Abstract  Two complementary studies were performed to examine (1) the effect of 18 years of nitrogen (N) fertilization, and (2) the effects of N fertilization during one growing season on soil microbial community composition and soil resource availability in a grassland ecosystem. N was added at three different rates: 0, 5.44, and 27.2g N m(-2) y(-1). In both studies, Schizachyrium scoparium was the dominant plant species before N treatments were applied. Soil microbial communities from each experiment were characterized using fatty acid methyl ester (FAME) analysis. Discriminant analysis of the FAMEs separated the three N fertilizer treatments in both experiments, indicating shifts in the composition of the microbial communities. In general, plots that received N fertilizer at low or high application rates for 18 years showed increased proportions of bacterial FAMEs and decreased fungal FAMEs. In particular, control plots contained a significantly higher proportion of fungal FAMEs C18:1(cis9) and C18:2(cis9,12) and of the arbuscular mycorrhizal fungal (AMF) FAME, C16:1 (cis11), than both of the N addition treatment plots. A significant negative effect of N fertilization on the AMF FAME, C16:1 (cis11), was measured in the short-term experiment. Our results indicate that high rates of anthropogenic N deposition can lead to significant changes in the composition of soil microbial communities over short periods and can even disrupt the relationship between AMF and plants.

Abstract  Soil organic carbon (SOC) change can be a major impact of land use change (LUC) associated with biofuel feedstock production. By collecting and analyzing data from worldwide field observations of major LUCs from cropland, grassland, and forest to lands producing biofuel crops (i.e. corn, switchgrass, Miscanthus, poplar, and willow), we were able to estimate SOC response ratios and sequestration rates and evaluate the effects of soil depth and time scale on SOC change. Both the amount and rate of SOC change were highly dependent on the specific land transition. Irrespective of soil depth or time horizon, cropland conversions resulted in an overall SOC gain of 6-14% relative to initial SOC level, while conversion from grassland or forest to corn (without residue removal) or poplar caused significant carbon loss (9-35%). No significant SOC changes were observed in land converted from grasslands or forests to switchgrass, Miscanthus, or willow. The SOC response ratios were similar in both 0-30 and 0-100 cm soil depths in most cases, suggesting SOC changes in deep soil and that use of top soil only for SOC accounting in biofuel life cycle analysis (LCA) might underestimate total SOC changes. Soil carbon sequestration rates varied greatly among studies and land transition types. Generally, the rates of SOC change tended to be the greatest during the 10 years following land conversion and had declined to approach 0 within about 20 years for most LUCs. Observed trends in SOC change were generally consistent with previous reports. Soil depth and duration of study significantly influence SOC change rates and so should be considered in carbon emission accounting in biofuel LCA. High uncertainty remains for many perennial systems and forest transitions, additional field trials, and modeling efforts are needed to draw conclusions about the site- and system-specific rates and direction of change.

Abstract  Grasslands in the Conservation Reserve Program (CRP) in the USA may be converted to grain crops for bioenergy. The effect of no-till conversion of a smooth bromegrass (Bromus inermis Leyss) grassland to no-till corn (Zea mays L.) production on soil organic carbon (SOC) in the western Corn Belt was monitored for over 6 yr. A different (13)C/(12)C isotope signature is imparted to SOC by C4 plants including corn versus C3 plants such as bromegrass. Changes in C isotope ratios in SOC in three soil depths (0- to 5-, 5-10, and 10-30 cm) by particle size was also monitored during similar to 6.5 yr of no-till corn production at two different N levels (60 and 120 kg ha(-1)). Soil was collected eight times during the study from the 0- to 5- and 5- to 10-cm depths, and at four of these times from the 10- to 30-cm depth from each of the N rate replicates. Because fertilizer N had no significant effect over years on any of the aboveground biomass production variables, the data from both N treatments was combined for regression analysis to determine the effects of years of no-till corn production on SOC variables. Total SOC did not change significantly at any depth during the study, but there was a significant change in the source of the SOC. Total C4-C increased over this time, while C3-C decreased in the 0- to 5- and 5- to 10-cm depth, while neither changed in the 10- to 30-cm depth. In the 0- to 5- and 5- to 10-cm depths, largest loss of C3-C was from 2-mm aggregates, while largest increases in C4-C were in the 1-, 0.5-, 0.25-, and 0.125-mm aggregates. If CRP grasslands are converted to grain crop production, the data from this study strongly support the use of no-till farming practices as a method of conserving the SOC that was sequestered during the time period that the land was in the CRP.

