of N2 and reduces the

production of NO and N2O (Obia et al., 2015). Nitrogen oxides (NOx) are major air

pollutants that react to form particulate matter and smog. High levels of NOx lead to acid

rain which is deleterious to both plant and fish life and damages stone buildings.

Retaining nitrogen in soil by reducing N2O emissions reduces the need for nitrogen

fertilizers. Nitrous oxide is also a potent greenhouse gas and reducing N2O emissions

will be beneficial for mitigating climate change.

7 7

Biochar provides substrate for microbial activity and this heavily alters the soil

biota in amended soils. Soils amended with biochar have higher levels of microbial

biomass and faster rates of microbial growth (Glaser, 2006). Biochar produced from

woody materials retains an internal layer of bio-oil that functions like glucose for

increasing microbe growth (Lone et al., 2015). Some arbuscular mycorrhizal and

ectomycorrhizal fungi increase in the presence of biochar (Lehmann et al., 2006). This

increase in beneficial arbuscular mycorrhizal fungi may be a driving factor behind the

increased availability of Zn, P, Mn, and Cu in biochar amended soils. The effects on

microbial activity are still seen in terra preta soils where the biochar was added hundreds

or even thousands of years ago (Glaser, 2006). Biochar may reduce pathogen presence in

the soil by increasing beneficial microbe populations. Biochar additions to soil decreased

the relative abundance of gram-negative bacteria and fungi decreased (Lehmann et al.,

2006). Additionally, gram-positive anaerobic bacteria increased in abundance (Lehmann

et al., 2006).

Biochar can form complexes with heavy metals through adsorption (Tan, Liu, and

Xiao, 2018). This reduces the availability of the heavy metals and mitigates the

deleterious effects of heavy metal contamination of soils. Organic pollutants are also

reduced in biochar amended soils (Lone et al., 2015). This can be detrimental by reducing

the efficacy of pesticides. The sorption ability of biochar can exceed the sorption ability

of natural soil organic matter by a factor of 10-100 (Lone et al., 2015). The sorption

ability of biochar is highly dependent on feedstock and temperature at which the biochar

was produced. High temperatures tend to produce more surface area but lower levels of

amorphous organic matter (Tan, Liu, and Xiao, 2018).

Unfortunately, the mechanisms by which biochar improves soil are poorly

understood. Biochar addition to soil had generally been found to be beneficial but the

results of studies can be inconsistent (e.g. biochar produced from woody materials has a

8 8

much more pronounced effect than biochar produced from grass) (Lone et al., 2015). The

extremely wide definition of biochar also adds to the inconsistent results. Biochar

produced from widely different feedstocks ranging from human feces to woody biomass

produced under widely different conditions ranging from low temperature smoldering to

fast pyrolysis at over 1000 F is all lumped under the same umbrella term of biochar. The

complex interactions between soil microbes, crops, and their environment are also poorly

understood. General trends in soil microbial populations can be ascertained but the exact

interactions occurring in the soil are elusive. The beneficial properties of biochar have

been strongly supported by a large body of evidence. Both biochar and the carbonaceous

byproduct of pyrolysis of waste plastic are rich in carbon and are produced through

pyrolysis. The carbonaceous byproduct of pyrolysis of waste plastic may have properties

similar to biochar.

SIGNIFICANCE OF THE PROJECT

Farmers have indicated in surveys that offering on-farm pickup of waste plastics,

easing cleanliness and tonnage requirements, and offering more recycling facilities would

encourage them to recycle their waste plastics (Hurley, 2008). Farmers travel an average

of 10.6 miles to dispose of waste plastics but would be willing to drive 150% farther if

recycling their plastic was offered for free (Hurley, 2008). Strawberry growers spent $16-

$18 per acre on landfill disposal fees but California farmers would be willing to pay an

average of $91 per ton for on-farm pick up for recycling (Hurley, 2008). This evidence

indicates there is substantial interest in recycling of agricultural waste plastics and that

farmers are willing to spend more than they currently do to dispose of plastic waste.

