Explore the vast range of titles available.

Many yield predictions in perennial bioenergy species have been made based on data collected during the establishment phase of growth or a limited number of long‐term studies. Few studies compare multiple perennial crops with the dominant agricultural vegetation of the landscape over long time periods. Here, we present the results of 11 years of perennial crop management on fertile agricultural soils in central Illinois, compared with conventional row crop maize/soybean (Zea mays L., Glycine max L.) production. We examined the long‐term productivity and drought susceptibility of Miscanthus x giganteus Greef et. Deu. ex. Hodkinson et Renvoize (miscanthus), Panicum virgatum L., Cave‐in‐Rock cultivar (switchgrass), and a native prairie mix, in contrast to annual maize/soybean agriculture. Long‐term yields for miscanthus and switchgrass failed to reach initial predictions made during the establishment phase; however, in miscanthus, the 11th year of production shows little progressive yield loss with age, exceeding the modeled limit for the onset of age‐related decline. Harvest timing and differences in yields from hand and machine harvests in perennial crops likely contribute to overestimates of potential yields. Application of fertilizer to mature miscanthus resulted in significant increases in yield after a severe drought, though modeled effects of management and drought in miscanthus point to a more complex mechanism for yield response. Here, we present the results of 11 years of perennial crop management on fertile agricultural soils in central Illinois, compared with conventional row crop maize/soybean production. Long‐term yields for miscanthus and switchgrass failed to reach initial predictions made during the establishment phase; however, in miscanthus, the 11th year of production shows little progressive yield loss with age, exceeding the modeled limit for the onset of age‐related decline. Application of fertilizer to mature miscanthus resulted in significant increases in yield after a severe drought, though modeled effects of management and drought in miscanthus point to a more complex mechanism for yield response.

Perennial crops have been the focus of bioenergy research and development for their sustainability benefits associated with high soil carbon (C) and reduced nitrogen (N) requirements. However, perennial crops mature over several years and their sustainability benefits can be negated through land reversion. A photoperiod‐sensitive energy sorghum (Sorghum bicolor) may provide an annual crop alternative more ecologically sustainable than maize (Zea mays) that can more easily integrate into crop rotations than perennials, such as miscanthus (Miscanthus × giganteus). This study presents an ecosystem‐scale comparison of C, N, water and energy fluxes from energy sorghum, maize and miscanthus during a typical growing season in the Midwest United States. Gross primary productivity (GPP) was highest for maize during the peak growing season at 21.83 g C m−2 day−1, followed by energy sorghum (17.04 g C m−2 day−1) and miscanthus (15.57 g C m−2 day−1). Maize also had the highest peak growing season evapotranspiration at 5.39 mm day−1, with energy sorghum and miscanthus at 3.81 and 3.61 mm day−1, respectively. Energy sorghum was the most efficient water user (WUE), while maize and miscanthus were comparatively similar (3.04, 1.75 and 1.89 g C mm−1 H2O, respectively). Maize albedo was lower than energy sorghum and miscanthus (0.19, 0.26 and 0.24, respectively), but energy sorghum had a Bowen ratio closer to maize than miscanthus (0.12, 0.13 and 0.21, respectively). Nitrous oxide (N2O) flux was higher from maize and energy sorghum (8.86 and 12.04 kg N ha−1, respectively) compared with miscanthus (0.51 kg N ha−1), indicative of their different agronomic management. These results are an important first look at how energy sorghum compares to maize and miscanthus grown in the Midwest United States. This quantitative assessment is a critical component for calibrating biogeochemical and ecological models used to forecast bioenergy crop growth, productivity and sustainability. Energy sorghum, maize and miscanthus are three crop candidates primed to contribute to bioenergy production in the United States. We showed that while energy sorghum is an annual crop much like maize in it's nitrogen fluxes, it behaves more like the perennial crop miscanthus in terms of its carbon capture per volume of water and mega joule of light used. Our assessment provides an important first step toward quantifying ecosystem scale biogeochemical fluxes between these three cropping systems that is required to assess their long‐term ecological sustainability.

