Abstract  Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.

Abstract  This dataset provides a U.S. national 60-meter, 19-class mapping of anthropogenic land uses for five time periods: 1974, 1982, 1992, 2002, and 2012. The 2012 dataset is based on a slightly modified version of the National Land Cover Database 2011 (NLCD 2011) that was recoded to a schema of land uses, and mapped back in time to develop datasets for the four earlier eras. The time periods coincide with U.S. Department of Agriculture (USDA) Census of Agriculture data collection years. Changes are derived from (a) known changes in water bodies from reservoir construction or removal; (b) housing unit density changes; (c) regional mining/extraction trends; (d) for 1999–2012, timber and forestry activity based on U.S. Geological Survey (USGS) Landscape Fire and Resource Management Planning Tools (Landfire) data; (e) county-level USDA Census of Agriculture change in cultivated land; and (f) establishment dates of major conservation areas. The data are compared to several other published studies and datasets as validation. Caveats are provided about limitations of the data for some classes. The work was completed as part of the USGS National Water-Quality Assessment (NAWQA) Program and termed the NAWQA Wall-to-Wall Anthropogenic Land Use Trends (NWALT) dataset. The associated datasets include five 60-meter geospatial rasters showing anthropogenic land use for the years 1974, 1982, 1992, 2002, and 2012, and 14 rasters showing the annual extent of timber clearcutting and harvest from 1999 to 2012.

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  The Conservation Reserve Program (CRP) is the largest agricultural land-retirement program in the United States, providing many environmental benefits, including wildlife habitat and improved air, water, and soil quality. Since 2007, however, CRP area has declined by over 25% nationally with much of this land returning to agriculture. Despite this trend, it is unclear what types of CRP land are being converted, to what crops, and where. All of these specific factors greatly affect environmental impacts. To answer these questions, we quantified shifts in expiring CRP parcels to five major crop-types (corn, soy, winter and spring wheat, and sorghum) in a 12-state, Midwestern region of the United States using a US Department of Agriculture (USDA), field-level CRP database and USDA's Cropland Data Layer. For the years 2010 through 2013, we estimate almost 30%, or more than 530 000 ha, of expiring CRP land returned to the production of these five crops in our study area, with soy and corn accounting for the vast majority of these shifts. Grasslands were the largest type of CRP land converted (360 000 ha), followed by specifically designated wildlife habitat (76 000 ha), and wetland areas (53 000 ha). These wetland areas were not just wetlands themselves, but also a mix of land covers enhancing or protecting wetland ecosystem services (e.g., wetland buffers). Areas in the Dakotas, Nebraska, and southern Iowa were hotspots of change, with the highest areas of CRP land moving back to agriculture. By contrast, we estimate only a small amount (similar to 3%) of the expiring land shifted into similar, non-CRP land-retirement or easement programs. Reconciling needs for food, feed, fuel, and healthy ecosystems is an immense challenge for farmers, conservationists, and state and federal agencies. Reduced enrollment and the turnover of CRP land from conservation to agriculture raises questions about sustaining ecosystem services in this region.

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  Transportation is the largest source of greenhouse gas emissions in the United States, with petroleum accounting for 90 percent of transportation fuels. Policymakers encounter a range of questions as they consider low-carbon fuel standards to reduce emissions, including total emissions released from production to use of a fuel or the potential consequences of a policy. Life-cycle assessment is an essential tool for addressing these questions. This report provides researchers and practitioners with a toolkit for applying life-cycle assessment to estimate greenhouse gas emissions, including identification of the best approach to use for a stated policy goal, how to reduce uncertainty and variability through verification and certification, and the core assumptions that can be applied to various fuel types. Policymakers should still use a tailored approach for each fuel type, given that petroleum-based ground, air, and marine transportation fuels necessitate different considerations than alternative fuels including biofuels, hydrogen, and electricity. Ultimately, life-cycle assessments should clearly document what assumptions and methods are used to ensure transparency.

Abstract  This report provides projections for the agricultural sector to 2030. Projections cover agricultural commodities, agricultural trade, and aggregate indicators of the sector, such as farm income. The projections are based on specific assumptions, including a consensus macroeconomic scenario, existing U.S. policy, and current international agreements. The Agriculture Improvement Act of 2018 is assumed to remain in effect through the projection period. The projections are one representative scenario for the agricultural sector and reflect a composite of model results and judgment-based analyses. The projections in this report were prepared using data through the October 2020 World Agricultural Supply and Demand Estimates (WASDE) report, except where noted otherwise.

