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Dedicated bioenergy crops such as switchgrass ( Panicum virgatum L.) can be grown on marginally productive lands and positively influence soil properties. However, nitrogen management, and landscape can alter soil structural attributes under bioenergy crop production. This study investigated the impacts of long-term nitrogen fertilization (0-N, 0 kg N/ha; 56-N, 56 kg N/ha and 112-N, 112 kg N/ha) and landscape positions (shoulder and footslope) on soil organic carbon (SOC) and structural attributes under switchgrass production. The 112-N rate enhanced the proportion of 2–4 mm water-stable aggregates by 49%, aggregate associated carbon in 2–4 mm and >4 mm aggregates by 16 and 24%, respectively, aggregate associated nitrogen in >4 mm aggregates by 33% and reduced soil bulk density by 19% compared to the 0-N rate. Footslope position increased the proportion of 2–4 mm water-stable aggregates by 26% and lowered bulk density by 8% compared to the shoulder position. Results showed a significant N-rate × landscape position interaction on SOC and glomalin related soil protein content in bulk soil. Overall, this study showed that nitrogen application to switchgrass planted at footslope on a marginally yielding cropland improved soil structure and physical conditions.

Core Ideas Nitrogen rate did not affect soil properties for Oklahoma, South Dakota, and Virginia. Landscape position affected soil properties under higher slope. Nitrogen rate affected root N, surface area, and weight for the total profile. Landscape position affected the root C and N. Switchgrass roots can increase C accumulation and reduce risk of N loss in soils. Switchgrass (Panicum virgatum L.) has been recognized as a potential bioenergy feedstock, and can positively impact soils and the environment. The experimental sites were established in 2008 at three locations with each in Oklahoma (OK), South Dakota (SD), and Virginia (VA) to assess the impacts of N fertilization rate (N rate; low, 0 kg ha−1; high, 112 kg ha−1) and landscape position (shoulder, backslope, and footslope) on select soil properties and root growth parameters. Data indicate that N rate did not affect soil bulk density (BD), pH, electrical conductivity (EC), soil organic carbon (SOC), and total nitrogen (TN) for any of five depths. Landscape position impacted some of these properties by depth, depending on location. The N rate influenced root weight (RW), root surface area (RSA), and root total nitrogen (RTN) for the total profile (0–100‐cm depth) depending on local site conditions. The landscape position impacted RW, root total carbon (RTC), and RTN for total profile according to different site conditions. The interactions of landscape position by N rate on switchgrass root parameters were significant. The findings in this study indicate that the root system of switchgrass could improve soils and increase C accumulation and reduce the risk of N loss to benefit the environment.

Switchgrass (Panicum virgatum L.) has been the principal perennial herbaceous crop investigated for bioenergy production in North America given its high production potential, relatively low input requirements, and potential suitability for use on marginal lands. Few large trials have determined switchgrass yields at field scale on marginal lands, including analysis of production costs. Thus, a field‐scale study was conducted to develop realistic yield and cost estimates for diverse regions of the USA. Objectives included measuring switchgrass response to fertility treatments (0, 56, and 112 kg N ha−1) and generating corresponding estimates of production costs for sites with diverse soil and climatic conditions. Trials occurred in Iowa, New York, Oklahoma, South Dakota, and Virginia, USA. Cultivars and management practices were site specific, and field‐scale equipment was used for all management practices. Input costs were estimated using final harvest‐year (2015) prices, and equipment operation costs were estimated with the MachData model ( $2015). Switchgrass yields generally were below those reported elsewhere, averaging 6.3 Mg ha−1 across sites and treatments. Establishment stand percent ranged from 28% to 76% and was linked to initial year production. No response to N was observed at any site in the first production year. In subsequent seasons, N generally increased yields on well‐drained soils; however, responses to N were nil or negative on less well‐drained soils. Greatest percent increases in response to 112 kg N ha−1 were 57% and 76% on well‐drained South Dakota and Virginia sites, where breakeven prices to justify N applications were over $ 70 and $63 Mg−1, respectively. For some sites, typically promoted N application rates may be economically unjustified; it remains unknown whether a bioenergy industry can support the breakeven prices estimated for sites where N inputs had positive effects on switchgrass yield. Biomass production is considered potentially beneficial for utilizing and conserving marginal lands and helping transitional rural economies. Our study tested switchgrass yield and economic responses to fertility on marginal soils in the USA. Switchgrass responded to nitrogen on this former tobacco land in Virginia (note tobacco barn in background), but fertility was not economically justified at all sites (photograph, John Fike).

