0

United States 

Department 

of Agriculture 

Office of the 

Chief Economist 

Office of Energy 

Policy and 

New Uses 

Agricultural 

Economic 

Report 

Number 847 

November 2012 

Biomass Supply From Corn Residues:   

Estimates and Critical Review of Procedures  

Paul W. Gallagher

Department of Economics

Iowa State University

Harry Baumes

Director, Office of Energy Policy and New Uses

Office of the Chief Economist, USDA   

   
   

1

Table of Contents

Introduction .......................................................................................................................................2

Overview of Estimation and Calculation Procedures..................................................................2

Harvest Index......................................................................................................................4

Sustainability................................................................................................................... .6

Stover Feed Demand .........................................................................................................9

Stover Supply for Industry............................................................................................. 11

Farm Cost.........................................................................................................................................13

Farm Cost Estimates........................................................................................................13

Handling Costs..................................................................................................................15

Handling Cost Estimates.................................................................................................15

Delivered Plant Cost .......................................................................................................16

U.S. Stover Supply Schedule........................................................................................................19

Conclusions...................................................................................................................................19

References ......................................................................................................................................21

Appendices

A:  Stover Harvest and Soil Carbon Maintenance  .................................................................. 23

B:  County Estimates of Stover Availability and Cost............................................................. 27

C:  Estimates of Stover Harvest Season Length  ........................................................................27

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provider and employer.   
   

2

Introduction 

Some early estimates suggested that accessible and sustainable corn residue supplies are adequate for a 

new biomass processing industry (Gallagher and Johnson; Gallagher, et al 2003a; Gallagher, et al 2003b). 

Revision is justified now because the agronomic and economic environment has changed. There is also 

interest in the location of low cost supplies, because construction of biomass processing facilities is 

underway. A critical review for suitable cost estimation assumptions and sustainability concepts should 

also be incorporated in the revised estimates, given subsequent discussion. 

 The corn stover cost and supply estimates presented here fit today’s yield and input situation. The 

revised estimates confirm that corn stover supplies are still adequate for new processing activity; several 

offsetting changes in economic environment and technology combine for a total supply estimate that is 

slightly larger and cost estimates that are highly competitive in today’s energy markets. The location and 

extent of lowest cost and sustainable supplies are also given. 

This paper is organized as follows. First, we summarize the supply model. Second, we present new data 

and spatial variation in critical parameters that impinge on estimates of usable supply: current estimates of 

the harvest index, local feed demand, and a conservation allowance are discussed in turn. We compare 

our assumptions with the literature, justifying, incorporating, and discarding as appropriate. 

Overview of Estimation and Calculation Procedures 

Stover output and cost are calculated for every corn-producing county in the United States, using a series 

of identities and proportional relationships that are defined by agronomy and current technology. Four 

groups of relations calculate production, feed demand, cost, and U.S. supply. The stover production 

group includes a relation that defines stover output as a proportion of the corn crop, and specifies the 

amount of stover that must remain on the field for soil conservation. The feed demand block calculates 

the excess demand defined by the forage demands of local livestock less hay and pasture supply. 

Potential industry supply to stover is production less feed demand. Costs include farm harvest (rake, bale 

fertilize) expenditure and handling costs such as shipping and storage. Lastly, county data is ordered by 

cost, and aggregated for a U.S.-level supply curve. The relationships are summarized in table 1. 

This report includes revised data and critical evaluation of important assumptions. Revisions include 

current data for agronomic and economic relationships. Specifically, current estimates for county corn 

yields, harvest index estimates, cattle populations, and energy input prices are employed. Local estimates 

are calculated for a conservation allowance of residue remaining after harvest and a sustainable fraction 

of corn area that is suitable for residue harvest while maintaining soil quality. 

 
   

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Table 1. County and U.S. Corn Stover Supply Model 

 Variable Definitions 

(1) Stover Production: 

Ysg = [ (1‐hi)/hi ] Yc θ 

Ysn = Ysg – Ca 

As= Ac * sf * fr 

Qsp = Ysn * As 

(2)Stover Feed Demand: 

Nfd = (Fdb+Fdm) – (Qpp + Qpwp + Qhp ) 

Fdb = 27.6 Cob+13.2Hb+30 Bu+5.8 Ho+8.8 Ca

Fdm=25.2Com + 9.6Hm

Qpp = dg * Fdb

Qwp=135 * Fdb

 (3)Cost: 

Cst =β f + αf / Ysn 

Cstd = Cst + βT +  βs

(4)Supply:

(a)Stover Supply to Industry: 

Nssi = Qsp – Nfd 

      (b)Supply Function:                                                                                                                                                   

‐Develop short list of counties (839 of 2805) from the condition that Cstd < $100/ton, and the

requirement that 20 surrounding counties or less would be required for a 25 MGY ethanol plant. ‐

Sort on Cstd and cumulate Nssi.

