Abstract  Intensive nutrient fertilisation of forests has been suggested as a method to increase production of biofuels as a replacement for fossil fuels. We used a field experiment in a Norway spruce, Picea abies (L.) Karst., stand in northern Sweden to examine possible long-term effects of forest fertilisation on soil fauna (Oribatida, Mesostigmata, Collembola, predatory macroarthropods). Fertilisers had been applied annually for a period of 13 years, both in solid and liquid form, and N was added as ammonium nitrate (75-100 kg N ha(-1) per year). For comparison, control plots and plots receiving only irrigation were included. An autumn sampling showed soil fauna decreases in Plots receiving fertiliser in solid form, but increases in plots receiving liquid fertiliser. Clear shifts in community composition following both fertilisation methods were seen in Oribatida and Collembola, but species number and diversity were not significantly affected. This was probably due to increases in tolerant species that balanced decreases in other species. Liquid fertilisation had less negative effects on many species than fertilisation in solid form. Irrigation alone did not affect faunal abundances and had no effect on community composition of Oribatida and Collembola. The study indicates that intensive forest fertilisation will cause large shifts in soil microarthropod communities, but that species richness may remain unaffected. The risk of species loss will probably depend upon the size of the areas used for this purpose.

Abstract  While many ecosystem processes depend on biodiversity, the relationships between agricultural plant diversity and soil carbon (C) and nitrogen (N) dynamics remains controversial. Our objective was to examine how temporal plant diversity (i.e. crop rotation) influences residue decomposition, a key ecosystem function that regulates nutrient cycling, greenhouse gas emissions, and soil organic matter formation. We incubated soils from five long-term crop rotations, located at W.K. Kellogg Biological Station LTER in southwestern Michigan, USA, with and without four chemically diverse crop residues. Increasing crop biodiversity increased soil potentially mineralizable C by 125%, increased hydrolytic enzyme activity by 46%, but decreased oxidative enzyme activity by 20% in soils before residue was added. After residue additions, soils from more diverse cropping systems decomposed all residues more rapidly (0.2-8.3% greater mass loss) compared to monoculture corn. The fast-cycling, 'Active C' pool and microbial biomass N increased with higher cropping diversity, but the differences among rotations in Active C pools was higher for the most recalcitrant residues. Further, the ratio of the cellulose degrading enzyme (beta-glucosidase) to the lignin degrading enzyme (phenol oxidase) was highest in the two most diverse crop rotations regardless of residue additions, providing additional evidence of enhanced microbial activity and substrate acquisition in more diverse rotations. Our study shows that crop diversity over time influences the processing of newly-added residues, microbial dynamics, and nutrient cycling. Diversifying crop rotations has the potential to enhance soil ecosystem functions and is critical to maintaining soil services in agricultural systems.

Abstract  Biofuel-induced landscape change will have an enormous impact on terrestrial ecosystems in the near future due to globally escalating energy demands, but investigations into the biological properties of soil under potential biofuel crops have not been well documented. The soil microbiota plays a significant role in ecosystem services and especially their regulation of carbon and nutrient cycles. To improve our knowledge about the structure of soil microbial community and the factors that influence it, we analyzed microbial lipids and various soil physicochemical factors under model biofuel cropping systems of corn, switchgrass and mixed prairie in southern Wisconsin, USA. Principal component analysis of lipid biomarkers from soil microbial communities indicated that there were consistent differences among the crop species. Microbial biomass was significantly lower in corn than prairie soils, with switchgrass intermediate to these systems. An increase in fungi to bacteria ratio was coinciding with a net growth in fungal biomass when converting conventionally managed corn system to perennial systems, which indicates the microbial community change could be affected by the creation or expansion of niches for certain functional groups, rather than rebalancing of competitive interactions among these groups. The soil microbial community structure under corn was distinct from the perennial systems with markers indicative of greater in situ stress in annual corn sites and a reduced proportional abundance of arbuscular mycorrhizal fungi and an increased of gram-positive bacteria. Redundancy analysis (RDA) using 21 lipid biomarkers concurrently with 17 physicochemical indices showed that these properties correlated with different subsets of the microbial communities. We conclude that the cropping system shifted the microbial community composition at this regional scale, which may also affect the microbial processes associated with these differing communities. This may be significant when scaled up from regional to national, continental or global scales.