Pyrolysis of waste plastic can be carried out on mixes of different plastic resins and can

be carried out on a small scale. Plastics do not need to be cleaned or sorted prior to

pyrolysis. Due to this, pyrolysis does not necessitate the cleanliness and tonnage

requirements that traditional recycling imposes. Pyrolysis facilities can be much smaller

than traditional recycling facilities due to the small amount of material required for

pyrolysis and small pyrolysis units can be transported. The mobility of small pyrolysis

units allows a single unit to process plastic from multiple plastic drop-off sites and even

allows on-farm pyrolysis of waste plastics. Multiple plastic drop-off points and on-farm

pyrolysis mitigate the challenge of transporting waste plastics for recycling. Pyrolysis has

been successfully used to produce liquid oils that can safely be used in diesel engines

(Wongkhorsub and Chindaprasert, 2013). Pyrolysis has the potential to convert over a

billion pounds annually (Hurley, 2008) of non-recyclable agricultural plastic waste into

fuel while also generating a beneficial soil amendment, similar to biochar, as a byproduct.

OBJECTIVES

The objectives of this research project are:

1. Determine the physical or chemical properties of liquids derived from pyrolysis of

agricultural waste plastic that are relevant for use as a potential fuel.

Null Hypothesis: There are no differences between the physical or chemical

properties of the liquids derived from pyrolysis of agricultural waste plastic and

the ASTM standards for diesel fuel.

2. Determine the effects, as a soil amendment, of the carbonaceous byproduct

remaining after pyrolysis of agricultural waste plastic. The effects on soil water

holding capacity, soil pH, cation exchange capacity[CEC], hydraulic conductivity,

and microbial respiration are determined.

Null hypotheses: Carbonaceous byproduct derived from pyrolysis of agricultural

waste plastic has no effect on soil pH.

Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has

no effect on soil cation exchange capacity.

Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has

no effect on soil water holding capacity.

Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has

no effect on soil microbial respiration.

Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has

no effect on soil hydraulic conductivity.

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3. Determine the effects of the carbonaceous byproduct on nitrate leaching if enough

of the carbonaceous byproduct is produced.

Null hypothesis: Carbonaceous byproduct derived from pyrolysis of agricultural

waste plastic has no effect on nitrate leaching.

MATERIALS & METHODS

Pyrolysis of Agricultural Waste Plastic

A custom device capable of maintaining the high temperatures and anaerobic

environment necessary for pyrolysis was designed and fabricated. Used drip irrigation

tubing was obtained from commercial agricultural operations. 350 g of used drip

irrigation tubing was placed into the pyrolysis device and 1 g of clinoptilolite zeolite

catalyst added. The pyrolysis device was then sealed. The pyrolysis device was heated to

940 °F (500 °C) and the waste plastic allowed to break down for 20 minutes. The

pyrolysis device was then allowed to cool to temperatures safe for handling. A sample of

the liquid products of the pyrolysis was taken. Any carbonaceous residue remaining in

the pyrolysis device was collected for evaluation as a soil amendment. The pyrolysis

device was cleaned of any solid or liquid residues and another 350 g of plastic and 1 g of

zeolite catalyst placed into the pyrolysis device. The cycle of adding plastic, heating,

sampling, and cleaning was repeated 10 times. All liquid samples were sent to a fuel

analysis laboratory for analysis of melting point, boiling point, and flash point.

Evaluation of the Carbonaceous Byproduct as a Soil Amendment

Sandy loam soil was collected from the CSUF campus. The carbonaceous

byproduct was mixed with the sandy loam soil at rates equivalent to 0.1%, 0.5%, and 2%

by weight of the carbonaceous byproduct.

1. The water holding capacity of the amended soil was measured by adding

water to a known mass of amended soil to form a saturated paste and allowing the soil to

equilibrate for 24 hours. The saturated soil was weighed and then dried at 105 °C for one

week. The dry soil was weighed and the amount of water lost recorded.

2. The pH of the amended soil was measured by moistening amended soil to

field capacity and allowing to soil to sit in an open container for 20 days. This allowed

13 13

long-term effects on pH to potentially be detected. After 20 days a saturated paste was

made from the soil and fluid from 150 g of saturated soil was vacuum extracted. The pH

of the extracted fluid was measured using a pH probe.

3. Soil microbial respiration was determined by moistening the amended soil

to field capacity and waiting 24 hours. After 24 hours, a 50 g portion of soil was

transferred to a 6 in diameter 5 in tall cylindrical chamber. The cylindrical chamber was

sealed with a lid with rubber stoppers and CO2 allowed to accumulate for 30 minutes at a

temperature of 26 Co. The CO2 produced by soil microbial activity was then measured

using a Draeger tube apparatus as described by Soil Quality Institute (2001).