Prairie cordgrass (PCG) ( Spartina pectinata Link) has a high tolerance to soil salinity and waterlogging, therefore, it can thrive on marginal lands. Optimizing the nitrogen (N) input is crucial to achieving desirable biomass production of PCG without negatively impacting the environment. Thus, this study was based on the hypothesis that the use of legumes such as kura clover ( Trifolium ambiguum M. Bieb.) (KC) as an intercrop with PCG can provide extra N to the crop reducing the additional N fertilizer and mitigating soil surface greenhouse gas (GHG) emissions. Specific objective of the study was to assess the impact of PCG managed with different N rates [0 kg N ha −1 (PCG-0N), 75 kg N ha −1 (PCG-75N), 150 kg N ha −1 (PCG-150N), and 225 kg N ha −1 (PCG-255N)], and PCG intercropped with KC (PCG-KC) on GHG fluxes and biomass yield. The experimental site was established in 2010 in South Dakota under a marginally yielding cropland. The GHG fluxes were measured from 2014 through 2018 growing seasons using the static chamber. Net global warming potential (GWP) was calculated. Data showed that cumulative CH 4 and CO 2 fluxes were similar for all the treatments over the study period. However, the PCG-KC, PCG-0N, and PCG-75N recorded lower cumulative N 2 O fluxes (384, 402, and 499 g N ha −1 , respectively) than the PCG-150N (644 g N ha −1 ) and PCG-255N (697 g N ha −1 ). The PCG-KC produced 85% and 39% higher yield than the PCG-0N in 2016 and 2017, respectively, and similar yield to the other treatments (PCG-75N, PCG-150N, and PCG-255N) in these years. Net GWP was 52% lower for the PCG-KC (112.38 kg CO 2 -eq ha −1 ) compared to the PCG-225N (227.78 kg CO 2 -eq ha −1 ), but similar to other treatments. Soil total N was 15%% and 13% higher under PCG-KC (3.7 g kg −1 ) than that under PCG-0N (3.2 g kg −1 ) and PCG-75N (3.3 g kg −1 ), respectively. This study concludes that intercropping prairie cordgrass with kura clover can enhance biomass yield and reduce fertilizer-derived N 2 O emissions and net global warming potential.

The exact mechanism of cadmium (Cd) immobilization by oyster shell (OS) has not been reported. The effect of OS on Cd immobilization and the exact mechanism should be known before applying remediation technology using OS to Cd contaminated soils. Therefore, the objective of this study was to elucidate the mechanism of Cd immobilization by OS. Three grams of OS (< 0.84 mm) was reacted with 30 mL of 0–3.56 mg Cd L−1 solution at 25 °C for 48 h. Cadmium adsorption increased with increasing initial concentration of Cd in solution. The X-ray diffraction patterns clearly demonstrated that precipitation of CdCO3 did not take place in suspensions of OS after reacting with up to 3.56 mol Cd L−1. Interestingly, we found formation of Ca0.67Cd0.33CO3 crystalline in suspension of OS after reacting with maximum initial Cd concentrations. Precipitation and chemisorption might contribute to Cd immobilization together. However, we feel confident that chemisorption is the major mechanism by which Cd immobilization occurs with OS. In conclusion, OS could be an effective bioadsorbent to immobilize Cd through formation of geochemically stable Cd mineral.

There have been few studies evaluating the effect of bottom ash (BA) on immobilization of heavy metals and reducing their phytoavailability. Further, work has not been conducted to evaluate the effect of BA along with mature animal manure compost (CP) on immobilization of cadmium (Cd) in soil and phytoavailability of this metal in contaminated soil. Therefore, this study was conducted to determine the effect of application of BA and CP on Cd phytoextractability. To elucidate the mechanism of Cd immobilization with BA and CP, soil was mixed without BA and CP, with BA only, with CP only, and with BA and CP together in the incubation. Bottom ash was applied at rates of 0 and 30 Mg/ha under different application rates of CP (0 and 30 Mg/ha) 2 weeks before sowing lettuce ( Lactuca sativa ). Our first experiment clearly demonstrated that reduced extractability of Cd with addition of BA, CP, and BA + CP was mainly the result of Cd adsorption by an increase in pH and negative charge of soil. Concentration of bioavailable Cd fraction ( F 1) effectively decreased with BA, CP, and BA + CP from 1.33 mg Cd/kg in control to 0.98, 0.29, and 0.26 mg Cd/kg, respectively. Applying BA and CP alone or together effectively reduced Cd uptake by lettuce. Concentration of Cd in lettuce decreased from 13.9 mg Cd/kg in control to 10.3 and 7.6 mg Cd/kg with application of BA and CP alone, respectively. However, applying BA with CP increased fresh lettuce yields more than BA applied alone. Therefore, combined application of BA and CP might be a good management practice in Cd contaminated arable soil from the view point of Cd phytoavailability and crop productivity.

The objectives of this study were to determine (1) the phosphorus (P) level required to induce cadmium (Cd) precipitation in a contaminated arable soil with low concentrations of Cd and (2) the primary mechanism of Cd immobilization at different P levels. Phosphorus was added at levels of 0 800, 1600, and 16,000 mg P kg −1 to a soil containing 5.57 mg Cd kg −1 . The concentration of 1 M NH 4 OAc extractable Cd decreased significantly with P levels up to 1600 mg kg −1 due to an increase in soil pH and negative charge of soil ( p  < 0.001). A further decrease in 1 M NH 4 OAc extractable Cd concentration was noted when P was increased to 16,000 mg P kg −1 and may have been the result of Cd precipitation. This study suggest that adding P at high levels may help in the formation of geochemically stable Cd minerals in soil containing low levels of this heavy metal.

