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Cover crops (CCs) offer ecosystem benefits, yet their impact on subsequent crop yields varies with climate, soil, and management practices. Using the Decision Support System for Agrotechnology Transfer (DSSAT) at the University of Nebraska-Lincoln’s Eastern Nebraska Research, Education, and Extension Center (ENREEC), we identified optimal cereal rye management strategies focusing on planting, termination, and the intervals between CC termination and corn planting. Results showed minimal impact of CC management variations on corn yield, underscoring corn’s resilience to management changes. Delayed planting notably decreased CC biomass, nitrogen uptake, and biomass nitrogen content on average by 8.8%, 11%, and 9.2% for every five-day delay from 25 September. Every 5-day increase in the interval between CC termination and corn planting reduced biomass by 19.3%. Conversely, each 5-day delay in CC termination from 10 September to 10 October increased biomass by 30%, enhancing SOC accumulation. SOC changes over the 30-year simulation ranged from 5.8% to 7.7%, peaking with late May terminations. The earliest termination showed the highest nitrogen content in biomass (3.4%), with the lowest (0.69%) in mid-May. Our results demonstrate that strategic CC management supports soil health without negatively impacting corn yield in Eastern Nebraska, providing valuable insights for farmers and practitioners aiming to implement sustainable CC practices while preserving crop productivity.

Managing annual row crops on marginally productive croplands can be environmentally unsustainable and result in variable economic returns. Incorporating perennial bioenergy feedstocks into marginally productive cropland can engender ecosystem services and enhance climate resiliency while also diversifying farm incomes. We use one of the oldest bioenergy-specific field experiments in North America to evaluate economically and environmentally sustainable management practices for growing perennial grasses on marginal cropland. This long-term field trial called 9804 was established in 1998 in eastern Nebraska and compared the productivity and sustainability of corn (Zea mays L.)—both corn grain and corn stover—and switchgrass (Panicum virgatum L.) bioenergy systems under different harvest strategies and nitrogen (N) fertilizer rates. This experiment demonstrated that switchgrass, compared to corn, is a reliable and sustainable bioenergy feedstock. This experiment has been a catalyst for other bioenergy projects which have also expanded our understanding of growing and managing bioenergy feedstocks on marginal cropland. We (1) synthesize research from this long-term experiment and (2) provide perspective concerning both the knowledge gained from this experiment and knowledge gaps and how to fill them as well as the role switchgrass will play in the future of bioenergy.

Crop residue removal may negatively affect soil mechanical properties, which are key components of soil quality. To evaluate potential long-term effects, we assessed the 10-yr impact of corn (Zea mays L.) residue removal (59 % of non-grain biomass annually) on surface soil mechanical properties (0–20 cm). We also evaluated whether adding carbon (C) amendments, such as using a winter rye (Secale cereale L.) cover crop or surface-applying cattle manure (24 Mg ha−1 biannually) can ameliorate the effects of crop residue removal. This long-term study was under irrigated no-till continuous corn on a silt loam soil in south-central Nebraska, USA. Measurements included soil penetration resistance, field bulk density, aggregate strength, Atterberg limits (liquid limit, plastic limit, and plasticity index), Proctor maximum bulk density, and the water content at which the Proctor maximum bulk density (critical water content) occurs. Reduction in soil organic carbon (SOC) concentration explained most of the changes in soil mechanical properties. Long-term corn residue removal increased penetration resistance (+40 %) for the 0–20 cm depth, and reduced aggregate strength (−44 %), plasticity index (−22 %), and critical water content (−13 %) in the 0–5 cm depth. Residue removal also reduced field bulk density (−5%), liquid limit (−12 %), and plastic limit (−10 %) in the 0–10 cm depth, but increased Proctor maximum bulk density (+8 %) in the 0–5 cm depth. Winter rye cover crop reduced field bulk density (−5%, 0–15 cm depth) and increased penetration resistance (+52 %, 0–20 cm depth). Surface-applied manure amendments increased the near-surface soil liquid limit (+8 %) and plastic limit (+8 %) in the 0–5 cm depth. Given the high rate of residue removal used in this experiment, our findings support that excessive corn residue removal over the long-term (∼10 years) negatively affects near-surface soil mechanical properties, but that use of winter rye cover crop or surface-applied manure can minimally to partially ameliorate these effects.

Increasing crop functional richness in rotations can support grain yields more than species diversity in many environments, suggest grain yield data from 32 long-term experiments across Europe and North America.

