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Synergies between cover crops and corn stover removal
Michelle R. Pratt a
, Wallace E. Tyner a,⇑
, David J. Muth Jr. b
, Eileen J. Kladivko c
Department of Agricultural Economics, Purdue University, 403 West State Street, West Lafayette, IN 47907-2054, USA
Praxik, Inc., 2701 Kent Ave, Suite 130, Ames, IA 50010, USA
Department of Agronomy, Purdue University, 915 West State Street, West Lafayette, IN 47907-2054, USA
a r t i c l e i n f o
Received 2 December 2013
Received in revised form 26 June 2014
Accepted 28 June 2014
Available online 25 July 2014
a b s t r a c t
The potential harvest of corn stover as a feedstock for biofuels to meet government mandates has raised
concerns about the agronomic impacts of its removal from ﬁelds. Furthermore, in order to meet these
mandates, larger quantities of stover will be required. As a result, increased attention has been placed
on sustainable agronomic practices, such as cover crops. While cover crops may offer desirable beneﬁts,
adoption comes at a cost. The objective of this study was to determine the extent to which cover crop
costs could be compensated by additional stover removal and additional agronomic beneﬁts from the
use of cover crops.
To meet the objective, we took three distinct approaches: (1) beneﬁt-cost analysis, (2) integrated model
analysis, and (3) representative farm analysis using the linear programming model PC-LP. Each approach
was a different take on the same issue; however, each provided different information. First, we estimated
cover crop costs and agronomic beneﬁts and employed beneﬁt-cost analyses, including stochastic anal-
ysis in @RISK. Second, we tested cover crops with stover removal for 24 Indiana farms using PC-LP. Cover
crop costs ranged from $81.76/ha to $172.50/ha, with variability being driven by differences in the seed-
ing rate and seed cost. Agronomic beneﬁts included reduced erosion, which was calculated using a newly
created integrated modeling system.
The mean estimated reduced soil erosion with a cover crop and no residue removal was 0.72 metric
tons/ha. An analysis of cover crop agronomic beneﬁts resulted in private beneﬁts (on-site) ranging from
$91.45/ha to $192.07/ha, and $97.63/ha to $198.27/ha from society’s perspective. These beneﬁts were
highly inﬂuenced by added or scavenged nitrogen (N) from the cover crop. For sensitivity we eliminated
the beneﬁt from added N and reevaluated the results. Without the N credit, beneﬁts ranged from
$74.72/ha to $134.62/ha. Beneﬁt-cost analyses when considering the agronomic beneﬁts of cover crops
resulted in a range of a net loss of $11.09/ha to a net beneﬁt of $87.32/ha for the private perspective.
The integrated modeling system results indicated that, on average, while holding soil erosion constant,
an additional 4.01 metric tons/ha of stover could be removed if a cover crop were used. Accounting for
cover crop costs and stover removal, a beneﬁt-cost analysis suggested that at a farm-gate stover price
of $66.14/metric ton, net beneﬁts ranged from a loss of $3.78/ha to a net beneﬁt of $86.93/ha. At a
farm-gate stover price of $88.18/metric ton, mean net beneﬁt ranged from $158.81/ha to $249.52/ha.
Results from the farm model (PC-LP) indicated that cover crops, along with increased stover removal,
impacted crop rotations, increased the total amount of stover harvested, and had the potential to increase
Ó 2014 Elsevier Ltd. All rights reserved.
As concerns with global warming increase, alternative energy
sources are continually being sought. The Energy Independence
and Security Act (EISA, 2007) established that by 2022, 36 billion
gallons (144 billion liters) of biofuel are to come from renewable
fuel sources. More speciﬁcally, the mandate requires the produc-
tion of cellulosic biofuels to increase to 16 billion gallons (64 bil-
lion liters) ethanol equivalent annually by 2022 (EISA, 2007).
Cellulosic biofuels are derived from several sources including corn
(Zea mays L.) residue, or corn stover. Of the 16 billion gallons man-
dated by 2022, 7.8 billion gallons (31.2 billion liters) are estimated
to come from corn stover (EPA, 2009). It is also favored due to the
fact that it is readily available and has a high cellulosic content
(Blanco-Canqui and Lal, 2009).
0308-521X/Ó 2014 Elsevier Ltd. All rights reserved.
⇑ Corresponding author. Tel.: +1 (756) 494 0199; fax: +1 (756) 494 9176.
E-mail address: firstname.lastname@example.org (W.E. Tyner).
Agricultural Systems 130 (2014) 67–76
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/agsy
Corn stover (also interchangeably referred to as ‘‘residue’’, ‘‘sto-
ver’’, and ‘‘biomass’’ throughout this study) is a crop residue which
is identiﬁed as the ‘‘above ground material left in ﬁelds after corn
grain harvest’’ (Karlen et al., 2011). The components of corn stover
were found to be 30% husks, shanks, silks, and cobs, and the rest
stalks, tassels, leaf blades, and leaf sheaths (Hoskinson et al.,
2007). Crop residues, such as corn stover, which typically remain
on the ﬁeld, are responsible in numerous ways for preserving the
soil (Huggins et al., 2011). While corn stover could be a promising
source of biofuels, several concerns have risen about its removal
from the ﬁelds. This has brought new attention to conservation
practices, such as planting cover crops. While it has been observed
that moderate removal of stover may actually be beneﬁcial (Swan
et al., 1994), increased removal can have many adverse effects
(Blanco-Canqui and Lal, 2009; Blanco-Canqui and Lal, 2007; Meki
et al., 2011; Wilhelm et al., 2004). Acceptable removal rates of corn
stover vary across studies, but there is evidence to suggest that
rates of removal may be limited to around 33% of total available
stover due to the potential negative effects on soil quality and pro-
ductivity (Blanco-Canqui and Lal, 2009; Graham et al., 2007; Kim
and Dale, 2004; McAloon et al., 2000; Nelson, 2002; Petrolia,
2006; Thompson and Tyner, 2011; Thompson and Tyner, 2014).
Over the years, much research has been conducted to show the
agronomic advantages and disadvantages of using various cover
crops (Frye and Blevins, 1989; Dapaah and Vyn, 1998; Stivers-
Young and Tucker, 1999; Kinyangi et al., 2001; Andraski and
Bundy, 2005; Snapp et al., 2005). More recent research has shown
that in addition to agronomic beneﬁts associated with cover crops,
there may also be an opportunity for economic gains if cover crop
residue could reduce subsequent fertilizer application and even
more so if it can be sold as forage (Gabriel et al., 2013). Given
the known beneﬁts of cover crops, it is believed that these beneﬁts
could mitigate the potentially adverse impacts of stover removal.