Abstract  The effectiveness of policies and management actions in reducing the release of excess nitrogen (N) to the environment is best assessed if N fluxes across air, land, and water are regularly quantified at relevant scales. Here we compiled 2002, 2007, and 2012 inventories of inputs and nonhydrologic N outputs along with fossil fuel emissions, food demand, and terrestrial N surpluses for all subbasins of the contiguous United States using peer-reviewed, publicly available data sets. We found that at the national scale, total inputs, outputs, and surpluses changed little (+/- 6%) between 2002 and 2012 and remained dominated by agricultural processes, despite efforts to curb N losses. This consistency at the national scale, however, obscured large counteracting shifts at regional levels driven by variable fluxes across regions. Throughout the eastern United States, declines in deposition and fertilizer inputs combined with increased crop yields resulted in a decrease in terrestrial N surpluses, which may explain recent water quality improvements in the region. On the other hand, fertilizer N inputs in the Midwest increased at a greater rate than crop harvest N increased, leading to a larger terrestrial surplus N. A large relative increase (~320%) in N emissions in the West due to an unusual wildfire season in 2012 was also observed. These changes coincided with national policies that decreased N emissions and increased demand for domestic biofuels, potentially highlighting the capacity to change the source and magnitude of N inputs and fluxes across the landscape through market and regulatory actions.

Abstract  This report provides projections for the agricultural sector to 2029. Projections cover agricultural commodities, agricultural trade, and aggregate indicators of the sector, such as farm income. The projections are based on specific assumptions about macroeconomic conditions, policy, weather, and international developments, with no domestic or external shocks to global agricultural markets. The Agriculture Improvement Act of 2018 is assumed to remain in effect through the projection period. The projections are one representative scenario for the agricultural sector for the next decade and reflect a composite of model results and judgment-based analyses. The projections in this report were prepared during July 2019 through January 2020, with the commodity projections based off the conditions as of the October 2019 WASDE. While agricultural crop prices are tending to trend upwards only slowly in nominal terms, U.S. trade disputes with China that existed at the time of these projections were formulated have dampened expectations, particularly for soybeans. These projections assume the trade disputes to continue the duration of the projection period. Planted acreage drops slightly overall compared to recent years, primarily due to expected lower soybean plantings, while corn and wheat plantings are expected to remain mostly unmoved. Acreage enrolled in the Conservation Reserve Program (CRP) is also expected to rise, lowering total acres to the eight main crops. Energy costs are expected to increase, with crude oil import prices reaching $91 per barrel at the end of the projection. Low feed costs and continued strong global demand provide economic incentives for expansion in the livestock sector. Long-run developments for global agriculture reflect steady world economic growth and continued global demand for biofuel feedstocks, factors which combine to support longer run increases in disappearance, trade, and, to a lesser extent, prices of agricultural products. Although a relatively strong but slowly weakening U.S. dollar is expected to dampen growth in U.S. agricultural exports, the United States remains competitive in global agricultural markets, in part due to efficiency gains. Net farm income is expected to increase $1.4 billion in 2020 to $93.9 billion and remaining between $88.8 and $98.6 billion for the remainder of the decade, trending upward during the latter half

Abstract  Over the last decade, growing demand for agricultural commodities—for both food and fuel—has increased the incentives for farm operators to increase production. One way to expand production and potentially increase the return to farming is by intensifying the use of existing cropland. One form of intensification is double cropping—the harvest of two crops from the same field in a given year. From 1999 to 2012 double cropping occurred on about 2 percent of total cropland in most years. Soybeans were, on average, the most common crop found on double-cropped acres over this time period, and, in 2012, winter wheat most commonly preceded these soybean plantings. However, regional and temporal variation is apparent in all double-cropping trends, likely indicating farmers’ responsiveness to local conditions and changing market incentives. Although double cropping has the potential to limit the environmental consequences associated with cropland expansion (such as increased soil erosion and loss of wildlife habitat or carbon sinks) as U.S. farmers increase production to meet growing global demand, it also may introduce negative environmental consequences of its own. The trends and analysis provided in this report are intended to support future discussion on the factors influencing its use and help inform discussions about the merits of expanding its use.

Abstract  In central regions of the U.S. Corn Belt, agricultural production since 2001 has changed in response to federal policies implemented to encourage production of biofuels. Such changes have influenced agricultural practices, land uses, and their spatial character. This study examines site-specific temporal and spatial patterns of agricultural land use dynamics from 2001 to 2012 in a nine-county region of East-Central Iowa using the United States Department of Agriculture National Agricultural Statistics Service Cropland Data Layer. Results indicate that increases in corn production in response to US biofuel policies and high grain prices have been achieved mainly by altering crop rotation patterns. These changes may be correlated with market forces, although variations suggest a multiplicity of causes. This study also examines spatial relationships between cultivated fields and crop rotation practices with respect to underlying soils and terrain. Intensity of cultivated land use depends on topographic and pedologic properties, although motivations and constraints perceived by producers and managers as they plan their use of landscapes are important. The most intensively cultivated lands have shallower slopes and fewer pedologic limitations than others, and corn was planted in higher quality soil while soybeans were moved to lesser quality soils. Declining acreage in the Conservation Reserve Program since 2007 indicates that they may be used for other crops displaced by corn.