Abstract  Accumulation of nitrogen (N) in reservoirs has negative effects, generating algal blooms, creating hypoxic zones, and degrading drinking water quality. Agricultural land use, specifically corn and soybean cultivation, contribute excess N to aquatic systems. This work examines whether the nitrate as nitrogen (NO3–N) export (load) from a watershed is correlated to the percentage of land devoted to growing corn or soybeans. To investigate potential relationships, Annual NO3–N load from within 10 watersheds in the US Midwest were calculated using discharge (Q) and NO3–N concentration data obtained from USGS gauging stations. The NO3–N load data were coupled with crop data from the watersheds. Watershed areas ranged from 106 to 154,767 km2. Corn was grown on between 14.3 and 56.1% of the land, while soybeans accounted for 7.2–45.4%. Crop percentages were compared to NO3–N loads per area, the quotient of annual NO3–N load (kg) to the watershed area (km2), from 2008 to 2017. The analyses of the collective data showed a positive trend between the percentage of land cultivated and the NO3–N exported. However, as the percentage of corn cultivated increased within the individual watersheds, NO3–N load per area decreased. At both the collective and individual scale, increases in soybean cultivation resulted in increases in NO3–N export. Extended cultivation of the same crop lead to higher NO3–N export. Strategies to decrease NO3–N export need to focus on enhanced crop rotation.

Abstract  Removal of crop residues for bioenergy, feedstock, or other purposes should be done with caution to avoid excessive soil erosion or loss of soil organic matter (SOM). This study examined average annual changes in soil erosion from rainfall and wind forces and trends in soil organic matter as a function of commodity and/or bioenergy-based crop rotations, yield variations, and different field management practices, including residue removal across all land capability class (LCC) I to VIII soils in selected areas of the U.S. Central Great Plains (CGP). Specifically, comparisons were made between various rotations including corn, winter wheat, sorghum, cotton, fallow, and canola, subject to reduced tillage and no-till management practices. The purpose was to assess cropping options, field management, and soil sustainability to provide a geospatial assessment for use in soil conservation planning and possible bioenergy resource assessments in the CGP. Soil erosion and SOM (proxied by a soil conditioning index, SCI) were analyzed on individual soil map unit components using the RUSLE2 and WEPS models. Results were grouped by LCC and organized with respect to three different spatial resolutions: field scale (individual soil type), field scale aggregated to county level, and field scale aggregated to regional level. Analyses indicate variation in soil erosion and SCI trends as a function of crop type, rotation, and field management practices across different soil types within a single county and at the regional level. Considerable variation in removable residue amounts also occurred across different rotations, especially with respect to crop type, rotation, soil type, and tillage. Results obtained in this study should help advance the overall knowledge base of both public and private-focused commodity and bioenergy crop production agriculture and soil sustainability by providing small informational resolution (i.e., soil type) data on soil erosion and health trends that could have a pronounced effect on producer economics and long-term land sustainability.

Abstract  Cover cropping in association with row crop rotation has been suggested as a favorable conservation practice in improving soil chemical characteristics. The main objective of this research was to investigate the effects of growing cover crops under conservation tillage on soil organic carbon (C), total nitrogen (N), pH, electrical conductivity (EC), soil organic matter (SOM) content, nitrate-nitrogen (NO3-N), and phosphorus (P) in different surface cover treatments, including (1) cover crop only without seed maize (Zea mays L.) or soybean (Glycine max L.) residue (CC), (2) cover crop mixtures planted in seed maize or soybean residue (SCCC), (3) seed maize or soybean residue only without cover crops (SC), and (4) bare soil. Field research was conducted from 2012 to 2015 on three center pivot-irrigated, seed maize/soybean cover crop rotation, large-scale production fields near Beaver Crossing, Nebraska. Changes in soil chemical properties exhibited variation between the treatments and between the soil layers within the same treatment as well as between the years. Inclusion of continuous cover cropping resulted in small increases of organic C and total N only in the top 0 to 5 cm soil depth in the SCCC treatment. During the winter period when cover crops were winter-killed and decomposed onto the soil surface, both C and N concentration in the topsoil (0 to 5 cm) SCCC plots had increased by 8% and 21%, respectively, and in the CC plots by 10% and 5%, respectively. Although cover crops are highly decomposable, an increase in SOM levels following cover crops was only limited to the topsoil (0 to 20 cm). Soil organic matter under cover cropped plots in the 0 to 5 cm soil layer was 28% higher than the bare soil treatment. Cover crops significantly (p < 0.05) reduced P and NO3-N quantities in the soil when they were alive and actively growing; however, they also contributed to providing N and P to the next maize crop by residue decomposition in winter. There was no significant (p > 0.05) change in soil pH among treatments. Cover cropped treatments had decreased soil EC at all soil layers and ranged from 7.3% decrease to 74% decrease from the beginning to the end of the research. This research showed that SOM, NO3-N, P, C, and N can be at least conserved or maintained and/or enhanced (primarily in the topsoil) by cover crop species researched, and thus, can contribute to improving the soil quality and, in turn, potentially improve crop productivity. However, it is important to note that most of the changes in soil chemical properties as a result of incorporating cover crops in the rotation appeared to be confined in the topsoil.

