Harvest Date Effects on Biomass Yield,Moisture Content,Mineral Concentration,and Mineral Export in Switchgrass and Native Polycultures Managed for Bioenergy

Various local factors influence the decision of when to harvest grassland biomass for renewable energy including climate, plant composition, and phenological stage. However, research on biomass yield and quality related to a wide range of harvest timing from multiple environments and years is lacking. Our objective was to determine the effect of harvest timing on yield, moisture, and mineral concentration of switchgrass (Panicum virgatum L.) and native polyculture biomass. Biomass was harvested on 56 unique days ranging from late summer (2 September) to late spring (20 May) spanning 3 years (2009 to 2011) and seven sites in Minnesota, USA. Biomass yield varied considerably by location and year (range?=?0.7–11.7 Mg ha^?1) and was lowest during the winter. On average, there was no difference in biomass yield harvested in early fall compared to late spring. Biomass moisture content was lowest in late spring, averaging 156 g kg^?1 across all locations and years when harvested after 1 April. Biomass N concentration did not change across harvest dates; however, P and K concentrations declined dramatically from late summer to late spring. Considering the economic costs of replacing exported minerals and changes in revenues from biomass yield through time, biomass harvest should be conducted in late summer–early fall or late spring and avoided in winter. However, biomass managed for gasification should be harvested in spring to reduce concentrations of minerals that lead to slagging and fouling. Changes in biomass yield and quality through time were similar for switchgrass and native polyculture biomass. These biomass harvest recommendations are made from data spanning multiple years and locations and should be applicable to various growing conditions across the Upper Midwest.     

Biomass and seed yields of big bluestem, switchgrass, and intermediate wheatgrass in response to manure and harvest timing at two topographic positions

A principle attribute of perennial grasses for biomass energy is the potential for high yields on marginal lands. Objectives of this study were to compare biomass and seed production of intermediate wheatgrass ( Thinopyrum intermedium [Host] Barkworth and D.R. Dewey), big bluestem ( Andropogon gerardii Vitman), and switchgrass ( Panicum virgatum L.) as affected by harvest timing and manure application on two topographic positions (footslope and backslope). Footslope is the hillslope position that forms the inclined surface at the base of a slope and backslope forms the steepest, middle position of the hillslope. Grasses were harvested for biomass at anthesis (summer), after a killing frost (autumn), or the following spring after overwintering in the field. Seed was harvested at maturity during 2003 and 2004. Two rates of beef cattle ( Bos taurus L.) manure (target rates of 0 and 150 kg total-N ha⁻¹) were surface applied annually. Maximum annual biomass yield ranged from 4.4 to 5.2, 2.7 to 4.2, and 3.7 to 5.6 Mg ha⁻¹ for intermediate wheatgrass, big bluestem, and switchgrass, respectively. Biomass yields were not different between fall and spring harvest treatments. Biomass yields of big bluestem and switchgrass at the backslope position were 86% and 96% of biomass yields at the footslope position with normal precipitation, respectively. Manure application increased biomass yield approximately 30% during the second year on both topographic positions. The highest seed yield was obtained from intermediate wheatgrass, followed by switchgrass and big bluestem. Utilizing these management practices in our environment, it appears that switchgrass and big bluestem could be allowed to overwinter in the field without suffering appreciable loss of biomass.     

Switchgrass Biomass and Nitrogen Yield with Over-Seeded Cool-season Forages in the Southern Great Plains

In dry climates with long, hot summers and freezing winters, such as that of the southern Great Plains of North America, switchgrass (Panicum virgatum L.) has proven potential as a cellulosic bioenergy feedstock. This trial looked at dry matter (DM) and N yield dynamics of switchgrass overseeded with cool-season legumes and rye (Secale cereale L.), compared to switchgrass fertilized with 0, 56 and 112 kg N ha^-1 yr^-1 at an infertile and a fertile location. Optimal N fertilizer rate on switchgrass was 56 kg N ha^-1 at the infertile location. Legume yield was greater in the first season after planting, compared to subsequent years where annual legumes were allowed to reseed and alfalfa (Medicago sativa L.) was allowed to grow. This suggests that the reseeding model for annual legumes will not work in switchgrass swards grown for biomass unless soil seed banks are built up for more than one year, and that overseeding with alfalfa may have to be repeated in subsequent years to build up plant populations. Overseeding rye and legumes generally did not suppress or enhance switchgrass biomass production compared to unfertilized switchgrass. However, cumulative spring and fall biomass yields were generally greater due to winter and spring legume production, which could be beneficial for grazing or soil conservation systems, but not necessarily for once-yearly late autumn harvest biofuel production systems.     

