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Economic viability of lime-treated corn stover in finishing beef cattle diets
The Professional Animal Scientist 33:73–84 https://doi.org/10.15232/pas.2016-01512 ©2017 American Registry of Professional Animal Scientists. All rights reserved.
Economic viability of lime-treated corn stover in finishing beef cattle diets Jeffrey J. Opgrand,1 Nicole J. Widmar, and Wallace E. Tyner Department of Agricultural Economics, Purdue University, 403 West State Street, West Lafayette, IN 47907
ABSTRACT Corn stover treated with a lime slurry has the potential to reduce feed costs for finishing feedlot cattle. Feed rations including lime-treated corn stover were profitable compared with the control rations for all scenarios investigated. The average annual increase in returns per feedlot space on a beef cattle feedlot operation when lime-treated corn stover was included in the rations of finishing cattle was $40.82 per feedlot space, with a range of increased returns of $7 to $90 per feedlot space depending on feed price assumptions. The range of corn prices tested was $118.10 to $196.84/Mg, and the range of corn stover prices tested was $38.58 to $60.63/dry Mg. Environmental impacts studied were soil erosion, changes in soil organic carbon, and nitrate leaching. Data from the Landscape Environmental Assessment Framework were used to quantify the environmental impacts resulting from the ration substitutions. Incorporation of environmental values with the economic results affects social values and can lead to negative social outcomes in some cases. Detrimental environmental impacts increase as the level of corn stover harvest increases, and the incorporation of environmental values to the on-farm economic values of the feed substitutions can affect the social outcome of the feed substitution. Key words: beef feed ration economics, economic and environmental assessment, lime-treated corn stover, livestock production
INTRODUCTION In January 2015 there were 13.1 million cattle and calves being fed for slaughter in United States feedlots (USDA, 2015). Feeding trials have been conducted using alternative corn products as feed replacements for beef cattle to investigate potential areas of improvement for feedlot margins. Shreck et al. (2012) studied the potential of treated corn cobs replacing a portion of dry-rolled corn but found a significant decrease in fat thickness. In the same study, Shreck et al. found that replacing a portion of corn grain with untreated corn stover resulted in decreased ADG, lower HCW, and diminished fat thickness. Nuñez et al. (2015) found that feeding dry distillers grains with solubles to cattle from growing through finishing resulted in adverse perCorresponding author: [email protected]
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formance compared with cattle fed no dry distillers grains with solubles, where the optimal strategy is to feed dry distillers grains with solubles during growing but not finishing stages. On the other hand, studies have shown that alkaline-treated corn stover can be substituted into the diet of beef cattle without sacrificing performance (Russell et al., 2011; Shreck et al., 2012; Johnson et al., 2013). Corn stover refers to the organic remnants (stalks, cobs, leaves) remaining on the field after corn grain harvest. Assuming the quantity of corn stover produced is equivalent to the amount of corn grain produced, as in Karlen et al. (2014), the United States produced 360 million megagrams of corn stover in 2015 (NASS, 2016). Harvesting corn stover can be environmentally detrimental, with effects ranging from reduction in soil organic carbon (SOC), an increase in soil erosion, and higher levels of nitrate leaching, among others. Up to 75% of corn stover can be harvested sustainably if managed properly with techniques including winter cover crop coverage (Pratt et al., 2014). Three primary objectives were addressed in this study. First, the study assessed the economic viability of limetreated corn stover as a replacement feedstock in the diet of finishing feedlot cattle. Second, the study quantified environmental outcomes under alternative corn stover harvest farm management practices. Finally, this study determined under what feed price and farm management conditions lime-treated corn stover is economically viable and environmentally sustainable.
MATERIALS AND METHODS Definitions Income Over Feed Cost. Income over feed cost (IOFC) is a simple calculation often used to assess and monitor dairy profitability. A modified version of IOFC, suitable for feedlot profitability analysis, is used in this study. Changes in IOFC are measured as $/feedlot space per year by subtracting changes in feed costs from changes in income when substituting lime-treated corn stover for base case feed ingredients. We did not measure IOFC in $/head because the feeding trials used in this study each fed lime-treated stover for different lengths of time. Thus $/feedlot space per year accounts for animals that are replaced in the feedlot within a year, and the timeframes of treated stover feeding are standardized. Corn Stover. Corn stover refers to all nongrain portions of a corn plant remaining after the harvest of corn
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grain. The proportion of corn stover to corn grain in a field is referred to as the corn stover harvest index, which is measured by dividing the dry weight of corn grain in a field by the total dry weight of the grain plus dry stover weight. This research assumes a corn stover harvest index of 0.50, following Sesmero (2011) and Ertl (2013). This study focuses on lime-treated corn stover, which refers to corn stover treated with calcium oxide (CaO) or calcium hydroxide (CaOH). Combs (2012) and Rust (2013) prescribe the method of treatment as grinding the corn stover coarsely and hydrating the stover to 50% moisture. Lime accounts for 5% of the DM in the feed. Soil Erosion. Wind and water erosion refer to the processes involving the detachment and transportation of soil from one location to another. Corn stover provides soil surface cover that serves as a natural defense against soil erosion. The Natural Resources Conservation Service identifies the maximum megagrams per hectare of soil erosion a landscape can tolerate each year without affecting future productivity, called the T-Factor. Midwestern soils typically have T-Factors between 2.24 and 11.21 Mg/ha per year. Decades of data collection document that increasing levels of corn stover harvest leads to increased soil erosion with no other change in management practice (Lindstrom, 1986; Pratt et al., 2014). Soil Organic Carbon. Soil organic carbon refers to carbon held by the soil, where the stock of soil carbon is a determinant of soil health and future productivity (Lal, 2014). Depending on farm management, weather, and other factors, the stock of SOC in a particular soil can increase or decrease in a given year. Johnson et al. (2014) found that the quantity of corn stover required to maintain SOC levels is 5.74 ± 2.40 Mg/ha per year. However, the authors caution that each site is subject to unique conditions and that there is no precise quantity of stover appropriate for all landscapes. The quantity of stover that can be harvested while maintaining SOC must be determined at the field level to avoid miscalculating sustainable stover removal. Nitrate Leaching. Nitrogen application in agriculture often results in the loss of nitrate (NO3) through a process called leaching (Ribaudo et al., 2011). Nitrogen lost to leaching often contaminates groundwater. When the concentration of nitrogen in a body of water reaches a certain level, the water becomes toxic for human consumption and hazardous for other animal species (Christianson et al., 2013). Corn stover contains nitrogen that is naturally recycled through its decomposition. When corn stover is harvested, this loss in naturally occurring nitrogen must be replaced by greater amounts of nitrogen fertilization.