Corn (Zea mays L.) stover demand as a forage or for an emerging bioeconomy has increased the importance of determining the long‐term effects of stover removal on grain yield and soil properties. Study objectives were to evaluate grain yield, soil organic carbon (SOC), and total soil N (0–150 cm) in a 20‐year, irrigated, continuous corn study, located in eastern Nebraska, under conventional tillage (CT) and no‐till (NT) with variable corn stover removal rates (none, medium, and high). After 20 years, grain yield was up to 6.0% greater under NT with stover removal compared with NT and no stover removal, while yield was similar for CT in all stover removal treatments. Grain yield was similar between NT with stover removal and CT in all stover removal treatments. High stover removal rates resulted in greater SOC loss at the surface soil layers (0–15 cm and 0–30 cm) after 20 years compared with no or medium stover removal. Corn stover retention under NT resulted in the same cumulative SOC stock loss as CT or stover removal. All management practices resulted in cumulative (0–120 cm) SOC stock loss (8% decrease) that occurred in the last 10 years of the study. Total soil nitrogen stocks were maintained or increased after 20 years at the surface soil layers (0–15 cm and 0–30 cm) and were similar between NT and CT. In an irrigated continuous corn system, neither NT nor stover retention was able to maintain cumulative SOC stocks over time. Core Ideas: Corn yield increased under no‐till with stover removal but not under conventional tillage.Corn yield was similar in conventional tillage under no, medium, and high stover removal rates.High residue removal rates decreased SOC stocks at the soil surface (0–30 cm) under both no‐till and conventional tillage.All management practices resulted in a net loss of cumulative SOC stocks. [ABSTRACT FROM AUTHOR]

Cover crops (CCs) offer ecosystem benefits, yet their impact on subsequent crop yields varies with climate, soil, and management practices. Using the Decision Support System for Agrotechnology Transfer (DSSAT) at the University of Nebraska-Lincoln's Eastern Nebraska Research, Education, and Extension Center (ENREEC), we identified optimal cereal rye management strategies focusing on planting, termination, and the intervals between CC termination and corn planting. Results showed minimal impact of CC management variations on corn yield, underscoring corn's resilience to management changes. Delayed planting notably decreased CC biomass, nitrogen uptake, and biomass nitrogen content on average by 8.8%, 11%, and 9.2% for every five-day delay from 25 September. Every 5-day increase in the interval between CC termination and corn planting reduced biomass by 19.3%. Conversely, each 5-day delay in CC termination from 10 September to 10 October increased biomass by 30%, enhancing SOC accumulation. SOC changes over the 30-year simulation ranged from 5.8% to 7.7%, peaking with late May terminations. The earliest termination showed the highest nitrogen content in biomass (3.4%), with the lowest (0.69%) in mid-May. Our results demonstrate that strategic CC management supports soil health without negatively impacting corn yield in Eastern Nebraska, providing valuable insights for farmers and practitioners aiming to implement sustainable CC practices while preserving crop productivity. [ABSTRACT FROM AUTHOR]

Abstract Environmental DNA (eDNA) methods are providing tools for detecting invasive species in aquatic environments. Targeted qPCR assays applied to eDNA samples promise to overcome limitations of traditional methods, especially for early detection. The European green crab (Carcinus maenas) is considered one of the most successful invasive species globally due to the large range it has invaded and negative impacts on native species, marine habitats, and shellfish industries. We developed, laboratory‐validated, and field‐tested a specific qPCR assay for the detection of green crab from eDNA samples. We also show that the assay can detect green crab in bulk DNA extracted from plankton samples. Assay design, optimization, sensitivity, and specificity testing generally followed the validation pathway recommended by the World Organization for Animal Health for assays used to manage global aquatic animal health and infectious disease. Assay specificity was verified in silico and in vitro by laboratory testing 26 nontarget species, none of which showed potential for amplification. Assay sensitivity was appropriately high, with the limit of detection approaching two gene copies/μl. The assay was field‐tested on eDNA samples collected from filtered seawater at five sites on the Pacific coast of Canada known to harbor green crab based on historical monitoring data; green crab DNA was amplified from all sites. We also present early pilot field testing of the assay done on bulk DNA extracted from plankton samples from four sites from Australia, two sites with and two sites without reported records of green crab presence. Green crab was detected at both sites with known green crab records. Significant inhibition was recorded for some plankton samples but not for eDNA samples. This is the first qPCR assay for detection of European green crab, providing researchers and managers with a valuable new tool to aid early detection and ongoing monitoring.

