Switchgrass Establishment Research Articles

Nitrogen use efficiency and productivity of first year switchgrass and big bluestem from low to high soil nitrogen

Despite an abundance of research on the biomass response to nitrogen fertilizer in established switchgrass fields, there is a dearth of knowledge of the first year response in switchgrass, and nothing yet available for big bluestem. Based on differences in their C4 photosynthetic subtypes, big bluestem may show greater photosynthetic (PNUE) and above-ground whole plant nitrogen use efficiency (NUE) over switchgrass. Here we report the first year biomass response to nitrogen fertilizer for two cultivars of upland switchgrass and three cultivars of big bluestem. We first performed a greenhouse experiment with four nitrogen treatments ranging from 1.5 dmol m−3 to 16 mol m−3 aqueous nitrogen solutions. Here we measured PNUE mid-way through the experiment and harvested plants green to measure above-ground whole plant NUE. We also compared these cultivars at two field sites with contrasting soil nitrogen content. At low soil nitrogen, big bluestem “Prairie View” achieved both the highest NUE in the greenhouse and greatest biomass in the field. Switchgrass produced significantly more biomass than big bluestem at the high nitrogen field site, whereas biomass production was similar for both species at the low nitrogen field site. Although both species responded positively to increasing soil nitrogen, switchgrass did increasingly more so compared to big bluestem, with a 20% greater biomass stimulation in the greenhouse from low to high soil nitrogen. Net CO2 assimilation rates showed a similar response with biomass production to the nitrogen treatments, allowing switchgrass “Sunburst” to achieve a slightly greater PNUE compared to big bluestem “Prairie View”.

Soil and Aggregate-Associated Carbon in a Young Loblolly Pine Plantation

In order to assess the carbon (C) footprint of forest-based bioenergy systems, it is necessary to quantify soil C storage. This study addressed effects of intercropping loblolly pine (Pinus taeda L.) with switchgrass (Panicum virgatum L.) for wood and bioenergy production on soil C storage in coastal North Carolina, USA. Spaces between rows of bedded pine were intercropped with switchgrass or contained native vegetative regrowth after site preparation. Two years after switchgrass establishment, soils were collected from beds and interbeds of each treatment, and C concentration and δ13C were measured in bulk soils and aggregate fractions. Soil C concentration, soil C density (Mg ha−1), and aggregate-associated C were lower in pine beds adjacent to switchgrass compared with pines adjacent to native regrowth. In the greater than 2,000-μm aggregate size class, 11% of C was derived from new pine inputs in beds of the pine-switchgrass treatment compared to the pine-native treatment. These results indicate that increased belowground C flow in pine beds adjacent to switchgrass may be driving breakdown soil C. In the pine-switchgrass intercropping treatment, a greater percentage of aggregates (by weight and C content) was found in the 2,000- to 250-μm size class of both beds and interbeds, suggesting that this aggregate size class is sensitive to management. This study provides a baseline analysis of C storage under different management scenarios in pine forests and for investigating long-term (10+ years) impacts. Although presence of switchgrass reduced soil C over the short term, bioenergy intercropping may still be pragmatic from an economical and land-use diversification view point.

White‐tailed deer carrying capacity, intercropping switchgrass, and pine plantations

