Switchgrass Biomass Yield Research Articles

Impact of Harvest Frequency on Biomass Yield and Nutrient Removal of Elephantgrass, Giant Reed, and Switchgrass

Although perennial grasses are being evaluated as a renewable source of biomass for energy production in many countries, no information exits regarding the use of these grasses in Uruguay. In 2008, an 8-year field study was implemented in western Uruguay to determine harvest frequencies for optimal biomass yield and nutrient removal for selected grass species. Elephantgrass (Pennisetum purpureum Schum.), giant reed (Arundo donax L.), and switchgrass (Panicum virgatum L.) were compared using two harvest frequencies: a single harvest after freeze (August) or two harvests (January and August) per year. We evaluated biomass yield, moisture content, nutrient concentration, and nutrient removal of these grasses. This study demonstrated the ability of these grasses to produce high biomass yields. Across years, the double harvest system significantly reduced cumulative biomass yield (~15%) compared to the single harvest of elephantgrass and giant reed; however, switchgrass had 18% more biomass yield (12.70 Mg ha−1 year−1) than the other grasses at the summer harvest but no cumulative difference was detected. The single winter harvest of elephantgrass had the highest cumulative biomass yield (140.8 Mg ha−1) and total nutrient removal (563 k N ha−1, 199 kg P ha−1, 2704 kg K ha−1) across a 6-year period among the grasses. Switchgrass may be the grass best suited for dual use systems under Uruguayan conditions because a farmer may utilize initial growth as forage while biomass regrowth is a good direct combustion o biofuel feedstock due to lower moisture content and nutrient removal compared to the other species evaluated.

Can Biomass Yield of Switchgrass be Increased without Increasing Nitrogen Requirements?

Switchgrass (Panicum virgatum L.) has been identified as a cellulosic bioenergy feedstock crop partly because of its potential to produce high biomass yields on marginal lands. Many breeding programs are focused on increasing biomass yields to improve the economic viability of the crop. However, increasing biomass yields without selecting for reduced biomass nitrogen (N) concentration will result in substantial increases in N removal at harvest. Our objectives were (i) to determine the current trajectory of biomass yield and N removal from breeding programs, (ii) to estimate the reduction in the rate of genetic gain for biomass yield when N concentration was incorporated into a breeding program, and (iii) to estimate the effects reduced N concentration might have on biofuel quality. Biomass yield and N concentration had a negative genetic correlation (−0.43), but a 50% increase in biomass yield likely will result in a 37% increase in N removal with direct selection for biomass yield. We estimated that incorporating the goal of reducing N concentration into a breeding program would result in a 225% greater reduction in N concentration while achieving 74% of the biomass yield gains achieved with direct selection for biomass yield only. Reducing N concentration in biomass was predicted to improve quality for use of biomass in a combustion system and to have minimal effects on quality in an ethanol conversion system. We conclude that simultaneous selection for increased biomass yield and reduced N concentration is both a worthy and feasible objective for switchgrass breeding programs that should improve the likelihood that improved yields from breeding are not undermined by increased N requirements.

Effect of Nitrogen Fertilization and Residual Nitrogen on Biomass Yield of Switchgrass

Switchgrass, Panicum virgatum L., grown for biomass has been extensively researched where the annual precipitation >760 mm and the climate varies from humid to moist-subhumid. Research is needed for areas that receive <700 mm of precipitation, where the climate varies from dry-subhumid to semiarid. The objectives were to determine (1) the effect of nitrogen fertilization on biomass production, (2) the effect of residual nitrogen on biomass production, (3) the nitrogen yield from harvested biomass, and (4) the concentration of soil organic carbon (SOC) from switchgrass plots. Plots were fertilized annually with nitrogen at the rates of 0, 40, 80, and 120 kg ha−1 from 2008 to 2011 and unfertilized from 2012 to 2015. The biomass yield varied with N rate × production year interactions (P < 0.05), and biomass yield as a function of N rate was either linear or curvilinear depending upon production year. When fertilized, the biomass yield averaged 4.4, 9.4, 11.6, and 13.2 ± 0.4 Mg ha−1 for the 0, 40, 80, and 120 kg ha−1 N rates, respectively. Residual nitrogen sustained high biomass yields for 1 year after fertilization ceased. The nitrogen harvested in biomass varied with N rate × production year interactions (P < 0.05), and the harvested nitrogen yield as a function of N rate was linear each year. Fertilization increased the concentration of SOC an average of 1.0 ± 0.2 mg g−1 of soil. The data suggest that producers could occasionally skip a year of nitrogen fertilization without detrimentally impacting the production of switchgrass biomass.