Data Whereas past research has investigated alternative corn feeds such as corn cobs and different types of distillers grains, this study focuses on research involving limetreated corn stover. This study employs results from 3
independent feeding trials (detailed below) involving the substitution of lime-treated corn stover for a portion of corn grain and other feedstuffs in the diets of finishing feedlot cattle as part of TMR. The 3 feeding trials did not test exactly the same control ration containing corn grain or experimental ration(s) containing lime-treated corn stover. Two of the 3 feeding trials resulted in unchanged feed performance and carcass merit, whereas the third feeding trial resulted in statistically significant changes in both categories. Relevant specifications and results that could affect IOFC from each feeding trial are outlined here. The Landscape Environmental Assessment Framework (LEAF), which provides the environmental data for this study, is also described. Feeding Trial 1. The first feeding trial included in this study, referred to as “feeding trial 1,” comes from the University of Nebraska Beef Cattle Reports collection (Johnson et al., 2013). One purpose of this feeding trial was to measure the effect of substituting lime-treated corn stover for corn grain on the performance of calves and yearlings. The feeding trial was divided into 2 experiments, winter and summer, where the winter experiment lasted 183 d from November to May and the summer experiment lasted 140 d from May to October. The specifications and results of the winter and summer trials were almost identical, so we only consider the summer experiment. The summer experiment was conducted with 192 steers. A control group was fed a diet with 51% DM dry-rolled corn, 5% DM untreated corn stover, and 0% DM lime-treated corn stover. The experimental group was fed 36% DM dryrolled corn, 0% DM untreated corn stover, and 20% DM lime-treated corn stover. All other feed ingredients were fed at equal levels to the control and experimental groups, such as modified distillers grains with solubles (MDGS) at 40% DM. The experiment found no difference in feed performance or carcass indicators in steers fed the control and treated stover rations. There was no statistical difference in estimated USDA YG for steers fed the treated stover versus those fed the control ration. Feeding Trial 2. The second feeding trial also comes from the Nebraska Beef Cattle Reports collection (Shreck et al., 2012). This feeding trial can be distinguished from feeding trial 1 in that the initial steer BW is approximately 45 kg heavier, and treated corn stover partially substitutes for roughage, which is defined as equal parts corn cobs, wheat straw, and corn stover. The experiment included 336 short-yearling steers in a randomized block design. The control ration fed 46% DM dry-rolled corn, 0% DM lime-treated corn stover, and 10% DM roughage, and the experimental ration fed 36% DM dry-rolled corn, 20% DM lime-treated corn stover, and 0% DM roughage. Both rations fed 40% DM wet distillers grains with solubles. Steers fed treated stover had comparable performance and carcass characteristics with those fed the control ration. The experiment yielded no statistically significant
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changes in ADG, HCW, DMI, marbling, or calculated USDA YG. Feeding Trial 3. The third feeding trial was published in Iowa State University’s Animal Industry Report (Russell et al., 2011). This feeding trial had a similar objective to the prior 2 feeding trials in that it sought to evaluate the potential of lime-treated corn stover as a replacement feed in growing and finishing beef cattle. The research refers to the treated stover as “treated stover silage” because the stover was stored for 95 d after treatment. The experiment involved 210 Angus steers in a Latin square design. The control ration fed 70% DM corn grain, 20% DM MDGS, 0% DM lime-treated corn stover, and 5% DM untreated corn stover, and the experimental ration fed 35% DM corn grain, 40% DM MDGS, 20% DM lime-treated corn stover, and 0% DM untreated corn stover. Both diets included 5% DM supplement. Steers fed the experimental ration containing limetreated corn stover from late-growing through finishing had similar ADG, HCW, and calculated USDA YG to steers fed the control ration. However, there was a statistically significant difference in DMI and marbling score. Importantly, the decrease in DMI did not negatively affect ADG. In other words, the stover-fed animals gained the same amount of weight and achieved the same YG as the control group while consuming less feed per day but finished with a lower marbling score. Feed Prices. Feed prices used in this study come from various sources and were calibrated for a hypothetical feedlot operation in Washington County, Indiana, at −86.10 latitude and 38.64 longitude. Washington County was chosen as the site for the study because it has a significant beef cattle population and planted corn area. Sensitivity analysis is carried out by using 3 prices for corn grain (118.10, 157.47, and 196.84 $/Mg) and 3 farm-gate prices for corn stover ($38.58, $49.60, and $60.63 per dry megagram). As the price of corn grain changes as part of the sensitivity analysis, several other feed prices change, such as dry-rolled corn, MDGS, and wet distillers grains with solubles. Assuming a corn grain price of $157.47/Mg and a corn stover price of $49.60/dry Mg, Table 1 summarizes the delivered feed price assumptions for the different feed ingredients used in this study. The prices include all purchasing, transport, and handling costs associated with the feed, and all prices are reported in dollars per dry megagram, unless otherwise specified. LEAF. LEAF is an integrated modeling system that combines 4 environmental modules with user-provided farm management practices to compute environmental scenarios on a geospatial scale. The 4 modules in the model are the Revised Universal Soil Loss Equation, Wind Erosion Prediction System, the Soil Conditioning Index (SCI), and the Denitrification and Decomposition model. The Revised Universal Soil Loss Equation models water erosion, whereas the Wind Erosion Prediction System models wind erosion. The SCI component of LEAF pro-
vides a measure of soil health based on organic composition, and the Denitrification and Decomposition portion of LEAF is used to model carbon and nitrogen fluctuations in different agricultural scenarios. The farm management practices available in the model are crop rotation, tillage practice, corn stover harvest regimen, and cover crop regimen. To obtain site-specific environmental results, LEAF requires the specification of different categories of farm management practices associated with the site under investigation. The crop rotations used in this study involve combinations of continuous corn grain and corn grain–soybean rotations. LEAF provides 2 options for tillage regimen: reduced tillage and no-till. Reduced tillage is defined as 15 to 30% of the soil surface covered by residue at the time of planting, and no-till is defined as greater than 30% of the soil surface covered by residue at the time of planting (Muth, 2012). There is no option for conventional tillage, as it has become uncommon in corn cropping rotations. LEAF provides 4 options for corn stover harvest: no residue harvest, low residue harvest, medium residue harvest, and high residue harvest. No, low, medium, and high residue harvest refer to 0, 33, 50, and 75% stover removal level, respectively. There are several cover crop regimens available in LEAF, but for simplicity this study considers only 2 cover crop options: no cover crop and a winter rye cover crop. County-level yield assumptions in the LEAF model are derived from yields reported by the National Agricultural Statistics Service for 2008 to 2010. The average slope gradient for Washington County used in LEAF is 5.22% over a range of slope gradients of approximately 1 to 9%. Once a combination of management practices is selected, LEAF returns site-specific environmental outputs that are the product of a site’s particular soil, climate, and management scenarios. The environmental outputs we are concerned with here are soil erosion, changes in SOC, changes in nitrate leaching, and SCI. Soil erosion is reported in megagrams per hectare per year and is strictly positive.
Table 1. Feed ingredient prices Ingredient1 Corn grain Dry-rolled corn Lime-treated corn stover Untreated corn stover WDGS MDGS Corn cobs Wheat straw
$/dry Mg 238.08 244.66 104.74 82.70 218.80 233.24 74.96 108.35
WDGS = wet distillers grains with solubles; MDGS = modified distillers grains with solubles.
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Table 2. Environmental values Environmental impact Lower-bound soil erosion (/Mg) Upper-bound soil erosion (/Mg) Soil organic carbon (/kg) Nitrate leaching (/kg)
Value ($) Source 4.17 31.04 0.13 2.09
Change in SOC is reported in kilograms per hectare per year and can be positive or negative because a management practice can either build or deplete soil carbon. Nitrate leaching is reported in kilograms per hectare per year and is strictly positive because there is always some level of nitrate leaching, even in the absence of cropping. The Soil Conditioning Index is qualitative, so it is interpreted according to the positive or negative output sign. If the SCI output is positive, then the specified management practice on that particular site results in building OM. Conversely, if the output is negative, then the specified management practice on that site is decreasing OM. Muth and Bryden (2013) provide a more complete description of the LEAF model. Environmental Values. To assess the social cost of the feed substitutions, monetary values are assigned to environmental damages resulting from changes in farm management practices due to the feed substitutions. Estimated values from the literature allow us to approximate the value of environmental damages from soil erosion, SOC, or nitrate leaching. Because of the vast disparity in the literature regarding the value of soil erosion, we use 2 values in the analysis as lower- and upper-bound values of soil erosion (Table 2). The lower- and upper-bound erosion measures can be divided into private and social components. The private component refers to on-site damages due to soil erosion (i.e., lost future productivity). The social component refers to on-site damages as well as damages to society at large, which includes the cost of cleaning waterways, increased healthcare costs, and so on. The social value of soil erosion is listed in Table 2. The private value of the lowerbound soil erosion estimate is $1.11/Mg, and the private value of the upper-bound estimate is $11.21/Mg.
Economic Methodology The economic analysis is conducted using the IOFC calculation in different feeding scenarios. For the 3 feeding trials outlined above, IOFC is compared between the control ration that does not include lime-treated corn stover and the experimental ration to determine net returns when lime-treated corn stover is substituted into the diet. There are 3 economic drivers for the decision to make a ration change: (1) the costs associated with each feed ingredient; (2) any change in income due to the ration
Hansen and Ribaudo (2008) USDA (2011) Lal (2014) Christiansen et al. (2013)
change; and (3) any change in daily feed consumption due to the ration change. The cost of each ingredient includes a payment for the feed itself, transportation and storage costs, and a treatment cost in the case of corn stover. The change in income reflects the possibility of a change of QG in animals being fed treated corn stover, or a change in DMI due to the ration change. Figure 1 outlines the methodology governing the economics of a change in a feedlot ration. To simplify the process outlined in Figure 1, we employ partial budgeting techniques and only calculate the difference in IOFC between the new and original feed rations. In other words, only factors that change due to the feed substitution are considered. Sensitivity analysis is conducted using 3 prices for corn grain, 3 prices for corn stover, and 2 feedlot herd sizes. The original analysis was done with a small and a large herd, but the results were roughly equivalent, so we only report here the results for 2,500 feedlot animals. We assume operator income is determined by the carcass weight/formula method, where changes in QG at the time of slaughter affect the selling price of the animal.