Furthermore, the use of cover crops may allow corn stover to be
removed at higher rates, which could potentially increase farm
While the Midwest Corn Belt region is seen as a major supplier
of corn stover, cover crops have not been widely adopted. The aim
of this study is to analyze the economic and agronomic impacts of
stover removal when done in combination with cover crops in the
Midwest. Speciﬁcally, to what extent would it pay for famers to
establish a cover crop if it were possible to increase stover removal
rates from 33% to 50% or higher. This analysis considers data from
several sources in order to quantify the beneﬁts and costs of cover
crops. Additionally, we evaluate the extent to which cover crops
allow for increased stover removal without adverse agronomic
consequences. Ultimately, the combination of information on sto-
ver removal and cover crops is used to determine if the additional
revenue from stover removal will compensate farmers for the costs
of establishing cover crops.
2. Materials and methods
The data used (or applied) in this study comes from several
sources including the Midwest Cover Crop Council (MCCC) Cover
Crop Decision Tool, farmer interviews, and anecdotal evidence.
We consider six pure cover crops and two cover crop mixes for
our analysis: (1) annual ryegrass (lolium multiﬂorum), (2) cereal
rye (secale cereal), (3) crimson clover (trifdium incarnatum), (4)
hairy vetch (vicia villosa), (5) oats (avena sativa), (6) oilseed radish
(raphanus sativus), (7) annual ryegrass/crimson clover mix, (8)
annual ryegrass/oilseed radish mix. Because of paucity of data,
and in some cases poor understanding of how management prac-
tices affect soils, we employ several methods and models to ana-
lyze the costs and beneﬁts of cover crops coupled with corn
stover removal. Each method allows us to approach our objective
from a different angle. In doing so, each approach brings something
to the overall picture and helps us conﬁrm our results.
First we estimate the cost of cover crops. Next we quantify the
beneﬁts of cover crops. Quantifying cover crop beneﬁts involves
two separate cases, both of which involve the use of an integrated
model: one for agronomic beneﬁts, and another for additional sto-
ver removal. Once costs and beneﬁts are quantiﬁed and estimated,
a beneﬁt-cost analysis with risk distributions is conducted. Finally,
cover crop costs are used in a linear programming model to simu-
late the impacts of cover crops and corn stover removal at the farm
level based on real data for 24 Midwest farmers.
2.1. Cover crop cost estimates
We develop a method of cover crop cost estimation which
breaks down costs into three components: (1) establishment, (2)
termination, and (3) unexpected costs. Establishment costs
assumed in this analysis are those costs that are required to aeri-
ally inter-seed the cover crop in the fall into the standing cash crop.
The components of the establishment cost therefore include the
recommended cover crop seeding rate, seed cost, and the cost of
Recommended aerial seeding rates for each cover crop come
from the MCCC Cover Crop Selector (MCCC, 2012) (available at
www.mccc.msu.edu) as a range and are measured as pounds of
pure live seed (PLS) per acre. This measure is adjusted to account
for the percent purity and the percent germination of a cover crop.
The percent purity for seeds is usually about 98–99% and percent
germination ranges from 85% to 90% (E. Kladivko, personal com-
munication, September 4, 2012). Since an actual plot is not being
tested, we increase the recommended PLS rates for each cover crop
provided by the MCCC by 10%. Given the recommended aerial
seeding rate for each cover crop and taking into account the cost
of seed, it is possible to estimate the seed costs of cover crops.
Using quotes from seed suppliers listed in Clark (2007) and prices
stated by several farmers, a range of seed costs for each cover crop
or cover crop mix is generated. The ﬁnal component of the estab-
lishment cost is the cost of aerial application, which is often done
at custom rates. Data for this component comes from anecdotal
evidence (Vollmer, 2011) and farmer interviews. The mean esti-
mated aerial application cost is $30.39/ha, the minimum is
$24.71/ha and the maximum is $37.06/ha.
Termination costs assumed in this analysis are those costs asso-
ciated with chemically killing the cover crop in the spring before
planting a cash crop, which very often is also done at a custom rate.
Using estimated custom rate costs from anecdotal evidence (USDA,
2011a) and farmer interviews, the estimated mean termination
cost is $15.76/ha. The minimum is $11.12/ha and the maximum
termination cost is $22.24/ha. It should be noted that in some
cases, this chemical application would occur regardless of the pres-
ence of cover crops or not. Therefore, since we cannot differentiate
the proportion of this cost that could be attributed to the use of
cover crops or standard ﬁeld operations, the full cost is used in
Due to the inherent risk that planting cover crops carries to a
farmer, a cost item has been included to account for an unexpected
negative event, such as needing more than one pass of cover crop
termination (chemical or mechanical) if it does not kill initially,
untimely termination, the cover crop becoming a weed issue in
the following cash crop and/or the need to disc an area twice in
the spring. Snapp et al. (2005) reports on similar events as ‘‘indirect
on-farm costs’’ where the establishment of a cover crop may inter-
fere with the following cash crop or where the cover crop has
excessive growth or becomes a weed. For this analysis, the total
unexpected cost is the probability that the unexpected cost will
be incurred multiplied by the associated cost per acre. Based on
68 M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76
two probability estimates of 10% (Ostendorf, 2010) and 15%
(A. & C. Ault, personal communication) at an estimated cost of
$32.12/ha (A. & C. Ault, personal communication, 2012), the mean
unexpected cost is $4.03/ha, the minimum is $3.21/ha, and the
maximum is $4.82/ha.
The total cost of a cover crop is then the summation of
establishment, termination, and unexpected costs.
2.2. Cover crop beneﬁts
In this analysis we consider the agronomic beneﬁts that cover
crops offer, as well as the additional beneﬁts that may be associ-
ated with the ability to sustainably harvest higher levels of residue.
Cover crop agronomic beneﬁts are estimated for four beneﬁt cate-
gories: (1) added nutrient content, (2) increase soil organic matter
(SOM), (3) reduced compaction, and (4) reduced soil erosion.