ABSTRACTSwitchgrass (Panicum virgatum) is a cellulosic feedstock for alternative energy production that can be grown between rows of planted pines (Pinus spp.) within intensively managed forests. Southeastern planted pine occupies 15.8 million ha and thus, switchgrass intercropping could have far‐ranging effects on plant communities and biomass production within these forests if broadly implemented. Such intercropping could lead to alterations to plant communities that may cause bottom‐up ecological changes affecting ecologically, economically, and socially important wildlife, such as white‐tailed deer (Odocoileus virginianus; deer). Therefore, we tested whether intercropping switchgrass in loblolly pine (P. taeda) plantations would cause switchgrass to dominate vegetative biomass thereby decreasing biomass of forages and reducing white‐tailed deer nutritional carrying capacity (NCC), or whether disturbance associated with establishment and harvest of switchgrass would facilitate ruderal forbs, and thereby increase biomass of preferred deer forages and increase NCC. In a randomized complete block design, we assigned 2 treatments (intercropped switchgrass and a standard pine management control) to 4 replicates of 10‐ha experimental units in Kemper County, Mississippi during summers of 2011−2015. We detected 323 plant species. Intercropping switchgrass had little effect on plant biomass production, and did not affect white‐tailed deer NCC at a maintenance diet of 6% crude protein. Intercropping provided additional disturbance allowing high‐protein content ruderal plants to colonize, and temporarily increased (3 yr) deer NCC at the 14% crude protein diet considered necessary to support lactation. However, concomitant with a sharp increase in switchgrass biomass in the third year of the study, NCC dropped to levels similar to traditionally managed pine stands. Switchgrass intercropping is not a reliable means of increasing deer NCC as a management strategy but does not appear to reduce carrying capacity in the short‐term relative to standard intensive pine management. © 2017 The Wildlife Society.

Water Quality Effects of Switchgrass Intercropping on Pine Forest in Coastal North Carolina

Abstract. Interplanting a cellulosic bioenergy crop (switchgrass, L.) between loblolly pine ( L.) rows could potentially provide a sustainable source of bio-feedstock without competing for land currently in food production. The objectives of this study were to: (1) quantify the concentrations and loads of drainage water nitrogen (N) and phosphorus (phosphate) associated with establishment and growth of switchgrass treatments and compare them with those for a mid-rotation pine forest (control), and (2) quantify the treatment effects on drainage water N and phosphate (IC) and switchgrass only (SG). Thinned mid-rotation loblolly pine with natural understory (MP) was used as the control. Pretreatment calibration equations for nutrients were obtained using a paired watershed approach and bootstrap geometric regression with 2007-2008 data, when pine on all sites had reached canopy closure. Treatment effects were calculated as the difference between expected values from the pretreatment relationship and measured data for the treatment period. Precipitation, outflow, and N and phosphate concentrations in the outflow were measured during calibration (Jan. 2007 to Dec. 2008), site preparation for switchgrass establishment (Nov. 2009 to Mar. 2012), and switchgrass growth (Apr. 2012 to Apr. 2014). Mean NO3-N concentrations and loads were significantly (a = 0.05) greater for SG than for IC during the switchgrass growth period. Average treatment concentrations with standard errors and total load effects during switchgrass growth for NO3-N followed the trends SG (-0.002 ±0.01 mg L-1) > IC (-0.12 ±0.04 mg L-1) and SG (0.75kg ha-1) > IC (0.23kg ha-1), respectively. For phosphate average concentrations and loads, the treatment effects during switchgrass growth followed the trends SG (-0.004 ± mg L-1) >IC ( -0.02 ± mg L-1) and IC (-0.43 kg ha-1) > SG (-0.70 kg ha-1), respectively. Average concentration effects for NO3-N and phosphate and total load effects for phosphate significantly (a = 0.05) decreased for IC compared to the MP control. These results suggest that the intercropping treatment (IC) with loblolly pine and switchgrass improved water quality by reducing NO3-N and phosphate concentrations and phosphate loads. Keywords: Bioenergy crop, Bootstrap geometric regression, Loblolly pine, Nutrients, Paired watershed.