   

Yc: yield , corn  ;  hi: harvest index;                                                                                      

Parameters    θ : adjustment for no till yield discount( and unit conversions)  

Ysg: Yield stover,gross;  Ysn: Yield stover, net(in ton/acre);                             

Ca: Conservation allowance;                                                                                  

As: Area, sustainable(fraction of corn area); Ac: Area, corn (in mil acre);     

sf: sustainable fraction( of corn area);  fr: fraction in rotation                         

Qsp: Quantity of Stover produced (in mil ton);                                           

Nfd: Net feed demand(for stover); Fdb:Feed demand , beef; Fdm: Feed

demand, milk; Qpp: Quantity pasture ; Qpwp: Quantity, winter wheat pasture;

Qhp: Quantity of hay produced  

Cob: cows, beef;   Hb: heifer, beef;   Bu: bull; Ca:calves;   Com: cows,milk;   Hm:

heifer, milk;  

Parameters:  dg: degree‐days(growing season);             135: length of wheat

pasture season                          

Nssi: Net Supply to Industry

Cst: Cost of stover, farm (in $/ton)

Paramaters: α acre constant costs (cut,rake bale);

 β ton constant costs(field haul)

Cstd:  Cost of Stover, delivered to plant

Parameters:  βT: transport costs to plant,   βs:Storage Costs
   

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Harvest Index

The harvest index is defined at corn grain’s proportion of the total above ground dry biomass in the corn 

plant: 

hi= dry weight grain / ( dry weight grain + dry weight residue) on an acre 

Previously, the harvest index was taken as a constant, hi=0.45, based on measurements from an Iowa 

experiment. Thus, the fraction of stover in the biomass, 1-hi=0.55. That is, stover provided 55 percent 

of the total biomass in corn. 

Subsequently, corn yields have typically increased and the harvest index has declined. Our revised 

estimates are based on a recent report from a Pioneer/Monsanto project with very recent yield levels and 

varieties (Edgerton). hi is generally lower, possibly because corn yield increases of the last decade were 

accomplished with higher plant populations. Specifically, we assume that there is a cubic relation 

between corn yield and harvest index: 

hi = Υ0 + Υ1 Yc1 + Υ2 Yc2+ Υ3 Yc3 , where Υi are parameters for estimation.

An estimate based on the 2008 cross section of plots yields from the Monsanto Experiment is given in 

figure 1. In supply estimation at the county level, county corn yield data are used in the cubic harvest 

index equation for a harvest index estimate for each county. The distribution of harvest index estimates 

suggests that the harvest index is in the range .50 to .55 in counties with highest average corn yield. But in 

counties with corn yields towards the lower end of the short list, the harvest index is still about 0.45. 

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

100 125 150 175 200 225 250

Figure 1.   The harvest index (hi)‐corn yield (Yc) relationship

harvest index (0/1)

corn yield (bu/ac)
   

5

        Figure 2.

   
   

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Sustainability

Four adjustments that reduce usable production below gross stover yield on corn area impose 

sustainability criteria on potentially harvestable supplies-there are two yield adjustments and two area 

adjustments. A fractional adjustment factor (θ) is applied because producers will likely need reduced 

tillage methods if residues are removed. The Conservation Allowance (CA) is subtracted from yield so 

that 30 percent of the physical area of harvested land is covered by residue. The sustainable fraction (sf) 

reduces the corn area (by a percentage) by approximating the amount of flat and erosion resistant land. 

The fraction in rotation (fr) indicates additional corn land that should be rotated through a cover crop for 

soil quality maintenance. Together these adjustments ensure sustainable production, from an erosion and 

soil quality viewpoint. 

We assume that producers who harvest stover will follow no-till corn planting. First, tillage aggravates 

erosion when residues are harvested. Second, tillage causes soil carbon release into the atmosphere. A 

yield adjustment multiplier of 0.905 accounts for the moderate reduction in corn yields when no till is 

used (Al-Kaisi, et al). The no-till discount is applied to observed county corn yields because most 

producers do not use reduced tillage. 

The Conservation Allowance is the amount of residue left on the field for erosion control. From the 

initial study, 1,430 lbs of chopped residue provides 30 percent cover on “typical” Class I or Class II land 

keeps water erosion within tolerance in the cornbelt. Also, 3,200 lbs of chopped residue provides more 

than 30 percent cover so that Class I or Class II land has water + wind erosion within tolerance on Great 

Plains irrigated corn (Gallagher, et al., 2003a, p.345). 

Sustainable fraction (sf) gives the proportion of relatively flat land with little or no erosion potential. The 

data for sf was revised for this study. Previously, land from the SCS soil survey in class I and class IIe 

(erosion limitation) were in the harvestable land area. Now class IIW land that requires drainage is also 

included in the harvestable land base (Staff, National Soil Survey ). 

Some judgment is required to calculate the overall land base (the denominator for the sustainable 

fraction), because the soil survey does not identify the present use of a parcel of land. In the Great Plain 

states (Kansas, Nebraska, North Dakota, Oklahoma, South Dakota, and Texas), the total land base for a 

county is approximated by the Agricultural Census estimate of cropland. Pasture and rangeland are 

excluded on the notion that most of this land is actually range land that would have yields too low for 

cultivation, due to limitations on rainfall or land quality. In cornbelt states, cropland and pasture are both 

included in the total land base available for crops. Finally, there are a few exceptions that probably apply 

in heavily wooded counties on the southeast or northern boundary of cornbelt states. To wit, when there 

is no cropland, the base is the entire land area in the county. Also, when there is cropland, but no pasture, 

cropland defines the base total. 