Efficiency of Spaced‐Plant Selection in Improving Sward Biomass and Ethanol Yield in Switchgrass

Switchgrass (Panicum virgatum L.) is an important emerging biofuel crop. In breeding nurseries, plants are typically widely spaced; however, production is in densely planted swards. This disconnect may hinder cultivar improvement. This study measured the efficiency of low‐density, spaced‐plant selection on improving biomass and ethanol yield in a high‐density, simulated sward. Fifty‐six full‐sib families were clonally replicated in two adjacent nurseries in Knoxville, TN. The spaced‐plant nursery consisted of single plants on 1‐m centers. The simulated‐sward nursery was created by planting four by seven plants on 0.33‐m centers with 1‐m alleys. In 2013 and 2014, biomass yield, ethanol yield, and morphological traits were evaluated. Trait means, correlations, and efficiency of indirect selection (E) were calculated. Significant interaction (p &lt; 0.05) between year and nursery was observed for all traits except ethanol yield. The identified high‐yielding ideotype differed between biomass and ethanol yield and between spaced‐plant and simulated‐sward nurseries. Selection under spaced‐plant conditions for simulated‐sward performance was efficient for ethanol yield (E = 0.96) but highly inefficient for biomass yield (E = −0.31). Several morphological traits evaluated under spaced‐plant conditions were identified as efficient indirect selectors for simulated‐sward biomass or ethanol yield. Results suggest selections for sward biomass yield may be more appropriate under sward‐like conditions, but that spaced‐plant nurseries are efficient for selection of ethanol yield performance under sward‐like conditions and for indirect selection of sward yield traits using morphological traits.

Identification, characterization, and gene expression analysis of nucleotide binding site (NB)-type resistance gene homologues in switchgrass.

BackgroundSwitchgrass (Panicum virgatum L.) is a warm-season perennial grass that can be used as a second generation bioenergy crop. However, foliar fungal pathogens, like switchgrass rust, have the potential to significantly reduce switchgrass biomass yield. Despite its importance as a prominent bioenergy crop, a genome-wide comprehensive analysis of NB-LRR disease resistance genes has yet to be performed in switchgrass.ResultsIn this study, we used a homology-based computational approach to identify 1011 potential NB-LRR resistance gene homologs (RGHs) in the switchgrass genome (v 1.1). In addition, we identified 40 RGHs that potentially contain unique domains including major sperm protein domain, jacalin-like binding domain, calmodulin-like binding, and thioredoxin. RNA-sequencing analysis of leaf tissue from ‘Alamo’, a rust-resistant switchgrass cultivar, and ‘Dacotah’, a rust-susceptible switchgrass cultivar, identified 2634 high quality variants in the RGHs between the two cultivars. RNA-sequencing data from field-grown cultivar ‘Summer’ plants indicated that the expression of some of these RGHs was developmentally regulated.ConclusionsOur results provide useful insight into the molecular structure, distribution, and expression patterns of members of the NB-LRR gene family in switchgrass. These results also provide a foundation for future work aimed at elucidating the molecular mechanisms underlying disease resistance in this important bioenergy crop.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3201-5) contains supplementary material, which is available to authorized users.

Biochar and plant growth promoting rhizobacteria effects on switchgrass (Panicum virgatum cv. Cave-in-Rock) for biomass production in southern Québec depend on soil type and location

Switchgrass (Panicum virgatum L.) is a fast growing native C4 perennial and a lignocellulosic biomass crop for North America. In combination with biochar, an active plant growth promoting rhizobacterial (PGPR) community can contribute to the long-term sequestration of carbon in soil, fix nitrogen, and enhance the availability of other nutrients to plants. Biochar and PGPR have the potential to improve grass biomass production, but they have not been tested together under high-latitude temperate zone field conditions. Therefore, the objective of this three-year field study was to determine whether there were effects on biomass yield and yield components of switchgrass (cv. Cave-in-Rock) due to a rhizobacterium that was able to mobilize soil phosphorus (Pseudomonas rhodesiae), a bacterial consortium that was able to supply nitrogen (Paenibacillus polymyxa, Rahnella sp., and Serrati sp.), and pine wood chip biochar applied as a soil amendment at 20 Mg ha−1. The incorporation of biochar, or inoculation with the N-fixing consortium, and the combined inoculation of the experimental bacteria had positive effects on switchgrass height. At a loam soil site in Sainte-Anne-de-Bellevue, Québec, when nitrogen fertilizer was not applied, the addition of biochar had a positive effect on stand count (tillers m−1 row). On the sandy soil in Sainte-Anne-de-Bellevue, when biochar was applied with 100 kg N ha−1, biomass yield increased over the control but did not provide additional benefits over plots receiving only 50 kg N ha−1. It remains unclear whether or not the increased C sequestration of this management system justifies increased N fertilizer usage.