Seedbed Preparation and Planting Depth Affect Switchgrass Establishment and Yield

Core Ideas Switchgrass has potential for renewable biofuel production. It is productive under nutrient‐ or water‐limited environments. It can be no‐till planted on lands that are susceptible to erosion. Switchgrass (Panicum virgatum L.) is a native, long‐lived, warm‐season perennial grass that is well adapted, has potential for biofuel production, and can improve soil chemical and physical properties. It can be difficult to establish, but it can be productive in marginally productive or difficult to cultivate lands, and its root system can aid in soil conservation. The objectives of this 2‐year field experiment were to determine the effects of seedbed preparation (burning, mowing, or tilling) and planting depth (0.25, 0.5, or 1.0 inches) on the establishment and yield of ‘EG 1101’ switchgrass. Planting between 0.25 and 0.5 inch generally resulted in more seedlings and greater stand percent and yield than 1.0‐inch depth. Tilling generally resulted in more initial seedlings at 30 days after planting (DAP) than no‐till with burning or mowing, but stand percent (150 DAP) and yield (postfrost) were not affected by seedbed preparation later in the growing season. However, all seedbed preparations and planting depths produced successful switchgrass stands of >1 seedling/ft2 and ≥50% stands. Producers planting on land susceptible to erosion could consider no‐till planting after burning or mowing in order to reduce soil erosion and promote better soil structure and fertility without any loss in switchgrass productivity.

Evaluation of Small Grain Cover Crops to Enhance Switchgrass Establishment

Establishment failures are a challenge to wide‐scale use of switchgrass (Panicum virgatum L.) for biomass feedstock and/or forage production. Small grain cover crops, because of their allelopathic properties, may inhibit (direct allelopathy) or enhance (competition reduction) switchgrass establishment, and provide indirect benefits such as soil conservation and forage/grain production during the establishment year. Objectives of this study were to evaluate stand density and yield based on seeding switchgrass into (i) four small grain cover crops: wheat (Triticum aestivum L.), cereal rye (Secale cereale L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), and fallow control at (ii) three dates (15 March, 1 May, and 10 June) that approximated typical timing for removal of small grain cover, haylage, or grain crops in Tennessee, respectively. Treatments were assigned in a split‐plot design with three replications at three locations in Tennessee in 2008 and repeated in 2009. Small grain cover crops influenced (P = 0.002) switchgrass seedling density at only one location (wheat > other small grains > control) and interacted with year at another, but was never related (P < 0.05) to yield. Planting date affected switchgrass density and yield, but always in the context of an interaction with year; yield varied by location and year with no clear pattern. Density also varied by year and location, with fewer plants occurring during May seeding dates. Therefore, switchgrass can be planted following small grains without an apparent penalty or advantage to switchgrass stand density or yield, while offsetting lost production during establishment.

Rapid kudzu eradication and switchgrass establishment through herbicide, bioherbicide and integrated programmes

ABSTRACTAmong the most important and visible weeds in the Southeastern USA is the exotic invasive vine, kudzu (Pueraria montana var. lobata). Efforts to eradicate it typically involve many years of application of restricted-use pesticides. Recent availability of effective, non-restricted-use pesticides and developments with the application of the bioherbicide Myrothecium verrucaria has made possible new control programmes for kudzu management. Field trials at three sites over two years with aminocyclopyrachlor, aminopyralid, fluroxypyr, metsulfuron methyl and combinations of these herbicides achieved 99–100% reduction in aboveground kudzu biomass. Additionally, programmes were developed that eradicated kudzu while simultaneously establishing native vegetation. One of these successful programmes integrated bioherbicide application, mechanical removal of kudzu biomass and planting switchgrass (Panicum virgatum) in an entirely chemical herbicide-free system. These field tests demonstrate a variety of methods that can be used independently or in an integrated approach for rapid kudzu eradication.