Abstract  Biofuel production from energy crops is land-use intensive. Land-use change (LUC) associated with bioenergy cropping impacts on the greenhouse gas (GHG) balance, both directly and indirectly. Land-use conversion can also impact on biodiversity. The current state of quantifying GHG emissions relating to direct and indirect land-use change (iLUC) from biomass produced for liquid biofuels or bioenergy is reviewed. Several options for reducing iLUC are discussed, and recommendations made for considering LUC in bioenergy and biofuel policies. Land used for energy cropping is subject to competing demands for conventional agriculture and forest production, as well as for nature protection and conservation. Biomass to be used for bioenergy and biofuels should therefore be produced primarily from excess farm and forest residues or from land not required for food and fiber production. The overall efficiency of biomass production, conversion, and use should be increased where possible in order to further reduce land competition and the related direct and iLUC risks. This review of several varying approaches to iLUC substantiates that, in principle, GHG emissions can be quantified and reductions implemented by appropriate policies. Such approaches can (and should) be refined and substantiated using better data on direct LUC trends from global monitoring, and be further improved by adding more accurate estimates of future trade patterns where appropriate. This brief discussion of current policies and options to reduce iLUC has identified a variety of approaches and options so that a quantified iLUC factor could be translated into practical regulations - both mandatory and voluntary - with few restrictions. Depending on the future development of energy cropping systems and yield improvements, sustainable bioenergy production could make a significant contribution to the future global energy demand.

Abstract  The corn (Zea mays L.)-based ethanol carbon footprint is impacted by many factors including the soils C sequestration potential. The studys objective was to determine the South Dakota corn-based ethanol surface SOC sequestration potential and associated partial C footprint. Calculated short-term C sequestration potentials were compared with long-term sequestration rates calculated from 95,214 producer soil samples collected between 1985 and 2010. National Agricultural Statistics Service (NASS) grain yields, measured root/shoot ratios and harvest indexes, soil organic C (SOC) and nonharvested C (NHC) first-order rate constants, measured SOC benchmarks [81,391 composite soil samples (0-15 cm) collected between 1985 and 1998], and 34,704 production surveys were used to calculate the short-term sequestration potentials. The SOC short-term, area weighted sequestration potential for the 2004 to 2007 time period was 181kg C (ha x yr)(-1). This relatively low rate was attributed to a drought that reduced the amount of NHC returned to soil. For the 2008 to 2010 time period, the area weighted short-term sequestration rate was 341 kg (ha x yr)(-1). This rate was similar to the long-term measured rate of368 kg C (ha x yr)(-1). Findings from these independent SOC sequestration assessments supports the hypothesis that many of the regions surface soils are C sinks when seeded with corn. Based on short-term C sequestration rates, corn yields, and the corn conversion rate to ethanol, the area weighted surface SOC footprints for the 2004 to 2007 and 2008 to 2010 time periods was -10.4 and -15.4 g CO2 (equ) MJ(-1), respectively.

Abstract  Low prices, trade conflict and a global pandemic are producing a potential perfect storm of problems for the farm economy that a flood of federal payments is unlikely to address. Whispered comments and quietly tentative questions about production controls and set aside acres are getting louder, more insistent. Whatever follows in the wake of this troubled year will likely require a substantial rethinking of federal farm policy. With that in mind, this article initiates a series discussing policies that seek to control production, including setting acres aside (i.e., not planting those acres to cash crops), with a review of the history for these policies.

Abstract  Accurate representation of crop responses to climate is critically important to understand impacts of climate change and variability in food systems. We use Random Forest (RF), a diagnostic machine learning tool, to explore the dependence of yield on climate and technology for maize, sorghum and soybean in the US plains. We analyze the period from 1980 to 2016 and use a panel of county yields and climate variables for the crop-specific developmental phases: establishment, critical window (yield potential definition) and grain filling. The RF models accounted for between 71% to 86% of the yield variance. Technology, evaluated through the time variable, accounted for approximately 20% of the yield variance and indicates that yields have steadily increased. Responses to climate confirm prior findings revealing threshold-like responses to high temperature (yield decrease sharply when maximum temperature exceed 29 °C and 30 °C for maize and soybean), and reveal a higher temperature tolerance for sorghum, whose yield decreases gradually as maximum temperature exceeds 32.5 °C. We found that sorghum and soybean responded positively to increases in cool minimum temperatures. Maize yield exhibited a unique and negative response to low atmospheric humidity during the critical phase that encompasses flowering, as well as a strong sensitivity to extreme temperature exposure. Using maize as a benchmark, we estimate that if warming continues unabated through the first half of the 21st century, the best climatic conditions for rainfed maize and soybean production may shift from Iowa and Illinois to Minnesota and the Dakotas with possible modulation by soil productivity.