4. A disc infiltrometer was used to determine hydraulic conductivity of the

amended soil. A 250 mL beaker was filled with amended soil and a disc infiltrometer

placed flat on the surface of the soil (Figure 1). The disc infiltrometer was set to a suction

of 2 cm and water flows from the disc infiltrometer into the soil. Water level readings are

taken every 30 seconds for 300 seconds. The hydraulic conductivity of the soil was

calculated using the method in Zhang (1997).

5. The effects of the carbonaceous byproduct on nitrate leaching was

determined by lining a funnel with filter paper and placing 40 g of amended soil into the

funnel. 40 mL of a 20 ppm nitrate solution was applied to the soil. The fluid was allowed

to percolate through the soil until no more liquids dripped from the funnel. All fluid that

percolated through the soil was collected. The solutions that percolated through the soil

were filtered through filter paper and the nitrate content of the solutions determined using

an AQ2 Discrete Analyzer. The filter paper used to filter the solution was weighed to

determine the mass of solution retained by the filter paper. The total amount of nitrate in

the solutions retained by the filter paper and the solutions that percolated through the soil

was determined.

14 14

6. Cation exchange capacity was determined using the ammonium

replacement method in Gavlak, Horneck, and Miller (2005).

Figure 1. Disc infiltrometer used to determine soil hydraulic conductivity.

STATISTICAL ANALYSIS

Pairwise T tests were used to determine any statistically significant differences

between untreated soil and soil amended with carbonaceous byproduct.

RESULTS & DISCUSSION

Pyrolysis of HDPE drip irrigation tubing produced 8% carbonaceous byproduct

and 63% pyrolysis oil. The pyrolysis oil was a solid, waxy substance at room

temperature. This is consistent with pyrolysis oil produced from polyethylene and

polypropylene that was separated from municipal waste (Wongkhorsub and

Chindaprasert, 2013). The pyrolysis oil had a melting point of 50 °C, a boiling point of

80 °C, and a flash point of 89 °F. HDPE used as feedstock to produce the pyrolysis oil

has a melting point of 125 C and a flash point of 645 F (National Pipe & Plastics Inc.,

2011). #1 Diesel fuel has a melting point of -20 °C, a boiling point of 150 °C and a flash

point of 125 °F (Citgo Petroleum Corporation, 2018a). #2 diesel fuel has a melting point

of -30 °C, a boiling point of 282 °C, and a flash point of 125 °F (Citgo Petroleum

Corporation, 2018b). The flash point and boiling point of the pyrolysis oil is lower than

in #1 or #2 diesel fuel (Figures 2c and 2b) but the melting point is higher than in #1 or #2

diesel fuel (Figure 2a). The high melting point renders the pyrolysis oil solid at room

temperature whereas diesel fuel is liquid at room temperature. The flash point of the

pyrolysis oil also falls below the legal minimum of 100 °C for #1 diesel fuel. The solid

nature of the pyrolysis oil at room temperature necessitates preheating before use in an

engine and prevents direct use of the pyrolysis oil as a substitute for diesel fuel.

Khan et al., 2016 successfully produced pyrolysis oil that met ASTM standards

for diesel fuel. Khan et al., 2016 used a fixed bed pyrolysis reactor and a reaction time of

160 minutes. The longer reaction time produced shorter chain hydrocarbons that were

liquid at room temperature. A reaction time of 20 minutes produced hydrocarbons that

were solid at room temperature. Some catalysts are selective for a specific fraction of

hydrocarbons (Auxilio et al., 2017). A catalyst that is highly selective for diesel-fraction

hydrocarbons can be used to produce pyrolysis oil that meets ASTM diesel fuel

standards.

17 17

Figure 2a. Melting points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE.

Figure 2b. Boiling points of #1 diesel fuel, #2 diesel fuel and pyrolysis oil.

0

50

100

150

200

250

300

Diesel #1 Diesel #2 Pyrolysis Oil

De

gre

es

C

Boiling Point

Boiling Point (Celsius)

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Figure 2c. Flash points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE.

Biochar is a close analogue of the carbonaceous byproduct. Biochar is produced

through pyrolysis of biomass. The carbonaceous byproduct is produced through pyrolysis

of plastic waste. Biochar, when used as a soil amendment, increases soil water holding

capacity (Lone et al., 2015). Biochar has a very high surface area and the high level of

microporosity gives biochar its beneficial properties like increasing soil water holding

capacity (Lone et al., 2015).