Mowing Reduces Exotic Annual Grasses but Increases Exotic Forbs in a Semiarid Grassland

Cheatgrass (Bromus tectorum) and other exotic winter‐active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre‐empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4‐year study, we investigated whether mowing and seeding with native perennial grasses could limit growth of exotic winter‐actives, and benefit growth of native plants in an invaded grassland in Colorado, United States. We established a split‐plot experiment in October 2008 with 3 mowing treatments: control, spring‐mowed, and spring/summer‐mowed (late spring, mid‐summer, and late summer), and 3 within‐plot seeding treatments: control, added B. tectorum seeds, and added native grass seeds. Cover of plant species and aboveground biomass were measured for 3 years. In March and June of 2010, 2011, and March of 2012, B. tectorum and other winter‐annual grasses were half as abundant in both mowing treatments as in control plots; however, cover of non‐native winter‐active forbs increased 2‐fold in spring‐mowed plots and almost 3‐fold in spring/summer‐mowed plots relative to controls. These patterns remained consistent 1 year after termination of treatments. Native cool‐season grasses were most abundant in spring‐mowed plots, and least abundant in control plots. There was higher cover of native warm‐season grasses in spring/summer‐mowed plots than in control plots in July 2011 and 2012. The timing of management can have strong effects on plant community dynamics in grasslands, and this experiment indicates that adaptive management can target the temporal niche of undesirable invasive species.     

青贮对柳枝稷制取燃料乙醇转化过程的影响

青贮是一种传统的生物质原料保存方法,广泛应用于纤维素乙醇炼制领域尚需要考察其对原料品质和下游乙醇转化过程的影响。文中以秋季(初、中和末)收割的柳枝稷为原料,通过青贮、高温水热(LHW)预处理、纤维素酶水解和同步糖化与发酵(SSF)实验对上述问题予以回答。结果显示,秋季初收割的柳枝稷以不同湿度青贮后pH均小于4.0,干重损失小于2%,各主要成分与青贮前相比无明显变化;LHW预处理中青贮样品半纤维素水解率普遍高于未贮存样品,但青贮同样使原料获得了更高的发酵抑制物产生水平;青贮柳枝稷葡萄糖、木糖和半乳糖产量(预处理+酶水解)高于未贮存柳枝稷;经过168 h的SSF,青贮样品乙醇浓度为12.1 g/L,未贮存的秋季初、秋季中和秋季末柳枝稷为底物的浓度分别为10.3 g/L、9.7 g/L和10.6 g/L。综上,青贮有助于提高柳枝稷LHW预处理效率、酶水解率和乙醇产量。     

Winter hardiness of Miscanthus (I): Overwintering ability and yield of new Miscanthus ×giganteus genotypes in Illinois and Arkansas

Miscanthus ×giganteus (M×g) is an important bioenergy feedstock crop. However, biomass production of Miscanthus has been largely limited to one sterile triploid cultivar, M×g ‘1993‐1780’, which we demonstrate can have insufficient overwintering ability in temperate regions with cold winters. Key objectives for Miscanthus breeding include greater biomass yield and better adaptation to different production environments than M×g ‘1993‐1780’. In this study, we evaluated 13 M×g genotypes, including ‘1993‐1780’, in replicated field trials conducted for three years at Urbana, IL; Dixon Springs, IL; and Jonesboro, AR. Entries were phenotyped for first‐winter overwintering ability and plant hardiness (ratio of new tillers to old), yield in years 2 and 3, and first heading date, plant height, and culm number in years 1 and 2. We observed substantial variation for overwintering ability and biomass yield among the M×g genotypes tested and identified ones with better overwintering ability and/or higher biomass yield than ‘1993‐1780’. Most entries at Urbana were damaged during the first winter, whereas few or no entries were damaged at Dixon Springs or Jonesboro. However, M×g ‘Nagara’ was entirely undamaged during the first winter and produced high biomass yields at Urbana (19.7 Mg/ha in year 2 and 20.9 Mg/ha in year 3), whereas M×g ‘1993‐1780’ exhibited an overwintering loss of 29%, had severely damaged survivors (hardiness score of 25%), and reduced biomass yield (8.1 Mg/ha in year 2 and 16.2 Mg/ha in year 3), indicating that M×g ‘Nagara’ could be a better choice in hardiness zone 5 (average annual minimum air temperature of ?23.3 to ?28.9°C) or lower. In Dixon Springs, where M×g ‘1993‐1780’ was undamaged by the first winter, it yielded highest among all the entries (21.6 Mg/ha in year 3), though not significantly higher than M×g ‘Nagara’ (18.2 Mg/ha in year 3).     