Genome-wide associations with flowering time in switchgrass using exome-capture sequencing data.

Flowering time is a major determinant of biomass yield in switchgrass (Panicum virgatum), a perennial bioenergy crop, because later flowering allows for an extended period of vegetative growth and increased biomass production. A better understanding of the genetic regulation of flowering time in switchgrass will aid the development of switchgrass varieties with increased biomass yields, particularly at northern latitudes, where late-flowering but southern-adapted varieties have high winter mortality. We use genotypes derived from recently published exome-capture sequencing, which mitigates challenges related to the large, highly repetitive and polyploid switchgrass genome, to perform genome-wide association studies (GWAS) using flowering time data from a switchgrass association panel in an effort to characterize the genetic architecture and genes underlying flowering time regulation in switchgrass. We identify associations with flowering time at multiple loci, including in a homolog of FLOWERING LOCUS T and in a locus containing TIMELESS, a homolog of a key circadian regulator in animals. Our results suggest that flowering time variation in switchgrass is due to variation at many positions across the genome. The relationship of flowering time and geographic origin indicates likely roles for genes in the photoperiod and autonomous pathways in generating switchgrass flowering time variation.

Impact of Growing Environment on Anthracnose Severity of Switchgrass Cultivars and Clones.

Anthracnose (caused by Colletotrichum navitas) has the potential to significantly reduce biomass yield of switchgrass (Panicum virgatum L.); however, limited information is available on the impact of growing environment on tolerance of switchgrass to anthracnose. Therefore, the major objectives of this study were to (i) examine genotype-environment (G × E) effects on anthracnose severity in populations of switchgrass cultivars and individual genotypes and (ii) determine clonal repeatability estimates and stability analysis of anthracnose tolerance on individual switchgrass genotypes. Two experiments were conducted at one prime and two marginal soil locations in New Jersey. In all, 14 switchgrass cultivars were established from seed in 2008 for experiment 1 and 50 replicated switchgrass clones were planted in 2009 for experiment 2 at all three locations. Anthracnose was rated visually in 2010 for experiment 1 and in 2010 and 2011 for experiment 2. Significant G × E interactions were detected for both experiments (P ≤ 0.05) and anthracnose severity varied by location and cultivar. Clonal repeatability estimates for disease tolerance among clones was 0.78 on a clonal basis and 0.32 on a single-plant basis. Lowland ecotypes exhibited less disease overall than upland ecotypes. Results from this study indicate that selection for improved tolerance to anthracnose should be conducted after evaluation across several environments over multiple years.

Land requirements, feedstock haul distance, and expected profit response to land use restrictions for switchgrass production

Energy crop production has been proposed for land of poor quality to avoid competition with food production and negative indirect land use consequences. The objective of this study was to determine the land area requirements, biomass transportation distance, and expected profit consequences of restricting switchgrass biomass production, for use as biofuel feedstock, to marginal land relative to unrestricted land use. The USA soils capability classification system was used to differentiate between high quality land and land of marginal quality. Fifty years of historical weather data were used in combination with a biophysical simulation model to estimate switchgrass biomass yield distributions for land of different quality for counties in the case study region. A mathematical programming model was designed and solved to determine the economic consequences. For the levels of biofuel price considered ($0.50, $0.75 and $1.00/L), and a 262.5ML/year biorefinery modeled, restricting land use to marginally productive capability Class IV soils, increases the quantity of land optimally leased by 42 to 52%; increases biomass trucking total transportation distance by 115 to 116%; and reduces the expected net returns by $11 to $15M/year compared to when land use is unrestricted. In the absence of government restrictions, for-profit companies are not likely to limit energy crop production to land of marginal quality.