Added nutrient content accounts for the ability of legume cover
crops to add N to the soil, as well as the ability of non-legume cover
crops to scavenge N and make it available for the subsequent cash
crop. Data on added N comes from the MCCC Cover Crop Decision
Tool as a range of values. Adjustments were then made to this data.
For annual ryegrass/oilseed radish mix and the oilseed radish cover
crop, the values for added N are quite high and would most likely
only be possible if the soil has manure applied to it as well.
Therefore, the annual ryegrass/oilseed radish mix is adjusted to
11.21–44.82 kg/ha, and oilseed radish cover crop is adjusted to
22.41–56.03 kg/ha (E. Kladivko, personal communication, Septem-
ber 4, 2012). Furthermore, data is adjusted to account for the fact
that some of the N contributes to building SOM, while some will
be available for the next crop. This avoids double counting when
the increase in SOM is considered. The assumption is that 50% of
the N could be available for the next crop (E. Kladivko, personal
communication, September 4, 2012). Added N is then valued. The
value of N comes from United States Department of Agriculture
(USDA) historical US average farm prices of N fertilizers (USDA,
2012). Average prices for three N fertilizers, anhydrous ammonia,
nitrogen solutions (30%), and urea 44–46% are considered for
2008–2012. By accounting for the percentage of N in each of the
fertilizers, the price of the fertilizer in dollars per ton is converted
to the price of N in dollars per kilogram. Combining prices for all N
fertilizers, the mean cost is $1.15/kg, the minimum is $0.66/kg, and
the maximum is $1.48/kg.
Increased SOM is the percentage increase in SOM, which is a
proxy for soil health, soil carbon and nutrient content, and thereby
linked to soil productivity and crop yields. SOM is converted from
the dry matter produced by each cover crop (Hoorman, 2012), and
the assumption here is that 25% of the dry matter produced from
the cover crop becomes decomposed organic matter. The percent-
age increase in SOM is that quantity (in tons) divided by the base
SOM. That % increase in SOM can be converted to a value per acre
using Eq. (1):
Increased SOM ð$=acreÞ ¼ SOM Increase ð%Þ
Ã Value of SOM ð$=ð1%ÞÞ ð1Þ
Reduced compaction accounts for the beneﬁt of not having to
deep rip ﬁelds, as well as enhanced root growth of the following
cash crop. This is the cost of deep tilling, assuming that the use
of cover crops reduces the need for deep tillage of a ﬁeld due to
root growth, which alleviates and/or prevents compaction of the
soil. The value of this is estimated to be between $74.13 and
$86.48/ha (Hoorman, 2010). However, it is unlikely that a farmer
would deep rip more than once in every ﬁve years if there is a com-
paction problem (E. Kladivko, personal communication, September
4, 2012). Therefore, the estimates provided by Hoorman are
adjusted to reﬂect the probability of deep ripping once in
ﬁve years, resulting in a reduced compaction value range of
$14.38–$17.30 per hectare per year.
The reduced erosion is the difference between soil erosion
(wind and water) with and without a cover crop. This estimate
comes from an integrated model, which will be discussed in more
detail below. The value of reduced soil erosion comes from the
USDA-NRCS (2011b) and is the cost to replace soil function and
remediate off-site damage. There are on-site and off-site values
of soil erosion. The on-site value represents the cost to the farmer
of soil erosion while the off-site value represents the cost of soil
erosion to society. The on-site value of soil erosion is $11.21/metric
ton, which accounts for reduced yields and water and nutrient loss.
The off-site value of soil erosion is $19.83/metric ton, which
includes impacts on air quality (health and property) and water
quality (USDA, 2011b). Although there may be other beneﬁts, they
are not considered to avoid overlap and due to lack of data. Once
the beneﬁts of each category listed above have been quantiﬁed, a
range of values, based on anecdotal evidence, is assigned to each
The second set of beneﬁts we consider are those associated with
stover removal. Cover crops alone appear to offer many beneﬁts.
We hypothesize that cover crops will allow for additional stover
to be removed. Provided there is an existing and viable market
for corn stover, there will be an economic beneﬁt associated with
corn stover removal. This beneﬁt is the value of stover beyond
the cost of removal. The beneﬁt from corn stover removal is
deﬁned by the value of stover multiplied by the total stover
removed, where the value of stover is equal to a farm-gate
stover price less the on-farm harvest costs associated with stover
removal. We test two farm-gate prices of stover: $66.14/metric
ton and $88.18/metric ton. These prices were selected based on
results from Thompson and Tyner (2014) which indicate that
signiﬁcant stover harvest begins around $60/Mg, and substantial
harvest at $80/Mg. On-farm harvest costs are those estimated by
Thompson and Tyner (2014) and Fiegel (2012).
In order to estimate the value of reduced erosion and estimate
the additional amount of corn stover that can be removed with a
cover crop, we utilize an integrated modeling system that com-
bines the Revised Universal Soil Loss Equation, Version 2 (RUSLE2),
the Wind Erosion Prediction System (WEPS), and the Soil Condi-
tioning Index (SCI). RUSLE2 simulates daily changes in ﬁeld condi-
tions based on soil aggregation, surface wetness, ﬁeld management
practices, and residue status, and is driven by daily weather
parameters. RUSLE2 is used to guide conservation planning activi-
ties and previous studies have shown the model to accurately rep-
resent trends in ﬁeld data (Ismail, 2008; Dabney et al., 2006; Foster
et al., 2006; Schmitt, 2009). RUSLE2 has also been applied to simu-
late water erosion processes within broader analysis efforts rang-
ing from watershed scale soil quality assessments (Karlen et al.,
2008), assessing risks at abandoned mining sites (Vaszita et al.,
2009), and socio-economic impacts of biophysical processes
(Halim et al., 2007). WEPS uses a process-based daily time-step
model to simulate soil erosion due to wind forces considering both
direction and magnitude (Wagner and Tatarko, 2001). WEPS mod-
els a three-dimensional simulation region requiring a set of param-
eters describing climate, soil aggregation, surface wetness, ﬁeld
scale, ﬁeld management practices (including crop rotation and
growth) and residue status, and is driven by daily weather projec-
tions. WEPS has been evaluated for erosion predictions on cropland
ﬁelds (Hagen, 2004) and has been used previously for case studies
in corn stover harvest (Wilhelm et al., 2007). RUSLE2 and WEPS
each calculate components of an NRCS-developed metric for estab-
lishing management practice impacts on overall soil health, named
the Soil Conditioning Index (SCI). The SCI provides qualitative pre-
dictions of the impact of cropping and tillage practices on soil
M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76 69
organic carbon, which is an important factor in sustainable agricul-
tural residue removal. The SCI has been used to support watershed
scale soil quality assessments (Karlen et al., 2008), evaluate crop-
ping systems in northern Colorado (Zobeck et al., 2008), and inves-
tigate southern high plains agroecosystems (Zobeck et al., 2007).