Soils amended with as little as 0.1% of carbonaceous byproduct by weight

experienced a statistically significant increase in mass water holding capacity (P<0.01).

Amendment with 0.1% carbonaceous byproduct increased water holding capacity by 5%

and amendment with 0.5% carbonaceous byproduct increased water holding capacity by

18% compared to the control (Figure 3). The 0.5% and 2% treatment levels had greater

water holding capacity than the 0.1% treatment level (P<0.05). Yu et al., 2017, found that

soil water holding capacity is proportional to the amount of biochar added to soil. The

carbonaceous byproduct behaved very similar to biochar and increased water holding

capacity. Larger increases in water holding capacity were observed after larger

0

100

200

300

400

500

600

700

Diesel #1 Diesel #2 Pyrolysis Oil HDPE

De

gre

es

F

Flash Point

Flash Point (F)

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incorporations of carbonaceous byproduct; the 0.5% and 2% treatment levels had a

significantly higher water holding capacity than the 0.1% treatment level.

Figure 3. Mass water holding capacity of soils amended with carbonaceous byproduct

Soil amended with carbonaceous byproduct can retain more water and this can

improve productivity in dryland farming systems by retaining more moisture from

rainfall (Jeffrey et al., 2011). Biochar application to soils resulted in a mean yield

increase of 10% (Jeffrey et al., 2011). The similar properties of biochar and the

carbonaceous byproduct indicate that the carbonaceous byproduct may have a similar

positive effect on yields when used as a soil amendment.

The 0.5% and 2% treatment levels had a statistically significant increase in pH

compared to the control and 0.1% treatments (Figure 4). Biochar has an alkalizing effect

on soils (Obia et al., 2015) and the carbonaceous byproduct had a similar effect. This

alkalizing effect reduces the amount of N2O and NO produced by soil (Obia et al., 2015).

Soil pH affects the availability of nutrients in the soil and excessively acidic (pH<5) soils

negatively impact yield (Brown et al., 2008). The alkalizing effect of the carbonaceous

A

B

CC

12.5

13

13.5

14

14.5

15

15.5

16

16.5

17

17.5

Control 0.1% 0.5% 2.0%

% M

ass

Wat

er

Co

nte

nt

Mass Water Content %

Mass Water Content

20 20

byproduct increases the pH of soils and could potentially increase crop yields when used

as an amendment in acidic soils.

Figure 4. pH of fluid vacuum extracted from saturated soil paste made with amended soil.

Soils amended with biochar have higher levels of microbial biomass and faster

rates of microbial growth (Glaser, 2006). Biochar has a high surface area and provides a

substrate for microbial activity. Soil amended with 2% by weight of carbonaceous

byproduct had significantly higher microbial respiration than untreated soil (P<0.001).

Soil amended with 2% carbonaceous byproduct produced 64% more CO2 than the control

treatment (Figure 5). Soils amended with 0.1% or 0.5% carbonaceous byproduct did not

have any statistically significant change in microbial respiration compared to the control.

Microbial respiration is an indirect indicator of soil health and beneficial arbuscular

mycorrhizal and ectomycorrhizal fungi increase in the presence of biochar (Lehmann et

al., 2006). Arbuscular mycorrhizal and ectomycorrhizal fungi increase the availability of

essential plant nutrients including phosphorus (Mcgonigle and Murray, 1996). The

carbonaceous byproduct had a beneficial effect on soil microbial respiration. The

AA

BB

6.5

6.6

6.7

6.8

6.9

7

7.1

7.2

7.3

7.4

7.5

Control 0.10% 0.50% 2%

pH

pH

21 21

carbonaceous byproduct may have a beneficial effect on the relative abundance of

beneficial soil microbes due to the similarity between the carbonaceous byproduct and

biochar.

Figure 5. ppm CO2 detected in 100 mL sample taken from respiration chamber.