Switchgrass Harvest Time Management Can Impact Biomass Yield and Nutrient Content

Switchgrass (Panicum virgatum L.) is a dedicated energy crop native to tallgrass prairie and savanna ecosystems of North America. Although high biomass yield is of significant importance for the development of switchgrass as a bioenergy crop, mineral nutrients in biomass are critically important for sustainable bioenergy crop production but are detrimental for thermochemical conversion of biomass to energy. To evaluate biomass yield and nutrient uptake or nutrient cycling in switchgrass cultivars, replicated trials across three sites (Arlington, WI; Marshfield, WI; and Urbana, IL) were established in 2009. The switchgrass cultivars were harvested once annually at upland peak, after killing frost, or post‐winter in the spring from 2010 to 2014. Switchgrass biomass yield was greatest at the upland peak harvest, averaging 9.9 Mg ha−1 with biomass decreasing as harvest was delayed. Similarly, nutrient content in the biomass was greatest at the upland peak harvest with N, P, and K at 69, 77, and 23 kg ha−1, respectively. The majority of the N, P, and K in the biomass at the upland peak harvest was absent from the biomass at the post‐frost harvest. The lower levels of nutrients and total ash in the biomass at the post‐frost harvests will be beneficial for downstream conversion to bioenergy and may also reduce the future fertilizer requirements of the biomass crop.

Quantitative Trait Loci Mapping for Tillering-Related Traits in Two Switchgrass Populations.

Plant tillering and related traits are morphologically important components contributing to switchgrass ( L.) biomass yield. The objectives of this study were to estimate broad-sense heritabilities for tillering-related traits, to analyze correlations between biomass yield and the traits, and to identify quantitative trait loci (QTL) for them. A first-generation selfed population of NL94 plant and a hybrid population between NL94 and SL93 plants were field established in a randomized complete block design with three replications in Stillwater and Perkins, OK. Phenotypic data were collected in 2 yr and genotypic data were obtained by genotyping simple-sequence repeat (SSR) markers in the two populations on the basis of two preexisting genetic maps. Plant base size (PBS), plant girth (PG), tillering ability (TA), tiller diameter (TD), and tiller dry weight (TDW) were positively correlated with biomass yield in both populations. Consistently, PBS had the largest correlation coefficients for biomass yield, suggesting its value as an indirect selection criterion for biomass yield. Twenty and 26 QTL for six tillering-related traits were detected in the hybrid and selfed population, respectively. Among the QTL, one on linkage group (LG) 5a between sww-2387/PVCAG-2197/2198 and PVGA-1649/1650 for PBS, PG, and TA and another on LG 2a between sww-2640/sww-2545 and PVCA-765/766 for TD and TDW were stably detected in multiple environments in the two populations. The findings add to the knowledge base regarding the genetics of tillering-related traits that could be used in accelerating the development of high-yielding cultivars through marker-assisted selection.

Sorghum and Switchgrass as Biofuel Feedstocks on Marginal Lands in Northern China

To avoid food versus fuel conflicts in China, the production of bioenergy crops requires the evaluation of marginal lands under arid and semiarid conditions. We conducted field experiments with sorghum (Sorghum bicolor (L.) Moench) and switchgrass (Panicum virgatum L.) in Northern China. The biomass yield and nutrient (N, P, and K) accumulation of sorghum (leaves and stalks) and switchgrass (aboveground portion) were examined in 2012 and 2013. The soil organic carbon (SOC) content at depths of 0–30 cm was quantified at sorghum, switchgrass, and native grassland sites. The aboveground biomass yield of sorghum averaged 13.9 t ha−1 (14.2 and 13.6 t ha−1 in 2012 and 2013, respectively), while the switchgrass yield had a higher variability (14.8 versus 8.1 t ha−1 in 2012 and 2013, respectively) and averaged 11.5 t ha−1. The removals of N, P, and K averaged 56, 10, and 160 kg ha−1, respectively, for sorghum and 41, 11, and 89 kg ha−1, respectively, for switchgrass. To attain maximum biomass yield with minimum nutrient removal and the lowest transportation costs (due to the moisture content), the switchgrass harvest should be delayed until approximately 160 days after regrowth (DAR) in this region, whereas sorghum, which matures earlier, can be harvested as early as 120 days after sowing (DAS). Earlier harvests would increase the flexibility for large-scale ethanol production facilities. The SOC content within the 0–15-cm layer averaged 15.8 and 11.6 g C kg−1 before and 3 years after the establishment of the switchgrass culture, respectively, although the SOC increased with the culture age. In contrast, the SOC content of the 15–30-cm layer did not differ between the adjacent native grassland and the switchgrass planting. Under sorghum, the SOC content was reduced although it did not differ significantly from that of the native grassland at a significance level of p < 0.05. We conclude that high biomass yields can be obtained from the two crops under natural rainfall in the arid and semiarid conditions of Northern China. To address nutrient removal and SOC reduction, the leaves of sorghum should be returned to the field to increase the input of organic materials into the soil and reduce nutrient removal, which enhances soil fertility and sustainable production.