Abstract  Although the United States has pursued rapid development of corn ethanol as a matter of national biofuel policy, relatively little is known about this policy's widespread impacts on agricultural land conversion surrounding ethanol refineries. This knowledge gap impedes policy makers' ability to identify and mitigate potentially negative environmental impacts of ethanol production. We assessed changes to the landscape during initial implementation of the Renewable Fuel Standard v2 (RFS2) from 2008 to 2012 and found nearly 4.2 million acres of arable non-cropland converted to crops within 100 miles of refinery locations, including 3.6 million acres of converted grassland. Aggregated across all ethanol refineries, the rate of grassland conversion to cropland increased linearly with proximity to a refinery location. Despite this widespread conversion of the landscape, recent cropland expansion could have made only modest contributions to mandated increases in conventional biofuel capacity required by RFS2. Collectively, these findings demonstrate a shortcoming in the existing 'aggregate compliance' method for enforcing land protections in the RFS2 and suggest an alternative monitoring mechanism would be needed to appropriately capture the scale of observed land use changes.

Abstract  Changes agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long-term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no-till (NT) can sequester 57 +/- 14 g C m(-2) yr(-1), excluding wheat (Triticum aestivum L.)-fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 +/- 12 g C m(-2) yr(-1), excluding a change from continuous corn (Zea mays L.) to corn-soybean (Glycine mar L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.

Abstract  An ongoing study initiated in August 1990 investigated the effects of disturbances (organic mulching, cultivation, herbicides) on the detritus food-web in annual (maize) and perennial (asparagus) cropping systems. In this paper we attempt to simultaneously assess the functional and taxonomic structure of various components of this food-web. Biota in the perennial system was the most responsive to disturbance. The microflora was strongly influenced by mulching, and through tritrophic effects caused increases in top predatory but not most microbe-feeding nematodes. These effects have become increasingly apparent as the study has progressed and, in the asparagus site, have worked their way down the soil profile over time. Cultivation in the asparagus site caused large increases in bacterial-feeding nematodes, probably due to the high weed levels which developed during the winter months under that treatment. Evidence appears to exist for a cascade effect operating due to top down effects of nematodes on lower trophic levels. Ordination analysis of the nematode data demonstrated that nematode populations were more closely related to the state of environmental factors at earlier samplings than at contemporary samplings, and that the linkages between the nematode and environmental data sets strengthened over time. For both the nematode and soil-associated beetle data distinct assemblages of organisms were found in the mulched plots; distinct assemblages of nematode genera also emerged in the cultivated asparagus plots after two years. The soil-associated macrofauna was usually linked to high weed and surface organic residue levels. Species diversity of soil associated nematodes was not particularly responsive to disturbance while that of the soil-associated beetles was strongly enhanced by mulching and (sometimes) high weed levels. Approaches based on either functional group or species composition data emerged in our study as reasonably sensitive indicators for assessing the response of the soil biota to disturbance.

Abstract  After decades of decline, croplands are once again expanding across the United States. A recent spatially explicit analysis mapped nearly three million hectares of US cropland expansion that occurred between 2008 and 2012. Land use change (LUC) of this sort can be a major source of anthropogenic carbon (C) emissions, though the effects of this change have yet to be analyzed. We developed a data-driven model that combines these high-resolution maps of cropland expansion with published maps of biomass and soil organic carbon stocks (SOC) to map and quantify the resulting C emissions. Our model increases emphasis on non-forest-i.e. grassland, shrubland and wetland-above and belowground biomass C stocks and the response of SOC to LUC-emission sources that are frequently neglected in traditional Caccounting. These sources represent major emission conduits in the US, where new croplands primarily replace grasslands. We find that expansion between 2008-12 caused, on average, a release of 55.0 MgCha(-1) (SDspatial = 39.9 MgCha(-1)), which resulted in total emissions of 38.8 TgC yr(-1) (95% CI = 21.6-55.8 TgC yr(-1)). We also find wide geographic variation in both the size and sensitivity of affected Cstocks. Grassland conversion was the primary source of emissions, with more than 90% of these emissions originating from SOC stocks. Due to the long accumulation time of SOC, its dominance as a source suggests that emissions may be difficult to mitigate over human-relevant time scales. While methodological limitations regarding the effects of land use legacies and future management remain, our findings emphasize the importance of avoiding LUC emissions and suggest potential means by which natural C stocks can be conserved.