The model, developed by Muth and Bryden (2013) utilizes a
data and software integration framework that tightly couples the
RUSLE2, WEPS, and SCI scenarios for fully automated high perfor-
mance computing applications. The integration framework has
been named the Landscape Environmental Assessment Framework
(LEAF) (LEAF, 2014; Moore and Karlen, 2013; Karlen and Muth,
2013). The LEAF integrated model has been used for a broad range
of studies investigating sustainable residue removal at the national
scale (Muth et al., 2012a), at the regional scale (English et al., 2013;
Bonner et al., 2014), at the subﬁeld scale (Muth et al., 2012b; Muth
and Bryden, 2012), and additionally for developing integrated bio-
energy landscape designs (Karlen and Muth, 2013; Koch et al.,
2012; Abodeely et al., 2012).
The data management and model inputs for the LEAF integrated
model are described in detail in Muth and Bryden, 2013. The meth-
odologies using publicly available data resources such as the NRCS
SSURGO soils database, the NASS Cropland Data Layer, NRCS devel-
oped climate databases, and Conservation Information Technology
tillage databases are detailed in Muth et al., 2012a. Extensive valida-
tion of the individual models is documented through the previously
mentioned studies. The integrated model has been veriﬁed to deli-
ver analyses consistent with validation studies (Muth and Bryden,
Using the LEAF integrated model, we have deﬁned the user
inputs as follows. The spatial area to be analyzed is the state of
Indiana, which has high corn production and large potential for
stover removal. The management practices speciﬁed include: cover
crops and cover crop combinations, residue removal, crop rota-
tions, tillage practices, vegetative barriers, and yield drag with con-
tinuous corn. Outputs from the integrated modeling system are the
SCI and its three sub-factors, wind erosion, water erosion, and
the amount of residue removed. Using various combinations of
the management practices, we will be able to extract two pieces
of information to be used in the beneﬁt-cost analyses: (1) the mean
avoided wind and water erosion with a cover crop; and (2) the
additional biomass that is available for removal with a cover crop
while holding total soil erosion constant. These values were esti-
mated econometrically from the nearly two million data points
that were obtained from all the combinations of soil types, slope,
management practices, etc.
First we sum the wind and water erosion values to obtain total
soil erosion. Next, a cover crop dummy variable was created, where
the value equals one if any cover crop is present and zero if no
cover crop is present. The mean avoided soil erosion is thus calcu-
lated as the difference between the mean erosion values with and
without a cover crop.
In order to estimate the additional total removable biomass with
a cover crop holding soil erosion constant, several steps were taken.
First, we wanted to separate the impacts of no-till cultivation and
cover crop. This is done by ﬁrst estimating the following equation
for observations under each crop rotation with a cover crop and
again for observations under each crop rotation with no cover crop.
y ¼ b0b1X1 þ b2X2 ð2Þ
where y is the total soil erosion, X1 is a tillage dummy variable
which equals 1 if no-till and 0 otherwise, X2 is the annual biomass
The additional removable biomass from no-till, holding soil ero-
sion constant is then:
Therefore, the contribution of a cover crop to the amount of
additional biomass removable with no-till and cover crops is the
difference between additional removable biomass by no-till with
a cover crop and additional removable biomass by no-till with no
2.3. Beneﬁt-cost analyses
After the costs and beneﬁts of cover crops have been estimated,
a beneﬁt-cost analysis is conducted to calculate the mean net ben-
eﬁt of a cover crop as well as the probability of a loss using Monte
Carlo simulation. To account for variability in the costs and bene-
ﬁts, the Palisades risk and decision analysis software @RISK
(2001), was used to perform the risk analysis. All of the uncertain
variables had a minimum, most likely (mode), and maximum. The
distributions that are normally used in this situation are the PERT
and triangular. We actually tested both distributions, but report
here only the results from the triangular distribution, as they were
There are two different perspectives for evaluating beneﬁts: (1)
there is no stover removal, and the beneﬁts of the cover crop are
agronomic (increased N, SOM, reduced compaction, and reduced
erosion), and (2) there is stover removal where the beneﬁt is the
value of stover removed, and there are no agronomic beneﬁts con-
sidered. Furthermore, in the case for which there is no stover
removal and cover crop beneﬁts are agronomic, we will assume
two cases of reduced erosion: (1) on-site value of reduced erosion
and (2) off-site value of reduced erosion. That is, we consider the
private gain for the farmer of reduced erosion as well and the
societal gain from reduced downstream erosion.
2.4. Analyzing costs and beneﬁts at the farm level
After the cover crop costs and beneﬁts are estimated, various
scenarios are analyzed using farm level data in PC-LP. PC-LP is a
linear programming model that was developed within the Agricul-
tural Economics department at Purdue University (West Lafayette,
IN). Users specify input data including land, labor, machinery, crop
yields, crop prices, and costs. Given these inputs, which are farm
speciﬁc, the PC-LP model determines the proﬁt-maximizing crop
mix (Doster et al., 2009a, 2009b). Input information for the pro-
gram comes from farmers participating in the Top Farmer Crop
Workshop at Purdue University. PC-LP is used to combine cover
crops and corn stover removal.
In 2011, Thompson added stover harvest options into the PC-LP
model by creating two new crops: BC + Stover (soybean corn rota-
tion) and CC + Stover (continuous corn). Thompson (2011, 2014)
assumed the stover-to-grain ratio to be 0.95 and the removal rate
to be 33%. The corn harvest index is the ratio of corn grain to the
sum of corn grain and stover, and is generally between 0.50 and
0.55 (Michigan State University Extension, 2013). Thus, our
assumption is consistent with the normal values for corn harvest
index. The addition of stover removal into PC-LP involved account-
ing for the harvest and storage costs associated with stover
Expanding upon the methodology developed by Thompson
(2011, 2014) cover crops can be added to the PC-LP model to esti-
mate the impact of corn stover removal and crop mix at a farm
level. We consider two cases: (1) a stover removal rate of 33% with
no cover crop and (2) a stover removal rate of 75% with a cover
crop. The difference between the two cases is the impact of cover
crops at the farm level. Three cases of cover crop costs are analyzed
as a means of conducting sensitivity analysis on the cover crop
cost. Additionally, calculations are done at varying levels of stover
price, beginning at $44.09/metric ton and increasing in $22.05/
metric ton increments up to $132.28/metric ton.