Environmental Methodology The purpose of the environmental analysis is to compare levels of soil erosion, changes in nitrate leaching, and changes in SOC under different farm management practices for the feedlot. The farm management practices are crop rotations involving corn grain without stover removal compared with rotations involving corn grain with stover removal. Figure 2 outlines the methodology governing the environmental impacts of changing farm management from no stover harvest to some level of stover harvest, though the same methodology applies to changing tillage regimen or cover crop practice. Data for the environmental analysis comes from LEAF. LEAF has 4 rotation options that suit this research: (1) continuous corn grain without stover removal; (2) continuous corn grain with stover removal; (3) corn grain with soybean rotation without stover removal; and (4) corn grain with soybean rotation with stover removal. Harvesting corn stover raises concerns regarding soil erosion, nitrate leaching, and SOC changes. We examine 2 management techniques that, if adopted, can lessen the impact of stover harvest on these environmental quality indicators. The 2
Feeding treated stover
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Figure 1. Economic methodology connections. IOFC = income over feed cost.
management techniques are no tillage and cover cropping. To evaluate the impact of the damage-mitigating management practices under scenarios with and without corn stover harvest, we implement these management practices using LEAF in various farm management scenarios.
To link the environmental results obtained from LEAF and the economic analysis, we need to focus on the environmental impacts occurring inside of the feed supply shed around the hypothetical feedlot operation. We achieve this by uploading our geospatially defined soil ero-
Figure 2. Environmental methodology connections. SOC = soil organic carbon.
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sion, SOC, and nitrate leaching results from LEAF into ArcMap (ESRI, Redlands, CA) and then partitioning the estimated feed sheds of various radii around the study location, which allows us to summarize the environmental outcomes around the hypothetical feedlot. Once environmental damages are measured under various farm management practices, monetary values are assigned to the damages using the values outlined in the data section. These monetary values can be parsed into private and social values as described above. The present value of future soil productivity, whose changes are measured by the private values in this analysis, should be given the same consideration as any other cost input in the production decision. External damages, on the other hand, do not factor in to the private production decision. Nevertheless, it is vitally important to capture the value of external damages to provide input into possible policy choices. Soil erosion has both private and external costs, where private costs measure changes to future soil productivity and external costs measure erosion’s effect on several resources and amenities including increased sedimentation in water reservoirs, diminished value from water recreation, loss of water potability, decreased fishery productivity, and increased dust particulate matter in the air, among many others. Yet it is difficult to separate gains or losses in SOC from soil erosion. A portion of the SOC lost in a given year is due to soil erosion. On average, the top 5 cm of topsoil contain approximately 5.5 to 9.1 kg of SOC per megagram of topsoil. For a corn stover removal level with an average loss of 90 Mg/ha of eroded soil, anywhere from 218 to 363 kg of SOC is lost due to erosion. To avoid the issue of double counting the value of changes in soil productivity due to this on-site environmental damage, we report the value of lost (or gained) SOC separately from the soil erosion values and acknowledge that combining the values would almost certainly over-report the true value to the producer. The value of nitrate leaching is assumed to be strictly a social cost to society as the producer does not internalize the damages caused by excess nitrogen entering an aquifer, water table, and so on. The system of Equations 1 to 4 contains the mathematical procedure for calculating the costs or benefits of the feed substitution in terms of soil erosion. Equation 1 calculates the change in harvested area with corn stover removal required by the feeding trial under study, and Equation 2 calculates the erosion increase incurred by switching from a crop rotation (either continuous corn or corn–soybeans) to a crop rotation with corn stover removal. Equation 3 denotes the selection of an economic value for the environmental damage. The results of Equations 1 through 3 are multiplied together in Equation 4, which calculates the total economic value of the environmental damage.
Stover Harvest Requirement (ha), A = Stover
Substitution (Mg)/Stover Yield (Mg/ha)
Change in Erosion Level (Mg/ha per yr), E = Corn Grain without Stover Removal Erosion Measure (Mg/ha per yr) − Corn Grain with Stover Removal Erosion
Measure (Mg/ha per yr)
Economic Value Assignment ($/Mg), V = Erosion
Value ($/Mg)
Total Erosion Impact Valuation ($/yr) =
(3)
A × E × V (4)
The result of Equation 4 is the social monetary value, in dollars per year, of soil erosion due to changes in farm management practices when lime-treated corn stover substitutes for corn grain and other feedstuffs. The system of Equations 1 to 4 is used for private and social erosion, nitrate leaching, and also SOC valuations.
RESULTS AND DISCUSSION Feeding Trial Economic Results For each feeding trial, 18 feeding scenarios were considered. These scenarios were designed with 3 corn prices ($118.10, $157.47, and $196.84 per Mg) and 3 farm-gate corn stover prices ($38.58, $49.60, and $60.63 per dry Mg). Each feeding trial included supplementary feed substitutions apart from lime-treated corn stover and corn grain, and feeding trial 3 found a change in carcass quality and DMI. Substitution of lime-treated corn stover for corn grain and other feeds in feedlot rations always decreased the operator’s feed costs, even if the price of corn stover is high ($60.63/dry Mg) and the price of corn is low ($118.10/ Mg). Sensitivity analysis to the price of corn grain and corn stover had a more substantial numerical effect on the change in IOFC, but price sensitivity never inverted the change in IOFC from positive to negative or vice ver-
Table 3. Average income over feed cost change ($/feedlot space per year) Corn price ($) 118.10 157.47 196.84
(1)
(2)
Stover price ($)
Trial 1
Trial 2
Trial 3
38.58 49.60 60.63 38.58 49.60 60.63 38.58 49.60 60.63
20.14 14.01 7.88 46.06 39.93 33.80 71.98 65.84 59.71
22.88 15.03 7.18 42.79 34.94 27.08 62.69 54.84 46.99
22.77 15.58 8.39 51.87 47.18 42.50 89.07 84.38 79.69
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Table 4. Corn–soybeans, reduced till, no cover crop environmental impacts1 Environmental impact
Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
17.54 44.11 268.09 7 24
19.16 45.12 187.63 2 19
22.52 46.28 99.32 0 12
24.97 47.48 25.01 0 7
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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sa. The change in IOFC ($/feedlot space per year) was positive for all feed price scenarios in all 3 feeding trials (Table 3). Because of the statistically significant decrease in marbling score, feeding trial 3 was the only potentially contrasting trial. However, the statistically significant decrease in DMI tended to offset the lost income due to a decreased marbling score. The results of the economic analysis of the beef feeding trials suggests that under the conditions examined in these studies, feeding lime-treated corn stover would be profitable. In the feed price scenario that is least favorable for the substitution ($118.10/Mg corn grain and $60.63/ dry Mg corn stover), the average return per feedlot space across the 3 feeding trials is $7.82. In a 2,500-animal herd, this is a yearly increase in IOFC of $19,950 for the feedlot operation. In the baseline feed price scenario of $157.47/ Mg corn grain and $49.60/dry Mg corn stover, the average return per feedlot space across the 3 feeding trials is $40.68, which amounts to $101,708 for the feedlot.
Environmental Impacts Twenty-four different farm management practices were analyzed. The farm management practices in the analysis include different combinations of crop rotations involving corn grain crop rotations, reduced or no tillage, a winter rye cover crop or no cover crop, and no corn stover harvest, low residue harvest (33%), medium residue harvest (50%), or high residue harvest (75%). The environmental
impacts analyzed are soil erosion, changes in SOC, changes in nitrate leaching, and qualitative SCI measurements. For the sake of simplicity, we report average results for a 13-km radius around the Washington County location because there were no drastic differences between different supply radii. The different management practices can be evaluated in terms of sustainability by the proportion of harvested area with erosion less than the T-Factor, whether the management practice builds or depletes SOC, the proportion of harvested area with a positive SCI measurement, and average levels of nitrate leaching. Tables 4 to 9 report the results of the 24 different farm management practices. As expected, soil erosion increased as the level of stover harvest increased. Although changes in the quantity of SOC often decreased rapidly as the level of stover harvest increased, levels of nitrate leaching did not change substantially as the level of stover harvest changed. Regardless of cropping pattern, high residue harvest could not meet the environmental sustainability criteria under any management scenario, including under a no-till regimen and winter rye cover crop, which had considerable environmental conservation potential. Medium residue harvest was only sustainable in a continuous corn, no-till, and winter rye cover crop management (Figure 3). Without a cover crop, medium residue harvest was considerably more environmentally degrading than when managed with a winter rye cover crop (Figure 4). On the other hand, low
Table 5. Corn–soybeans, no-till, no cover crop environmental impacts1 Environmental impact Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
3.48 48.12 205.97 100 60
4.78 47.40 144.53 60 58
6.75 45.73 21.90 24 24
10.45 45.67 19.65 24 24
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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Table 6. Corn–soybeans, no-till, winter rye cover crop environmental impacts1 Environmental impact
Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
0.96 34.50 294.63 100 100
3.02 33.96 248.01 100 100
4.31 32.61 126.98 56 52
5.71 32.59 124.66 52 30
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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Table 7. Continuous corn, reduced till, no cover crop environmental impacts1 Environmental impact
Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
8.94 76.13 431.25 24 24
12.21 85.70 267.89 24 24
21.23 89.54 −13.29 0 15
25.66 98.93 −72.02 0 7
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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Table 8. Continuous corn, no-till, no cover crop environmental impacts1 Environmental impact Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
0.92 87.43 309.56 100 100
2.51 93.26 182.76 100 100
6.90 92.20 −62.04 52 15
17.23 96.12 −66.91 15 15
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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Table 9. Continuous corn, no-till, winter rye cover crop environmental impacts1 Environmental impact Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
0.10 59.92 460.99 100 100
0.40 65.38 361.17 100 100
1.90 67.87 303.64 100 100
3.81 69.96 215.65 100 60
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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Figure 3. Southwest Washington County, medium residue harvest, winter rye cover crop annual soil erosion (Mg/ha per year).
residue harvest could be achieved sustainably without a cover crop in a continuous corn and no-till management.