Effects of Giant Foxtail (Setaria faberi) and Yellow Foxtail (Setaria pumila) Competition on Establishment and Productivity of Switchgrass

Switchgrass is a potential feedstock for cellulosic bioenergy production. Weed competition from annual grass during the establishment year can reduce switchgrass establishment and resulting productivity, but the relationship between early season grass densities and outcomes of competition are not well understood. We measured how a range of giant and yellow foxtail densities in the establishment year influenced switchgrass establishment and resulting productivity in the first production year (second year of the growing season). In two of the three site–yr more than four foxtail plants m−2reduced switchgrass plant densities below documented thresholds of establishment success. A lesser effect of foxtails in the third site–year suggested that higher switchgrass emergence rates reduced foxtail competitive ability during establishment. Effects on yield were consistent over the three site–yr. The yield (10.96 Mg ha−1± 0.77) decreased rapidly as foxtail density increased. One foxtail plant m−2reduced switchgrass yield in the first production year by 25%, and yield loss was 90% or greater at densities > 50 foxtail plants m−2. Although switchgrass can establish in the presence of foxtail competition, these weed species should be controlled to maximize yields in the first production year.

Dormant‐Season Planting and Seed‐Dormancy Impacts on Switchgrass Establishment and Yield

ABSTRACTEstablishment failures linked to seed dormancy are a challenge to wide‐scale use of switchgrass (Panicum virgatum L.) for biomass feedstock and forage production. One prospective strategy for breaking dormancy is dormant‐season planting. The objectives of this study were to evaluate (i) three switchgrass dormant‐season planting dates (1 December, 1 February, and 15 March) vs. a growing‐season (1 May) control; (ii) two seeding rates (6.7 and 10.1 kg pure live seed [PLS] ha−1); and (iii) high‐ and low‐dormancy seed lots. Treatments were assigned in a split‐plot design with three replications at two locations in Tennessee in 2008 and 2009. Neither seeding rate nor seed‐dormancy level affected plant density or yield (P > 0.05). However, a seeding date × year interaction impacted first‐year density at both locations. Although patterns differed by year for the two locations, density of March plantings equaled or exceeded (P < 0.05) those at other dates for both locations and years. These variations in density did not carry over to impact yield in year two. A sigmoidal regression of seedling density vs. yield was significant (P < 0.001) albeit not strong (R2 = 0.13); yield response approached an asymptote above ∼8 plants m−2. Results suggest March planting dates, using standard seeding rate recommendations (6.7 kg PLS ha−1) irrespective of seed‐dormancy rates, may be more reliable than planting in May. Thus, a broader establishment window than traditionally used may be practical. However, results should be validated over a broader range of soils and climatic conditions, especially over a winter severity gradient.

Switchgrass rhizospheres stimulate microbial biomass but deplete microbial necromass in agricultural soils of the upper Midwest, USA

Rhizosphere microbial communities play an essential role in determining plant productivity, particularly in agriculturally marginal environments. Perennial plants like switchgrass (Panicum virgatum) are thought to particularly influence microbial community composition and function within their rhizosphere. We compared microbial communities in switchgrass rhizospheres and their associated bulk soils in two regions of the U.S. upper Midwest (Michigan and Wisconsin) with contrasting soil types, and at two site types with differing switchgrass establishment ages and management intensities. We characterized microbial communities with a range of culture-independent methods, including amplicon sequencing of 16S/18S rRNA and nifH genes, and membrane lipid profiling. In addition, we quantified abundances of soil amino sugars, a time-integrative indicator of microbial necromass. We found that amino sugar contents and microbial lipid profiles differed between rhizosphere and bulk soils, while DNA-based assays did not provide this discriminatory power. Differences between rhizosphere and bulk soils were not significantly affected by region or site type. Rhizosphere soils had higher microbial lipid abundances, particularly those associated with arbuscular mycorrhizal fungi and Gram-negative bacteria, while amino sugar abundances decreased in the rhizosphere. Our findings suggest switchgrass rhizospheres systematically stimulate microbial growth and microbial residue turnover.