70 M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76
There are three ways in which the addition of a cover crop
affects the current methodology in PC-LP. First, the addition of
the cover crop is an extra cost to the farm. To account for the costs
incurred by a cover crop, the cost will be added to the harvest cost;
doing so allows us to adjust the crop price to reﬂect the use of
cover crops without changing the existing model. Second, it is
assumed that a cover crop will increase the acceptable rate of sto-
ver removal due to beneﬁcial agronomic properties. Third, we
assume the increase in stover removal rate will impact the harvest
and storage costs associated with stover removal. Given the exist-
ing methodology in PC-LP for the incorporation of stover removal,
costs for all cases are estimated by ton and by hectare. Costs used
for the base case (no cover crop) in this analysis are those esti-
mated by Fiegel (2012) for stover that is harvested at 15% moisture.
Costs used for the cover crop cases are those used for the base case
adjusted to reﬂect the increase in stover removal.
Cost components associated with stover removal include: stor-
age, net wrap, labor, equipment, nutrients, and fuel. Harvest cost is
the sum of net wrap, fuel, labor and equipment used in harvesting
stover per hectare. We assume that per ton, net wrap and nutrient
costs will remain the same for all cases, while storage, labor, equip-
ment, and fuel costs will exhibit some economies of scale. Per hect-
are we assume that storage, net wrap, and nutrient costs will
increase to match the full increase in the stover removal rate, while
labor, equipment, and fuel costs will increase, however by a per-
centage of the increase in the stover removal rate. Given the bales
per hectare assumption, 15% moisture, and tons per bale assump-
tion estimated by Thompson (2011) and Fiegel (2012), and our
estimated increase in the stover removal rate, we estimate these
costs to increase by 64%.
For BC + Stover, the harvest cost was estimated at $87.47/ha for
the base case and $159.70/ha for the cover crop cases. A cost-sav-
ing of $61.77/ha (Karlen et al., 2011) is assumed by Thompson
(2014) for CC + Stover from reduced tillage, making the harvest
cost for CC + Stover $25.70/ha for the base case and $97.92/ha for
the cover crop cases. Since tillage practice was not indicated in
the PC-LP model data, we assume reduced or conventional tillage,
so the $61.77/ha savings will apply to the CC + Stover crop for all
farms in our analysis. A summary of the cost components for all
cases is presented in Table 1.
Given the estimated values of stover harvest, and the assumed
farm-gate prices for stover ($/ton), the mean net value of stover
harvest is estimated. Using a stover farm-gate price of $66.14/met-
ric ton, the average value of stover harvest (mean between
BC + Stover and CC + Stover for the cover crop cases) is $22.87/met-
ric ton. At a stover farm-gate price of $88.18/metric ton, the aver-
age value of stover harvest is $41.92/metric ton. These mean values
are used in the beneﬁt-cost analysis as the value of stover removal
per ton of stover removed.
3. Results and discussion
3.1. Cover crop costs
Estimation of the cover crop costs involved the use of Monte
Carlo simulation in @RISK using the triangular distributions. There
is a wide range of variability in cover crop costs. This is derived
from the differences in cover crop seeding rates and seed costs
(Table 2). Annual rye had the lowest cost. While oats have the sec-
ond highest average seeding rate, the seed costs is the second low-
est on average. Similarly, annual ryegrass has a relatively moderate
seeding rate and seed cost. Hairy vetch was the most expensive
cover crop and appears to be a bit of an outlier since its mean cost
is more than $49.42/ha higher than any other cover crop. While
hairy vetch does not have the highest seeding rate, it does have
the second highest seed cost. Oilseed radish has the highest seed
cost, but its seeding rate is two to three times less than hairy vetch.
As expected, the cover crop mixes have a mean cost that lies
between the mean costs for the two individual crops that make
up the mix. This may indicate that cover crop mixes provide an
opportunity for farmers to combine cover crops for maximum ben-
eﬁts at a lower cost.
3.2. Cover crop beneﬁts
The integrated modeling system yields two results that are con-
sidered as beneﬁts of cover crops. The ﬁrst is reduced soil erosion
and the second is the potential for additional stover removal. We
analyze the mean reduced soil erosion overall with and without
a cover crop. The mean difference in soil erosion with and without
a cover crop is 0.72 metric tons/ha. This value is used for the
reduced erosion cover crop beneﬁt category.
Second, using Ordinary Least Squares (OLS) regression analysis
and holding soil erosion constant, we estimate the additional sto-
ver that can be removed with a cover crop. Regression results are
shown in Table 3 for our two sets of observations (those with cover
crops and those without cover crops). Soil erosion is the dependent
variable, and total biomass removed and a dummy variable (NT)
indicating no till or conventional till are the independent variables.
By dividing the negative of the coefﬁcient of NT by the coefﬁcient
of totBioRem_1 and converting to tons/ha we estimate the addi-
tional removable biomass holding erosion constant. Comparing
the two results yields the beneﬁt of a cover crop. Based upon the
results for all rotations combined, a cover crop appears to provide
a 4.01 metric tons/ha gain over no-till alone, with a larger gain for
corn-soybean than continuous corn. This value for additional
removable stover with a cover crop is used for the beneﬁt cost
analysis case with stover removal.
Costs associated with stover harvest for the base case (no cover crop and 33% stover
removal) and scaled for the cover crop cases (cover crop and 75% stover removal.