Impact of Harvest Time and Cultivar on Conversion of Switchgrass to Bio-oils Via Fast Pyrolysis

The study of the effects of harvest time on switchgrass (Panicum virgatum L.) biomass and bioenergy production reported herein encompasses a large study evaluating the harvest of six switchgrass cultivars grown at three northern US locations over 3 years, harvested at upland peak crop (anthesis), post-frost, and post-winter. Delaying harvest of switchgrass until after frost and until after winter has resulted in decreased yields of switchgrass and reduced amounts of minerals in the biomass. This report examines how changes in biomass composition as a result of varying harvest time and other factors affect the distribution of products formed via fast pyrolysis. A subset (50) of the population (n = 864) was analyzed for fast pyrolysis and catalytic pyrolysis (zeolite catalyst) product yields using a pyrolysis-GC/MS system. The subset was used to build calibrations that were successful in predicting the pyrolysis product yield using near-infrared reflectance spectroscopy (NIRS), and partial least squares predictive models were applied to the entire sample set. The pyrolysis product yield was significantly affected by the field trial location, year of harvest, cultivar, and harvest time. Delaying harvest time of the switchgrass crop led to greater production of deoxygenated aromatics improving the efficiency of the catalytic fast pyrolysis and bio-oil quality. The changes in the pyrolysis product yield were related to biomass compositional changes, and key relationships between cell wall polymers, potassium concentration in the biomass, and pyrolysis products were identified. The findings show that the loss of minerals in the biomass as harvest time is delayed combined with the greater proportion in cellulose and lignin in the biomass has significant positive influences on conversion through fast pyrolysis.     

Seasonal Changes of Nitrogen Storage Compounds in a Rhizomatous Grass Calamagrostis epigeios

The seasonal dynamics in content and distribution of N-rich compounds between overwintering organs of Calamagrostis epigeios were examined. Samples were taken both from plants grown in natural conditions and in containers with controlled nutrient supply. There were significant changes in content of nitrate, free amino acids and soluble protein in all investigated plant parts during the course of a year. Amino acids showed both the highest maximum and seasonal fluctuation among the all N compounds observed and, therefore, appear to have a central role in N storage. Their content rises in the autumn, remains stable during winter and declines quickly at the beginning of spring. The most abundant amino acids in the end of winter storage period - asparagine, arginine and glutamine - constituted about 90 % of N in fraction of free amino acids. The portion of N stored in soluble proteins, however, was considerably smaller compare to both amino acids and nitrate. The amount of N stored in rhizomes of C. epigeios was smaller than in roots and stubble base before the onset of spring re-growth. This indicates that roots and stubble base are particularly important for winter N storage in this species.     

Biomass Yield and Quality of Reed Canarygrass under Five Harvest Management Systems for Bioenergy Production

Reed canarygrass, Phalaris arundinacea L., produces high biomass yields in cool climates and wetlands. The number and timing of harvests during a growing season directly affect biomass yield and biofuel quality. In order to determine optimum harvest management, seven cultivars of reed canarygrass were planted in field experiments at Ames, IA; McNay, IA; and Arlington, WI in the upper Midwestern USA and harvested once in autumn or in winter, twice in spring + autumn or spring + winter, or three times during the season as hay. Biomass yield varied considerably among harvest treatments, locations, and years, ranging up to 12.6 Mg ha^?1. Dry matter percentage ranged from 37% for spring-harvested biomass to 84% for overwintered biomass. The three harvest hay and two harvest spring + autumn managements produced the highest biomass yield compared to other systems, but the advantage, if any, of hay management was small and probably does not justify the cost of additional fieldwork. More mature biomass, such as that found in the single harvest systems, had higher fiber concentrations. Overwintered biomass had superior biofuel quality, being low in P, K, S, and Cl and high in cell wall concentration. However, winter harvest systems had lower yield than autumn harvest and in some years, no harvest was possible due to lodging from snow compaction. The main limitation of a two harvest system is the high moisture content of the late spring/early summer biomass.     

