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  Neonicotinoids are the most widely used class of insecticides worldwide, but patterns of their use in the U.S. are poorly documented, constraining attempts to understand their role in pest management and potential nontarget effects. We synthesized publicly available data to estimate and interpret trends in neonicotinoid use since their introduction in 1994, with a special focus on seed treatments, a major use not captured by the national pesticide-use survey. Neonicotinoid use increased rapidly between 2003 and 2011, as seed-applied products were introduced in field crops, marking an unprecedented shift toward large-scale, preemptive insecticide use: 34-44% of soybeans and 79-100% of maize hectares were treated in 2011. This finding contradicts recent analyses, which concluded that insecticides are used today on fewer maize hectares than a decade or two ago. If current trends continue, neonicotinoid use will increase further through application to more hectares of soybean and other crop species and escalation of per-seed rates. Alternatively, our results, and other recent analyses, suggest that carefully targeted efforts could considerably reduce neonicotinoid use in field crops without yield declines or economic harm to farmers, reducing the potential for pest resistance, nontarget pest outbreaks, environmental contamination, and harm to wildlife, including pollinator species.

Abstract  Long-term loss of soil C stocks under conventional tillage and accrual of soil C following adoption of no-tillage have been well documented. No-tillage use is spreading, but it is common to occasionally till within a no-till regime or to regularly alternate between till and no-till practices within a rotation of different crops. Short-term studies indicate that substantial amounts of C can be lost from the soil immediately following a tillage event, but there are few field studies that have investigated the impact of infrequent tillage on soil C stocks. How much of the C sequestered under no-tillage is likely to be lost if the soil is tilled? What are the longer-term impacts of continued infrequent no-tillage? If producers are to be compensated for sequestering C in soil following adoption of conservation tillage practices, the impacts of infrequent tillage need to be quantified. A few studies have examined the short-term impacts of tillage on soil C and several have investigated the impacts of adoption of continuous no-tillage. We present: (1) results from a modeling study carried out to address these questions more broadly than the published literature allows, (2) a review of the literature examining the short-term impacts of tillage on soil C, (3) a review of published studies on the physical impacts of tillage and (4) a synthesis of these components to assess how infrequent tillage impacts soil C stocks and how changes in tillage frequency could impact soil C stocks and C sequestration. Results indicate that soil C declines significantly following even one tillage event (1–11% of soil C lost). Longer-term losses increase as frequency of tillage increases. Model analyses indicate that cultivating and ripping are less disruptive than moldboard plowing, and soil C for those treatments average just 6% less than continuous NT compared to 27% less for CT. Most (80%) of the soil C gains of NT can be realized with NT coupled with biannual cultivating or ripping.

Abstract  Spatiotemporal patterns of crop nitrogen (N) budget have important implications for agricultural N management and environmental policy. Previous studies examined crop N budget in different countries but often overlooked cross-crop differences at sub-national scales. In this study, we synthesize multiple databases to examine the N budget of eight major crops in the United States at the county scale during 1970–2019. Our analyses show that national crop N use efficiency (NUE) increased from 0.55 kg N kg−1 N in the 1970s to 0.65 kg N kg−1 N in the 2010s. Four out of eight crops such as corn, rice, cotton, and sorghum demonstrated an increasing NUE trend during the study period, whereas the other crops overall presented a declining NUE trend. Nationwide, about 41% of the total N input was not used by these crops (i.e., N surplus) over the study period, of which temporal variation was mainly driven by corn due to its large planting area and high N input. The national N surplus first increased in the 1970s and remained relatively stable till the 2000s. Since the early 2010s, however, N surplus began to decline and approached the levels in the early 1970s—an encouraging development that may lead to decreased N pollution to the environment. The hotspots of national N surplus coincided with corn- and rice-producing counties. The sub-national variations and temporal dynamics in crop N budget revealed in this study highlight the urgent need to understand the farm-level crop N balance and the dominant factors controlling crop NUE for mitigating N pollution.