One method of offsetting the slow and steady decline in soil organic carbon that has been associated with 

corn production the past is an occasional rotation into a cover crop such as alfalfa and low-till corn 

production. We review alternative approaches to soil quality maintenance in the appendix. We use the 

rotation method of soil quality maintenance, because it is likely the least cost means of stover production 

that maintains soil quality.
   

7

For now, we assume that fr = 1.0, for two reasons. First, modern drought tolerant corn varieties have more 

extensive roots than traditional varieties, so soil carbon may no longer decline with corn production. 

Second, in the event that rotation is required, there is not yet evidence that more crop rotation should be 

imposed-current corn acreage may already reflect adequate rotation practices. Existing rotation practices 

are not known, because data on the land use transition matrix is not available. 
   

8

Figure 3.
   

9

Stover Feed Demand

Revised estimates of local feed demand use the animal forage estimates from the earlier report and the 

most recent data for cattle population and hay supplies. The only revision of procedure is that winter 

wheat pasture is included as a forage source. Lastly, some county data by livestock type is no longer 

available, so estimates were based on allocation procedures. 

The geographic distribution of stover feed demand in the short list of 839 counties (figure 4) is colored to 

show how many counties of diverted feed stover would be required for a 25 MGY ethanol plant. In a few 

isolated areas with many feedlots or dairy producers, less than one county is shown in red, 1-5 counties is 

shown in dark brown, and 5-10 counties is in grey. Otherwise, most of the low cost counties are shown in 

blue, indicating negligible potential competition between feed stover and a potential processing plant. 

Stover feed demand is excluded because the feed demand price tends to be higher than the harvest cost, so 

Stover used for feed would not be available to a processing plant under most circumstances. Stover is a 

close substitute for hay, so stover’s feed values are calculated with discounts to the hay price, according 

to a formula given in Gallagher and Johnson, p.102). Calculations based on current market conditions are 

given at http://www2.econ.iastate.edu/faculty/gallagher. At current conditions, the feed price of stover is 

$60.8/ton. 
   

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Figure 4.

   
   

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Stover Supply for Industry 

Figure 5 shows the county distribution of net stover supply for industry (nssi), which is production less 

feed demand. Most of the counties with the highest density of stover supply (red), requiring less than one 

county for a 25 MGY plant are concentrated in North central Iowa, southwestern Minnesota, central 

Illinois and south central Nebraska. However, the remaining sections of these same states also have high 

density (brown) supplies, requiring 1-5 counties for a 25 mgy plant. These high-density supplies are also 

found in parts of adjoining states: South Dakota, Kansas, Indiana, and Ohio. The dairy area in Wisconsin 

and counties near feed lots appear to have the lowest supplies. 
   

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Figure 5.

   
   

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Farm Cost

 For perspective, let’s begin with the question “what distinguishes these estimates from some subsequent 

stover cost estimates?” Our approach has three distinguishing characteristics. 

The first distinguishing feature of the farm cost estimates concerns the conservation assumptions used 

here and in some other studies. First, our conservation assumptions are very restrictive on the production 

techniques (no till), the land that is used for harvest (erosion potential), and the use of crop rotations. But 

after the land passes through these three filters, relatively high stover harvest yields are permitted, 

because Water erosion potential is low on flat land, even with small values like Ca=1430 lb/acre. 

Together, these conservation assumptions give very low cost stover on the selected segment of the land 

base. High harvest rates get cost per ton much lower, because costs are mostly constant on a per acre 

basis. 

Other cost estimates have used different conservation assumptions. Some suggest higher conservation 

allowances that may some erosion prone land (Perlak and Turhollow, p. 1,397). Others restrict stover 

harvest yields on the conviction that soil carbon should be controlled by restricting stover harvest 

(Wilhelm, et al). 1 In contrast, we have advocated soil carbon maintenance through crop rotation. There is 

a need for further economic research that finds production methods that best balance costs against 

conservation constraints and broader environmental requirement. However, our proposed production 

techniques are adequate for conservation and low on cost (Appendix A). 

1

A few studies have assumed that 25 percent of stover yield is left on the field after harvest due to machinery limitations

(Graham, et al, p.2; Petrolia).  Based on interviews with operators and casual observation of actual harvesting practices in

central Iowa, we have not included this constraint on harvest.  Some dirt may be captured with harvest rates less than 25

percent, but the dirt would dissolve in water of ethanol processing.  Furthermore, new harvesting technology yields a clean

harvest even when all stover is removed ( Atchinson and Hettenhaus).     

The second distinguishing feature concerns the structure of the stover input market. 

At the farm level, our cost estimates reflect the cost of a farm owner operator-harvest costs reflect the 

variable and ownership costs of harvesting equipment. Owner-operators are likely the low cost providers 

of stover. Some other estimates refer to landowner costs, possibly for a retired farmer or absentee ownerharvest costs reflect the market rates for renting custom hire services for the harvesting operations. 