Abstract  Harvesting of corn stover (plant residues) for cellulosic ethanol production must be balanced with the requirement for returning plant residues to agricultural fields to maintain soil structure, fertility, crop protection, and other ecosystem services. High rates of corn stover removal can be associated with decreased soil organic matter (SOM) quantity and quality and increased highly erodible soil aggregate fractions. Limited data are available on the impact of stover harvesting on soil microbial communities which are critical because of their fundamental relationships with C and N cycles, soil fertility, crop protection, and stresses that might be imposed by climate change. Using fatty acid and DNA analyses, we evaluated relative changes in soil fungal and bacterial densities and fungal-to-bacterial (F:B) ratios in response to corn stover removal under no-till, rain-fed management. These studies were performed at four different US locations with contrasting soil-climatic conditions. At one location, residue removal significantly decreased F:B ratios. At this location, cover cropping significantly increased F:B ratios at the highest level of residue removal and thus may be an important practice to minimize changes in soil microbial communities where corn stover is harvested. We also found that in these no-till systems, the 0- to 5-cm depth interval is most likely to experience changes, and detectable effects of stover removal on soil microbial community structure will depend on the duration of stover removal, sampling time, soil type, and annual weather patterns. No-till practices may have limited the rate of change in soil properties associated with stover removal compared to more extensive changes reported at a limited number of tilled sites. Documenting changes in soil microbial communities with stover removal under differing soil-climatic and management conditions will guide threshold levels of stover removal and identify practices (e.g., no-till, cover cropping) that may mitigate undesirable changes in soil properties.

Abstract  Long-term effects of cropping systems on soil properties, such as organic soil C and N levels is necessary so more accurate projections can be made regarding the sequester and emission of CO2 by agricultural soils. This information can then be used to predict the effects of cropping systems on both soil degradation, maintenance, or improvement and global climate changes. My objective was to evaluate the effects of crop rotation and N fertilizer management on changes in total soil C and N concentrations that have occurred during an 8-yr period in a long-term study, in the Western Corn Belt. Seven cropping systems (three monoculture, two 2-yr, and two 4-yr rotations) with three rates of N fertilizer were compared. Monocultures included continuous corn (Zea mays L.), soybean [Glycine - (L.) Merr.], and grain sorghum [Sorghum bicolor (L.) Moench]. The 2-yr rotations were corn-soybean and grain sorghum-soybean, and the two 4-yr rotations were corn-oat (Avena sativa L.) + dover (80% Melilotus officinalis Lam. and 20% Trifolium pratense). grain sorghum-soybean and corn-soybean-grain sorghum-oat + clover. Soil samples were taken in the spring both in 1984 and 1992 to a depth of 30 cm in 0- to 7.5-cm, 7.5- to 15-cm, and 15-to 30-cm increments. No differences were obtained in 1984, but both rotation and N rate significantly affected total soil C and N concentrations in 1992. The results indicate that C could be sequestered at 10 to 20 g m-2 yr-1 in some cropping systems with sufficient levels of N fertilizer. Greater storage of C in soils suggests CO2 emissions from agricultural soils could be decreased with improved management practices and may in the long term have a significant effect on CO2 in the atmosphere under current climate conditions.