Abstract Background Cardiovascular magnetic resonance (CMR) angiography (CMRA) is an important non-invasive imaging tool for congenital heart disease (CHD) and aortopathy patients. The conventional 3D balanced steady-state free precession (bSSFP) sequence is often confounded by imaging artifacts. We sought to compare the respiratory navigated and electrocardiogram (ECG) gated modified Dixon (mDixon) CMRA sequence to conventional non-gated dynamic multi-phase contrast enhanced CMRA (CE-CMRA) and bSSFP across a variety of diagnoses. Methods We included 24 patients with CHD or aortopathy with CMR performed between September 2017 to December 2017. Each patient had undergone CE-CMRA, followed by a bSSFP and mDixon angiogram. Patients with CMR-incompatible implants or contraindications to contrast were excluded. The studies were rated according to image quality at a scale from 1 (poor) to 4 (excellent) based on diagnostic adequacy, artifact burden, vascular border delineation, myocardium-blood pool contrast, and visualization of pulmonary and systemic veins and coronaries. Contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR) and quantitative vascular measurements were compared between the two gated sequences. Bland-Altman plots were generated to compare paired measures. Results All scans were diagnostically adequate. Mean (SD) quality scores were 3.4 (0.7) for the mDixon, 3.2 (0.5) for the bSSFP and 3.4 (0.5) for the CE-CMRA. Qualitatively, the intracardiac anatomy and myocardium-blood pool definition were better in the bSSFP; however, mDixon images showed enhanced vessel wall sharpness with less blurring surrounding the anatomical borders distally. Coronary origins were identified in all cases. Pulmonary veins were visualized in 92% of mDixon sequences, 75% of bSSFP and 96% of CE-CMRA. Similarly, neck veins were identified in 92, 83 and 96% respectively. Artifacts prevented vascular measurement in 6/192 (3%) and 4/192 (2%) of total vascular measurements for the mDixon and bSSFP, respectively. However, the size of signal void and field distortion were significantly worse in the latter, particularly for flow and metal induced artifacts. Conclusion In patients with congenital heart disease, ECG gated mDixon angiography yields high fidelity vascular images including better delineation of head and neck vasculature and pulmonary veins and fewer artifacts than the comparable bSSFP sequence. It should be considered as the preferred strategy for successful CHD imaging in patients with valve stenosis, vascular stents, or metallic implants.

Abstract Understanding the impacts of long‐term fertilizer management and rotation diversity on soil C and N is needed under a changing climate. The objective of this study was to evaluate the effects of N fertilizer level and crop rotation diversity on soil organic carbon (SOC) and soil N stocks from a 34‐yr study located in eastern Nebraska. Seven crop rotations (three continuous cropping systems; two 2‐yr crop rotations; and two 4‐yr crop rotations) and three N levels were compared. Soil samples were taken to a depth of 150 cm. Differences in SOC stocks were largely confined to the 0‐ to 7.5‐cm depth, with greater SOC (P = .0002) in rotations than continuous cropping systems and greater SOC (P = .0004) in 4‐yr vs. 2‐yr rotations. Total soil N was greater with increased crop rotation diversity for the 0‐ to 30‐cm soil profile. Greater SOC levels occurred with N fertilization for the 0‐ to 7.5‐cm depth. At the 0‐ to 150‐cm soil depth, SOC stocks were similar between N levels and greater for the 4‐yr vs. 2‐yr crop rotations (P = .0492). Trends in total N stocks were similar to those of SOC stocks. Overall, crop rotation had a larger effect on SOC and N stocks than N fertilizer.

Information on corn (Zea mays L.) residue removal and organic amendment additions to ameliorate removal effects on soil properties is limited. Thus, we compared impacts of corn residue removal at 59% and organic amendments (winter rye [Secale cereale L.]) cover crop and manure every other year at 24 Mg ha−1 on soil organic carbon (SOC) and physical properties after 10 years under irrigated no‐till continuous corn on a silt loam in the western US Corn Belt. We collected soil property data after 10 years and then compared it with earlier results from this experiment (3 and 6 years). Cover crop and manure amendments maintained SOC concentration, but no amelioration practice reduced SOC concentration (−15%) from 3 to 10 years when residues were annually removed in 0‐ to 5‐cm depth. Under residue retention, SOC concentration increased with time with largest increase (+41%) occurring under manure amelioration practice in the 0‐ to 5‐cm depth. Residue removal reduced soil wet aggregate stability by 34%, soil dry aggregate stability by 73%, bulk density by 6%, water content at −33 kPa matric potential by 14%, and plant available water by 17% after 10 years in the 0‐ to 5‐cm soil depth but did not affect infiltration rate. Cover crops increased wet aggregate stability (32%), but manure and cover crops had limited effects on other soil properties. Residue removal increased the susceptibility of the soil to erosion and reduced water retention and SOC after 3 years, but such effects were not fully offset by amendments. Core Ideas: Corn residue removal at 59% reduced soil wet and dry aggregate stability and water content at field capacity.Residue removal did not negatively affect soil bulk density, infiltration rate, and saturated hydraulic conductivity.Cover crops partially offset residue removal effects on soil organic carbon and soil wet aggregate stability.Manure partially offsets the negative effects of residue removal on soil organic carbon after 3 and 10 years. [ABSTRACT FROM AUTHOR]