Impact of Harvest Equipment on Ash Variability of Baled Corn Stover Biomass for Bioenergy

Cost-effective conversion of agricultural residues for renewable energy hinges not only on the material’s quality but also the biorefinery’s ability to reliably measure quality specifications. The ash content of biomass is one such specification, influencing pretreatment and disposal costs for the conversion facility and the overall value of a delivered lot of biomass. The biomass harvest process represents a primary pathway for accumulation of soil-derived ash within baled material. In this work, the influence of five collection techniques on the total ash content and variability of ash content within baled corn stover in southwest Kansas is discussed. The equipment tested included a mower for cutting the corn stover stubble, a basket rake, wheel rake, or shred flail to gather the stover, and a mixed or uniform in-feed baler for final collection. The results showed mean ash content to range from 11.5 to 28.2 % depending on operational choice. Resulting impacts on feedstock costs for a biochemical conversion process range from $5.38 to $22.30 Mg^?1 based on the loss of convertible dry matter and ash disposal costs. Collection techniques that minimized soil contact (shred flail or nonmowed stubble) were shown to prevent excessive ash contamination, whereas more aggressive techniques (mowing and use of a wheel rake) caused greater soil disturbance and entrainment within the final baled material. Material sampling and testing were shown to become more difficult as within-bale ash variability increased, creating uncertainty around feedstock quality and the associated costs of ash mitigation.     

Management of warm-season grass mixtures for biomass production in South Dakota USA

Switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and indiangrass (Sorghastrum nutans (L.) Nash) are native warm-season grasses commonly used for pasture, hay, and conservation. More recently switchgrass has also been identified as a potential biomass energy crop, but management of mixtures of these species for biomass is not well documented. Therefore, the objectives of our study were to: (1) determine the effects of harvest timing and N rate on yield and biomass characteristics of established warm-season grass stands containing a mixture of switchgrass, big bluestem, and indiangrass, and (2) evaluate the impact of harvest management on species composition. Five N rates (0, 56, 112, and 224 kg ha(-1) applied annually in spring and 224 kg ha(-1) evenly split between spring and fall) and two harvest timings (anthesis and killing frost) were applied to plots at two South Dakota USA locations from 2001 to 2003. Harvesting once a year shortly after a killing frost produced the greatest yields with high concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) along with lower concentrations of total nitrogen (TN) and ash. This harvest timing also allowed for the greatest percentage of desirable species while maintaining low grass weed percentages. While N rates of 56 and 112 kg ha(-1) tended to increase total biomass without promoting severe invasion of grass and broadleaf weed species, N application did not always result in significant increases in biomass production. Based on these results, mixtures of switchgrass and big bluestem were well suited for sustainable biomass energy production. Furthermore, N requirements of these mixtures were relatively low thus reducing production input costs.     

A 30% reduction in switchgrass rhizome reserves did not decrease biomass yield

A long-standing question in perennial grass breeding and physiology is whether yield improvement strategies could compromise winter survival. Since perennial grasses rely on stored carbohydrates for winter maintenance and spring regrowth, yield improvement strategies could reduce winter survival if they increase biomass and grain yields at the expense of carbon allocation to storage. Therefore, it is crucial to comprehend the dependence of regrowth on storage reserves. We experimentally depleted switchgrass (Panicum virgatum L.) rhizome reserves by storing rhizomes for 2 weeks at 5°C (control treatment) and 25°C (reserve-depleted treatment). During the storage period rhizome respiration was 5.3× higher at 25°C (0.010 μmol CO₂ g⁻¹ min⁻¹ at 5°C vs. 0.054 μmol CO₂ g⁻¹ min⁻¹ at 25°C; p < 0.0001) and the starch content was depleted by 30% by the end of storage. Surprisingly, reserve-depleted switchgrass had 60% larger leaf area (LA; LA_control = 149 cm² pot⁻¹ vs. LA_depleted = 239 cm² pot⁻¹; p = 0.013) and produced ~40% more aboveground biomass than control plants (9.46 g pot⁻¹ vs. 6.63 g pot⁻¹; p = 0.112). In addition, reserve-depleted switchgrass restored its rhizome starch reserves to pre-storage levels. Switchgrass showed a large plasticity among its source-sink components to buffer the imposed reserve depletion. It increased plant photosynthesis by increasing the photosynthetic leaf area while keeping photosynthesis constant on a leaf area basis and readjusted the timing and activity of sink organs. These results suggest that switchgrass, and potentially other perennial grasses, largely over-invest in storage reserves. Therefore, current breeding strategies in perennial grasses aimed to extend the aboveground growing season should not compromise crop persistence. Our study also has implications on long-term yield dynamics as it highlights sink limitations as potential driver of the yield decline commonly observed in perennial grasses 5+ years after cultivation.     