Abstract  Energy production in the United States for domestic use and export is predicted to rise 27% by 2040. We quantify projected energy sprawl (new land required for energy production) in the United States through 2040. Over 200,000 km2 of additional land area will be directly impacted by energy development. When spacing requirements are included, over 800,000 km2 of additional land area will be affected by energy development, an area greater than the size of Texas. This pace of development in the United States is more than double the historic rate of urban and residential development, which has been the greatest driver of conversion in the United States since 1970, and is higher than projections for future land use change from residential development or agriculture. New technology now places 1.3 million km2 that had not previously experienced oil and gas development at risk of development for unconventional oil and gas. Renewable energy production can be sustained indefinitely on the same land base, while extractive energy must continually drill and mine new areas to sustain production. We calculated the number of years required for fossil energy production to expand to cover the same area as renewables, if both were to produce the same amount of energy each year. The land required for coal production would grow to equal or exceed that of wind, solar and geothermal energy within 2-31 years. In contrast, it would take hundreds of years for oil production to have the same energy sprawl as biofuels. Meeting energy demands while conserving nature will require increased energy conservation, in addition to distributed renewable energy and appropriate siting and mitigation.

Abstract  Regions of land that are brought into crop production from native vegetation typically undergo a period of soil erosion instability, and long term erosion rates are greater than for natural lands as long as the land continues being used for crop production. Average rates of soil erosion under natural, non-cropped conditions have been documented to be less than 2 Mg ha−1 yr−1. On-site rates of erosion of lands under cultivation over large cropland areas, such as in the United States, have been documented to be on the order of 6 Mg ha−1 yr−1 or more. In northeastern China, lands that were brought into production during the last century are thought to have average rates of erosion over this large area of as much as 15 Mg ha−1 yr−1 or more. Broadly applied soil conservation practices, and in particular conservation tillage and no-till cropping, have been found to be effective in reducing rates of erosion, as was seen in the United States when the average rates of erosion on cropped lands decreased from on the order of 9 Mg ha−1 yr−1 to 6 or 7 Mg ha−1 yr−1 between 1982 and 2002, coincident with the widespread adoption of new conservation tillage and residue management practices. Taking cropped lands out of production and restoring them to perennial plant cover, as was done in areas of the United States under the Conservation Reserve Program, is thought to reduce average erosion rates to approximately 1 Mg ha−1 yr−1 or less on those lands.

Abstract  The EPIC model was used to simulate soil erosion and soil C content at 100 randomly selected sites in the US corn belt. Four management scenarios were run for 100 years: (1) current mix of tillage practices maintained; (2) current trend of conversion to mulch-till and no-till maintained; (3) trend to increased no-till; (4) trend to increased no-till with addition of winter wheat cover crop. As expected, the three alternative scenarios resulted in substantial decreases in soil erosion compared to the current mix of tillage practices. C content of the top 15 cm of soil increased for the alternative scenarios, while remaining approximately constant for the current tillage mix. However, total soil C to a depth of 1 m from the original surface decreased for all scenarios except for the no-till plus winter wheat cover crop scenario. Extrapolated to the entire US corn belt, the model results suggest that, under the current mix of tillage practices, soils used for corn and/or soybean production will lose 3.2 x 106 tons of C per year for the next 100 years. About 21% of this loss will be C transported off-site by soil erosion; an unknown fraction of this C will be released to the atmosphere. For the base trend and increased no-till trend, these soils are projected to lose 2.2 x 106 t-C yr-1 and 1.0 x 106 t-C yr-1, respectively. Under the increased no-till plus cover crop scenario, these soils become a small sink of 0.1 x 106 t-C yr-1. Thus, a shift from current tillage practices to widespread use of no-till plus winter cover could conserve and sequester a total of 3.3 x 106 t-C yr-1 in the soil for the next 100 years.

Abstract  This report updates the findings of the first Report to Congress, published in 2011, with respect to environmental and resource conservation impacts, which together are intended to address the Section 204 statutory impacts since the passage of the EISA. This report reflects the current scientific understanding of the Section 204 impacts as presented in the published literature about biofuel use and production using data gathered through May 2017. Data on U.S. land use and the scientific literature through April 2017 were also reviewed. Greenhouse gas emission reductions that result from replacing biofuel with fossil fuel are not assessed in this report. This report does not make comparisons to estimated environmental impacts of other transportation fuels or energy sources.