Landowner costs are higher. First, custom hire service data apply to relatively small jobs for the livestock 

feed industry, and so include equipment moving costs that do not apply to biomass jobs. Second, the 

profit margins for custom hire services are included. Another study included a $10/ton profit margin for 

the farmer to encourage farmer participation. (Sheehan, et al, p. 129). In general, our cost estimate is 

lower, because it excludes profit margins and irrelevant costs. 

   
   

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A third distinguishing feature is that hired labor costs for the stover harvesting activities is included. The 

underlying notion is that the owner’s labor may constrain timely harvest, and simultaneous harvest of 

corn and stover during a short harvest season may increase extra-firm labor demand during the harvest 

season. 

One study did assert that there is only a 20-day stover harvesting season, casting doubt on the technical 

feasibility of stover harvest (Petrolia). Apparently, this statement is based on the time that a corn 

harvesting crew in Redwood County Minnesota has between the end of the most active corn harvesting 

period, November 8, and the date when the probability of a week without snow falls below 40 percent, 

November 26 (see appendix C). Another important area where standard corn harvest crews would be 

impeded by early snowfall is Seneca County, Ohio. Otherwise, comparable snowy weather tends to come 

a month later in the dominant production area of Illinois. And enough clear weather is likely in 

production areas of Iowa and Nebraska, so harvest could likely proceed throughout the winter with the 

existing organization of corn harvest crews. Lastly, harvest crews will likely reorganize with more labor 

to accomplish simultaneous harvest of corn if it is necessary. Then the stover harvest season would 

extend to include the entire corn harvest period - above 43 days in Minnesota and Ohio, and up to 75 days 

in central Illinois (appendix C). 

Storage and handling costs are included in a fashion that is consistent with CIF plant pricing in an 

established competitive market. That is, handling, shipping and storage costs are calculated and added to 

farm costs as if the farmer transfers ownership after he performs these functions. We do use the price 

semi-truck services and the rental of a storage building, then adjust capacity to apply to stover; farmers 

routinely purchase these services when marketing commodities. Producer cost could be further lowered if 

they integrate backwards to perform these functions, too. 

It is useful to separate cost estimation from profit margins to the extent possible. First, the supply curve 

for a competitive relies on the marginal cost, ie, the break-even price for the marginal producer. Second, 

FOB firm pricing may well be monopsonistic (Gallagher, Wisner and Brubacker, p. 123). Here, 

monopsonistic pricing could evolve with processors or their middlemen providing transport, harvest, and 

handling services to the farmer. Calculations of farm cost and handling services will indicate when 

competition or a cooperative might be viable. 

Farm Cost Estimates  

Revised cost estimates reflect today’s technology and input cost environment. Updated information is 

used for the variables hi, Ysn, and the fertilizer and fuel prices that define stover harvest costs. 

The corn stover cost estimates of table 2 refer to 2011 input prices in Story County, Iowa, an important 

production region. Fixed and variable costs for the main harvest activities, chop, rake, and field 

transportation are included. Also, fertilizer replacement for the soil nutrient loss in stover harvest is 

valued at 2011 fertilizer prices. Hired labor costs for the stover harvesting activities is now included, 

because peak harvesting period labor is more likely to constrain owner’s labor when a stover enterprise is 

added.2

 In comparison to the earlier study using this method, the overall Farm cost estimate, $32.71/ton, 

has doubled due to increasing energy and fertilizer prices. But corn stover does remain the lowest cost 

biomass source in the Midwest.
   

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Also, the parameters for the farm cost function are defined in table 2. 

The ton-constant costs , βf = 18.37, are the sum of field hauling and fertilizer replacement costs. The 

acre-constant costs, αf = 36.72 , includes rake chop, bale and labor costs. Overall farm costs are tonconstant costs + acre-constant costs divided by net stover yield. Net Stover yield is Ysn=2.72 ton/acre for 

Story County, Iowa. 

Lastly, let us demonstrate the important role of harvested stover yield in Stover costs (per ton). Consider 

the case where Ysn=0.95 (Hildalgo County, Texas). Then, using the farm cost function, overall Stover 

costs are Cst=$58.46/ton. Comparing Story County and Douglas County, costs per ton increase by 60 

percent because many of the same operations are conducted on the same land because the yield is reduced 

by 65 percent. 

Handling Costs  

Handling costs include expenditures for loading the bales that are stored in the corner of the farmer’s field 

onto the truck, expenditures for the truck’s trip to the processing plant, and stover storage, say near the 

plant. 

Handling costs can vary widely according to location, length of run, and assumptions about marketing 

technology. First, the northwest section of the stover harvest belt likely requires storage during a snowy 

winter, but elsewhere, stover recovery could match processing needs and avoid storage. Second, analyses 

of the “first plant” typically have very high transport costs because producer participation is low and 

trucks have to travel great distances to secure input supplies. In contrast, established markets will likely 

follow the S-shaped adoption curve with very high farmer participation rates. Third, “first plant” analyses 

have a tendency to use capital expenditure analyses for new equipment. These analyses tend to 

overestimate costs; sometimes a useful asset life from the tax tables is used while equipment really lasts 

longer; the tax advantages of equipment leasing are not recognized; and sometimes these estimates are 

over capitalized by imposing investments on every farm that may ultimately match the local processing 

capacity. 