The carbonaceous byproduct was hydrophobic in nature. The carbonaceous

byproduct readily adhered to skin but could not be washed off, without soap. Amendment

with 2% by weight of carbonaceous byproduct reduced soil hydraulic conductivity by

40% (P<0.05). Lower treatment levels, 0.1% and 0.5%, did not adversely impact soil

hydraulic conductivity (Figure 6). The adverse effect on soil hydraulic conductivity may

be related to the hydrophobic properties of the carbonaceous byproduct. Freshly made

biochar is hydrophobic but oxidation by air and water make the surface of biochar

hydrophilic over time (Basso et al., 2012). The carbonaceous byproduct used in this study

was stored in airtight plastic bags and was exposed to minimal water and air. These

storage conditions minimized oxidation of the carbonaceous byproduct. Oxidation may

make the carbonaceous byproduct hydrophilic. A hydrophilic carbonaceous byproduct

A A A

B

0

100

200

300

400

500

600

700

800

900

Control 0.10% 0.50% 2%

PP

M C

O2

Microbial Respiration

ppm CO2

22 22

may increase soil hydraulic conductivity. Soils with low hydraulic conductivity, like

soils with a high sodium absorption ratio (Oster et al., 1999), suffer from poor water

infiltration. Improving soil hydraulic conductivity improves water infiltration.

Figure 6. Hydraulic conductivity in cm/s of soils amended with carbonaceous byproduct.

Amendment with carbonaceous byproduct did not affect the amount of nitrate

leaching from the soil at the 0.1% and 0.5% treatment levels (Figure 7). Amendment with

2% carbonaceous byproduct increased nitrate leaching by 5.6% compared to the control

(p<0.01). Nitrate leaching results in nitrate contamination of groundwater and excessive

intake of nitrate can adversely affect human health (Harter et al., 2012). The

carbonaceous byproduct was expected to reduce nitrate leaching. Biochar can reduce

nitrate leaching (Yao et al., 2012) and increases nitrogen use efficiency of crops (Chan et

al., 2007) when used as a soil amendment. However the properties of biochar vary

depending on the feedstock and temperature at which the biochar was manufactured.

Biochar made from Brazilian pepperwood reduced the amount of phosphate leaching

from a sandy soil but biochar made from peanut hulls increased phosphate leaching from

A

AA

B

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

Control 0.10% 0.50% 2%

cm/s

Soil Hydraulic Conductivity

Soil HydraulicConductivity

23 23

sandy soil (Yao et al., 2012). Biochar made from switchblade grass can hold 450% of its

weight in water and biochar made from hemlock can hold 270% of its weight in water

(Yu et al., 2017). Biochar produced at temperatures ranging from 250 ºC – 750 ºC

increased soil water holding capacity from 7%-16% (Novak et al., 2009).A higher water

holding capacity reduces nitrate leaching by retaining water and nitrate dissolved in the

water.

Figure 7. mg nitrate that leached through soils amended with carbonaceous byproduct

Elemental analysis of the carbonaceous byproduct was not within the scope of this

research. The carbonaceous byproduct may have contained nitrogenous compounds that

falsely inflated nitrate readings. The exact interactions between the carbonaceous

byproduct and the soil matrix were beyond the scope of this research. This makes it

difficult to determine the exact mechanisms responsible for the increase in nitrate

leaching.

The carbonaceous byproduct did not significantly alter soil cation exchange

capacity (Figure 8). Cation exchange capacity is a measure of how well a soil can hold

A

A

A

B

1.02

1.04

1.06

1.08

1.1

1.12

1.14

1.16

1.18

1.2

Control 0.10% 0.50% 2%

mg

Nit

rate

Le

ach

ed

Nitrate Leaching

Nitrate Leaching

24 24

cationic nutrients like potassium or magnesium. The carbonaceous byproduct used in this

project experienced minimal oxidation. Oxidation of biochar produces carboxylic

functional groups that increase the cation exchange capacity of the biochar (Cheng et al.,

2006). Incubation at 30 °C and 70 °C increased the cation exchange capacity of biochar

by 53% and 538% respectively (Cheng et al., 2006). Oxidizing the carbonaceous

byproduct may result in a significant increase in cation exchange capacity.

Figure 8. mg NH4 N /L in leachate produced by the ammonium replacement method of

determining cation exchange capacity.