Abstract  Crop residues are potential biofuel feedstocks, but residue removal may reduce soil carbon (C). The inclusion of a cover crop in a corn bioenergy system could provide additional biomass, mitigating the negative effects of residue removal by adding to stable soil C pools. In a no-till continuous corn bioenergy system in the northern US Corn Belt, we used 13CO2 pulse labeling to trace plant C from a winter rye (Secale cereale) cover crop into different soil C pools for 2 years following rye cover crop termination. Corn stover left as residue (30% of total stover) contributed 66, corn roots 57, rye shoots 61, rye roots 50, and rye rhizodeposits 25 g C m−2 to soil. Five months following cover crop termination, belowground cover crop inputs were three times more likely to remain in soil C pools than were aboveground inputs, and much of the root-derived C was in mineral-associated soil fractions. After 2 years, both above- and belowground inputs had declined substantially, indicating that the majority of both root and shoot inputs are eventually mineralized. Our results underscore the importance of cover crop roots vs. shoots and the importance of cover crop rhizodeposition (33% of total belowground cover crop C inputs) as a source of soil C. However, the eventual loss of most cover crop C from these soils indicates that cover crops will likely need to be included every year in rotations to accumulate soil C.

Abstract  Continuous no-till (NT) is an effective practice to control soil erosion, conserve water, and reduce monetary and energy costs, but it can be challenged by inadequate weed control, soil organic C (SOC) and nutrient stratification, and risks for compaction, runoff, and acidification. Occasional tillage in NT (OT) could be a potential solution to such problems, but the question is: Does OT reduce or undo the beneficial soil ecosystem services from NT? To answer this, we 1) synthesized and interpreted published data on OT impacts in long-term NT systems on erosion, soil properties, crop yields, and other ecosystem services and 2) discussed potential factors that affect OT effects. The limited literature on OT provides important insights. It indicates that OT can increase runoff and sediment loss, reduce losses of dissolved nutrients and pesticides in runoff and have small effects on soil physical properties. Occasional tillage does not generally reduce soil water content needed for the crops nor reduce stocks of SOC, but it reduces vertical stratification of SOC and nutrients. Soil microbial biomass decreases with OT in some cases, but this reduction appears to have limited agronomic significance. Crop yield increases in about 15%, decreases in 5%, and does not change in 80% of cases. Impacts of OT on soils and crops generally lasted <2 yr. Controlled traffic, cover crops, diversified crop rotations, and soil amendments may accelerate soil recovery after OT, reduce the need for OT, and prolong the OT benefits. Tillage method, depth, frequency, and timing, and also soil temperature and water content affect OT performance. More research is needed to better target OT and choose among OT options for benefit optimization. Overall, OT one in 5–10 yr has limited or no effects on soil ecosystem services while reducing compaction and stratification, and aiding weed control as part of integrated weed management.

Abstract  Perennial grass energy crop production is necessary for the successful and sustainable expansion of bioenergy in North America. Numerous environmental advantages are associated with perennial grass cropping systems, including their potential to promote soil carbon accrual. Despite growing research interest in the abiotic and biotic factors driving soil carbon cycling within perennial grass cropping systems, soil fauna remain a critical yet largely unexplored component of these ecosystems. By regulating microbial activity and organic matter decomposition dynamics, soil fauna influence soil carbon stability with potentially significant implications for soil carbon accrual. We begin by reviewing the diverse, predominantly indirect effects of soil fauna on soil carbon dynamics in the context of perennial grass cropping systems. Since the impacts of perennial grass energy crop production on soil fauna will mediate their potential contributions to soil carbon accrual, we then discuss how perennial grass energy crop traits, diversity, and management influence soil fauna community structure and activity. We assert that continued research into the interactions of soil fauna, microbes, and organic matter will be important for advancing our understanding of soil carbon dynamics in perennial grass cropping systems. Furthermore, explicit consideration of soil faunal effects on soil carbon can improve our ability to predict changes in soil carbon following perennial grass cropping system establishment. We conclude by addressing the major knowledge gaps that should be prioritized to better understand and model the complex connections between perennial grass bioenergy systems, soil fauna, and carbon accrual.