Handling Cost Estimates

Our handling costs assumptions are designed for a resource assessment; high farmer participation is high; 

and rental rates for marketing services are used. Farmers usually purchase product transport, storage and 

labor services, so we combine market rental rates and input requirements for handling cost estimates. 

The estimate for field-loading the truck is $0.78/ton. The underlying machinery cost estimate is $33.46/hr 

for variable (fuel and repair) cost of farm machinery (ISU extension bulletin PM-710, estimating farm 

machinery costs). The physical input factors are 26 bales / truck and 0.5 hour/truck. 

The estimate for truck transport to plant is $2.33/ton. This estimate is based on a formula for the average 

delivered transport cost for a processing plant (Gallagher and Johnson, p. 117). The formula gives 

average transport cost (ATC) is a function of the market transport charge (t) and the radius of the market 

area ( r ) :                                                                              

     ATC  = 2/3 * t *   r                                                                                      

In turn the market area times the density of corn equals the plant capacity (Q). So the radius of the market 
   

16

area is defined by the condition: 

      ݎ ൌ ඥܳ/ሺߨ	݀	ܻ݊ሻ,                                                                                   

where d is the density of stover (in acre/mi2

) and Yn is the net stover yield (in tons/acre). The market is 

defined by a 25 MGY biomass ethanol plant. But the size of the market area varies across counties 

because the stover yield and corn density vary. We assume that 100 percent of the corn area that can have 

sustainable stover harvest is actually used. A typical value is d=235 acre stover / sq. mi. In effect, we 

estimate transport costs in a well-developed industry. 3 

3

Others have estimated startup cost for the first plant locating in an area with a new technology, with participation rates as low as 

20% (Perlak and Turhollow, p.1401). Then d=0.20*235 acre / mi2

.

The market rate for local trucking services, t=$0.14/ton/mile, is converted from a rate per truck quote, 

using the loading factors one truck/26 bale and 1.2 bales / ton. The truck rate of $3.00/mile/truck comes 

from a survey (ISU extension custom rate survey, 2011). 

The input market area required to supply a 25 MGY biomass ethanol plant defines an estimate of r=25 

miles. 

The estimate for stover storage cost is $3.44/ton. This estimate is calculated from a market rate of 

machine storage estimate of $0.30/ft2

/yr (ISU extension Farm Building Rental Survey, 2010). The input 

requirement is a biomass storage density of 11.25 ft2

/ton. Also, a biomass Storage loss of 2 percent / year 

is assumed. 

Handling costs vary across counties with local input supply areas because r varies with the density of 

biomass supply in the local input market. For the example above: 

Total handling costs = field haul + truck to plant + storage =0.78 + 2.33+ 3.44 =$6.55/ton 

But counties with low density corn supplies would have higher average handling costs. The formula 

giving the relation between corn density and transport cost is given in Gallagher and Johnson. 

Delivered Plant Cost

Delivered Plant cost is the sum of farm cost, transport and storage. The Figure 4 shows the spatial 

distribution of delivered plant cost for the short list of counties. Throughout the interior cornbelt, 

delivered plant cost converts to a biomass cost in ethanol production of $.50/gallon or less. The higher 

cost counties, in the $.50/gal to $.75/gal range, are all on the outer boundary. Higher delivered costs 

result from a combination of factors, such of higher conservation allowances where wind erosion 

becomes a factor, and lower density of corn plantings. 
   

17

Table 2. Corn Stover Harvest Cost Details

story county corn yield 161.4 (bu/acre)

harvest index 0.515281

gross stover yield 6861.2 (dw lb/ac) 3.43 dwt/acre

conservation 1430.0 (dw lb/ac) 0.72 (dwt/acre)

net stover yield 5431.2 (dw lb/ac) 2.72 (dwt/acre)

Direct Harvest Costs

operation fixed cost             variable cost total

reported per ton s reported per ton s cost

chop 4.0 ($/acre) 1.472979 ($/ton) 3.5 ($/acre) 1.289 ($/ton s)

bale 7.7 ($/acre) 2.835484 ($/ton) 4.5 ($/acre) 1.657

haul 1.40000 ($/ton) 1.700

5.708463 ($/ton) 4.646 10.35

Fertilizer Replacement Costs

    fertilizer application rates            fertilizer price fertilizer

gross dilute strength pure expense

(t f/ dwt s) $/ton f) ($/ton f) ($/ton s)

p2o5 0.001604 509 0.45 1131.111 1.814302

k2o 0.012227 511 0.6 851.6667 10.41333

NH3 0.008093 398 1 398 3.221014 15.45

Hired Labor Costs

labor requirement 1.33 hr/acre wage 12.8 $/hr 6.27

Total Farm Costs For Owner-Operator 32.07

Cst = 18.55 + 36.72 / Ysn costs constant per

acre 36.72

ton 18.55

Ysn 2.72

Farm owner-operator cost w/ hired labor $/tn 32.07
   

18

Figure 6.