Cost component Base case Cover crop cases
$/ha $/metric ton $/ha $/metric ton
Storage 74.87 18.15 151.52 15.80
Net wrap 26.02 6.17 59.15 6.17
Labor 14.31 3.40 23.40 2.44
Equipment 30.44 7.21 49.81 5.19
Nutrients 59.20 14.03 134.57 14.03
Fuel 16.70 3.96 27.33 2.85
BC + stover total 221.55 52.50 445.81 46.48
Tillage savings À61.77 À14.64 À61.77 À6.44
CC + stover total 159.77 37.86 384.04 40.05
Total costs of each cover crop/cover crop mix as estimated by the mean of a triangular
probability distribution based on the cost of establishment, termination, and
Cover crop/mix Seed ($/ha) Total ($/ha)
60% Annual ryegrass/40% Oilseed radish 43.38 94.87
60% Crimson clover/40% Annual ryegrass 48.41 99.90
Annual ryegrass 36.93 88.41
Cereal rye 52.07 103.56
Crimson clover 55.98 107.47
Hairy vetch 121.01 172.50
Oats 59.18 93.92
Oilseed radish 53.91 105.40
Note: While uncertainty is included in all the cost components, the mean values are
the same for aerial application (30.72), termination (16.75), and unexpected costs
(4.02). There is no termination cost for oats. The mean values for seed costs do vary
considerably, so seed costs and total costs are included here.
M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76 71
Cover crop beneﬁts were estimated for two cases. The ﬁrst case
assumes that no stover is harvested. Therefore, the agronomic ben-
eﬁts of cover crops are accrued by the farmer. The second case
assumes that some stover is harvested. Cover crop beneﬁts in the
case where no stover is harvested are shown in Table 4. Results
for the second case, where stover is harvested, are shown in Table 5
along with results from the farmer perspective.
The estimated cover crop beneﬁts suggest that a crimson clover
cover crop provides the greatest beneﬁt, while oilseed radish pro-
vides the least beneﬁt. Crimson clover has the second highest con-
tribution of N and the largest SOM percent accumulation.
Therefore, we can expect a large beneﬁt overall. Oilseed radish
on the other hand has low added N and low SOM percent accumu-
lation. Although hairy vetch has the highest mean cost, it does not
have the highest mean beneﬁt. The crimson clover/annual ryegrass
cover crop mix offers larger beneﬁts than the two individual cover
crops. While the annual ryegrass/oilseed radish mix offers higher
beneﬁts than the oilseed radish cover crop, the mean beneﬁt is
slightly lower than the annual ryegrass beneﬁt, which is due to
the low mean beneﬁt of the oilseed radish cover crop. Cover crop
beneﬁts from the societal perspective are uniformly higher by
In both of these cases, the beneﬁt from crimson clover is signif-
icantly larger than other cover crops. This is largely due to the N
credit associated with crimson clover. Hairy vetch also has a high
N credit. The standard assumption behind the N credit is that if a
cover crop is adding N, a farmer will reduce N application. How-
ever, in our farmer interviews, many farmers do not abide by this
assumption. In other words, regardless of the N credit provided by
a cover crop, they assume it to be zero and continue with their nor-
mal regimen of N application. While we consider added N to be a
cover crop beneﬁt, as there is added value into the soil, if farmers
assume this value to be zero, it can impact beneﬁt-cost analysis
results, speciﬁcally for legume cover crops such as crimson clover
and hairy vetch. Therefore, an additional case was tested to dem-
onstrate the impact of the N credit becoming zero for all cover
crops and it is also shown in Table 4.
While only legumes can add N to the soil, the other crops orig-
inally had a value associated with the scavenged N, which is why
there is a decrease in net beneﬁt for all cover crops. However,
removing the added N beneﬁt provides more balanced results.
While crimson clover still has the highest beneﬁt, hairy vetch no
longer has second highest beneﬁt; cereal rye is higher. Further-
more, crimson clover now has a beneﬁt closer to cereal rye and
annual ryegrass. The most commonly used cover crops from the
farmers we interviewed were annual ryegrass and cereal rye. These
results seem to conﬁrm that farmers do not at present place a value
on added or scavenged N from cover crops.
The second case for which we estimate cover crop beneﬁts is
when there is corn stover harvest. The beneﬁt of a cover crop with
stover removal is the proﬁt that can be made from stover once sto-
ver harvest costs have been accounted for. Assuming that a
Ordinary Least Squares (OLS) regression results used to estimate additional remov-
able biomass when a cover crop is present. These regressions are the result of
observations from the integrated modeling system developed by Muth and Bryden
Variable No cover crop Cover crop
R-squared 0.237 0.1035
No. Observations 35679 115692
Standard errors are reported in parentheses.
Signiﬁcant at the 99% level.
The beneﬁt of a cover crop measured in $/ha from the private perspective for the case where no N credit is assumed from the use of the cover crop versus the case where an N
credit is accounted for.
Cover crop/mix Increased SOM No N Credit With N Credit
60% Annual ryegrass/40% Oilseed radish 69.87 93.99 106.29
60% Crimson clover/40% Annual ryegrass 84.32 108.44 143.33
Annual ryegrass 84.32 108.44 108.44
Cereal rye 102.39 126.51 126.51
Crimson clover 108.42 132.54 192.07
Hairy vetch 69.87 93.99 167.89
Oats 96.37 120.49 120.49
Oilseed radish 50.59 74.71 93.17
Note: The beneﬁts for reduced soil compaction (16.06) and reduced soil erosion from the private perspective (8.06) are the same for all cover crops. The increased soil organic
matter and N credit are the major differences among cover crops.
Summary of cover crop beneﬁt-cost analysis for (i) the private perspective, where a cover crop is present and no stover is harvested, and (ii) the case where a cover crop is
presented and there is 75% stover removal. The net beneﬁt for each case is the mean of a triangular probability distribution.
Cover crop/mix Private perspective With stover removala
net beneﬁt < 0
net beneﬁt < 0
60% Annual ryegrass/40% Oilseed radish 11.44 21.28 0.311 73.83 10.97 0
60% Crimson clover/40% Annual ryegrass 43.44 17.1 0.003 68.82 12.06 0
Annual ryegrass 20.04 26.59 0.239 80.28 11.02 0
Cereal rye 22.96 21.52 0.148 65.16 12.8 0
Crimson clover 84.61 23.25 0 61.23 14.9 0
Hairy vetch À4.6 24.51 0.588 À3.78 15.12 0.582
Oats 26.56 29.26 0.184 74.8 22.14 0.002
Oilseed radish À12.21 15.34 0.773 63.31 13.69 0
The assumed stover price is $66.14/mt.