Abstract  Soil carbon sequestration (SCS) has emerged as a technology with significant potential to help stabilize atmospheric CO2 concentrations and thus reduce the threat of global warming. Methods and models are needed to evaluate and recommend SCS practices based on their effects on carbon dynamics and environmental quality. Environment Policy Integrated Climate (EPIC) is a widely used and tested model for simulating many agroecosystem processes including plant growth, crop yield, tillage, wind and water erosion, runoff, soil density, and leaching. Here we describe new C and N modules developed in EPIC built on concepts from the Century model to connect the simulation of soil C dynamics to crop management, tillage methods, and erosion processes. The added C and N routines interact directly with soil moisture, temperature, erosion, tillage, soil density, leaching, and translocation functions in EPIC. Equations were also added to describe the effects of soil texture on soil C stabilization. Lignin concentration is modeled as a sigmoidal function of plant age. EPIC was tested against data from a conservation reserve program (CRP) 6-year experiment at five sites in three U.S. Great Plains states and a 61-year long-term agronomic experiment near Breton, Canada. Mean square deviations (MSD) calculated for CRP sites were less than 0.01 (kg C m−2)2, except for one site where it reached 0.025 (kg C m−2)2. MSD values in the 61-year experiment ranged between 0.047 and 0.077 (kg C m−2)2. The version of the EPIC model presented and tested here contains the necessary algorithms to simulate SCS and improve understanding of the interactions among soil erosion, C dynamics, and tillage. A strength of the model as tested is its ability to explain the variability in crop production, C inputs and SOC and N cycling over a wide range of soil, cropping and climatic conditions over periods from 6 to 61 years. For example, at the Breton site over 61 years, EPIC accounted for 69% of the variability in grain yields, 89% of the variability in C inputs and 91% of the variability in SOC content in the top 15 cm. Continued development is needed in understanding why it overpredicts at low SOC and underpredicts at high SOC. Possibilities now exist to connect the C and N cycling parts of EPIC to algorithms to describe denitrification as driven by C metabolism and oxygen availability.

Abstract  Goals, Scope and Background Eutrophication and hypoxia, which are already serious environmental issues in the Midwestern region of the United States and the Gulf of Mexico, could worsen with an increase emphasis on the use of corn and soybeans for biofuels. Eutrophication impacts from agriculture are difficult to integrate into an LCA due to annual variability in the nutrient loads as a factor of climatic conditions. This variability has not been included in many relevant energy or row crop LCAs. The objective of this research was to develop a relatively simple method to accurately quantify nutrient loadings from row crop production to surface water that reflects annual variations due to weather. A set of watersheds that comprise most of eastern Iowa was studied. Ample data describing corn-soybean agriculture in this region and nutrient loadings to the Mississippi River enabled the development, calibration and validation of the model for this particular region. Methods A framework for estimating lifecycle inventory data for variable nutrient loading from corn-soybean agriculture was developed. The approach uses 21 years of country-average data for agricultural and annual rainfall for 33 counties that approximate three major watersheds in eastern Iowa. A linear equation describes the relationship between the fraction of the applied nutrients that leach into the surface water and the annual rainfall. Model parameters were calibrated by minimizing the error in the difference between actual and modeled cumulative discharge to the Mississippi River over the period 1988–1998. Data from 1978–1987 were used to validate the method. Two separate approaches were then used to allocate the nutrient flows between the corn and soybeans. Results and Discussion The total nitrogen (TN) and total phosphorus (TP) leaching models provide good representation of the variability in measured nutrient loads discharged from eastern Iowa watersheds to the Mississippi River. The calibrated model estimates are within 1.1% of the actual 11-year cumulative TN load and 0.3% of the TP load. In contrast, a standard method used in other lifecycle assessments for estimating nutrient leaching based on a constant fraction of the nutrients leached provides a reasonable average, but does not capture the annual variability. Estimates of the TN load that can be allocated to corn range from 60 and 99% between two allocation methods considered. This difference stems from a poorly understood symbiosis of nitrogen flows within the corn-soybean rotation that is difficult to integrate into an LCA. Conclusions Lifecycle inventories can include improved estimates non-point source nutrient flows to surface waters by incorporating climatic variability. Nutrient discharges to surface water are estimated with emission factors as a linear function of the annual rainfall rate. Water quality data is required to calibrate this model for a given region. In comparison with a standard approach that uses an average emission factor, the model presented here is superior in terms of capturing the variability that is correlated to an increase in the size of the hypoxic zone in the Gulf of Mexico. Recommendations and Perspectives Lifecycle inventories quantifying nutrient discharges from corn-soybean production should include the variability in these flows that occur due to climatic conditions. Failure to do so will reduce the LCA’s capability of quantifying the very significant eutrophication and hypoxia impacts associated with wet years.