Switchgrass SBP-box transcription factors PvSPL1 and 2 function redundantly to initiate side tillers and affect biomass yield of energy crop.

BackgroundSwitchgrass (Panicum virgatum L.) is a dedicated lignocellulosic feedstock for bioenergy production. The SQUAMOSA PROMOTER-BINDING PROTEIN (SBP-box)-LIKE transcription factors (SPLs) change plant architecture and vegetative-to-reproductive phase transition significantly, and as such, they are promising candidates for genetic improvement of switchgrass biomass yield. However, the genome-wide identification and functional characterization of SPL genes have yet to be investigated in herbaceous energy crops.ResultsWe identified 35 full-length SPL genes in the switchgrass genome. The phylogenetic relationship and expression pattern of PvSPLs provided baseline information for their function characterization. Based on the global overview of PvSPLs, we explored the biological function of miR156-targeted PvSPL1 and PvSPL2, which are closely related members of SPL family in switchgrass. Our results showed that PvSPL1 and PvSPL2 acted redundantly to modulate side tiller initiation, whereas they did not affect phase transition and internode initiation. Consistently, overexpression of the miR156-resistant rPvSPL2 in the miR156-overexpressing transgenic plants greatly reduced tiller initiation, but did not rescue the delayed flowering and increased internode numbers. Furthermore, suppression of PvSPL2 activity in switchgrass increased biomass yield and reduced lignin accumulation, which thereby elevated the total amount of solubilized sugars.ConclusionsOur results indicate that different miR156-targeted PvSPL subfamily genes function predominantly in certain biological processes in switchgrass. We suggest that PvSPL2 and its paralogs can be utilized as the valuable targets in molecular breeding of energy crops for developing novel germplasms with high biofuel production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0516-z) contains supplementary material, which is available to authorized users.

Potential of loblolly pine: switchgrass alley cropping for provision of biofuel feedstock

Integrating bioenergy feedstock production with existing agricultural production systems and available land, resources, economic systems, and communities is critical for long-term sustainability of production systems. The ability of an agroforestry system of loblolly pine and switchgrass to produce biomass feedstock in flood prone sites are strategies to advance towards. The specific objective of this study is to assess and compare the performance of agroforestry against monoculture systems based on land use and production yield, by measuring various efficiency indices. Results across plots indicated biomass yield of switchgrass and loblolly pine grown in monoculture system were consistently higher in comparison to those grown in agroforestry system, where an average of 2.27 Mg/ha year−1 and 2.50 Mg/ha year−1 were seen respectively. The combined analysis of land equivalent ratio (LER) for loblolly pine and switchgrass intercrops, however, was a ratio ranging 1.25–1.74, which shows that pure strand or monoculture system would require 25–74 % more land to produce the same amount of yield relative to intercropping (agroforestry) system. An Agroforestry system has great potential for producing biomass feedstock for bioenergy. Using agroforestry intercropping of woody and perennial herbaceous bioenergy crops enhances combined biomass yield, decreases the need for input, and therefore reduces the cost of biomass production.

Spatial Variability in Biomass Yield of Switchgrass, Native Prairie, and Corn at Field Scale

Evaluating biofuel crop yield and its spatial variability on a field scale is important for determining the proper bioenergy crops suitable for specific lands. Within field spatial variability of switchgrass (Panicum virgatum L.), native prairie mix, and corn (Zea mays L.) biomass yield and its relation to soil properties were investigated in 2011 and 2012 at two farms in southwestern Michigan. At all sites and years, the order of biomass yields was corn &gt; switchgrass &gt; native prairie, which was consistent with fertilization rates of the crops. Short stand age of the perennial grass also contributed to the relatively lower yield. At both sites, switchgrass yield was not significantly different between 2011 and 2012, while corn yield was significantly lower in 2012 than in 2011. For switchgrass, within‐field variation was found considerably larger than the variation between years or between sites, while the variation between years or sites were comparable or greater than the within field variation for corn or native prairie. Two factors extracted from partial least square regressions (PLSRs) between biomass yield with soil and topographic variables could explain the majority of within field spatial variation for most of the fields in the study. Weight values of predictor variables from PLSRs were found strongly correlated between the 2 yr for a given crop at the same site with correlation coefficients from 0.65 to 0.89, as well as between switchgrass and native prairie at a given site.