   
   

19

U.S. Stover Supply Schedule  

The corn stover supply curve for the United States is shown in figure 6.  The supply schedule is

calculated by sorting the short list of counties by delivered cost and cumulating for the stover supply, or

production less feed demand, at each price.  Also, feed use of stover is added to industry supply when

the price exceeds the livestock feed value.  

Inspection reveals that the lowest entry price is about $37.5/ton.  Further, 100 mill. Mt would be

available at a slightly higher supply price of $40.4/ton.  Beyond that, the supply schedule becomes

steeper to attract supplies from low density supply areas and supplies in feed use; 117 million tons

would be available at a supply price of $59.7/ton.  Also, the supply schedule becomes vertical at the

point, $62.9/ton and 133 million tons, the point where forage use is converted to industry supply.

Conclusions

Previous estimates suggested that accessible and sustainable corn residue supplies are adequate for a  

new biomass processing industry.  Revision is justified now because the agronomic and economic

environment has changed.  Also, there is an interest in the location of low cost biomass supplies.

The revised estimates of corn stover cost and supply fit today’s yield and input situation.  The revised

estimates confirm that corn stover supplies could be a low cost feedstock for a low cost and extensive

bioenergy industry.  Supplies of 100 million metric tons of stover would be available to an established

industry at a delivered plant price between $37.5/ton and $40.5/ton.   At moderately higher prices, the

feedstock for a 10.5 MGY ethanol industry would be available.  Several offsetting changes in economic

environment and technology have occurred since we calculated our first estimates, but the new supply

estimate is still slightly larger.  Stover cost remains highly competitive in today’s energy market.   

Ample supplies of the lowest cost and sustainable supplies are likely found in the middle of the corn‐ 

belt: Illinois, Indiana, Eastern Ohio, and Iowa.  Also, sections of other states have some very low‐cost

supplies: eastern Nebraska, southern Minnesota, southern Wisconsin, and southern Michigan.  Lastly,

considerable stover supplies would be available at a somewhat higher but still very competitive price in

some new cornbelt areas: eastern North Dakota, central Wisconsin/Michigan, and perhaps western New

York. Supply estimates for specific counties are given in appendix B.  

   
   

20

  

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Supply Price (Delivered PLant Cost, in $/ton

Quantity,  in million tons

Figure 6. U.S. Corn Stover Supply
   

21

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Selecting No-Till, Iowa State University Extension Service, PM 1901d, July 2009. 

D.A. Angers, “Changes in Soil Aggregation and Organic Sarbon under Corn and Alfalfa”, Vol. 56 No.4, 

July-August 1992:1,244-1,248. 

Atchison, J.E. and J.R. Hettenhaus, Innovative Methods for Corn Stover Collecting, Handling, Storing 

and Transporting, National Renewable Energy Laboratory, NREL/SR-510-33893, April 2004. 

John M. Baker, Tyson E Oshsner, Rodney T. Venterea, Timothy J. Griffis, “Tillage and Soil Carbon 

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soil carbon ans associated properties on Pennsylvania dairy farms” Journal of Soil and Water 

Conservation, May/June 2008-Vol.63,No.3: 136-142. 

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Workshop, Aug 30, 2010, Ankeney, Iowa. 

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Estimates for Biomass from Crop Residues in the United States,” Environmental and Resource 

Economics 24 (April 2003):335-358. 

Gallagher, P., R. Wisner, H. Brubaker, “Price Relationships in Processors’ Input market Areas: Testing 

Theories for Corn Prices near Ethanol Plants,” Canadian Journal of Agricultural Economics

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Residues: Cost and Supply Estimates. U.S. Department of Agriculture, Office of the Chief Economist, 

Office of Energy Policy and New Uses, Agricultural Economic Report No. 819 (2003). 

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Stover Supplies,” Agronomy Journal 99 (2007):1-19. 

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Systems with Stover Removal,” Crop Science 52 (2012):327-338. 
   

23

Appendix A:  Stover Harvest and Soil Carbon Maintenance

Soil Organic Carbon is an important quality indicator that defines the long term productive potential of a 

plot of land. There are several strategies available for maintaining SOC. There are also several relevant 

externalities associated with bio-fuel production, and each SOC maintenance strategy makes a distinct 

contribution to the set of externalities. Eventually, SOC strategies should be evaluated as a constraint in a 

market context that includes the entire set of externalities. 

Methods of Soil Carbon Control

There are three approaches to maintaining SOC while planting corn and harvesting stover. Now we 

review these techniques, and the advantages and disadvantages. 

One approach it to restrict or eliminate corn stover harvest on the notion that some of the stover left on the 

ground will decompose and turn to soil carbon. Wilhelm, et al, provide the reference study for this 

approach. To illustrate their results, use the story county, Ia corn yield of Yc=161.4 bu/acre (from the cost 

table) and notice that the gross stover yield is Ysg= 3.43 ton/acre. Using Wilhelm, et al’s table 1b with 

the conservation tillage assumption, the allowable stover harvest is 0.73 ton/acre. Using results from this 

reference study, the stover harvest rates are likely so low that harvesting is not worth it. 