Abstract  No-tillage (NT) farming is superior to intensive tillage for conserving soil and water, yet its potential for sequestering soil organic carbon (SOC) in all environments as well as its impacts on soil profile SOC distribution are not well understood. Thus, we assessed the impacts of long-term NT-based cropping systems on SOC sequestration for the whole soil profile (0-60-cm soil depth) across 11 Major Land Resource Areas (MLRAs: 121, 122, and 125 in Kentucky; 99, 124, 139A in Ohio; and 139B, 139C, 140, 147, and 148 in Pennsylvania) in the eastern United States. Soil was sampled in paired NT and plow tillage (PT) based cropping systems and an adjacent woodlot (WL). No-tillage farming impacts on SOC and N were soil specific. The SOC and N concentrations in NT soils were greater than those in PT soils in 5 out of 11 MLRAs (121, 122, 124, 139A, and 148), but only within the 0- to 10-cm depth. Below 10 cm, NT soils had lower SOC than PT soils in MLRA 124. The total SOC with NT for the whole soil profile (0-60 cm) did not differ from that with PT (P > 0.10) in accord with several previous studies. In fact, total soil profile SOC in PT soils was 50% higher in MLRA 125, 21% in MLRA 99, and 41% in MLRA 124 compared with that in NT soils. Overall, this study shows that NT farming increases SOC concentrations in the upper layers of some soils, but it does not store SOC more than PT soils for the whole soil profile.

Abstract  Understanding the environmental effects of alternative fuel production is critical to characterizing the sustainability of energy resources to inform policy and regulatory decisions. The magnitudes of these environmental effects vary according to the intensity and scale of fuel production along each step of the supply chain. We compare the spatial extent and temporal duration of ethanol and gasoline production processes and environmental effects based on a literature review and then synthesize the scale differences on space-time diagrams. Comprehensive assessment of any fuel-production system is a moving target, and our analysis shows that decisions regarding the selection of spatial and temporal boundaries of analysis have tremendous influences on the comparisons. Effects that strongly differentiate gasoline and ethanol-supply chains in terms of scale are associated with when and where energy resources are formed and how they are extracted. Although both gasoline and ethanol production may result in negative environmental effects, this study indicates that ethanol production traced through a supply chain may impact less area and result in more easily reversed effects of a shorter duration than gasoline production.

Abstract  Reducing tillage and increasing soil cover (through crop rotations and cover crops) can enhance soil health. To gauge the intensity of tillage over time, this report estimates the number of years no-till or strip-till are used over a 4-year period. Conservation tillage was used on 70 percent of soybean (2012), 65 percent of corn (2016), and 67 percent of wheat (2017) acres. Errata: On October 12, 2018, the report Tillage Intensity and Conservation Cropping in the United States was reposted to correct for coding errors that resulted in the miscalculation of some estimates for conservation cropping, cover crops, and other practices that affect crop residue. Specifically, Figure 3, Figure 4, Table 1a, and Table 1b have been replaced. Conforming changes have been made in the text on pages 6, 9, 10, 11, 12, and 18. The largest changes are an increase in cover crop acreage for corn (2016) and cotton (2015) and an increase in conservation cropping for wheat (2017). Acreages for tillage types in Tables 1a and 1b are lower because observations with less than 4 years of crop and tillage data were inadvertently included (but have now been excluded). All changes are restricted to figures, tables, and text that rely on ARMS cropping and tillage history data.