Private Versus Social Costs of Feed Substitution This section integrates the environmental results into the economic analysis of the feed substitution by applying values to environmental changes when corn grain harvest-
ed area is transitioned into corn grain with stover harvest. The purpose is to estimate overall social costs and benefits of the feed substitution under various farm management scenarios. The prices of corn grain and corn stover assumed in this section are $157.47/Mg and $49.60/dry Mg. Because we assume management practices will transition from no stover harvest to some level of stover harvest, environmental valuations are always negative in terms of soil erosion and changes in SOC. Changes in levels of ni-
Figure 4. Southwest Washington County, medium residue harvest, no cover crop annual soil erosion (Mg/ha per year).
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Figure 5. Feeding trial 1 private and social costs, high erosion value.
trate leaching can be positive or negative when stover harvest is introduced, but in any case nitrate leaching changes are not substantial. In the presence of a cover crop, there is a relatively smaller tradeoff in environmental outcomes when corn stover harvest is introduced because environmental damages are less pronounced in the presence of a cover crop. The difference is not always trivial, as transitioning from no corn stover harvest to high residue harvest under corn–soybeans in the presence of a cover crop reduces the proportion of area with erosion less than the T-Factor from 100 to 30%.
Recall that each feeding trial produced unambiguously positive changes in IOFC. This analysis examines the tradeoffs between the positive IOFC realized by producers and the environmental damages realized by corn growers and society at large. The environmental value calculations combine the value of soil erosion and nitrate leaching changes. The majority of private economic and social environmental combinations result in net positive social impacts. One example that demonstrates this majority of outcomes is when the corn stover supplied to feeding trial 1 comes from continuous corn rotations, low residue
Figure 6. Feeding trial 2 private and social costs, high erosion value.
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Figure 7. Feeding trial 2 private and social costs, low erosion value.
harvest, and no cover crop (Figure 5). Even when using the upper-bound erosion value and incorporating damages from increased nitrate leaching, the net social impact of the feed substitution is approximately $41,000 per year. A counterexample to the usual outcome of positive total social impacts comes from feeding trial 2. The environmental value of soil erosion under a corn–soybeans, no-till, no cover crop, and high residue harvest is a loss of $152,936, which easily outweighs the private economic benefits of $87,350 due to the feed substitution (Figure 6). However, this outcome is derived using the upper-bound erosion value. Examining the same scenario using the lower-bound erosion value (Figure 7), the net social impact of the feed substitution is positive. In fact, when the lowerbound erosion value is used, there are no scenarios where
the net social impact is negative. This result highlights the importance of using an appropriate, site-specific value of soil erosion to properly measure net social impacts due to changes in farm management practices. Valuations of changes in SOC were not included as either a private or social environmental damage to avoid overestimating on-site losses of future productivity. However, changes in SOC were substantial when farm management shifted from no corn stover harvest to increasing levels of stover harvest. Table 10 provides the values of changes in SOC in the context of the different feeding trials when farm management switches from no corn stover harvest to higher levels of stover harvest. As expected, all values are negative to reflect the lost soil carbon due to stover harvest.
Table 10. Soil organic carbon valuations ($/yr) Crop rotation Continuous corn grain
Stover harvest Cover crop Low Medium High
Corn grain–soybeans
Low Medium High
No cover Rye cover No cover Rye cover No cover Rye cover No cover Rye cover No cover Rye cover No cover Rye cover
Trial 1
Trial 2
Trial 3
(8,910) (4,561) (13,545) (4,276) (11,826) (5,644) (4,340) (4,655) (8,715) (4,538) (5,881) (6,242)
(11,407) (5,839) (17,240) (5,623) (15,141) (7,226) (5,556) (5,959) (11,105) (5,585) (7,529) (7,991)
(7,502) (3,840) (11,405) (3,601) (9,957) (4,752) (3,654) (3,919) (7,338) (3,821) (4,952) (5,255)
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IMPLICATIONS The results of feeding experiments involving lime-treated corn stover suggest its potential as a cost-saving replacement feed for corn grain. In this study, a one-to-one substitution of lime-treated corn stover for corn grain and other feed ingredients in beef feedlot rations decreased the feedlot’s feed costs in all scenarios, even when the price of corn grain was as low as $118.10/Mg. This suggests corn stover harvest could provide an additional revenue stream for corn farmers facing low corn grain prices. Transitioning from no corn stover harvest to any level of corn stover harvest always induces greater levels of soil erosion and decreases the amount of SOC returned to the soil. When the value of environmental outcomes is integrated into the private changes in IOFC, the overall social cost or benefit of the substitution can change from positive to negative depending on which value of soil erosion is used, while also indicating potential divergence in private versus social outcomes. This suggests that policy interventions may be necessary to achieve a socially desired outcome regarding the harvest of corn stover.
Karlen, D. L., S. J. Birrell, J. M. F. Johnson, S. L. Osborne, T. E. Schumacher, G. Varvel, R. B. Ferguson, J. M. Novak, J. R. Fredrick, J. M. Baker, J. A. Lamb, P. R. Adler, G. W. Roth, and E. D. Nafziger. 2014. Multilocation corn stover harvest effects on crop yields and nutrient removal. BioEnergy Res. 7:528–539. Lal, R. 2014. Societal value of soil carbon. J. Soil Water Conserv. 69:186–192. Lindstrom, M. J. 1986. Effects of residue harvesting on water runoff, soil erosion and nutrient loss. Agric. Ecosyst. Environ. 16:103–112. Muth, D. 2012. Nomenclature. MS Excel. AgSolver Inc., Ames, IA. Muth, D. J., Jr., and K. M. Bryden. 2013. An integrated model for assessment of sustainable agricultural residue limits for bioenergy systems. Environ. Model. Softw. 39:50–69. NASS (National Agricultural Statistics Service). 2016. CropScape— Cropland Data Layer. USDA, Washington, DC. Nuñez, A. J. C., T. L. Felix, S. C. Loerch, and J. P. Schoonmaker. 2015. Effect of dried distillers grains with solubles or corn in growing cattle diets, followed by a corn-based finishing diet, on performance of feedlot cattle. Anim. Feed Sci. Technol. 207:267–273. Pratt, M. R., W. E. Tyner, D. J. Muth Jr., and E. J. Kladivko. 2014. Synergies between cover crops and corn stover removal. Agric. Syst. 130:67–76.
LITERATURE CITED
Ribaudo, M., J. Delgado, L. Hansen, M. Livingston, R. Mosheim, and J. Williamson. 2011. Nitrogen in Agricultural Systems: Implications for Conservation Policy. Econ. Res. Serv., Washington, DC.
Christianson, L. E., J. Tyndall, and M. J. Helmers. 2013. Financial comparison of seven nitrate reduction strategies for Midwestern agricultural drainage. Water Resour. Econ. 2–3:30–56.
Russell, J., D. Loy, J. Anderson, and M. Cecava. 2011. Potential of chemically treated corn stover and modified distiller grains as a partial replacement for corn grain in feedlot diets. Iowa State University Animal Industry Report, leaflet R2586. Iowa State Univ., Ames.
Combs, D. 2012. Lime-Treated Corn Stover: How to Do It and Its Feed Value. Accessed Jun. 2015. http://www.uwex.edu/ces/dairynutrition/ documents/Combs-CaO-cornstover.pdf.
Rust, S. 2013. Feeding Value of Untreated and Treated Corn Stover in High Grain Diets. Michigan State Univ. Ext., Dept. Anim. Sci., East Lansing.
Ertl, D. 2013. Sustainable Corn Stover Harvest. Iowa Corn Promotion Board, Johnston.
Sesmero, J. 2011. Sustainability of Corn Stover Harvest for Biomass. Selected Paper for 2011 American Agricultural Economics Association Meeting. Purdue Univ., West Lafayette.