Abstract  Neonicotinoids, broad-spectrum systemic insecticides, are the fastest growing class of insecticides worldwide and are now registered for use on hundreds of field crops in over 120 different countries. The environmental profile of this class of pesticides indicate that they are persistent, have high leaching and runoff potential, and are highly toxic to a wide range of invertebrates. Therefore, neonicotinoids represent a significant risk to surface waters and the diverse aquatic and terrestrial fauna that these ecosystems support. This review synthesizes the current state of knowledge on the reported concentrations of neonicotinoids in surface waters from 29 studies in 9 countries world-wide in tandem with published data on their acute and chronic toxicity to 49 species of aquatic insects and crustaceans spanning 12 invertebrate orders. Strong evidence exists that water-borne neonicotinoid exposures are frequent, long-term and at levels (geometric means=0.13μg/L (averages) and 0.63μg/L (maxima)) which commonly exceed several existing water quality guidelines. Imidacloprid is by far the most widely studied neonicotinoid (66% of the 214 toxicity tests reviewed) with differences in sensitivity among aquatic invertebrate species ranging several orders of magnitude; other neonicotinoids display analogous modes of action and similar toxicities, although comparative data are limited. Of the species evaluated, insects belonging to the orders Ephemeroptera, Trichoptera and Diptera appear to be the most sensitive, while those of Crustacea (although not universally so) are less sensitive. In particular, the standard test species Daphnia magna appears to be very tolerant, with 24-96hour LC50 values exceeding 100,000μg/L (geometric mean>44,000μg/L), which is at least 2-3 orders of magnitude higher than the geometric mean of all other invertebrate species tested. Overall, neonicotinoids can exert adverse effects on survival, growth, emergence, mobility, and behavior of many sensitive aquatic invertebrate taxa at concentrations at or below 1μg/L under acute exposure and 0.1μg/L for chronic exposure. Using probabilistic approaches (species sensitivity distributions), we recommend here that ecological thresholds for neonicotinoid water concentrations need to be below 0.2μg/L (short-term acute) or 0.035μg/L (long-term chronic) to avoid lasting effects on aquatic invertebrate communities. The application of safety factors may still be warranted considering potential issues of slow recovery, additive or synergistic effects and multiple stressors that can occur in the field. Our analysis revealed that 81% (22/27) and 74% (14/19) of global surface water studies reporting maximum and average individual neonicotinoid concentrations respectively, exceeded these thresholds of 0.2 and 0.035μg/L. Therefore, it appears that environmentally relevant concentrations of neonicotinoids in surface waters worldwide are well within the range where both short- and long-term impacts on aquatic invertebrate species are possible over broad spatial scales.

Abstract  Systemic insecticides are applied to plants using a wide variety of methods, ranging from foliar sprays to seed treatments and soil drenches. Neonicotinoids and fipronil are among the most widely used pesticides in the world. Their popularity is largely due to their high toxicity to invertebrates, the ease and flexibility with which they can be applied, their long persistence, and their systemic nature, which ensures that they spread to all parts of the target crop. However, these properties also increase the probability of environmental contamination and exposure of nontarget organisms. Environmental contamination occurs via a number of routes including dust generated during drilling of dressed seeds, contamination and accumulation in arable soils and soil water, runoff into waterways, and uptake of pesticides by nontarget plants via their roots or dust deposition on leaves. Persistence in soils, waterways, and nontarget plants is variable but can be prolonged; for example, the half-lives of neonicotinoids in soils can exceed 1,000 days, so they can accumulate when used repeatedly. Similarly, they can persist in woody plants for periods exceeding 1 year. Breakdown results in toxic metabolites, though concentrations of these in the environment are rarely measured. Overall, there is strong evidence that soils, waterways, and plants in agricultural environments and neighboring areas are contaminated with variable levels of neonicotinoids or fipronil mixtures and their metabolites (soil, parts per billion (ppb)-parts per million (ppm) range; water, parts per trillion (ppt)-ppb range; and plants, ppb-ppm range). This provides multiple routes for chronic (and acute in some cases) exposure of nontarget animals. For example, pollinators are exposed through direct contact with dust during drilling; consumption of pollen, nectar, or guttation drops from seed-treated crops, water, and consumption of contaminated pollen and nectar from wild flowers and trees growing near-treated crops. Studies of food stores in honeybee colonies from across the globe demonstrate that colonies are routinely and chronically exposed to neonicotinoids, fipronil, and their metabolites (generally in the 1-100 ppb range), mixed with other pesticides some of which are known to act synergistically with neonicotinoids. Other nontarget organisms, particularly those inhabiting soils, aquatic habitats, or herbivorous insects feeding on noncrop plants in farmland, will also inevitably receive exposure, although data are generally lacking for these groups. We summarize the current state of knowledge regarding the environmental fate of these compounds by outlining what is known about the chemical properties of these compounds, and placing these properties in the context of modern agricultural practices.