Managing annual row crops on marginally productive croplands can be environmentally unsustainable and result in variable economic returns. Incorporating perennial bioenergy feedstocks into marginally productive cropland can engender ecosystem services and enhance climate resiliency while also diversifying farm incomes. We use one of the oldest bioenergy-specific field experiments in North America to evaluate economically and environmentally sustainable management practices for growing perennial grasses on marginal cropland. This long-term field trial called 9804 was established in 1998 in eastern Nebraska and compared the productivity and sustainability of corn (Zea mays L.) --both corn grain and corn stover--and switchgrass (Panicum virgatum L.) bioenergy systems under different harvest strategies and nitrogen (N) fertilizer rates. This experiment demonstrated that switchgrass, compared to corn, is a reliable and sustainable bioenergy feedstock. This experiment has been a catalyst for other bioenergy projects which have also expanded our understanding of growing and managing bioenergy feedstocks on marginal cropland. We (1) synthesize research from this long-term experiment and (2) provide perspective concerning both the knowledge gained from this experiment and knowledge gaps and how to fill them as well as the role switchgrass will play in the future of bioenergy. [ABSTRACT FROM AUTHOR]

Diversifying agronomic production systems by combining crops and livestock (i.e., Integrated Crop Livestock systems; ICL) may help mitigate the environmental impacts of intensive single-commodity production. In addition, harvesting row-crop residues and/or perennial biomass could increase the multi-functionality of ICL systems as a potential source for second-generation bioenergy feedstock. Here, we evaluated non-CO2 soil greenhouse gas (GHG) emissions from both row-crop and perennial grass phases of a field-scale model ICL system established on marginally productive, poorly drained cropland in the western US Corn Belt. Soil emissions of nitrous oxide (N2O) and methane (CH4) were measured during the 2017–2019 growing seasons under continuous corn (Zea mays L.) and perennial grass treatments consisting of a common pasture species, ‘Newell’ smooth bromegrass (Bromus inermis L.), and two cultivars of switchgrass (Panicum virgatum L.), ‘Liberty’ and ‘Shawnee.’ In the continuous corn system, we evaluated the impact of stover removal by mechanical baling vs. livestock grazing for systems with and without winter cover crop, triticale (x Triticosecale neoblaringhemii A. Camus; hexaploid AABBRR). In perennial grasslands, we evaluated the effect of livestock grazing vs. no grazing. We found that (1) soil N2O emissions are generally higher in continuous corn systems than perennial grasslands due to synthetic N fertilizer use; (2) winter cover crop use had no effect on total soil GHG emissions regardless of stover management treatment; (3) stover baling decreased total soil GHG emissions, though grazing stover significantly increased emissions in one year; (4) grazing perennial grasslands tended to increase GHG emissions in pastures selected for forage quality, but were highly variable from year to year; (5) ICL systems that incorporate perennial grasses will provide the most effective GHG mitigation outcomes.

The spread of nonindigenous species by shipping is a large and growing global problem that harms coastal ecosystems and economies and may blur coastal biogeographical patterns. This study coupled eukaryotic environmental DNA (eDNA) metabarcoding with dissimilarity regression to test the hypothesis that ship‐borne species spread homogenizes port communities. We first collected and metabarcoded water samples from ports in Europe, Asia, Australia and the Americas. We then calculated community dissimilarities between port pairs and tested for effects of environmental dissimilarity, biogeographical region and four alternative measures of ship‐borne species transport risk. We predicted that higher shipping between ports would decrease community dissimilarity, that the effect of shipping would be small compared to that of environment dissimilarity and shared biogeography, and that more complex shipping risk metrics (which account for ballast water and stepping‐stone spread) would perform better. Consistent with our hypotheses, community dissimilarities increased significantly with environmental dissimilarity and, to a lesser extent, decreased with ship‐borne species transport risks, particularly if the ports had similar environments and stepping‐stone risks were considered. Unexpectedly, we found no clear effect of shared biogeography, and that risk metrics incorporating estimates of ballast discharge did not offer more explanatory power than simpler traffic‐based risks. Overall, we found that shipping homogenizes eukaryotic communities between ports in predictable ways, which could inform improvements in invasive species policy and management. We demonstrated the usefulness of eDNA metabarcoding and dissimilarity regression for disentangling the drivers of large‐scale biodiversity patterns. We conclude by outlining logistical considerations and recommendations for future studies using this approach. [ABSTRACT FROM AUTHOR]