Hansen, L., and M. Ribaudo. 2008. Economic Measures of Soil Conservation Benefits. Econ. Res. Serv. Accessed Jun. 2015. http:// ageconsearch.umn.edu/bitstream/184312/2/tb1922.pdf. Johnson, J. M. F., D. B. Burken, W. A. Griffin, B. L. Nuttelman, G. E. Erickson, T. J. Klopfenstein, and M. J. Rincker. 2013. Effect of feeding greater amounts of calcium oxide treated corn stover and Micro-Aid® on performance and nutrient mass balance. Pages 70–73 in 2013 Nebraska Beef Cattle Reports. Univ. Nebraska, Lincoln. Johnson, J. M. F., J. M. Novak, G. E. Varvel, D. E. Stott, S. L. Osborne, D. L. Karlen, J. A. Lamb, J. Baker, and P. R. Adler. 2014. Crop residue mass needed to maintain soil organic carbon levels: Can it be determined? BioEnergy Res. 7:481–490.
Shreck, A. L., B. L. Nuttelman, W. A. Griffin, G. E. Erickson, T. J. Klopfenstein, and M. J. Cecava. 2012. Chemical treatment of lowquality forages to replace corn in finishing cattle diets. Pages 106–107 in 2012 Nebraska Beef Cattle Reports. Univ. Nebraska, Lincoln. USDA. 2011. Soil Organic Matter: What is Topsoil Worth? Nat. Res. Conserv. Serv. Accessed Jun. 2015. http://soils.usda.gov/sqi/ concepts/soil_organic_matter/som_value.html. USDA. 2015. Cattle. Natl. Agric. Stat. Serv. Accessed Apr. 15, 2015. https://www.nass.usda.gov/Statistics_by_ Subject/?sector=ANIMALS%20&%20PRODUCTS.
Economic viability of lime-treated corn stover in finishing beef cattle diets Jeffrey J. Opgrand,1 Nicole J. Widmar, and Wallace E. Tyner Department of Agricultural Economics, Purdue University, 403 West State Street, West Lafayette, IN 47907
ABSTRACT Corn stover treated with a lime slurry has the potential to reduce feed costs for finishing feedlot cattle. Feed rations including lime-treated corn stover were profitable compared with the control rations for all scenarios investigated. The average annual increase in returns per feedlot space on a beef cattle feedlot operation when lime-treated corn stover was included in the rations of finishing cattle was $40.82 per feedlot space, with a range of increased returns of $7 to $90 per feedlot space depending on feed price assumptions. The range of corn prices tested was $118.10 to $196.84/Mg, and the range of corn stover prices tested was $38.58 to $60.63/dry Mg. Environmental impacts studied were soil erosion, changes in soil organic carbon, and nitrate leaching. Data from the Landscape Environmental Assessment Framework were used to quantify the environmental impacts resulting from the ration substitutions. Incorporation of environmental values with the economic results affects social values and can lead to negative social outcomes in some cases. Detrimental environmental impacts increase as the level of corn stover harvest increases, and the incorporation of environmental values to the on-farm economic values of the feed substitutions can affect the social outcome of the feed substitution. Key words: beef feed ration economics, economic and environmental assessment, lime-treated corn stover, livestock production
INTRODUCTION In January 2015 there were 13.1 million cattle and calves being fed for slaughter in United States feedlots (USDA, 2015). Feeding trials have been conducted using alternative corn products as feed replacements for beef cattle to investigate potential areas of improvement for feedlot margins. Shreck et al. (2012) studied the potential of treated corn cobs replacing a portion of dry-rolled corn but found a significant decrease in fat thickness. In the same study, Shreck et al. found that replacing a portion of corn grain with untreated corn stover resulted in decreased ADG, lower HCW, and diminished fat thickness. Nuñez et al. (2015) found that feeding dry distillers grains with solubles to cattle from growing through finishing resulted in adverse perCorresponding author: [email protected]
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formance compared with cattle fed no dry distillers grains with solubles, where the optimal strategy is to feed dry distillers grains with solubles during growing but not finishing stages. On the other hand, studies have shown that alkaline-treated corn stover can be substituted into the diet of beef cattle without sacrificing performance (Russell et al., 2011; Shreck et al., 2012; Johnson et al., 2013). Corn stover refers to the organic remnants (stalks, cobs, leaves) remaining on the field after corn grain harvest. Assuming the quantity of corn stover produced is equivalent to the amount of corn grain produced, as in Karlen et al. (2014), the United States produced 360 million megagrams of corn stover in 2015 (NASS, 2016). Harvesting corn stover can be environmentally detrimental, with effects ranging from reduction in soil organic carbon (SOC), an increase in soil erosion, and higher levels of nitrate leaching, among others. Up to 75% of corn stover can be harvested sustainably if managed properly with techniques including winter cover crop coverage (Pratt et al., 2014). Three primary objectives were addressed in this study. First, the study assessed the economic viability of limetreated corn stover as a replacement feedstock in the diet of finishing feedlot cattle. Second, the study quantified environmental outcomes under alternative corn stover harvest farm management practices. Finally, this study determined under what feed price and farm management conditions lime-treated corn stover is economically viable and environmentally sustainable.
MATERIALS AND METHODS Definitions Income Over Feed Cost. Income over feed cost (IOFC) is a simple calculation often used to assess and monitor dairy profitability. A modified version of IOFC, suitable for feedlot profitability analysis, is used in this study. Changes in IOFC are measured as $/feedlot space per year by subtracting changes in feed costs from changes in income when substituting lime-treated corn stover for base case feed ingredients. We did not measure IOFC in $/head because the feeding trials used in this study each fed lime-treated stover for different lengths of time. Thus $/feedlot space per year accounts for animals that are replaced in the feedlot within a year, and the timeframes of treated stover feeding are standardized. Corn Stover. Corn stover refers to all nongrain portions of a corn plant remaining after the harvest of corn
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grain. The proportion of corn stover to corn grain in a field is referred to as the corn stover harvest index, which is measured by dividing the dry weight of corn grain in a field by the total dry weight of the grain plus dry stover weight. This research assumes a corn stover harvest index of 0.50, following Sesmero (2011) and Ertl (2013). This study focuses on lime-treated corn stover, which refers to corn stover treated with calcium oxide (CaO) or calcium hydroxide (CaOH). Combs (2012) and Rust (2013) prescribe the method of treatment as grinding the corn stover coarsely and hydrating the stover to 50% moisture. Lime accounts for 5% of the DM in the feed. Soil Erosion. Wind and water erosion refer to the processes involving the detachment and transportation of soil from one location to another. Corn stover provides soil surface cover that serves as a natural defense against soil erosion. The Natural Resources Conservation Service identifies the maximum megagrams per hectare of soil erosion a landscape can tolerate each year without affecting future productivity, called the T-Factor. Midwestern soils typically have T-Factors between 2.24 and 11.21 Mg/ha per year. Decades of data collection document that increasing levels of corn stover harvest leads to increased soil erosion with no other change in management practice (Lindstrom, 1986; Pratt et al., 2014). Soil Organic Carbon. Soil organic carbon refers to carbon held by the soil, where the stock of soil carbon is a determinant of soil health and future productivity (Lal, 2014). Depending on farm management, weather, and other factors, the stock of SOC in a particular soil can increase or decrease in a given year. Johnson et al. (2014) found that the quantity of corn stover required to maintain SOC levels is 5.74 ± 2.40 Mg/ha per year. However, the authors caution that each site is subject to unique conditions and that there is no precise quantity of stover appropriate for all landscapes. The quantity of stover that can be harvested while maintaining SOC must be determined at the field level to avoid miscalculating sustainable stover removal. Nitrate Leaching. Nitrogen application in agriculture often results in the loss of nitrate (NO3) through a process called leaching (Ribaudo et al., 2011). Nitrogen lost to leaching often contaminates groundwater. When the concentration of nitrogen in a body of water reaches a certain level, the water becomes toxic for human consumption and hazardous for other animal species (Christianson et al., 2013). Corn stover contains nitrogen that is naturally recycled through its decomposition. When corn stover is harvested, this loss in naturally occurring nitrogen must be replaced by greater amounts of nitrogen fertilization.