But the below-ground biomass that grows with the corn plant may be higher than Wilhelm, et al assumed. 

Baker, et al argued that the root/shoot ratio (R/S) is higher than many thought. Further, recent 

measurements by seed companies with their newest varieties gave a root shoot ratio of R/S= 0.55 

(Edgerton, et al). 

To illustrate the effect of a higher R/S on allowable stover harvest, consider an estimated relationship 

(Clay, p.787 ) between the percentage of corn stover that can be harvested for SOC maintenance( H ) and 

R/S: 

H = 34.6 + 39.4 R/S.  So H=56.3 when R/S=0.55.  

Continue with The Story County, Iowa example, Ysg=3.43 t/ acre. The stover harvest that would maintain 

SOC is Ysn = 0.55*3.43 t/ acre= 1.9 ton/acre. At harvest rates near 2 t/acre, it is more worthwhile to run 

harvesting equipment across the field. 

A second technique for soil carbon maintenance is adding manure. In corn silage production, all of the 

stover is harvested with the corn while it is still green. Since corn silage is only produced on dairy farms, 

there is always an ample manure supply. A recent crop experiment included corn silage and measured 

soil organic carbon (SOC) (Dell, et al). The results showed that SOC accumulated in corn silage 

experiments. Also, SOC accumulated faster when conservation tillage was used. 

   
   

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A third technique is to harvest corn stover at a high rate, mindful of soil erosion constraints. 

Periodically, the land is rotated into a perennial such as alfalfa in order to rebuild the carbon if necessary.* 

This rotation approach is used in developing the estimates of this report. The rotation approach differs 

from the previous two techniques in that soil carbon cycles over a crop rotation period were used, instead 

of satisfying an annual carbon budget. 

Agronomic experiments do support the rotation approach to SOC maintenance (Angers). Specifically, in 

a 5-year experiment, corn for silage (i.e., all residue is harvested) was grown on one set of plots 

continuously-there was no soil maintenance in the fall, and 6”deep tiller treatment in the spring. The 

second set of plots contained alfalfa that was planted in the first year and maintained through the 

remainder of the experiment. 

Regressions for SOC observations from the corn and alfalfa plots are: 

Corn:  C = 25.6 ‐0.24 X and Alfalfa: C = 29.5 – 4.62 exp[ ‐0.023*exp(1.71x} ],                             

where X=0,1,2,3,4,5 corresponding to the beginning of the experiment and each season.  

As the figure below shows, the SOC decline is slow, steady and moderate for corn. For alfalfa, not much 

SOC change occurs at first, but accumulations become substantial as the experiment progresses. 

   
   

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Using the regressions above, we calculated the estimated soil carbon when alfalfa is planted first for 4 

years and then followed by corn. After 19 years with corn, the SOC had returned to the initial level from 

before alfalfa was planted. The implication is that a farm in continuous corn with 100% stover harvest 

could maintain SOC could be maintained if 82.6 percent of the available land is in corn with stover 

harvest, and the other 16 percent of the land would be in alfalfa. 

Others confirm the crop rotation approach to SOC maintenance. For instance, carbon rebuilding with 

alfalfa would take a few years because the relatively long carbon assimilation season for alfalfa extends 

into the early spring pre-planting period and late fall post-harvest period (Baker, et al). Also, the IPCC 

seems to share this view on crop rotation and SOC; they estimate that the equilibrium SOC level for hay 

is 55 percent higher than it is for cropped land (Gallagher, et al, provide a summary of IPCC estimates 

and references). 

We did not adjust the sustainable area base in my corn stover supply calculations (fr=1.0 instead of 0.82). 

We need to know the “land transition matrix” from corn to hay and back to corn, in order to see if 

adjustments to the sustainable area base are needed. Producers could already be rotating crops in a 

fashion consistent with SOC maintenance. Future research and data collection could resolve this 

uncertainty. 

A fourth technique for managing SOC in conjunction with stover harvest is the joint production of corn, 

stover and a living mulch (e.g., blue grass) or cover crop (e.g., clover). From preliminary results, 

reductions in corn yield and stover yield do occur when living mulch or cover crop are used. However, 

there was a living mulch treatment (blue grass) that maintained corn yields (Wiggans, et al). 

External Benefits and Costs

The four methods of controlling soil carbon (restricted stover harvest, added manure, rotated crops, and 

jointly planted cover crop) differ in the external benefit that they produce for society as a whole. First, 

there are external benefits associated with the production of biofuels: reduce Midwestern unemployment , 

reduce oil market disruption and disengage from middle east politics, clean air in urban areas, reduce 

global warming emissions. The size of these external benefits are proportional to the level of stover (and 

biofuel) production. Hence, the external benefit of restricted harvest is less than the external benefit of 

rotated crops. 

Second, it is important that all carbon control methods are used in conjunction with low till methods of 

crop production because tillage releases soil carbon into the atmosphere, possibly aggravating global 

warming. All four of the SOC control methods can be combined with low-till agriculture. Perhaps 

policies should be revised to ensure that SOC control methods are combined with low till agriculture, if 

stover harvest is practiced. 