Quantifying the carbon (C) uptake of Miscanthus × giganteus (M × g) in both aboveground and belowground structures (e.g., net primary productivity (NPP)) and differences among methodological approaches is crucial. Our objectives were to directly measure Mxg NPP and evaluate the effects of nitrogen application, location, and belowground biomass sampling methods. We hypothesize that increased nitrogen application increases the overall NPP of M × g and that quantifying rhizome biomass using excavations will produce the lowest variability between replicates. We collected biomass from mature M × g stands from three locations in Iowa with three nitrogen application rates and one site in Illinois. We destructively sampled at two time points, when rhizome mass is anticipated to be at a minimum (initial) and anticipated to be at its maximum (peak). Biomass was collected from 1 × 1 m quadrats in which one in‐clump and one beside‐clump cores were collected and then excavated to 30 cm depth to extract all rhizomes. We found that aboveground M × g NPP ranged from 15.4 Mg Da ha–1 year–1 to 36.4 Mg Da ha–1 year–1 and belowground M × g NPP ranged from 4.4 Mg Da ha–1 year–1 to 19.6 Mg Da ha–1 year–1. M × g NPP varied across sites, fertilization, and calculation assumptions. Aboveground NPP (yield) was on average 68.7% of the total NPP. Root‐to‐shoot ratios at peak biomass decreased with nitrogen application rate, from an average of 1.9 for 0 N plots to 0.89 for 224 N fertilized plots. There was more variation in core data than from excavations; however, when in‐clump and beside‐clump cores were averaged together, core and excavation averages were not different. Overall, these results show that the range of mature M × g NPP is driven by aboveground productivity, influenced by nitrogen application and site. Our results provide useful data to constrain agro‐ecosystem models and provide crucial insights for future perennial belowground sampling. Many estimates of Miscanthus × giganteus (M × g) productivity focus on aboveground harvestable yields and do not directly address belowground biomass in this perennial crop. To more accurately constrain the amount of carbon taken up by M × g in both aboveground and belowground plant parts, we calculated the net primary productivity (NPP) of mature M × g at three sites with three nitrogen application rates using collections of aboveground and belowground biomass at two time points during the growing season. These estimates help improve our understanding of M × g carbon sequestration potential and will improve the representation of M × g in agro‐ecosystem models.

In the age of biofuel innovation, bioenergy crop sustainability assessment has determined how candidate systems alter the carbon (C) and nitrogen (N) cycle. These research efforts revealed how perennial crops, such as switchgrass, increase belowground soil organic carbon (SOC) and lose less N than annual crops, like maize. As demand for bioenergy increases, land managers will need to choose whether to invest in food or fuel cropping systems. However, little research has focused on the C and N cycle impacts of reverting purpose‐grown perennial bioenergy crops back to annual cropping systems. We investigated this knowledge gap by measuring C and N pools and fluxes over 2 years following reversion of a mature switchgrass stand to an annual maize rotation. The most striking treatment difference was in ecosystem respiration (ER), with the maize‐converted treatment showing the highest respiration flux of 2,073.63 (± 367.20) g C m−2 year−1 compared to the switchgrass 1,412.70 (± 28.72) g C m−2 year−1 and maize‐control treatments 1,699.16 (± 234.79) g C m−2 year−1. This difference was likely driven by increased heterotrophic respiration of belowground switchgrass necromass in the maize‐converted treatment. Predictions from the DayCent model showed it would take approximately 5 years for SOC dynamics in the converted treatment to return to conditions of the maize‐control treatment. N losses were highest from the maize‐converted treatment when compared to undisturbed switchgrass and maize‐control, particularly during the first conversion year. These results show substantial C and N losses occur within the first 2 years after reversion of switchgrass to maize. Given farmers are likely to rotate between perennial and annual crops in the future to meet market demands, our results indicate that improvements to the land conversion approach are needed to preserve SOC built up by perennial crops to maintain the long‐term ecological sustainability of bioenergy cropping systems. With biofuel innovation comes a need to sustainably manage this fuel source, and understanding how different bioenergy crop varieties can alter ecosystem carbon and nitrogen cycles is one way to achieve this. We quantified these changes by reverting a mature perennial switchgrass cropping system to an annual maize cropping system. Soil organic carbon built up under the perennial switchgrass was quickly consumed by enhanced heterotrophic respiration and nitrogen loss increased from the reverted system, with the reverted system resembling the reference maize treatment within 5 years.