Data Whereas past research has investigated alternative corn feeds such as corn cobs and different types of distillers grains, this study focuses on research involving limetreated corn stover. This study employs results from 3
independent feeding trials (detailed below) involving the substitution of lime-treated corn stover for a portion of corn grain and other feedstuffs in the diets of finishing feedlot cattle as part of TMR. The 3 feeding trials did not test exactly the same control ration containing corn grain or experimental ration(s) containing lime-treated corn stover. Two of the 3 feeding trials resulted in unchanged feed performance and carcass merit, whereas the third feeding trial resulted in statistically significant changes in both categories. Relevant specifications and results that could affect IOFC from each feeding trial are outlined here. The Landscape Environmental Assessment Framework (LEAF), which provides the environmental data for this study, is also described. Feeding Trial 1. The first feeding trial included in this study, referred to as “feeding trial 1,” comes from the University of Nebraska Beef Cattle Reports collection (Johnson et al., 2013). One purpose of this feeding trial was to measure the effect of substituting lime-treated corn stover for corn grain on the performance of calves and yearlings. The feeding trial was divided into 2 experiments, winter and summer, where the winter experiment lasted 183 d from November to May and the summer experiment lasted 140 d from May to October. The specifications and results of the winter and summer trials were almost identical, so we only consider the summer experiment. The summer experiment was conducted with 192 steers. A control group was fed a diet with 51% DM dry-rolled corn, 5% DM untreated corn stover, and 0% DM lime-treated corn stover. The experimental group was fed 36% DM dryrolled corn, 0% DM untreated corn stover, and 20% DM lime-treated corn stover. All other feed ingredients were fed at equal levels to the control and experimental groups, such as modified distillers grains with solubles (MDGS) at 40% DM. The experiment found no difference in feed performance or carcass indicators in steers fed the control and treated stover rations. There was no statistical difference in estimated USDA YG for steers fed the treated stover versus those fed the control ration. Feeding Trial 2. The second feeding trial also comes from the Nebraska Beef Cattle Reports collection (Shreck et al., 2012). This feeding trial can be distinguished from feeding trial 1 in that the initial steer BW is approximately 45 kg heavier, and treated corn stover partially substitutes for roughage, which is defined as equal parts corn cobs, wheat straw, and corn stover. The experiment included 336 short-yearling steers in a randomized block design. The control ration fed 46% DM dry-rolled corn, 0% DM lime-treated corn stover, and 10% DM roughage, and the experimental ration fed 36% DM dry-rolled corn, 20% DM lime-treated corn stover, and 0% DM roughage. Both rations fed 40% DM wet distillers grains with solubles. Steers fed treated stover had comparable performance and carcass characteristics with those fed the control ration. The experiment yielded no statistically significant
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changes in ADG, HCW, DMI, marbling, or calculated USDA YG. Feeding Trial 3. The third feeding trial was published in Iowa State University’s Animal Industry Report (Russell et al., 2011). This feeding trial had a similar objective to the prior 2 feeding trials in that it sought to evaluate the potential of lime-treated corn stover as a replacement feed in growing and finishing beef cattle. The research refers to the treated stover as “treated stover silage” because the stover was stored for 95 d after treatment. The experiment involved 210 Angus steers in a Latin square design. The control ration fed 70% DM corn grain, 20% DM MDGS, 0% DM lime-treated corn stover, and 5% DM untreated corn stover, and the experimental ration fed 35% DM corn grain, 40% DM MDGS, 20% DM lime-treated corn stover, and 0% DM untreated corn stover. Both diets included 5% DM supplement. Steers fed the experimental ration containing limetreated corn stover from late-growing through finishing had similar ADG, HCW, and calculated USDA YG to steers fed the control ration. However, there was a statistically significant difference in DMI and marbling score. Importantly, the decrease in DMI did not negatively affect ADG. In other words, the stover-fed animals gained the same amount of weight and achieved the same YG as the control group while consuming less feed per day but finished with a lower marbling score. Feed Prices. Feed prices used in this study come from various sources and were calibrated for a hypothetical feedlot operation in Washington County, Indiana, at −86.10 latitude and 38.64 longitude. Washington County was chosen as the site for the study because it has a significant beef cattle population and planted corn area. Sensitivity analysis is carried out by using 3 prices for corn grain (118.10, 157.47, and 196.84 $/Mg) and 3 farm-gate prices for corn stover ($38.58, $49.60, and $60.63 per dry megagram). As the price of corn grain changes as part of the sensitivity analysis, several other feed prices change, such as dry-rolled corn, MDGS, and wet distillers grains with solubles. Assuming a corn grain price of $157.47/Mg and a corn stover price of $49.60/dry Mg, Table 1 summarizes the delivered feed price assumptions for the different feed ingredients used in this study. The prices include all purchasing, transport, and handling costs associated with the feed, and all prices are reported in dollars per dry megagram, unless otherwise specified. LEAF. LEAF is an integrated modeling system that combines 4 environmental modules with user-provided farm management practices to compute environmental scenarios on a geospatial scale. The 4 modules in the model are the Revised Universal Soil Loss Equation, Wind Erosion Prediction System, the Soil Conditioning Index (SCI), and the Denitrification and Decomposition model. The Revised Universal Soil Loss Equation models water erosion, whereas the Wind Erosion Prediction System models wind erosion. The SCI component of LEAF pro-
vides a measure of soil health based on organic composition, and the Denitrification and Decomposition portion of LEAF is used to model carbon and nitrogen fluctuations in different agricultural scenarios. The farm management practices available in the model are crop rotation, tillage practice, corn stover harvest regimen, and cover crop regimen. To obtain site-specific environmental results, LEAF requires the specification of different categories of farm management practices associated with the site under investigation. The crop rotations used in this study involve combinations of continuous corn grain and corn grain–soybean rotations. LEAF provides 2 options for tillage regimen: reduced tillage and no-till. Reduced tillage is defined as 15 to 30% of the soil surface covered by residue at the time of planting, and no-till is defined as greater than 30% of the soil surface covered by residue at the time of planting (Muth, 2012). There is no option for conventional tillage, as it has become uncommon in corn cropping rotations. LEAF provides 4 options for corn stover harvest: no residue harvest, low residue harvest, medium residue harvest, and high residue harvest. No, low, medium, and high residue harvest refer to 0, 33, 50, and 75% stover removal level, respectively. There are several cover crop regimens available in LEAF, but for simplicity this study considers only 2 cover crop options: no cover crop and a winter rye cover crop. County-level yield assumptions in the LEAF model are derived from yields reported by the National Agricultural Statistics Service for 2008 to 2010. The average slope gradient for Washington County used in LEAF is 5.22% over a range of slope gradients of approximately 1 to 9%. Once a combination of management practices is selected, LEAF returns site-specific environmental outputs that are the product of a site’s particular soil, climate, and management scenarios. The environmental outputs we are concerned with here are soil erosion, changes in SOC, changes in nitrate leaching, and SCI. Soil erosion is reported in megagrams per hectare per year and is strictly positive.
Table 1. Feed ingredient prices Ingredient1 Corn grain Dry-rolled corn Lime-treated corn stover Untreated corn stover WDGS MDGS Corn cobs Wheat straw
$/dry Mg 238.08 244.66 104.74 82.70 218.80 233.24 74.96 108.35
WDGS = wet distillers grains with solubles; MDGS = modified distillers grains with solubles.
1
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Table 2. Environmental values Environmental impact Lower-bound soil erosion (/Mg) Upper-bound soil erosion (/Mg) Soil organic carbon (/kg) Nitrate leaching (/kg)
Value ($) Source 4.17 31.04 0.13 2.09
Change in SOC is reported in kilograms per hectare per year and can be positive or negative because a management practice can either build or deplete soil carbon. Nitrate leaching is reported in kilograms per hectare per year and is strictly positive because there is always some level of nitrate leaching, even in the absence of cropping. The Soil Conditioning Index is qualitative, so it is interpreted according to the positive or negative output sign. If the SCI output is positive, then the specified management practice on that particular site results in building OM. Conversely, if the output is negative, then the specified management practice on that site is decreasing OM. Muth and Bryden (2013) provide a more complete description of the LEAF model. Environmental Values. To assess the social cost of the feed substitutions, monetary values are assigned to environmental damages resulting from changes in farm management practices due to the feed substitutions. Estimated values from the literature allow us to approximate the value of environmental damages from soil erosion, SOC, or nitrate leaching. Because of the vast disparity in the literature regarding the value of soil erosion, we use 2 values in the analysis as lower- and upper-bound values of soil erosion (Table 2). The lower- and upper-bound erosion measures can be divided into private and social components. The private component refers to on-site damages due to soil erosion (i.e., lost future productivity). The social component refers to on-site damages as well as damages to society at large, which includes the cost of cleaning waterways, increased healthcare costs, and so on. The social value of soil erosion is listed in Table 2. The private value of the lowerbound soil erosion estimate is $1.11/Mg, and the private value of the upper-bound estimate is $11.21/Mg.