Abstract  Since its commercial introduction in 1974, glyphosate [N-(phosphonomethyl)glycine] has become the dominant herbicide worldwide. There are several reasons for its success. Glyphosate is a highly effective broad-spectrum herbicide, yet it is very toxicologically and environmentally safe. Glyphosate translocates well, and its action is slow enough to take advantage of this. Glyphosate is the only herbicide that targets 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS), so there are no competing herbicide analogs or classes. Since glyphosate became a generic compound, its cost has dropped dramatically. Perhaps the most important aspect of the success of glyphosate has been the introduction of transgenic, glyphosate-resistant crops in 1996. Almost 90% of all transgenic crops grown worldwide are glyphosate resistant, and the adoption of these crops is increasing at a steady pace. Glyphosate/glyphosate-resistant crop weed management offers significant environmental and other benefits over the technologies that it replaces. The use of this virtually ideal herbicide is now being threatened by the evolution of glyphosate-resistant weeds. Adoption of resistance management practices will be required to maintain the benefits of glyphosate technologies for future generations.

Abstract  Nitrogen management recommendations may change as yield levels and efficiency of crop production increase. The mean yield with nutrients applied in 32 irrigated corn (Zea mays L.) trials conducted across Nebraska from 2002 to 2004 to evaluate crop response to split-applied N was 14.8 Mg ha−1 The mean economically optimal nitrogen rates (EONR) for irrigated corn varied with the fertilizer N/grain price ratio. At a fertilizer N/corn price ratio of 7 the EONR was 171, 122, and 93 kg ha−1, respectively, for cropping systems with corn following corn (CC), soybean [Glycine max (L.) Merr.] (CS), and drybean (Phaseolus vulgaris L.) (CD). At this price ratio the present University of Nebraska (UNL) recommendation procedure gave mean N recommendations that were 17.2 and 68.1 kg ha−1 higher than the mean EONR determined in this study for CC and CD, respectively, but essentially equal to mean EONR for CS. The UNL algorithm, adjusted for mean cropping system EONR gave more accurate prediction of site-year EONR than alternative N rate predictions for CC and CD with returns to applied nitrogen (RTN) of –$22 and –$13 ha−1 compared with measured site-year EONR. Prediction of site-year EONR using mean EONR adjusted for soil organic matter was more accurate for CS than other methods with an RTN of –$6 ha−1 compared with measured site-year EONR. Further research is needed to extend the results to: lower yield situations, alternatives to split application of N, and adjustment of EONR to protect against inadequate N in atypical seasons or for environmental protection.

Abstract  Worldwide, aviation accounts for 2% of all manmade carbon dioxide emissions and 12% of all transportation CO2 emissions In 2018, the U.S. accounted for 25% of the world jet fuel consumption and 21% of global enplanements. Airports and airlines are considering alternative fuel to meet environmental and sustainability goals and mandates. Sustainable aviation fuel (SAF), made from non-petroleum feedstocks, has the potential to significantly reduce emissions from air transportation. SAF must be blended with petroleum based jet fuel prior to its use in aircraft. This report explores background information on jet fuel use, quality standards and best practices, airport infrastructure, and options for delivering SAF to airports.

Abstract  The 2015 feedlot consulting nutritionist survey is a collaborative project between New Mexico State University and Texas Tech University that focuses on summarizing the professional practices of consulting feedlot nutritionists and updates a 2007 survey. Forty-nine consulting feedlot nutritionists were asked to participate, of which 24 completed the survey. The nutritionists surveyed service over 14,000,000 cattle annually and were representatives from individual consulting practices (54.2%), corporate cattle feeding companies (20.8%), corporate feed manufacturing companies (20.8%), or a combination of consulting practices (4.2%). The survey was completed using a web-based survey tool and contained 101 questions that were divided into sections regarding general information about the consulting practice; general cattle management; receiving cattle management, diet adaption; mixers, feed mills, and feeding management; grains and grain processing; grain by-product use; roughage use; information about supplements and microingredients; liquid feed use; nutrient formulation; feed additive use; and information used as a basis for nutritional recommendations. In most cases, the results of the current survey were similar to those reported for the 2007 survey, with a few notable exceptions such as shifts in cattle numbers and preferences for specific feedstuffs. The present study introduced a number of new questions not included in the 2007 survey that focused on management strategies used in the receiving period. Data from this survey provide insight into current nutritional and management practices of consulting nutritionists and, as in past surveys, should be useful for informing national committees that make nutritional recommendations for cattle, as well as nutrition and management strategies employed within university research settings.