Evapotranspiration, water use efficiency, and energy partitioning of a mature switchgrass stand

With the current interest in cellulosic biofuel feedstocks, switchgrass (Panicum virgatum L.) research has increased in North America over the past decades. However, implications of large-scale switchgrass production on local and regional water budgets are largely unknown. We conducted eddy covariance measurements over a large (60ha) commercial switchgrass field in Southern Ontario, Canada, to determine evapotranspiration and energy fluxes during the sixth (2012) and seventh (2013) year since establishment of switchgrass. Annual total evapotranspiration was slightly smaller in the wet year of 2013 compared to the dry year of 2012 (562±12 and 598±9mm, respectively; error estimate based on gap filling error). Canopy conductance was larger in the wet year (11.2±1.5mms−1 in 2013; average±standard error) than in the dry year (7.7±0.9mms−1 in 2012), which suggests that switchgrass regulated stomatal opening to reduce water loss. Although this regulation reduced atmospheric CO2 fixation, it did not result in yield reduction. Water use efficiency of harvested dry matter was larger in 2012 compared to 2013 (1.82±0.12 and 1.40±0.11gDM(kgH2O)−1, respectively; error estimates based on Gaussian error propagation). Water use efficiency based on gross ecosystem production (EWUE) in 2013 was 14.0±0.6gCO2(kgH2O)−1, compared to 13.3±0.3gCO2(kgH2O)−1 in 2012 (error estimates based on Gaussian error propagation). Daily, monthly, and seasonal EWUE showed a trend to lower values in the dry year of 2012 compared to 2013. These results indicate that the switchgrass crop was able to reduce the water cost of aboveground biomass in the dry year by relocating carbon from belowground structures, but it fixed more atmospheric carbon per unit water evapotranspired in the wet year. Our findings show that mature switchgrass has the potential to withstand the impact of moderate drought or dry conditions. However, the impact of repeated drought and prolonged dry conditions on switchgrass and implications for regional water budgets are not clear yet.

Switchgrass Population and Cold–Moist Stratification Mediate Germination

ABSTRACTSwitchgrass (Panicum virgatum L.) breeding and selection have enhanced the agronomic qualities of this species as a crop for forage and bioenergy applications. Previous work has characterized variation in phenotypic traits (e.g., survival, biomass yield, and cell wall carbohydrates) among wild and cultivated populations. Despite the importance of low dormancy to the establishment of a productive switchgrass stand, there is little information characterizing the dormancy of selectively bred cultivars vs. wild populations of switchgrass. The objectives of this study were to use growth chamber experiments to quantify germination vs. dormancy (confirmed by tetrazolium tests) of eight wild and four cultivar populations and evaluate the relationship between seed size and germination. While cultivars generally showed higher germination than wild populations, there was marked variation in germination among wild populations; for those with lower germination, the ungerminated fraction comprised mostly live (i.e., dormant) seeds. These data led us to perform a subsequent experiment testing the application of a seed treatment, cold–moist stratification, on a subset of eight populations representing the wide variation in germination observed in the first experiment. Cold–moist stratification substantially increased germination, but the magnitude of the effect varied among populations. Populations with higher dormancy showed a much larger increase in germination after cold–moist stratification. These data clearly show that seed dormancy in wild populations can be easily overcome by cold–moist stratification in the short term and breeding and selection in the long term.

Multi-Year Pathogen Survey of Biofuel Switchgrass Breeding Plots Reveals High Prevalence of Infections by Panicum mosaic virus and Its Satellite Virus.

Switchgrass (Panicum virgatum) cultivars are currently under development as lignocellulosic feedstock. Here we present a survey of three established switchgrass experimental nurseries in Nebraska in which we identified Panicum mosaic virus (PMV) as the most prevalent virus. In 2012, 72% of 139 symptomatic plants tested positive for PMV. Of the PMV-positive samples, 19% were coinfected with its satellite virus (SPMV). Less than 14% of all sampled plants in 2012 were positive for four additional viruses known to infect switchgrass. In 2013, randomized sampling of switchgrass individuals from the same 2012 breeding plots revealed that infection by PMV or PMV+SPMV was both more prevalent and associated with more severe symptoms in the cultivar Summer, and experimental lines with Summer parentage, than populations derived from the cultivar Kanlow. A 3-year analysis, from 2012 to 2014, showed that previously uninfected switchgrass plants acquire PMV or PMV+SPMV between harvest cycles. In contrast, some plants apparently did not maintain PMV infections at detectable levels from year-to-year. These findings suggest that PMV and SPMV should be considered important pathogens of switchgrass and serious potential threats to biofuel crop production efficiency.