Abstract  To determine the relative responsiveness to and dependency on vesicular-arbuscular mycorrhizae (VAM) of annual and perennial plants, this study compared the responses of congeneric, sympatric pairs of species in the grass genera Panicum and Bromus to inoculation with two VAM fungal isolates from the genus Glomus. When inoculated with G. intraradices, the perennials P. virgatum and B. inermus showed significantly greater response at both high and low phosphorus (P) than did the annuals P. capillare and B. secalinus. Responsiveness of perennials was significant at both P levels, whereas annuals responded significantly only at low P. Neither Bromus species responded strongly to inoculation with G. etunicatum. Overall, the perennial grasses were more responsive and dependent than were the annuals. A survey of 26 studies including 84 plant-VAM fungus combinations yielded similar patterns of responsiveness in relation to P level and plant life span, especially for grasses. The greater responsiveness of perennial grasses to VAM infection must be considered within the suite of life history traits used to erect hypotheses concerning successional replacement of annuals by perennials in graminoid-dominated ecosystems.

Abstract  The first US commercial-scale plant to make ethanol fuel from agriculture waste will cease production and convert to an R&D facility. The plant, in Emmetsburg, Iowa, was built by a joint venture of enzyme specialist DSM and ethanol producer Poet. The two partnered in 2012 to produce cellulosic ethanol, a second-generation biofuel that fuel blenders were mandated to purchase under the Renewable Fuel Standard (RFS), part of a law enacted during the George W. Bush administration. The plant began operating in 2014, but in the years since, the US Environmental Protection Agency, under pressure from the refinery industry, has reduced—rather than grown as expected—the required purchases of biofuels using a waiver program. The waning power of the RFS has also hurt the market for traditional corn ethanol and spurred farmers to lobby the Trump administration to strengthen the standard, with little success. “Over the last three years, EPA management of the RFS has held back cellulosic ethanol advancement, hindered future agricultural markets for U.S. farmers, and undermined what the President has promised,” Poet spokesperson Kyle Gilley says in a statement. Poet-DSM will reduce head count at the plant in February.

Abstract  This article reviews literature about the impacts of cover crops in cropping systems that affect soil and water quality and presents limited new information to help fill knowledge gaps. Cover crops grow during periods when the soil might otherwise be fallow. While actively growing, cover crops increase solar energy harvest and carbon flux into the soil, providing food for soil macro and microrganisms, while simultaneously increasing evapotranspiration from the soil. Cover crops reduce sediment production from cropland by intercepting the kinetic energy of rainfall and by reducing the amount and velocity of runoff. Cover crops increase soil quality by improving biological, chemical and physical properties including: organic carbon content, cation exchange capacity, aggregate stability, and water infiltrability. Legume cover crops contribute a nitrogen (N) to subsequent crops. Other cover crops, especially grasses and brassicas, are better at scavenging residual N before it can leach. Because growth of these scavenging cover crops is usually N limited, growing grass/legume mixtures often increases total carbon inputs without sacrificing N scavenging efficiency. Cover crops are best adapted to warm areas with abundant precipitation. Water use by cover crops can adversely impact yields of subsequent dryland crops in semiarid areas. Similarly, cooler soil temperatures under cover crop residues can retard early growth of subsequent crops grown near the cold end of their range of adaptation. Development of systems that reduce the costs of cover crop establishment and overcome subsequent crop establishment problems will increase cover crop utilization and improve soil and water quality.

Abstract  Recent expansion of croplands in the United States has caused widespread conversion of grasslands and other ecosystems with largely unknown consequences for agricultural production and the environment. Here we assess annual land use change 2008-16 and its impacts on crop yields and wildlife habitat. We find that croplands have expanded at a rate of over one million acres per year, and that 69.5% of new cropland areas produced yields below the national average, with a mean yield deficit of 6.5%. Observed conversion infringed upon high-quality habitat that, relative to unconverted land, had provided over three times higher milkweed stem densities in the Monarch butterfly Midwest summer breeding range and 37% more nesting opportunities per acre for waterfowl in the Prairie Pothole Region of the Northern Great Plains. Our findings demonstrate a pervasive pattern of encroachment into areas that are increasingly marginal for production, but highly significant for wildlife, and suggest that such tradeoffs may be further amplified by future cropland expansion.