72 M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76
removal rate of 33% allows for about 3.36 metric tons/ha of stover
to be sustainably removed, and that an additional 4.01 metric tons/
ha of stover can be removed with a cover crop, the total amount of
stover removed is 7.38 metric tons/ha. Accounting for the on-farm
harvest costs, including nutrient replacement, the beneﬁt of stover
removal at a stover price of 66.14/metric ton is $168.69/ha and at a
stover price of $88.18/metric ton the beneﬁt is $331.26/ha.
3.3. Beneﬁt-cost analyses
We now combine the beneﬁts and costs to obtain net beneﬁts.
In the cases with the use of a cover crop and no stover removal, the
cost of the cover crop is incurred, and the agronomic beneﬁts of the
cover crop are accrued. The results from the private perspective
beneﬁt cost analysis are presented in Table 5. All cover crops
except hairy vetch and oilseed radish yield a net beneﬁt. Although
hairy vetch has large beneﬁts, the seed costs are high enough that
the mean net beneﬁt is negative. Crimson clover has the highest
net beneﬁt. While crimson clover had the second highest mean
cost, it had the largest mean beneﬁt. As for the cover crop mixes,
while crimson clover/annual ryegrass and annual ryegrass/oilseed
radish had similar mean costs, crimson clover/annual ryegrass has
much higher mean beneﬁts, yielding a net beneﬁt about four times
larger than annual ryegrass/oilseed radish.
The probability of a loss (probability that net beneﬁt is less than
zero) is simply the probability in the stochastic analysis that net
beneﬁt is negative. Most cover crops incur some probability of a
loss, with the exception of crimson clover. Hairy vetch and oilseed
radish are the two cover crops with a probability of a loss greater
than 50% (58.8% and 77.3%, respectively). Although oilseed radish
has a negative net beneﬁt, and the probability of a loss is high, mix-
ing it with annual ryegrass yields a positive net beneﬁt and reduces
the probability of a loss by about 50%. Furthermore, combining
annual ryegrass with crimson clover yields the second highest
mean net beneﬁt and a probability of loss very close to zero. From
the social perspective, the net beneﬁt for each cover crop is uni-
formly higher by $6.20/ha while the standard deviations remain
the same. The probability of a loss for each cover crop is slightly
less for the societal case.
The second beneﬁt-cost analysis scenario is where a cover crop
is present, and instead of accumulating additional agronomic ben-
eﬁts from the cover crop, beneﬁts from stover removal, given a via-
ble stover market, are included (also Table 5). The stover removed
for sale is the additional removable biomass holding erosion con-
stant with a cover crop on top of a base of 3.36 metric tons/ha. This
stover then is assigned a value. Since the market for stover has not
been commercially established, we use a range of values based on
prior research (Thompson and Tyner, 2014). In this case we analyze
two farm-gate stover prices. The cover crop acts to hold agronom-
ics constant (in other words, there should be no adverse effects
from stover removal). However, stover removal means that nutri-
ents are removed from the ground. These removed nutrients are
accounted for by subtracting the cost of nutrient replacement from
the value of stover. Although we account for nutrient replacement,
it should be noted that other agronomic costs, such as increased
compaction due to harvest machinery, are not accounted for. Har-
vest costs associated with collecting the stover are included.
The ﬁrst stover price tested is $66.14/metric ton with results in
Table 5. Hairy vetch is the only cover crop with a negative mean
net beneﬁt (under a triangular distribution). For hairy vetch the
probability of a loss is 58%. The probability of a loss for all other
cover crops is essentially zero, and the mean net beneﬁt is between
$61 and $80/ha. The standard deviation is about $11–$22/ha across
all cover crops. Comparing this case to the cases with no stover
removal and agronomic beneﬁt, we can see that stover removal
with a cover crop offers signiﬁcantly increased beneﬁts.
Since actual stover prices are unknown, the sensitivity of stover
value is tested but detailed results are not included here. The sec-
ond case tests a stover value of $88.18/metric ton. Although the
value of stover has increased by $22.05/metric ton, the net beneﬁt
for each cover crop increases by $162.59/ha. This is because once
the harvest cost and nutrient replacement costs have been
accounted for, the remaining value of the stover for $88.18/metric
ton is much higher than $66.14/metric ton, yielding higher mean
net beneﬁts in the beneﬁt-cost analysis. Furthermore, the probabil-
ity that the net beneﬁt is less than zero is essentially zero with a
stover price of $88.18/metric ton.
3.4. Costs and beneﬁts at the farm level (PC-LP)
The 24 PC-LP farms have a total of 62,632 acres available.
Results are for a base case with no cover crop and three cases of
cover crops at varying corn stover prices (Table 7). The base case
assumes no cover crop and 33% stover removal, while the two
cover crop scenarios are estimated using a stover removal rate of
75%. Cover crop costs used include those associated with annual
ryegrass and crimson clover. Furthermore, since our beneﬁt-cost
analyses suggest crimson clover as signiﬁcantly outperforming
annual ryegrass due to added N, we test a sub-case of the crimson
clover cover crop. In this sub-case, we assume that the farmers rec-
ognize the added N from crimson clover and adjust their usual N
inputs accordingly. Therefore, this sub-case considers the per acre
cost of a crimson clover cover crop less the value of added N per
Farms will not begin to harvest stover until the beneﬁt of stover
harvest exceeds the costs. Results from PC-LP indicate that at a sto-
ver price lower than $44.09/metric ton, no farms will participate in
stover harvest, while at prices of $88.18/metric ton and greater, all
24 farms will participate in some stover harvest. At $44.09/metric
ton, 8 farms harvest some stover for the base case and 0 farms har-
vest some stover for all three cover crop cases. At $66.14/metric
ton, 24 farms harvest some stover for the base case, 21 for annual
ryegrass, 19 for crimson clover, and all 24 farms harvest some sto-
ver for crimson clover adjusted for N.