Effects of Site Preparation for Pine Forest/Switchgrass Intercropping on Water Quality.

A study was initiated to investigate the sustainability effects of intercropping switchgrass ( L.) in a loblolly pine ( L.) plantation. This forest-based biofuel system could possibly provide biomass from the perennial energy grass while maintaining the economics and environmental benefits of a forest managed for sawtimber. Operations necessary for successful switchgrass establishment and growth, such as site preparation, planting, fertilizing, mowing and baling, may affect hydrology and nutrient runoff. The objectives of this study were (i) to characterize the temporal effects of management on nutrient concentrations and loadings and (ii) to use pretreatment data to predict those treatment effects. The study watersheds (∼25 ha each) in the North Carolina Atlantic Coastal Plain were a pine/switchgrass intercropped site (D1), a midrotation thinned pine site with natural understory (D2), and a switchgrass-only site (D3). Rainfall, drainage, water table elevation, nitrogen (total Kjedahl N, NH-N, and NO-N), and phosphate were monitored for the 2007-2008 pretreatment and the 2009-2012 treatment periods. From 2010 to 2011 in site D1, the average NO-N concentration effects decreased from 0.18 to -0.09 mg L, and loads effects decreased from 0.86 to 0.49 kg ha. During the same period in site D3, the average NO-N concentration effects increased from 0.03 to 0.09 mg L, and loads effects increased from -0.26 to 1.24 kg ha. This study shows the importance of considering water quality effects associated with intensive management operations required for switchgrass establishment or other novel forest-based biofuel systems.

Switchgrass Stand Density and Yield as Influenced by Seedbed Preparation Methods in a Sandy Loam Soil

Successful establishment of switchgrass (Panicum virgatum L.) remains a challenge. It is reported that increasing seed-soil contact using a roller could improve switchgrass establishment in silt-loam soils. However, use of rollers is not common among growers and operating them could be difficult. The objective of this study was to assess whether rolling could improve switchgrass stand establishment in sandy-loam soils by increasing seed-soil contact through compacting the soil, and to evaluate the use of cultipacker as a more user-friendly alternative to roller. An experiment was conducted in 2012 and repeated in the 2013 growing season at the University of Massachusetts Agricultural Experiment Station farm in Deerfield. The soil type at the experimental site was Hadley fine sandy loam (nonacid, mesic Typic Udifluvent). The experimental design was a randomized complete block design with four replicates. There were eight treatments including disking-planting (D-P), disking-cultipacking-planting (D-C-P), disking-cultipacking-planting-cultipacking (D-C-P-C), disking-cultipacking-planting-cultipacking-cultipacking (D-C-P-C-C), disking-rolling-planting (D-R-P), disking-rolling-planting-rolling (D-R-P-R), disking-rolling-planting-rolling-rolling (D-R-P-R-R), and disking-rolling-planting-rolling-rolling-rolling (D-R-P-R-R-R). Tiller density was influenced rolling and cultipacking frequency but not by the compaction equipment. Tiller density increased by cultipacking or rolling the soil once (D-C-P-C; D-R-P-R) and two times after planting (D-C-P-C-C; D-R-P-R-R). Disking-planting had the lowest tiller density with 188 and 110 plants (m−2) in 2012 and 2013 growing seasons, respectively. Similar to tiller density, biomass yield was not influenced by compaction equipment but by compaction frequency. Higher biomass yield was obtained from soils that were firmed once before and at least once after planting (D-C-P-C; D-R-P-R) compared with seedbed firming only once before planting (D-C-P; D-R-P). In a dry season (2012), a twofold yield increase (1.06 Mg ha−1) was obtained from D-C-P-C compared with D-C-P (0.55 Mg ha−1). However, two times rolling (D-R-P-R-R-) or cultipacking (D-C-P-C-C) after planting was needed in 2013 to increase the yield compared with D-C-P by 41 %. Our results indicated that using cultipacker as an alternative to roller can be a solution to improve switchgrass establishment. We conclude that D-C-P-C-C could ensure switchgrass establishment and improve switchgrass biomass production in the establishment year in a sandy-loam soil.