Understanding agroecosystem carbon (C) cycle response to climate change and management is vital for maintaining their long-term C storage. We demonstrate this importance through an in-depth examination of a ten-year eddy covariance dataset from a corn–corn–soybean crop rotation grown in the Midwest United States. Ten-year average annual net ecosystem exchange (NEE) showed a net C sink of −0.39 Mg C ha −1 yr −1 . However, NEE in 2014 and 2015 from the corn ecosystem was 3.58 and 2.56 Mg C ha −1 yr −1 , respectively. Most C loss occurred during the growing season, when photosynthesis should dominate and C fluxes should reflect a net ecosystem gain. Partitioning NEE into gross primary productivity (GPP) and ecosystem respiration (ER) showed this C ‘burp’ was driven by higher ER, with a 51% (2014) and 57% (2015) increase from the ten-year average (15.84 Mg C ha −1 yr −1 ). GPP was also higher than average (16.24 Mg C ha −1 yr −1 ) by 25% (2014) and 37% (2015), but this was not enough to offset the C emitted from ER. This increased ER was likely driven by enhanced soil microbial respiration associated with ideal growing season climate, substrate availability, nutrient additions, and a potential legacy effect from drought.

Understanding controls on soil organic carbon (SOC) will be crucial to managing soils for climate change mitigation and food security. Climate exerts an overarching influence on SOC, affecting both carbon (C) inputs to soil and soil physicochemical properties participating in C retention. To test our hypothesis that climate, C inputs, and soil properties would differently affect particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), we sampled 16 agricultural sites (n = 124 plots) in the United States, ranging in climate (mean annual precipitation (MAP)—potential evapotranspiration (PET; MAP-PET)), soil pH (5.8–7.9), and soil texture (silt + clay = 13–96%). As MAP-PET increased, soils increased in oxalate-extractable iron (FeO) and aluminum (AlO), decreased in exchangeable calcium (Caex) and magnesium (Mgex), and received greater C inputs. Soil physicochemical properties did not strongly predict POC, confirming the relative independence of this SOC fraction from the soil matrix. In contrast, MAOC was well predicted by combining AlO + [1/2]FeO with Caex + Mgex in a ‘matrix capacity index’, which performed better than individual soil physicochemical properties across all pH levels (r > 0.79). Structural equation modeling indicated a similar total effect of MAP-PET on MAOC and POC, which was mediated by total C inputs and the matrix capacity index for MAOC but not POC. Our results emphasize the need to separately conceptualize controls on MAOC and POC and justify the use of a unified soil matrix capacity index for predicting soil MAOC storage.

Current biofuel feedstock crops such as corn lead to large environmental losses of N through nitrate leaching and N2O emissions; second‐generation cellulosic crops have the potential to reduce these N losses. We measured N losses and cycling in establishing miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum L. fertilized with 56 kg N ha−1 yr−1), and mixed prairie, along with a corn (Zea mays L.)–corn–soybean [Glycine max (L.) Merr.] rotation (corn fertilized at 168–202 kg N ha−1). Nitrous oxide emissions, soil N mineralization, mid‐profile nitrate leaching, and tile flow and nitrate concentrations were measured. Perennial crops quickly reduced nitrate leaching at a 50‐cm soil depth as well as concentrations and loads from the tile systems (year 1 tile nitrate concentrations of 10–15 mg N L−1 declined significantly by year 4 in all perennial crops to <0.6 mg N L−1, with losses of <0.8 kg N ha−1 yr−1). Nitrous oxide emissions were 2.2 to 7.7 kg N ha−1 yr−1 in the corn–corn–soybean rotation but were <1.0 kg N ha−1 yr−1 by year 4 in the perennial crops. Overall N balances (atmospheric deposition + fertilization + soybean N2 fixation – harvest, leaching losses, and N2O emissions) were positive for corn and soybean (22 kg N ha−1 yr−1) as well as switchgrass (9.7 kg N ha−1 yr−1) but were −18 and −29 kg N ha−1 yr−1 for prairie and miscanthus, respectively. Our results demonstrate rapid tightening of the N cycle as perennial biofuel crops established on a rich Mollisol soil.