Economic Methodology The economic analysis is conducted using the IOFC calculation in different feeding scenarios. For the 3 feeding trials outlined above, IOFC is compared between the control ration that does not include lime-treated corn stover and the experimental ration to determine net returns when lime-treated corn stover is substituted into the diet. There are 3 economic drivers for the decision to make a ration change: (1) the costs associated with each feed ingredient; (2) any change in income due to the ration
Hansen and Ribaudo (2008) USDA (2011) Lal (2014) Christiansen et al. (2013)
change; and (3) any change in daily feed consumption due to the ration change. The cost of each ingredient includes a payment for the feed itself, transportation and storage costs, and a treatment cost in the case of corn stover. The change in income reflects the possibility of a change of QG in animals being fed treated corn stover, or a change in DMI due to the ration change. Figure 1 outlines the methodology governing the economics of a change in a feedlot ration. To simplify the process outlined in Figure 1, we employ partial budgeting techniques and only calculate the difference in IOFC between the new and original feed rations. In other words, only factors that change due to the feed substitution are considered. Sensitivity analysis is conducted using 3 prices for corn grain, 3 prices for corn stover, and 2 feedlot herd sizes. The original analysis was done with a small and a large herd, but the results were roughly equivalent, so we only report here the results for 2,500 feedlot animals. We assume operator income is determined by the carcass weight/formula method, where changes in QG at the time of slaughter affect the selling price of the animal.
Environmental Methodology The purpose of the environmental analysis is to compare levels of soil erosion, changes in nitrate leaching, and changes in SOC under different farm management practices for the feedlot. The farm management practices are crop rotations involving corn grain without stover removal compared with rotations involving corn grain with stover removal. Figure 2 outlines the methodology governing the environmental impacts of changing farm management from no stover harvest to some level of stover harvest, though the same methodology applies to changing tillage regimen or cover crop practice. Data for the environmental analysis comes from LEAF. LEAF has 4 rotation options that suit this research: (1) continuous corn grain without stover removal; (2) continuous corn grain with stover removal; (3) corn grain with soybean rotation without stover removal; and (4) corn grain with soybean rotation with stover removal. Harvesting corn stover raises concerns regarding soil erosion, nitrate leaching, and SOC changes. We examine 2 management techniques that, if adopted, can lessen the impact of stover harvest on these environmental quality indicators. The 2
Feeding treated stover
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Figure 1. Economic methodology connections. IOFC = income over feed cost.
management techniques are no tillage and cover cropping. To evaluate the impact of the damage-mitigating management practices under scenarios with and without corn stover harvest, we implement these management practices using LEAF in various farm management scenarios.
To link the environmental results obtained from LEAF and the economic analysis, we need to focus on the environmental impacts occurring inside of the feed supply shed around the hypothetical feedlot operation. We achieve this by uploading our geospatially defined soil ero-
Figure 2. Environmental methodology connections. SOC = soil organic carbon.
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sion, SOC, and nitrate leaching results from LEAF into ArcMap (ESRI, Redlands, CA) and then partitioning the estimated feed sheds of various radii around the study location, which allows us to summarize the environmental outcomes around the hypothetical feedlot. Once environmental damages are measured under various farm management practices, monetary values are assigned to the damages using the values outlined in the data section. These monetary values can be parsed into private and social values as described above. The present value of future soil productivity, whose changes are measured by the private values in this analysis, should be given the same consideration as any other cost input in the production decision. External damages, on the other hand, do not factor in to the private production decision. Nevertheless, it is vitally important to capture the value of external damages to provide input into possible policy choices. Soil erosion has both private and external costs, where private costs measure changes to future soil productivity and external costs measure erosion’s effect on several resources and amenities including increased sedimentation in water reservoirs, diminished value from water recreation, loss of water potability, decreased fishery productivity, and increased dust particulate matter in the air, among many others. Yet it is difficult to separate gains or losses in SOC from soil erosion. A portion of the SOC lost in a given year is due to soil erosion. On average, the top 5 cm of topsoil contain approximately 5.5 to 9.1 kg of SOC per megagram of topsoil. For a corn stover removal level with an average loss of 90 Mg/ha of eroded soil, anywhere from 218 to 363 kg of SOC is lost due to erosion. To avoid the issue of double counting the value of changes in soil productivity due to this on-site environmental damage, we report the value of lost (or gained) SOC separately from the soil erosion values and acknowledge that combining the values would almost certainly over-report the true value to the producer. The value of nitrate leaching is assumed to be strictly a social cost to society as the producer does not internalize the damages caused by excess nitrogen entering an aquifer, water table, and so on. The system of Equations 1 to 4 contains the mathematical procedure for calculating the costs or benefits of the feed substitution in terms of soil erosion. Equation 1 calculates the change in harvested area with corn stover removal required by the feeding trial under study, and Equation 2 calculates the erosion increase incurred by switching from a crop rotation (either continuous corn or corn–soybeans) to a crop rotation with corn stover removal. Equation 3 denotes the selection of an economic value for the environmental damage. The results of Equations 1 through 3 are multiplied together in Equation 4, which calculates the total economic value of the environmental damage.
Stover Harvest Requirement (ha), A = Stover
Substitution (Mg)/Stover Yield (Mg/ha)
Change in Erosion Level (Mg/ha per yr), E = Corn Grain without Stover Removal Erosion Measure (Mg/ha per yr) − Corn Grain with Stover Removal Erosion
Measure (Mg/ha per yr)
Economic Value Assignment ($/Mg), V = Erosion
Value ($/Mg)
Total Erosion Impact Valuation ($/yr) =
(3)
A × E × V (4)
The result of Equation 4 is the social monetary value, in dollars per year, of soil erosion due to changes in farm management practices when lime-treated corn stover substitutes for corn grain and other feedstuffs. The system of Equations 1 to 4 is used for private and social erosion, nitrate leaching, and also SOC valuations.
RESULTS AND DISCUSSION Feeding Trial Economic Results For each feeding trial, 18 feeding scenarios were considered. These scenarios were designed with 3 corn prices ($118.10, $157.47, and $196.84 per Mg) and 3 farm-gate corn stover prices ($38.58, $49.60, and $60.63 per dry Mg). Each feeding trial included supplementary feed substitutions apart from lime-treated corn stover and corn grain, and feeding trial 3 found a change in carcass quality and DMI. Substitution of lime-treated corn stover for corn grain and other feeds in feedlot rations always decreased the operator’s feed costs, even if the price of corn stover is high ($60.63/dry Mg) and the price of corn is low ($118.10/ Mg). Sensitivity analysis to the price of corn grain and corn stover had a more substantial numerical effect on the change in IOFC, but price sensitivity never inverted the change in IOFC from positive to negative or vice ver-
Table 3. Average income over feed cost change ($/feedlot space per year) Corn price ($) 118.10 157.47 196.84
(1)
(2)
Stover price ($)
Trial 1
Trial 2
Trial 3
38.58 49.60 60.63 38.58 49.60 60.63 38.58 49.60 60.63
20.14 14.01 7.88 46.06 39.93 33.80 71.98 65.84 59.71
22.88 15.03 7.18 42.79 34.94 27.08 62.69 54.84 46.99
22.77 15.58 8.39 51.87 47.18 42.50 89.07 84.38 79.69
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Table 4. Corn–soybeans, reduced till, no cover crop environmental impacts1 Environmental impact
Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
17.54 44.11 268.09 7 24
19.16 45.12 187.63 2 19
22.52 46.28 99.32 0 12
24.97 47.48 25.01 0 7
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
1
sa. The change in IOFC ($/feedlot space per year) was positive for all feed price scenarios in all 3 feeding trials (Table 3). Because of the statistically significant decrease in marbling score, feeding trial 3 was the only potentially contrasting trial. However, the statistically significant decrease in DMI tended to offset the lost income due to a decreased marbling score. The results of the economic analysis of the beef feeding trials suggests that under the conditions examined in these studies, feeding lime-treated corn stover would be profitable. In the feed price scenario that is least favorable for the substitution ($118.10/Mg corn grain and $60.63/ dry Mg corn stover), the average return per feedlot space across the 3 feeding trials is $7.82. In a 2,500-animal herd, this is a yearly increase in IOFC of $19,950 for the feedlot operation. In the baseline feed price scenario of $157.47/ Mg corn grain and $49.60/dry Mg corn stover, the average return per feedlot space across the 3 feeding trials is $40.68, which amounts to $101,708 for the feedlot.