Simulated biomass, environmental impacts and best management practices for long-term switchgrass systems in a semi-arid region

Long-term information on switchgrass (Panicum virgatum L.) as a biomass energy crop grown on marginally saline soil and the associated impacts on soil carbon (C) and nitrogen (N) dynamics, greenhouse gas (GHG) emissions, and best management practices (BMPs) are limited. In this study, we employed the DAYCENT model, based on a 4-year switchgrass field experiment, to evaluate the long-term biomass yield potential and environmental impacts, and further to develop BMPs for switchgrass in a semi-arid region.The model showed that long-term (14-year) annual mean biomass yields were 9.6 and 5.2 Mg ha−1 for irrigated and rainfed switchgrass systems, respectively. The simulated biomass yields correlated well with field-measured biomass with r2 values of 0.99 and 0.89 for irrigated and rainfed systems, respectively. Soil organic carbon (SOC) and soil total nitrogen (STN) accumulated rapidly after switchgrass establishment, with mean accrual rates of 0.99–1.13 Mg C ha−1 yr−1 and 0.04–0.08 Mg N ha−1 yr−1, respectively. Based on the outputs of numerous long-term model simulations with variable irrigation water supplies and N rates, the irrigation regime and N rate with the highest yield to input ratio were chosen as BMPs. The DAYCENT model predicted-BMP was irrigating every 14 days at 70% potential evapotranspiration combined with an N rate of 67 kg ha−1 yr−1. Switchgrass established and produced biomass reasonably well in this semi-arid region; however, appropriate irrigation and N fertilization were needed for optimal biomass yield. Switchgrass had a great potential to sequester C into soils with low N2O emissions while supplying significant quantities of biomass for biofuel synthesis.

Switchgrass Establishment and Biomass Yield Responses to Fungicide and Insecticide Seed Treatments

Switchgrass (Panicum virgatum L.) is being evaluated for both forage and bioenergy in the Great Plains of the USA. Management strategies to improve switchgrass seedling vigor and emergence may result in more successful switchgrass stands due to better competitive advantage for switchgrass seedlings over weedy species. The objectives of this field experiment were to determine the effects of seven broad‐spectrum fungicide and insecticide seed treatments on the establishment and yield of lowland type ‘EG1101’ switchgrass. The combination of fungicide + insecticide (regardless of formulation) tended to result in taller seedlings and greater seedling densities and stands of switchgrass as compared to untreated control (UTC), fungicide only, and insecticide only. These advantages didn’t result in greater switchgrass dry matter (DM) yield, probably due to adequate stands (>1–2 plants per ft2) that were achieved by all fungicide–insecticide seed treatments including UTC. However, given the relatively small cost per acre of seed treatments, there may be early‐season benefits to treating seeds with a broad‐spectrum insecticide as an insurance measure to increase switchgrass seedling vigor and reduce the chance of stand failure, especially when used with a proven weed management program.