The PIN1 family gene PvPIN1 is involved in auxin-dependent root emergence and tillering in switchgrass.

Switchgrass (Panicum virgatum L.; family Poaceae) is a warm-season C4 perennial grass. Tillering plays an important role in determining the morphology of aboveground parts and the final biomass yield of switchgrass. Auxin distribution in plants can affect a variety of important growth and developmental processes, including the regulation of shoot and root branching, plant resistance and biological yield. Auxin transport and gradients in plants are mediated by influx and efflux carriers. PvPIN1, a switchgrass PIN1-like gene that is involved in regulating polar transport, is a putative auxin efflux carrier. Neighbor-joining analysis using sequences deposited in NCBI databases showed that the PvPIN1gene belongs to the PIN1 family and is evolutionarily closer to the Oryza sativa japonica group. Tiller emergence and development was significantly promoted in plants subjected toPvPIN1 RNA interference (RNAi), which yielded a phenotype similar to that of wild-type plants treated with the auxin transport inhibitor TIBA (2,3,5-triiodobenzoic acid). A transgenic approach that inducedPvPIN1 gene overexpression or suppression altered tiller number and the shoot/root ratio. These data suggest that PvPIN1plays an important role in auxin-dependent adventitious root emergence and tillering.

Evaluating the impacts of landscape positions and nitrogen fertilizer rates on dissolved organic carbon on switchgrass land seeded on marginally yielding cropland

Dissolved organic carbon (DOC) through leaching into the soils is another mechanism of net C loss. It plays an important role in impacting the environment and impacted by soil and crop management practices. However, little is known about the impacts of landscape positions and nitrogen (N) fertilizer rates on DOC leaching in switchgrass (Panicum virgatum L.). This experimental design included three N fertilizer rates [0 (low); 56 (medium); 112 (high) kg N ha−1] and three landscape positions (shoulder, backslope and footslope). Daily average DOC contents at backslope were significantly lower than that at shoulder and footslope. The DOC contents from the plots that received medium N rate were also significantly lower than the plots that received low N rates. The interactions of landscape and N rates on DOC contents were different in every year from 2009 to 2014, however, no significant consistent trend of DOC contents was observed over time. Annual average DOC contents from the plots managed with low N rate were higher than those with high N rate. These contents at the footslope were higher than that at the shoulder position. Data show that there is a moderate positive relationship between the total average DOC contents and the total average switchgrass biomass yields. Overall, the DOC contents from leachate in the switchgrass land were significantly influenced by landscape positions and N rates. The N fertilization reduced DOC leaching contents in switchgrass field. The switchgrass could retain soil and environment sustainability to some extent. These findings will assist in understanding the mechanism of changes in DOC contents with various parameters in the natural environment and crop management systems. However, use of long-term data might help to better assess the effects of above factors on DOC leaching contents and loss in the switchgrass field in the future.

Biomass yield assessment of five potential energy crops grown in southern Ontario, Canada