Abstract  This study summarizes the detailed techno-economic analysis of the ethanol-to-jet (ETJ) process based on two different feedstocks (corn grain and corn stover) at the plant scale of 2000 dry metric tons per day. Ethanol biologically derived from biomass is upgraded catalytically to jet blendstocks via alcohol dehydration, olefin oligomerization, and hydrotreating. In both pathways, corn-grain-derived ethanol to jet (corn mill ETJ) and corn-stover-derived ethanol to jet (corn stover ETJ), there are portions of gasoline and diesel produced as coproducts. Two cost bases are used in this study: the minimum jet fuel selling prices (MJSP) for jet-range blendstocks and the minimum fuel selling prices (MFSP) for all the hydrocarbons (gasoline, jet, and diesel) produced using a gallon gasoline equivalent (GGE) basis. The nth-plant MJSPs for the two pathways are estimated to be $4.20 per gal for corn mill and $6.14 per gal for corn stover, while MFSPs are $3.91 per GGE for corn mill and $5.37 per GGE for corn stover. If all of the hydrocarbon products (gasoline, jet, and diesel ranges) can be considered as fuel blendstocks using a GGE basis, the total hydrocarbon yield for fuel blendstock is 49.6 GGE per dry ton biomass for corn stover and 71.0 GGE per dry ton biomass for corn grain. The outcome of this study shows that the renewable jet fuel could be cost competitive with fossil derived jet fuel if further improvements could be made to increase process yields (particularly yields of sugars, sugar to ethanol, and ethanol to hydrocarbons), research and development of sustainable feedstocks, and more effective catalytic reaction kinetics. Pioneer plant analysis, which considers the increased capital investment and the decreased plant performance over the nth-plant analysis, is also performed, showing a potential 31%–178% increase in cost compared to the nth-plant assumptions for the dry mill pathway, but with a much wider range of 69%–471% cost increase over the nth-plant assumptions for the corn stover pathway. While there are large differences between the estimated first of a kind plant cost and the targeted nth-plant case, reduction of costs is possible through improvement of the overall process efficiency, yields, reduction in overall capital, co-product revenues and strategically improve performance by process learnings.

Abstract  Cool tolerant soybean (Glycine max (L.) Merrill) cultivars are a potential new crop for Canterbury, New Zealand, but cool temperatures during seed maturation may prevent seed desiccation to the 'safe' harvest moisture content of ca. 15%. In an experiment in the 2000/2001 season with cv. Northern Conquest and March, the effect of seed moisture content (SMC) at harvest on seed quality (germination and vigour) was determined. Seeds were hand harvested to avoid mechanical damage. At the first harvest (54–56% SMC) the mean germination was 96%, accelerated ageing (AA) germination was 94%, and conductivity was 17.06 μS/cm/g. At 'harvest ripeness' (11–14% SMC) the corresponding data were 93%, 82% and 21.57 μS/cm/g. Germination had therefore not changed but vigour had declined. In an adjacent experiment in the same season the effect of seed moisture content at machine threshing was examined. Germination was reduced by machine threshing at SMC > 16–19%. Seed vigour was highest at a SMC of 13–15%, and was reduced (lower AA germination and higher conductivity) when seed was harvested at higher SMC. Machine threshing at 10–12% SMC also reduced seed vigour. For these two cultivars in this environment, soybeans can be machine threshed at ca. 15% SMC without dramatically impairing seed quality, provided desiccation in the field can continue long enough for them to reach this seed moisture content.

Abstract  Increasing consolidation and concentration in the U.S. grain-elevator gathering system characterized by larger capacity elevators (shuttle) has altered shippers’ relative usage and demand for transportation services. In this study, we estimate modal demand for individual elevator wheat shipments from the U.S. Northern Plains to export and domestic destinations between 2006 and 2013. We find a much higher rail dependence for shuttle elevators in comparison to non-shuttle elevators reflected by the relative size of modal demand elasticities. On the other hand, truck is more competitive for non-shuttle elevators. Shuttle shippers saved 24% in total transportation cost in 2013 in comparison to non-shuttle shippers, with savings in rail transportation costs alone of 22%. Our results support the idea that shippers receive better service and view rail more favorably after adopting shuttle facilities. Moreover, these service benefits may partially mitigate the disadvantages captive shippers (such as those in the Northern Plains) realize in comparison to shippers with more transport options.

Abstract  Field corn is important in Florida for both grain and silage. Production has declined over the past two decades because of limited opportunities for profit, increased financial risks with less insurance coverage as compared to cotton and peanut, reduction in infrastructure for handling, and higher production costs.