Switchgrass Establishment and Biomass Yield Response to Seeding Date and Herbicide Application

Weed interference is a major challenge in the establishment of switchgrass (Panicum virgatum L.). A field experiment was conducted in 2011–2012 and 2012–2013 growing seasons to study the response of switchgrass to seeding date (November, May, June, and July) combined with pre‐emergence (PRE) application of atrazine (A) [6‐chloro‐N‐ethyl‐N’‐(1‐methylethyl)‐1,3,5‐triazine‐2.4‐dimine] and quinclorac (Q), or PRE A+Q followed by post‐emergence (POST) application of 2,4‐D ([2,4‐dichlorophenoxy] acetic acid) and dicamba dicamba (3,6‐dichloro‐o‐anisic acid). Switchgrass tiller density was increased with delaying the seeding date until July (194 tiller m−2) in 2012; however, no significant differences in tiller density were observed among seeding dates in 2013. Switchgrass was more morphologically developed (plant height and adventitious root numbers) at earlier seeding dates (November and May) compared with later seeding dates. Weed biomass was reduced by 18% as a result of application of PRE A+Q followed by POST compared with PRE A+Q treatment. The highest weed biomass was recorded from May seeding date in both years. The highest switchgrass biomass yield was consistently obtained from May (0.87 and 1.38 Mg ha−1 in 2012 and 2013, respectively) and June seeding dates (0.66 and 1.22 Mg ha−1 in 2012 and 2013, respectively). Our results suggested that although higher tiller density and lower weed biomass was observed with later planting date, switchgrass was more morphologically developed and produced higher biomass yield when seeded earlier. To ensure a successful long‐term switchgrass establishment an early seeding date (May) and application of PRE A+Q followed by POST 2,4‐D and dicamba could be a sustainable management practice.

Switchgrass and Prairie Cordgrass Response to Foliar- and Soil-Applied Herbicides

Perennial grasses are expected to comprise a substantial portion of the lignocellulosic biomass to meet renewable energy mandates in the U.S. in the next decade. As many warm-season grasses are slow to establish from seed, plantings are often compromised by weed interference during the establishment year. Greenhouse experiments were conducted to determine the tolerance of switchgrass and prairie cordgrass to several herbicides applied PRE or POST (at four different growth stages). Preemergence atrazine at rates ≤ 1.684 kg ai ha−1in switchgrass and quinclorac at rates ≤ 0.279 kg ai ha−1in prairie cordgrass did not significantly reduce emergence, plant height, or biomass yield 8 wk after treatment. When treatments were applied at the two- to three-leaf stage, only atrazine (≤ 0.123 kg ai ha−1) did not reduce switchgrass fresh weight and only 2,4-D ester (≤ 0.533 kg ae ha−1), nicosulfuron (0.018 kg ai ha−1), and quinclorac (0.140 kg ha−1) did not significantly reduce prairie cordgrass yield. Phytotoxic effects decreased for all herbicides with increasing growth stage at the time of treatment for both species. All evaluated herbicides were safe with respect to biomass yield on the respective grasses when applied at the latest growth stage (approximately five-leaf stage). These results show that viable PRE and POST herbicides are available for weed control during establishment of switchgrass and prairie cordgrass; however, all evaluated herbicides would likely reduce biomass yield in a mixture planting of both grasses.

A simple vigor test for adjusting switchgrass seeding rate in marginal and fertile soils

AbstractCalculating switchgrass (Panicum virgatum L.) seeding rate is misleading and often causes stand failure. Our objective was to introduce a simple vigor test to adjust the seeding rate and enhance switchgrass establishment and productivity in the establishment year in fertile and marginal soils. Seeding rate for four switchgrass varieties (‘Blackwell,’ ‘Carthage,’ ‘Cave‐in‐Rock’ and ‘Shawnee’) was adjusted ranging from 25 to 125% based on a vigor test. Results indicated increase in seedling emergence and establishment with increasing the seeding rate. Higher established seedlings were recorded from the fertile soil (131 seedlings m−2) compared with the marginal soil (78 seedlings m−2). Based on our previous findings, 100 established seedlings often is considered as a successful establishment; therefore, a 50% (6.89 kg ha−1) and 100% (13.82 kg ha−1) adjusted seeding rates could provide sufficient stand density (111 and 94 seedlings m−2) in the establishment year in fertile and marginal soils, respectively.