Biomass yields of five commonly grown bioenergy crops, miscanthus, switchgrass, poplar (2293-19), willow (SX 67) and a mix of native grasses (polyculture) were assessed on a marginal land. When long-term yield responses were examined, miscanthus yield significantly increased from 5.96 ± 1.06 odt ha−1 y−1 in 2011 to 17.03 ± 8.1 odt ha−1 y−1 in 2014. Willow yield also increased from 3.21 ± 2.92 odt ha−1 y−1 in 2011 to 12.15 ± 4.94 odt ha−1 y−1 in 2014. However, for willow at this stage, we only compared the 1st year yields between 2011 and 2014, hence, three-year mature average yield in 2016 (mature stage) may not be much different from 12.15 odt ha−1 y−1, as willow yield increase over time is not linear. Among all other tested biomass species; polyculture, switchgrass and poplar, they recorded numerically higher yields during the mature growth stage (2013/2014) but, failed to reach statistical significance (p > 0.05). In this study, we separated the growth stages as; early (2010/2011) and mature (2013/2014) stages. At the early stage, poplar and polyculture recorded significant yield differences (p = 0.005) and poplar biomass yield was significantly higher (7.71 ± 2. odt ha−1 y−1) than polyculture (2.96 ± 0.43 odt ha−1 y−1). At the mature stage (2013/2014), miscanthus biomass yield was significantly higher than the two other tested herbaceous species (polyculture and switchgrass). Miscanthus yield was 17.03 ± 8.10 odt ha−1 y−1, which was almost three times higher than polyculture (5.64 ± 0.40 odt ha−1 y−1) and switchgrass (5.99 ± 0.46 odt ha−1 y−1) biomass yields. In relation to fertilization effect, miscanthus, polyculture and willow significantly and positively responded to fertilization. The significant yield increases between unfertilized and fertilized treatments were: 12.06, 10.61, and 8.8 odt ha−1 y−1 for willow, miscanthus and polyculture, respectively. Miscanthus, willow and polyculture yields as influenced by fertilizer treatment were 23.81 ± 3.55, 21.80 ± 5.99, 12.13 ± 0.66 odt ha−1 y−1, respectively.

Nitrogen Application Rate and Genotype Effects on Switchgrass Production and Chemical Characteristics

Switchgrass (Panicum virgatum L.) is considered as an important biofuel crop but further studies on factors that may have an effect on agronomic performance and energy attributes are needed to help elucidate management strategies for the crop. A 2-yr field study at the Brown Loam Branch Experiment Station, Raymond, Mississippi, USA, quantified the effects of four N application rates and four genotypes on biomass yield, ethanol yield, and nutrient removal of switchgrass. Biomass yield response to N rate was linear in 2008 and quadratic in 2009. Among genotypes, biomass yield averaged across N rate and years, ranked lowland NF/GA992 (13.9 Mg·ha-1) = lowland NF/GA001 (13.4 Mg·ha-1) > lowland Alamo (11.5 Mg·ha-1) > upland Cave-in-Rock (6.1 Mg·ha-1). There was no effect of N rate on tissue mineral concentrations but there was an N rate effect on Ca and Mg removal. Also, N use (biomass yield produced per unit N applied) and recovery (N removed in biomass) declined as N rate increased. Total ethanol yield was the greatest in Alamo (165.8 L·Mg-1) and averaged 162.0 L·Mg-1 for the other three genotypes. Total ethanol production was related more to biomass yield than chemical composition differences and was similar among lowland genotypes but different from Cave-in-Rock in 2008 (1.7 vs. 0.9 kL·ha-1) and 2009 (2.6 vs. 1.1 kL·ha-1). Feedstock grown from lowland Alamo, NF/GA001 or NF/GA992 produced greater biomass yield and ethanol as well as greater N use efficiency and recovery. These results indicate that there is opportunity to increase switchgrass biomass production through genotype selection and N management.

Insecticide Applications have Minor Effects on Switchgrass Biomass Yield

Large‐scale production of switchgrass (Panicum virgatum L.) as a bioenergy crop will depend on producing abundant yields without significant loss to insects. Despite the fact that crop losses to insect pests are observed in virtually every crop grown, we know little of how insects affect switchgrass biomass yield. We performed two multi‐year experiments in South‐Central Wisconsin where we measured Hiawatha switchgrass biomass responses to insecticides targeting aboveground and belowground insects. Experiment 1 was repeated for 3 yr in one location and Exp. 2 was repeated for 2 yr at a separate location. In Exp. 2, we also manipulated N levels to increase crop yields and potentially offset biomass loss by herbivores. We expect similar management practices to be used by farmers to reduce insect populations and increase crop yields as biomass crops become widely adopted. In the first year of Exp. 1, we found approximately 6.8% increase in yield in insecticide‐treated switchgrass but the effect was not significant in subsequent years, likely due to increased variance in crop yields across plots. In Exp. 2, N application resulted in a doubling of switchgrass yield (4.65 Mg ha−1 compared to 9.18 Mg ha−1 in unfertilized vs. fertilized plots, respectively), but insecticide treatments had no effect in both years. We conclude that if insect herbivory on switchgrass is occurring aboveground or belowground, this negative impact is small relative to other sources of variation in yield and it will not likely be a source of management concern for growers in the near term.