稻茬冬小麦氮肥吸收、残留和损失特性

为推进稻茬小麦氮肥合理施用,采取田间¹⁵N示踪技术研究了施氮量(0、150、225、300 kg·hm^-2,分别表示为N₀、N₁₅₀、N₂₂₅、N₃₀₀)对氮肥回收、残留、损失和籽粒产量的影响。结果表明: 随施氮量增加,小麦植株不同来源氮素积累量显著增加,氮肥回收率则显著下降。基肥氮以越冬至拔节期在植株中的积累量最高,追肥氮以拔节至开花期积累量最高;成熟期各处理追肥氮在植株中的积累量均高于基肥氮,N₁₅₀处理植株中土壤氮的积累量高于肥料氮,N₂₂₅、N₃₀₀处理呈相反趋势。随施氮量增加,成熟期0～100 cm土层氮肥残留量显著增加,肥料氮在60～100 cm土层残留比例逐渐升高。小麦全生育期氮肥损失量和损失率均随施氮量增加而增加,基肥氮损失量以播种至越冬期最高,追肥氮损失量以拔节至开花期最高。综合考虑籽粒产量,N₂₂₅处理可作为稻茬小麦氮肥推荐用量,相应的籽粒产量为6735 kg·hm^-2,氮肥回收率、土壤残留率和损失率分别为42.6%、34.0%和23.3%。     

Impact severity in self-initiated sits and falls associates with center-of-gravity excursion during descent

Although the energy available during a fall from standing greatly exceeds that required to produce hip fracture, this occurs in only about 2% of falls in the elderly. This is thought to be due in part to one's ability to reduce the vertical impact velocity (nu(nu)) and kinetic energy (KE(nu)) of the body through energy absorption in the lower extremity muscles during descent. The present study tested the hypothesis that the magnitude and percent attenuation in nu(nu) and KE(nu) associate with the horizontal and vertical excursion of the body's center-of-gravity during descent. Measures were acquired of whole-body kinematics and lower extremity kinetics as young subjects underwent backward descents involving vertical drops of either thigh length (SIT) or lower extremity length (FALL), and horizontal pelvis excursions of either 33 or 66% of lower extremity length. In all trials, subjects attempted to "land as softly as possible." While attenuation in nu(nu) and KE(nu) (which averaged 62 and 92% respectively), did not associate with trial type, raw magnitudes of these parameters did, with nu(nu) averaging 2-fold greater, and KE(nu) averaging 6-fold greater, in 66% FALL than in 33% SIT or 66% SIT trials. This was due to a rapid increase in downward velocity accompanying the final stage of descent in 66% SIT and 66% FALL trials, which coincided with the knee moving posterior to the ankle. Accordingly, severe impacts likely accompany not only large fall heights, but also falls where the feet are thrown rapidly forward, as during a backward slip.     