Switchgrass (Panicum virgatum L.) production has the potential to improve soils and the environment. However, little is known about the long‐term future assessment of soil and environmental impacts associated with switchgrass production. In this study, soil organic carbon (SOC), soil nitrate (NO3−), water‐filled pore space (WFPS), carbon dioxide (CO2) and nitrous oxide (N2O) fluxes, and biomass yield from switchgrass field were predicted using DAYCENT models for 2016 through 2050. Measured data for model calibration and validation at this study site managed with nitrogen fertilization rates (N rates) (low, 0 kg N ha−1; medium, 56 kg N ha−1; and high, 112 kg N ha−1) and landscape positions (shoulder and footslope) for switchgrass production were collected from the previously published studies. Modeling results showed that the N fertilization can enhance SOC and soil NO3−, but increase soil N2O and CO2 fluxes. In this study, medium N fertilization was the optimum rate for enhancing switchgrass yield and reducing negative impact on the environment. Footslope position can be beneficial for improving SOC, NO3−, and yield, but contribute higher greenhouse gas (GHG) emissions compared to those of the shoulder. An increase in temperature and decrease in precipitation (climate scenarios) may reduce soil NO3−, WFPS, and N2O flux. Switchgrass production can improve and maintain SOC and NO3−, and reduce N2O and CO2 fluxes over the predicted years. These findings indicate that switchgrass could be a sustainable bioenergy crop on marginally yielding lands for improving soils without significant negative impacts on the environment in the long run.

Switchgrass (Panicum virgatum L.) is a promising feedstock for bioenergy and bioproducts; however, its inherent variability in chemical attributes creates challenges for uniform conversion efficiencies and product quality. It is necessary to understand the range of variation and factors (i.e., field management, environmental) influencing chemical attributes for process improvement and risk assessment. The objectives of this study were to (1) examine the impact of nitrogen fertilizer application rate, year, and location on switchgrass chemical attributes, (2) examine the relationships among chemical attributes, weather and soil data, and (3) develop models to predict chemical attributes using environmental factors. Switchgrass samples from a field study spanning four locations including upland cultivars, one location including a lowland cultivar, and between three and six harvest years were assessed for glucan, xylan, lignin, volatiles, carbon, nitrogen, and ash concentrations. Using variance estimation, location/cultivar, nitrogen application rate, and year explained 65%–96% of the variation for switchgrass chemical attributes. Location/cultivar × year interaction was a significant factor for all chemical attributes indicating environmental‐based influences. Nitrogen rate was less influential. Production variables and environmental conditions occurring during the switchgrass field trials were used to successfully predict chemical attributes using linear regression models. Upland switchgrass results highlight the complexity in plant responses to growing conditions because all production and environmental variables had strong relationships with one or more chemical attributes. Lowland switchgrass was limited to observations of year‐to‐year environmental variability and nitrogen application rate. All explanatory variable categories were important for lowland switchgrass models but stand age and precipitation relationships were particularly strong. The relationships found in this study can be used to understand spatial and temporal variation in switchgrass chemical attributes. The ability to predict chemical attributes critical for conversion processes in a geospatial/temporal manner would provide state‐of‐the‐art knowledge for risk assessment in the bioenergy and bioproducts industry. Switchgrass is a promising feedstock for bioenergy and bioproducts. Chemical attributes were assessed for switchgrass from a field study spanning five locations and up to six harvest years. Production variables and environmental conditions occurring during the switchgrass field trials were used to successfully predict chemical attributes using linear regression models. The relationships found in this study can be used to understand spatial and temporal variation in switchgrass chemical attributes. The ability to predict chemical attributes critical for conversion processes in a geospatial/temporal manner would provide state‐of‐the‐art knowledge for risk assessment in the bioenergy and bioproducts industry.

The potential ecological impacts of switchgrass (Panicum virgatum L.), as a biofuel feedstock, have been assessed under different environmental conditions. However, limited information is available in understanding the integrated analysis of nitrogen (N) dynamics including soil nitrate (NO3−), nitrous oxide (N2O) emissions, and NO3− leaching under switchgrass land management. The specific objective was to explore N dynamics for 2009 through 2015 in switchgrass seeded to a marginally yielding cropland based on treatments of N fertilization rate (N rate; low, 0; medium, 56; high, 112 kg N ha−1) and landscape position (shoulder, backslope, and footslope). Our findings indicated that N rate impacted soil NO3− (0–5 cm depth) and surface N2O fluxes but did not impact NO3− leaching during the observed years. Medium N (56 kg N ha−1) was the optimal rate for increasing biomass yield with reduced environmental problems. Landscape position impacted the N dynamics. At the footslope position, soil NO3−, soil NO3− leaching, and N2O fluxes were higher than the other landscape positions. Soil N2O fluxes and NO3− leaching had downward trends over the observed years. Growing switchgrass on marginally yielding croplands can store soil N, reduce N losses via leaching, and mitigate N2O emissions from soils to the atmosphere over the years. Switchgrass seeded on marginally yielding croplands can be beneficial in reducing N losses and can be grown as a sustainable bioenergy crop on these marginal lands.