Belowground carbon (C) dynamics of terrestrial ecosystems play an important role in the global C cycle and thereby in climate regulation. Globally, land-use change is a major driver of changes in belowground C storage. The emerging bioenergy industry is likely to drive widespread land-use changes, including the replacement of annually tilled croplands with perennial bioenergy crops, and thereby to impact the climate system through alteration of belowground C dynamics. Mechanistic understanding of how land-use changes impact belowground C storage requires elucidation of changes in belowground C flows; however, altered belowground C dynamics following land-use change have yet to be thoroughly quantified through field measurements. Here, we show that belowground C cycling pathways of establishing perennial bioenergy crops (0- to 3.5-year-old miscanthus, switchgrass, and a native prairie mix) were substantially altered relative to row crop agriculture (corn-soy rotation); specifically, there were substantial increases in belowground C allocation (>400%), belowground biomass (400—750%), root-associated respiration (up to 2,500%), moderate reductions in litter inputs (20—40%), and respiration in root-free soil (up to 50%). This more active root-associated C cycling of perennial vegetation provides a mechanism for observed net C sequestration by these perennial ecosystems, as well as commonly observed increases in soil C under perennial bioenergy crops throughout the world. The more active root-associated belowground C cycle of perennial vegetation implies a climate benefit of grassland maintenance or restoration, even if biomass is harvested annually for bioenergy production.

Perennial bioenergy crops accumulate carbon (C) in soils through minimally disturbing management practices and large root inputs, but the mechanisms of microbial control over C dynamics under bioenergy crops have not been clarified. Root‐derived C inputs affect both soil microbial contribution to and degradation of soil organic matter resulting in differing soil organic carbon (SOC) concentrations, storage, and stabilities under different vegetation regimes. Here, we measured biomarker amino sugars and neutral sugars and used diffuse reflectance mid‐infrared Fourier transform spectroscopy (DRIFTS) to explore microbial C contributions, degradation ability, and SOC stability, respectively, under four potential bioenergy crops, M.×giganteus (Miscanthus × giganteus), switchgrass (Panicum virgatum L.), a mixed prairie, and a maize (Zea mays L.)–maize–soybean (Glycine max(L.) Merr.) (MMS) rotation over six growing seasons. Our results showed that SOC concentration (g/kg) increased by 10.6% in mixed prairie over the duration of this experiment and SOC storage (Mg/ha) increased by 17.0% and 15.6% in switchgrass and mixed prairie, respectively. Conversion of row crops to perennial grasses maintained SOC stability and increased bacterial residue contribution to SOC in M.×giganteus and switchgrass by 20.0% and 15.0%, respectively, after 6 years. Degradation of microbe‐derived labile SOC was increased in M.×giganteus, and degradation of both labile and stable SOC increased in MMS rotation. These results demonstrate that microbial communities under perennial grasses maintained SOC quality, while SOC quantity increased under switchgrass and mixed prairie. Annual MMS rotation displayed decreases in aspects of SOC quality without changes in SOC quantity. These findings have implications for understanding microbial control over soil C quantity and quality under land‐use shift from annual to perennial bioenergy cropping systems. Microbial substrate preference is speculated to be driven by labile carbon inputs and available nitrogen. The results from this study demonstrate optimal conditions for increasing soil organic carbon quantity and quality beyond a cessation of tillage include a diverse aboveground ecosystem, high belowground labile carbon inputs, and available nitrogen.

Aims Root architecture drives plant ecology and physiology, but current detection methods limit understanding of root placement within soil profiles. We developed a statistical model of root volume along depth gradients and used it to infer carbon storage potential of land-use changes from conventional agriculture to perennial bioenergy grasses. Methods We estimated root volume of maize-soybean rotation and three perennial grass systems (Miscanthus × giganteus, Panicum virgatum, tallgrass prairie mix) by Bayesian modeling from minirhizotron images, correcting for small images and near-surface underdetection. We monitored seasonal and inter-annual changes in root volume distribution, then validated our estimates against root mass from core samples. Results The model explained 29% of root volume variation and validated well against core mass. Seventh-year perennials had greater belowground biomass than maize-soybean both in total (11-16×) and throughout the profile (2-17× at every depth < 120 cm). Perennials' relative depth allocations were stable over time, while total root volume increased through five years. In 2012 a historically hot, dry summer damaged maize while perennials appeared resilient, suggesting their large-deep root systems aid drought resistance. Conclusions Perennial root systems are large, deep, and persistent. Converting row crops to perennial bioenergy grasses likely sequesters carbon in a large, potentially very stable, soil pool.