Efficient Methods of Estimating Switchgrass Biomass Supplies

Switchgrass (Panicum virgatum L.) is being developed as a biofuel feedstock for the United States. Efficient and accurate methods to estimate switchgrass biomass feedstock supply within a production area will be required by biorefineries. Our main objective was to determine the effectiveness of indirect methods for estimating biomass yields and composition of switchgrass fields. Indirect measurements were conducted in eastern Nebraska from 2003 to 2007 in which switchgrass biomass yields were manipulated using three nitrogen rates (0 kg N ha^-1, 60 kg N ha^-1, and 120 kg N ha^-1) and two harvest periods (August and post-killing frost). A modified Robel pole was used to determine visual obstruction, elongated leaf height, and canopy height measurements. Prediction models from the study showed that elongated leaf height, visual obstruction, and canopy height measurements accounted for >?91%, >?90%, and >?82% of the variation in switchgrass biomass, respectively. Regression slopes were similar by cultivar (“Cave-in-Rock” and “Trailblazer”), harvest period, and across years indicating that a single model is applicable for determining biomass feedstock supply within a region, assuming similar harvesting methods. Sample numbers required to receive the same level of precision were as follows: elongated leaf height<canopy height<visual obstruction. Twenty to 30 elongated leaf height measurements in a field could predict switchgrass biomass yield within 10% of the mean with 95% confidence. Visual obstruction is recommended on switchgrass fields with low to variable stand densities while elongated leaf height measurements would be recommended on switchgrass fields with high, uniform stand densities. Incorporating an ocular device with a Robel pole provided reasonable frequency estimates of switchgrass, broadleaf weeds, and grassy weeds at the field scale.     

Spatial and Temporal Effects on Switchgrass Stands and Yield in the Great Plains

Switchgrass (Panicum virgatum L.) is being developed into a perennial, herbaceous, cellulosic feedstock crop for use in temperate regions of the USA. Information on spatial and temporal variation for stands and biomass yield among and within fields in large agroecoregions is not available. Spatial and temporal variation information is needed to model feedstock availability for biorefineries. In this 5-yr study, the spatial and temporal variation for biomass yield and stands was determined among and within 10 fields located in North Dakota, South Dakota, and Nebraska. Switchgrass fields were managed for bioenergy from 2000 to 2004 for the Nebraska locations and 2001 to 2005 for the South Dakota and North Dakota locations. A global positioning system (GPS) receiver was used to repeatedly measure within field quadrat sites for switchgrass stands using frequency grid (2.25 m²) measurements in June for five growing seasons. Sixteen quadrat (≥1 m²) yield samples were taken post-killing frost in the establishment year and in August in subsequent years at each location. Topographic within field effects on switchgrass stand frequency and biomass yields were largely insignificant. Stands tended to increase from establishment year to year 3 and then begin to plateau. Weather factors, which were the principal source of temporal variation, were more important in switchgrass yield variation than on switchgrass stand frequencies. Temporal standard deviations for yield were higher on quadrat sites with higher than average field means while temporal standard deviations were smaller in quadrat sites that had lower than average field means at six locations. In the Northern Great Plains agroecoregion, there is greater temporal and spatial variation for switchgrass biomass yields among fields than within fields. Results indicate that modeling feedstock availability for a biorefinery can be based on field scale yields.     

Metabolism and cold tolerance of overwintering adult mountain pine beetles (Dendroctonus ponderosae): Evidence of facultative diapause?

We sought evidence for a distinct diapause in adult overwintering mountain pine beetles (Dendroctonus ponderosae Hopkins) by measuring metabolic rate and supercooling ability of field collected beetles throughout the year. Metabolic rates measured at 0, 5, and 10°C declined significantly from October through November, then rose slowly, reaching levels as high as those recorded in October by late May. From December to February metabolic rates were not correlated with minimum weekly phloem temperatures (R(2)=0.0%, P=0.592), but were correlated with phloem temperatures as winter advanced to spring (R(2)=44.8%, P=0.010), a pattern consistent with progression through the maintenance and termination phases of diapause. Supercooling points were also significantly lower in winter compared to fall and spring (F((8,143))=32.6, P<0.001) and were closely correlated with metabolic rates (R(2)>79% for all three temperatures). Dry mass declined linearly with winter progression (F((8,150))=8.34, P<0.001), explained by catabolism of metabolic reserves, with a concomitant accumulation of metabolic water (F((8,147))=35.24, P<0.001). The strong mid-winter metabolic suppression correlated with improved supercooling ability, coupled with their lack of response to variation in environmental temperature, are evidence of possible diapause in adult overwintering mountain pine beetles.     