A

AA A

0

5

10

15

20

25

Control 0.10% 0.50% 2%

mg

NH

4 N

/L in

Le

ach

ate

Cation Exchange Capacity

Cation Exchange Capacity

CONCLUSIONS

Enormous amounts of waste plastic are produced by California agriculture and

this plastic is largely disposed of in landfills. This project demonstrated that used

irrigation tubing can be converted into diesel-like fuel through pyrolysis. The pyrolysis

oil that was produced during this project had a high melting point and was unsuitable for

use as a direct diesel fuel substitute. Pyrolysis oils that fall within ASTM specifications

for diesel fuel have been successfully produced (Khan et al., 2016). The properties of the

pyrolysis oil could potentially be improved by longer pyrolysis times (Khan et al., 2016;

Wongkhorsub and Chindaprasert, 2013) or a different catalyst (Auxilio et al., 2017).

The carbonaceous byproduct improved the water holding capacity and increased

the microbial respiration rates of amended soils. Very high levels of carbonaceous

byproduct exceeding 0.5% of soil weight should be avoided due to potential increases in

nitrate leaching and adverse effects on soil hydraulic conductivity. Soil amended with 2%

carbonaceous byproduct had 40% lower hydraulic conductivity and 5.6% increased

nitrate leaching compared to the control. The adverse effect of carbonaceous residue on

soil hydraulic conductivity may be due to the hydrophobic properties of the carbonaceous

byproduct. Biochar becomes hydrophilic after oxidation by air and water (Basso et al.,

2012). Biochar also increases cation exchange capacity after being oxidized (Cheng et al.,

2006). Oxidation of the carbonaceous byproduct may reduce or eliminate the negative

effects of the carbonaceous byproduct on soil hydraulic conductivity. The carbonaceous

byproduct of pyrolysis of waste plastic can be effectively used as an soil amendment that

improves several aspects of soil quality including water holding capacity. The exact

interactions between the carbonaceous byproduct and the soil matrix were beyond the

scope of this research. This makes it difficult to determine the exact mechanisms

responsible for the effects observed during this research. Future work may include an

26 26

investigation of equilibrium adsorption capacity and adsorption kinetics of the

carbonaceous byproduct.

REFERENCES

Almeida, Débora, & Marques, Maria de Fátima. (2016). Thermal and catalytic pyrolysis

of plastic waste. Polímeros, 26(1), 44-51. https://dx.doi.org/10.1590/0104-

1428.2100

Auxilio, A. R., Choo, W-L., Kohli, I., Chakravartula Srivatsa, S., & Bhattacharya, S.

(2017). An experimental study on thermo-catalytic pyrolysis of plastic waste using

a continuous pyrolyser. Waste Management, 67, 143-154.

https://research.monash.edu/en/publications/an-experimental-study-on-thermo-

catalytic-pyrolysis-of-plastic-wa

Basso, A., et al. (2012). Assessing Potential of Biochar for Increasing Water-Holding

Capacity of Sandy Soils. GCB Bioenergy, 5(2), 132–143., doi:10.1111/gcbb.12026.

Brown, T., et al. (2008). Lime Effects on Soil Acidity, Crop Yield, and Aluminum

Chemistry in Direct-Seeded Cropping Systems. Soil Science Society of America

Journal, 72(3), 634. doi:10.2136/sssaj2007.0061.

Chan, K. Y., et al. (2007). Agronomic Values of Greenwaste Biochar as a Soil

Amendment. Soil Research, 45(8). 629., doi:10.1071/sr07109.

Cheng, C, et al. (2006). Oxidation of Black Carbon by Biotic and Abiotic Processes.

Organic Geochemistry, 37(11), 1477–1488, doi:10.1016/

j.orggeochem.2006.06.022.

Citgo Petroleum Corporation. (2018a) Safety Data Sheet CITGO No. 1 Diesel Fuel, All

Grades. Citgo, www.docs.citgo.com/msds_pi/AG1DF.pdf.

Citgo Petroleum Corporation. (2018b). Safety Data Sheet CITGO No. 2 Diesel Fuel, All

Grades, Low Sulfur. Citgo, www.docs.citgo.com/msds_pi/AG2DF.pdf.

Donaj, P. J., Kaminsky, W., Buzeto, F., & Yang, W.(2012). Pyrolysis of polyolefins for

increasing the yield of monomers’ recovery.Waste Management (New York, N.Y.),

32(5), 840-846. http://dx.doi.org/10.1016/j.wasman.2011.10.009. PMid:22093704.

Gavlak, R. G., Horneck, D. A., and R. O. Miller. (2005). Soil, Plant, and Water

Reference Methods for the Western Region. WREP-125.