PC-LP also determines the proﬁt-maximizing crop mix for
farms. For the base case, at stover price of $0 and $22.05/metric
ton no acres are allocated to stover acres. However, beginning at
a stover price of $41.51/metric ton, there is a shift from continuous
corn with no stover removal (CCorn), corn-soybean with no stover
removal (BCorn), soybean acres, and other (such as wheat or milo)
acres to include continuous corn with stover removal (CC + Stover)
and corn-soybean with stover removal (BC + Stover) acres. Stover
is ﬁrst harvested from all CCorn acres, then from BCorn acres. As
stover price increases, more acres are assigned to stover acres,
and increasingly to CC + Stover acres. As a result, there is a decline
in the assignment of acres to other crops. This is an indication that
as stover prices increase, there will be more incentive for farms to
not only harvest corn stover, but to also allot more acres to corn
production. This pattern of acreage assignments also holds true
for the three cover crop cases. However, the shift to more corn
acres with stover removal is rapid. For example, at a stover price
of $66.14/metric ton the percentage of acres assigned to CC + Sto-
ver removal for all cases is as follows: 21% for the base case, 22%
for annual ryegrass, 20% for crimson clover, and 24% for crimson
clover adjusted for N. Figs. 1 and 2 illustrate the acreage allocation
by stover price for the base case and annual ryegrass, respectively.
From the PC-LP results we also analyze the total amount of sto-
ver harvested at each stover price. Fig. 3 illustrates these results.
Since for cases involving cover crops the stover removal rate is
increased to 75%, we expect to see greater quantities of stover har-
vested in the cover crop cases. We observe that crimson clover
with the N reduction allows for the greatest amount of stover to
M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76 73
be harvested. At stover prices of $88.18/metric ton and greater, the
amount of stover harvested levels off and is almost indistinguish-
able among the three cover crop cases; this is due to the limit
placed on the amount of stover that can be harvested. Since we
allow for 75% removal in the PC-LP model, once this limit is
reached, so long as the yield and stover-to-grain ratio remain the
same, the amount of total stover harvested will eventually ﬂatten.
Finally, PC-LP allows us to analyze total farm proﬁt. Given that
cover crops allow for increased stover removal, and greater
amount of stover to be harvested, we expect that as stover price
increases and more farms harvest stover, proﬁts will also increase.
Fig. 4 illustrates the results for farm proﬁt for all cases. As shown,
the farm proﬁt with crimson clover after adjusting N, yields the
largest proﬁt after a stover price of $44.09/metric ton. While the
lowest cover crop cost yields the highest proﬁt, all three cover crop
cases are relatively similar, especially after a stover price of $66.14/
metric ton. Furthermore, the cover crop cases offer signiﬁcantly
higher proﬁt than the base case.
The results from the four PC-LP simulations provide an insight
to the activities of proﬁt-maximizing farms in Indiana. This is key
because farms such as those whose data are in PC-LP are targeted
for stover removal in the Midwest to meet biofuel standards. It
tests how farms will react to added costs associated with cover
cropping if the practice will allow them to increase their stover
removal without concern for farm agronomics. Furthermore,
results conﬁrm the ﬁndings from our beneﬁt cost analysis; based
on cost alone, annual ryegrass offers greater farm beneﬁts than
crimson clover, but when the cost of crimson clover is adjusted
to reﬂect the value of added N, crimson clover provides greater
beneﬁts than annual ryegrass.
44 66 88 110 132
Stover Price ($/Mg)
Fig. 1. Assignment of total farm area in the base case, where no cover crop is used
and stover removal is at 33%.
44 66 88 110 132
Stover Price ($/Mg)
Fig. 2. Assignment of total farm area where an annual ryegrass cover crop is
assumed and stover removal is increased to 75%.
40 60 80 100 120
Stover Price ($/Mg)
No Cover Crop Annual Ryegrass
Crimson Clover Crimson Clover N Adjusted
Fig. 3. Tons of total stover harvested for each case run in PC-LP, where the no cover
crop case is the base case.
40 60 80 100 120
Stover Price ($/Mg)
No Cover Crop Annual Ryegrass
Crimson Clover Crimson Clover N Adjusted
Fig. 4. Total farm proﬁt for each case run in PC-LP, where the no cover crop case is
the base case.
Comparison of beneﬁt-cost analysis results for annual ryegrass and crimson clover
cover crop. Results include cost estimates, private and societal beneﬁts and net
beneﬁts without stover removal, and net beneﬁt with stover removal for two prices of
Cost ($/ha) 88.41 107.46
Private beneﬁt ($/ha) 108.45 192.07
Society beneﬁt ($/ha) 114.63 198.27
Private beneﬁt ($/ha); N credit = $0 108.45 132.54
Private agronomic net beneﬁt ($/ha) 20.04 84.61
Probability of net beneﬁt < 0 0.239 0
Societal agronomic net beneﬁt ($/ha) 26.22 90.81
Probability of net beneﬁt < 0 0.177 0
Net beneﬁt at stover price = $66.14/metric ton 35.81 27.31
Probability of net beneﬁt < 0 0 0
Net beneﬁt at stover price = $88.18/metric ton 108.34 99.85
Probability of net beneﬁt < 0 0 0
Note: The beneﬁt and cost values are means of the triangular probability
74 M.R. Pratt et al. / Agricultural Systems 130 (2014) 67–76
The results from the two cases, which involved cover crops and
stover removal, tell us several important things: (1) from the
agronomic beneﬁt analysis, in most cases cover crop alone offer
potential net beneﬁts to farmers, (2) the net beneﬁt of cover crop
with stover removal is sensitive to the value of stover (farm-gate
price), (3) cover crops with stover removal appear to have the abil-
ity to substantially increase farm proﬁt over cover crops alone, and
(4) adding a cover crop to stover removal can, in many cases, pay
the cost of the cover crop while allaying fears of increased erosion
and SOM loss from corn stover removal. These cases are fairly gen-
eralized and contain a certain amount of risk.
Overall, we can draw several key conclusions: (1) cover crop
costs and beneﬁts vary by the selected cover crop, (2) the use of
a cover crop allows stover removal to sustainably increase by
about 4.0 metric tons/ha, and (3) the increase in stover removal,
along with increases in stover price, changes farm acreage alloca-
tions, increases the total amount of stover available, and increases
farm proﬁt. However, based on farmer interviews, and the results
for cover crop beneﬁts when the value of added N is eliminated
(Table 6), the beneﬁts of cover crops perceived by farmers may
be lower than those estimated in this analysis.
Monsanto Corporation provided funding for this research. Addi-
tionally, several Monsanto personnel were consulted during the
study. Several farmers from Indiana were also consulted for infor-
mation on cover crop usage and corn stover harvest.
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Farms participating 24 21 19 24
% BC + stover acres 34.67% 32.46% 25.67% 33.66%
% CC + stover acres 21.04% 21.60% 20.29% 23.99%
Tons of stover harvested 50,352 111,152 95,887 117,736
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