Overwintering Ability and High-Yield Biomass Production of <Emphasis Type="Italic">Erianthus arundinaceus</Emphasis> in a Temperate Zone in Japan

Erianthus arundinaceus, a warm-season perennial species in the Gramineae family, is currently being considered as a bioenergy crop candidate due to its capacity for high yields. Several experiments to explore this possibility have been conducted in Nasushiobara, Japan, where the mean minimum air temperature in January over the last three decades has been ??4.4 °C. Some accessions and breeding lines have demonstrated overwintering abilities, and annual dry matter yields of up to 52 t ha^?1 were recorded in the 7th year after planting. Cutting to a 0.05-m height in February contributed more to subsequent regrowth and yield than did similar cutting in November. However, when performed in November, cutting to a 0.3-m height was more beneficial to subsequent regrowth and yield than cutting to a 0.05-m height. Allowing the foliage to run dry during winter led to a dry (approximately 70% dry matter ratio) biomass harvest in late winter. During winter, nutrient remobilization within the plants decreases nutrient removal from the soil. Although nitrogen fertilizer use efficiency was quite high (60%), only 20% of the nitrogen in an individual plant in the 2nd year after planting originated from fertilizer. This was likely due to a large amount of nitrogen obtained from non-fertilizer sources, i.e., soil and stored in the stubble from the previous harvest. Future experiments should focus on designing a fertilizer application program that could lead to sustainable and long-term high-yield E. arundinaceus biomass production in temperate zones.     

The perennial biogas crops cup plant (Silphium perfoliatum L.) and field grass pose better autumn and overwintering habitats for arthropods than silage maize (Zea mays L.)

Perennial energy crops (PECs) can reduce the negative impacts of intensive silage maize cultivation on agroecosystems in Central Europe. Furthermore, the remaining vegetation of PECs after harvest may provide suitable habitat and more beneficial overwintering conditions for arthropods than maize. It was hypothesized that after harvest and in winter, arthropod abundance and biomass are higher in PECs than in silage maize. In a field experiment arranged in a factorial split-plot design of eight main plots (plot size: 240 m²), the two PECs cup plant (Silphium perfoliatum L.) and field grass were compared with silage maize (Zea mays L.) regarding their suitability as autumn (post-harvest) and overwintering habitats for arthropods. Soil temperature, moisture as well as biomass and abundance of autumn-active and overwintering arthropods were analyzed for these three crops. Suction sampling was used during autumn and emerging arthropods were sampled with emergence trap sets in spring. In PEC plots, soils were moister and less exposed to cold temperatures than in silage maize. Compared with silage maize, total arthropod abundance and biomass were higher in PEC plots for both sampling periods. Results were similar for most examined arthropod taxa. The results of this study demonstrate that, compared with silage maize, PECs provide suitable post-harvest habitats and constitute more suitable overwintering habitats for arthropods. Differences are likely to be based on lack of disturbance and the provision of vegetation structures after harvest that function as overwintering habitats for arthropods. It can be concluded that the positive effects of PECs on ground arthropods are not limited to their growing time but continue to a certain extend after harvest and during winter.     

Incorporating sheep into dryland grain production systems: II. Impact on changes in biomass and weed density

Weed control in fallow management to conserve soil moisture and nutrients is the largest variable cost to dryland grain production. Our objective was to compare burning, grazing, tilling, trampling and clipping wheat stubble fields on changes in total aboveground biomass and weed density. Treatments were evaluated in three experiments using a randomized complete block design for each experiment with four replications at each site. Contrasts statements were used to make pre-planned comparisons. For experiment 1, treatments were fall tilled, fall grazed, spring grazed, fall and spring combined (Fall/Spr) grazed, and an untreated control. For grazing treatments, five mature ewes were confined with electric fence to 111 m² plot for 24 h for fall and spring resulting in a stocking rate of 452 sheep day/ha. For Fall/Spr the stocking rate was 904 sheep day/ha. For experiment 2, treatments were fall grazed, fall burned, fall tilled, and an untreated control. In experiment 3, treatments were fall trampling by sheep, spring trampling by sheep, fall and spring combined (Fall/Spr) trampling by sheep, stubble hand clipped to a height of 4.5 cm, and an untreated control. Trampling treatments were applied at the same stocking rates as grazing treatments but sheep were muzzled to prevent intake. Data were collected in the fall, prior to treatment imposition, and spring, after treatments had been removed. Post treatment biomass and weed density were greater (P < 0.05) in either control or tilled plots when compared to grazed plots. Post treatment biomass and weed density were greater (P < 0.01) for control than burned plots. Post treatment biomass, weed density, and percent change in these variables, did not differ (P > 0.08) between burned and tilled, and burned and grazed treatments. These results indicate the potential for using grazing sheep as a component in fallow management to reduce biomass and control weeds.