Third, the added manure method may not perform with the other three methods in regards to global 

warming emissions, in the final analysis. But it is possible that emissions to air are reduced when 

manure is incorporated in soil. And careful use on cropland could reduce phosphate leaching to surface 

water. Lastly, the external benefits of ethanol production are usefully arranged in a hierarchy: CO2 is 

important, but the employment and trade disruption benefits are first order benefits. It makes sense to use
   

26

a SOC maintenance technique like manure addition that may not include strong performance on global 

warming.  

The Need for Further Economic Evaluation

A more systematic look at opportunity costs is needed. Generally speaking, this means that an initial 

reference situation, or baseline, is fully defined. Then the improvement or deterioration associated with 

adding one of these SOC management strategies can be measured. 

For instance, the baseline for U.S. agriculture likely includes a devaluing dollar and expanding livestock 

exports to china. The reference situation includes growing manure disposal problems. If we do not use 

the added manure strategy, the manure could possibly end up in the water and the air instead of the soil. 

Also, a qualitative comparison of the restricted harvest and rotation is helpful. First, the annual carbon 

budget constraint of the restricted harvest approach is unnecessary. Restricted harvest seems like a game 

of ‘mother may I’ where you can only win by taking small steps forward. In contrast, the rotation strategy 

looks like several small steps backwards and one large step forward to get to the same end. Both 

approaches are pretty good wrt CO2. Second, the stover harvest costs are much higher with the restricted 

harvest. Using restricted stover harvest, the estimate is usually about TWICE the cost using rotation. 

Why? Most of the harvest costs are roughly constant on a per acre basis. Under rotation the harvest 

equipment travels across the same number of acres and harvests twice the amount of stover. 

Lastly, it may be time to move the corn production, stover harvest, and soil maintenance to the next level 

of economic analysis for a systematic look at costs and benefits of the alternatives. Using the discounted 

Present Value Mathematical Programming setup of this problem, four different production techniques 

could be specified: restricted harvest, rotation, manure application, and joint cover crop. Techniques 

would have (i) a stream of corn outputs and stover outputs, (ii) may have a maintenance crop over the 

production cycle, (iii) may have a lower or higher corn yield than another technique, (iv )a set of 

coefficients indicating the effect on one of the external benefits. The solution to this problem could 

suggest that several techniques are useful, or there could be one dominant technique. The jury is still out 

on this one. 

Until then our approach, which limits harvest to land with low erosion potential but allows high stover 

harvest rates, is a good candidate for the low cost method of harvesting stover that controls soil erosion 

and stabilizes carbon. 

   
   

27

Appendix B:  County Estimates of Stover Availability and Cost

See:  http://www2.econ.iastate.edu/faculty/gallagher  

Appendix C:  Estimates of Stover Harvest Season Length

   
28

Appendix Table C1: The Length of the Stover and Corn Harvest Season in Main U.S. Production Areas with Simultaneou

HarvestLocation Beginning of most active Date when the probability of a week Length o

(Co/ Station) Corn harvest period1 without snow Falls below 40%2 harvest 

Minnesota Oct 8 Nov 26 

(Redwood/Lamberton)Iowa Oct 5        ‐‐‐‐  (Story/Ames)Nebraska Oct 4        ‐‐‐‐‐  

(Adams/Hastings)

Illinois Oct 1 Dec 8 

(McClean/Bloomington)Ohio (Seneca/Tiffin) Oct 11 Nov 27 

1See Staff/NASS2Scalculated as P0.4t = (1‐pt )7 , where pt = the probability that there is rainfall > 0.1 inches on day t. The snowfall probabil

Staff/NOAA. Also see figure C
29

Appendix Table C2: The Length of the Stover and Corn Harvest Season in Main U.S. Production Areas with Sequential C

HarvestLocation End of most active Date when the probability of a week Length o

(Co/ Station) Corn harvest period1 without snow Falls below 40%2 harvest 

Minnesota Nov 8 Nov 26 

(Redwood/Lamberton)Iowa Nov 9        ‐‐‐‐‐  

(Story/Ames)

Nebraska Nov 10        ‐‐‐‐‐‐  

(Adams/Hastings)

Illinois Nov 5 Dec 8 (McClean/Bloomington)Ohio (Seneca/Tiffin) Nov 20 Nov 27 

1See Staff/NASS2Scalculated as P0.4t = (1‐pt )7 , where pt = the probability that there is rainfall > 0.1 inches on day t. The snowfall probabil

Staff/NOAA. Also see figure C
30

0.000.100.200.300.400.500.600.700.800.901.00

30‐Sep 7‐Oct 14‐Oct 21‐Oct 28‐Oct 4‐Nov 11‐Nov 18‐Nov 25‐Nov 2‐Dec 9‐Dec 16‐Dec 23‐Dec 30‐Dec 6‐J

mn (redwood)ia(story)ne(adams)il(McClean)oh (seneca)

Figure C. The probability of a week without snowfall at major 

state(county):

1 data shown are 5‐day centered moving averages, Pt = (1/12) pt‐2 +(1/6) pt‐2 +pt +(1/6) pt‐+1+(1/12) pt+2

of the calculated probability for a particular day( pt‐+i )