Environmental Impacts Twenty-four different farm management practices were analyzed. The farm management practices in the analysis include different combinations of crop rotations involving corn grain crop rotations, reduced or no tillage, a winter rye cover crop or no cover crop, and no corn stover harvest, low residue harvest (33%), medium residue harvest (50%), or high residue harvest (75%). The environmental
impacts analyzed are soil erosion, changes in SOC, changes in nitrate leaching, and qualitative SCI measurements. For the sake of simplicity, we report average results for a 13-km radius around the Washington County location because there were no drastic differences between different supply radii. The different management practices can be evaluated in terms of sustainability by the proportion of harvested area with erosion less than the T-Factor, whether the management practice builds or depletes SOC, the proportion of harvested area with a positive SCI measurement, and average levels of nitrate leaching. Tables 4 to 9 report the results of the 24 different farm management practices. As expected, soil erosion increased as the level of stover harvest increased. Although changes in the quantity of SOC often decreased rapidly as the level of stover harvest increased, levels of nitrate leaching did not change substantially as the level of stover harvest changed. Regardless of cropping pattern, high residue harvest could not meet the environmental sustainability criteria under any management scenario, including under a no-till regimen and winter rye cover crop, which had considerable environmental conservation potential. Medium residue harvest was only sustainable in a continuous corn, no-till, and winter rye cover crop management (Figure 3). Without a cover crop, medium residue harvest was considerably more environmentally degrading than when managed with a winter rye cover crop (Figure 4). On the other hand, low
Table 5. Corn–soybeans, no-till, no cover crop environmental impacts1 Environmental impact Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
3.48 48.12 205.97 100 60
4.78 47.40 144.53 60 58
6.75 45.73 21.90 24 24
10.45 45.67 19.65 24 24
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
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Table 6. Corn–soybeans, no-till, winter rye cover crop environmental impacts1 Environmental impact
Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
0.96 34.50 294.63 100 100
3.02 33.96 248.01 100 100
4.31 32.61 126.98 56 52
5.71 32.59 124.66 52 30
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
1
Table 7. Continuous corn, reduced till, no cover crop environmental impacts1 Environmental impact
Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
8.94 76.13 431.25 24 24
12.21 85.70 267.89 24 24
21.23 89.54 −13.29 0 15
25.66 98.93 −72.02 0 7
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
1
Table 8. Continuous corn, no-till, no cover crop environmental impacts1 Environmental impact Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
0.92 87.43 309.56 100 100
2.51 93.26 182.76 100 100
6.90 92.20 −62.04 52 15
17.23 96.12 −66.91 15 15
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
1
Table 9. Continuous corn, no-till, winter rye cover crop environmental impacts1 Environmental impact Avg. soil erosion Avg. nitrate leaching Avg. SOC change Positive SCI Erosion < T-Factor
Units Mg/ha per yr kg/ha per yr kg/ha per yr % of ha % of ha
Grain + NRH
Grain + LRH
Grain + MRH
Grain + HRH
0.10 59.92 460.99 100 100
0.40 65.38 361.17 100 100
1.90 67.87 303.64 100 100
3.81 69.96 215.65 100 60
NRH = no residue harvest; LRH = low residue harvest; MRH = medium residue harvest; HRH = high residue harvest; SOC = soil organic carbon; SCI = Soil Conditioning Index.
1
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Figure 3. Southwest Washington County, medium residue harvest, winter rye cover crop annual soil erosion (Mg/ha per year).
residue harvest could be achieved sustainably without a cover crop in a continuous corn and no-till management.
Private Versus Social Costs of Feed Substitution This section integrates the environmental results into the economic analysis of the feed substitution by applying values to environmental changes when corn grain harvest-
ed area is transitioned into corn grain with stover harvest. The purpose is to estimate overall social costs and benefits of the feed substitution under various farm management scenarios. The prices of corn grain and corn stover assumed in this section are $157.47/Mg and $49.60/dry Mg. Because we assume management practices will transition from no stover harvest to some level of stover harvest, environmental valuations are always negative in terms of soil erosion and changes in SOC. Changes in levels of ni-
Figure 4. Southwest Washington County, medium residue harvest, no cover crop annual soil erosion (Mg/ha per year).
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Figure 5. Feeding trial 1 private and social costs, high erosion value.
trate leaching can be positive or negative when stover harvest is introduced, but in any case nitrate leaching changes are not substantial. In the presence of a cover crop, there is a relatively smaller tradeoff in environmental outcomes when corn stover harvest is introduced because environmental damages are less pronounced in the presence of a cover crop. The difference is not always trivial, as transitioning from no corn stover harvest to high residue harvest under corn–soybeans in the presence of a cover crop reduces the proportion of area with erosion less than the T-Factor from 100 to 30%.
Recall that each feeding trial produced unambiguously positive changes in IOFC. This analysis examines the tradeoffs between the positive IOFC realized by producers and the environmental damages realized by corn growers and society at large. The environmental value calculations combine the value of soil erosion and nitrate leaching changes. The majority of private economic and social environmental combinations result in net positive social impacts. One example that demonstrates this majority of outcomes is when the corn stover supplied to feeding trial 1 comes from continuous corn rotations, low residue
Figure 6. Feeding trial 2 private and social costs, high erosion value.
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Figure 7. Feeding trial 2 private and social costs, low erosion value.
harvest, and no cover crop (Figure 5). Even when using the upper-bound erosion value and incorporating damages from increased nitrate leaching, the net social impact of the feed substitution is approximately $41,000 per year. A counterexample to the usual outcome of positive total social impacts comes from feeding trial 2. The environmental value of soil erosion under a corn–soybeans, no-till, no cover crop, and high residue harvest is a loss of $152,936, which easily outweighs the private economic benefits of $87,350 due to the feed substitution (Figure 6). However, this outcome is derived using the upper-bound erosion value. Examining the same scenario using the lower-bound erosion value (Figure 7), the net social impact of the feed substitution is positive. In fact, when the lowerbound erosion value is used, there are no scenarios where
the net social impact is negative. This result highlights the importance of using an appropriate, site-specific value of soil erosion to properly measure net social impacts due to changes in farm management practices. Valuations of changes in SOC were not included as either a private or social environmental damage to avoid overestimating on-site losses of future productivity. However, changes in SOC were substantial when farm management shifted from no corn stover harvest to increasing levels of stover harvest. Table 10 provides the values of changes in SOC in the context of the different feeding trials when farm management switches from no corn stover harvest to higher levels of stover harvest. As expected, all values are negative to reflect the lost soil carbon due to stover harvest.
Table 10. Soil organic carbon valuations ($/yr) Crop rotation Continuous corn grain
Stover harvest Cover crop Low Medium High
Corn grain–soybeans
Low Medium High
No cover Rye cover No cover Rye cover No cover Rye cover No cover Rye cover No cover Rye cover No cover Rye cover
Trial 1
Trial 2
Trial 3
(8,910) (4,561) (13,545) (4,276) (11,826) (5,644) (4,340) (4,655) (8,715) (4,538) (5,881) (6,242)
(11,407) (5,839) (17,240) (5,623) (15,141) (7,226) (5,556) (5,959) (11,105) (5,585) (7,529) (7,991)
(7,502) (3,840) (11,405) (3,601) (9,957) (4,752) (3,654) (3,919) (7,338) (3,821) (4,952) (5,255)
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IMPLICATIONS The results of feeding experiments involving lime-treated corn stover suggest its potential as a cost-saving replacement feed for corn grain. In this study, a one-to-one substitution of lime-treated corn stover for corn grain and other feed ingredients in beef feedlot rations decreased the feedlot’s feed costs in all scenarios, even when the price of corn grain was as low as $118.10/Mg. This suggests corn stover harvest could provide an additional revenue stream for corn farmers facing low corn grain prices. Transitioning from no corn stover harvest to any level of corn stover harvest always induces greater levels of soil erosion and decreases the amount of SOC returned to the soil. When the value of environmental outcomes is integrated into the private changes in IOFC, the overall social cost or benefit of the substitution can change from positive to negative depending on which value of soil erosion is used, while also indicating potential divergence in private versus social outcomes. This suggests that policy interventions may be necessary to achieve a socially desired outcome regarding the harvest of corn stover.
Karlen, D. L., S. J. Birrell, J. M. F. Johnson, S. L. Osborne, T. E. Schumacher, G. Varvel, R. B. Ferguson, J. M. Novak, J. R. Fredrick, J. M. Baker, J. A. Lamb, P. R. Adler, G. W. Roth, and E. D. Nafziger. 2014. Multilocation corn stover harvest effects on crop yields and nutrient removal. BioEnergy Res. 7:528–539. Lal, R. 2014. Societal value of soil carbon. J. Soil Water Conserv. 69:186–192. Lindstrom, M. J. 1986. Effects of residue harvesting on water runoff, soil erosion and nutrient loss. Agric. Ecosyst. Environ. 16:103–112. Muth, D. 2012. Nomenclature. MS Excel. AgSolver Inc., Ames, IA. Muth, D. J., Jr., and K. M. Bryden. 2013. An integrated model for assessment of sustainable agricultural residue limits for bioenergy systems. Environ. Model. Softw. 39:50–69. NASS (National Agricultural Statistics Service). 2016. CropScape— Cropland Data Layer. USDA, Washington, DC. Nuñez, A. J. C., T. L. Felix, S. C. Loerch, and J. P. Schoonmaker. 2015. Effect of dried distillers grains with solubles or corn in growing cattle diets, followed by a corn-based finishing diet, on performance of feedlot cattle. Anim. Feed Sci. Technol. 207:267–273. Pratt, M. R., W. E. Tyner, D. J. Muth Jr., and E. J. Kladivko. 2014. Synergies between cover crops and corn stover removal. Agric. Syst. 130:67–76.
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