Glaser, B. (2006). Prehistorically modified soils of central Amazonia: a model for

sustainable agriculture in the twenty-first century. Philos Trans R Soc Lond B Biol

Sci. 362(1478).

Goldy, Ron. (2005). Baling Used Agricultural Plastic. College of Agriculture & Natural

Resources, Michigan State University, https://www.canr.msu.edu/uploads/files/

Research_Center/SWMREC/special_reports/bale_plastic_2005.pdf

28 28

Harter, T., et al. (2012). Addressing Nitrate in California's Drinking Water with a Focus

on Tulare Lake Basin and Salinas Valley Groundwater. Report for the State Water

Resources Control Board Report to the Legislature. Center for Watershed Sciences,

University of California, Davis. http://groundwaternitrate.ucdavis.edu.

Hurley, Sean. (2008). Postconsumer Agricultural Plastic Report. California Integrated

Waste Management Board

Inal, A., Gunes, A., Sahin, O., Taskin, M., and Kaya, E. (2015). Impacts of biochar and

processed poultry manure, applied to a calcareous soil, on the growth of bean and

maize. Soil Use and Management. 31 (1),106-113.

Jaeger, W. E (2006). Economic Analysis of the Cost of producing Juniper-Plastic Fuel

Cubes in the Upper Klammath Basin. A report prepared for ORE-CAL RC&D, PO

Box 785, Dorris, CA.

Jeffery, S., et al. (2011). A Quantitative Review of the Effects of Biochar Application to

Soils on Crop Productivity Using Meta-Analysis. Agriculture, Ecosystems &

Environment, 144(1), 175–187., doi:10.1016/j.agee.2011.08.015.

Hamidi, Nasrollah, et al. (2013). Pyrolysis of Household Plastic Wastes.” British Journal

of Applied Science and Technology, 3(3), 417–439.

Khaghanikavkani E, Farid MM, Holdem J, Williamson A. (2013). Microwave Pyrolysis

of Plastic. J Chem Eng Process Techno.4(150). doi:10.4172/2157-7048.1000150

Khan, M., Sultana, M., Al-Mamun, M., and Hasan, M. (2016). Pyrolytic Waste Plastic

Oil and Its Diesel Blend: Fuel Characterization. J Environ Public Health.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4940549/

Kumar, P. Senthil, et al. (2015). Conversion of Waste Plastics into Low-Emissive

Hydrocarbon Fuels through Catalytic Depolymerization in a New Laboratory Scale

Batch Reactor. International Journal of Energy and Environmental Engineering,

8(2), 167–173. doi:10.1007/s40095-015-0167-z.

Lehmann, J, Gaunt J, Rondon M. (2006). Bio-char sequestration in terrestrial

ecosystems—a review. Mitig. Adapt. Strat. Global Change. 11, 395-419.

Le Quere, C., Andrew, R., Friedlingstein, P., Sitch, S., et al. (2018). Global Carbon

Budget 2018. Earth Syst. Sci. Data, 10, 2141-2194.

Liu, L., et al. (2014).Effect of Biochar on Nitrous Oxide Emission and Its Potential

Mechanisms. J Air Waste Manag Assoc. 64(8),894-902.

www.ncbi.nlm.nih.gov/pubmed/25185392.

Lone, A., Najar, G., Ganie, M., Sofi, J., and Ali, T. (2015). Biochar for Sustainable Soil

Health: A Review of Prospects and Concerns. Pedosphere 25 (5): 639-653.

29 29

Mandal, S., et al. (2016). Application of Biochar Produced From Biowaste Materials for

Environmental Protection and Sustainable Agriculture Production. Environmental

Materials and Waste, 73–89. doi:10.1016/b978-0-12-803837-6.00004-4.

Marcilla, A., Beltrán, M. I., & Navarro, R. (2009). Thermal and catalytic pyrolysis of

polyethylene over HZSM5 and HUSY zeolites in a batch reactor under dynamic

conditions. Applied Catalysis B: Environmental, 86(1-2), 78-86.

http://dx.doi.org/10.1016/j.apcatb.2008.07.026.

Mcgonigle, T., and Murray H. (1996). Mycorrhizae, Phosphorus Absorption, and Yield

of Maize in Response to Tillage. Soil Science Society of America Journal, 60(6),

1856, doi:10.2136/sssaj1996.03615995006000060034x.

National Pipe & Plastics Inc. (2011). Material Safety Data Sheet -HDPE. National Pipe

& Plastics Inc. www.nationalpipe.com/pdf_files/msds-hdpe.pdf.

Novak M., et al. (2009). Characterization of designer biochar produced at different

temperatures and their effects on a loamy sand. Annals of Environmental Science.

3(1). 195–206.

Obia, A., et al. (2015). Effect of Soil PH Increase by Biochar on NO, N2O and N2

Production during Denitrification in Acid Soils. Plos One, 10(9).

doi:10.1371/journal.pone.0138781.

Oster, J.D., I. Shainberg, and I.P. Abrol. (1999). Reclamation of salt-affected

soil.Agricultual Drainage, Agronomy monograph no. 38. 315–346.

Puncochar, M, et al. (2012). Development of Process for Disposal of Plastic Waste Using

Plasma Pyrolysis Technology and Option for Energy Recovery. Procedia

Engineering, 42, 420-430. doi:10.18411/a-2017-023.

Randall Conrad and Assoc. LTD. (2006). The Market Feasibility of

Recycling/Recovering Post Consumer Polypropylene Baler Twine in Alberta. A

research report submitted to the Poly-Twine Market Feasibility Steering Committee,

Canadian Plastics Industry Association. http://www.cpia.ca/files/files/

files_baler_twine_study.pdf,

Sanderman, J., Hengl, T., and Fiske, G. (2017) Soil carbon debt of 12,000 years of human

land use. PNAS. 114 (36) 9575-9580.

Scheirs, J. (2006). Overview of commercial pyrolysis processes for waste plastics. In J.

Scheirs, & W. Kaminsky (Orgs.), Feedstock recycling and pyrolysis of waste

plastics (pp. 383-434). Hoboken: John Wiley & Sons.

Soil Quality Institute. (2001). Soil Quality Test Kit Guide. Natural Resources

Conservation Service, USDA.

www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_050956.pdf.

30 30

Tan, G., Liu, Y., and Xiao, D. (2018). Influence of different pyrolysis methods on the

sorption property of rice straw biochar, Separation Science and Technology,

https://www.tandfonline.com/doi/abs/10.1080/01496395.2018.1553981?journalCod

e=lsst20

Transparency Market Research. (2013). Agricultural Films (LDPE, LLDPE, HDPE,

EVA/EBA, Reclaims and Others) Market for Greenhouse, Mulching and Silage

Applications - Global Industry Analysis, Size, Share, Growth, Trends and Forecast,

2013 - 2019. Transparency Market Research.

www.transparencymarketresearch.com/report-toc/996.

U.S. EPA. (2018). Advancing Sustainable Materials Management: 2015 Fact Sheet

Assessing Trends in Material Generation, Recycling, Composting, Combustion

with Energy Recovery and Landfilling in the United States.

https://www.epa.gov/sites/production/files/2018-07/documents/

2015_smm_msw_factsheet_07242018_fnl_508_002.pdf

Wongkhorsub, C, and N. Chindaprasert . (2013). A Comparison of the Use of Pyrolysis

Oils in Diesel Engine. Energy and Power Engineering, 5, 350–355.

doi:10.4236/epe.2013.54B068.

Yao, Y., et al. (2012). Effect of Biochar Amendment on Sorption and Leaching of

Nitrate, Ammonium, and Phosphate in a Sandy Soil. Chemosphere, 89(11)1467–

1471., doi:10.1016/j.chemosphere.2012.06.002.

Yu, O., et al. (2017). Characterization of Biochar and Its Effects on the Water Holding

Capacity of Loamy Sand Soil: Comparison of Hemlock Biochar and Switchblade

Grass Biochar Characteristics. Environmental Progress & Sustainable Energy,

36(5), 1474–1479., doi:10.1002/ep.12592.

Zang Oo, A., Sudo, S., Matsuura, S., Win, K., and Gonai, T. (2018). Aerated Irrigation

and Pruning Residue Biochar on N2O Emission, Yield and Ion Uptake of

Komatsuna. Horticulturae. 4(4), 33

Zhang, R. (1997). Determination of Soil Sorptivity and Hydraulic Conductivity from the

Disk Infiltrometer. AGRIS: International Information System for the Agricultural

Science and Technology, Hillsdale, N.J. : B.L. Erlbaum Associated, 1982.

agris.fao.org/openagris/search.do?recordID=US199705