Killing Frost Research Articles

Changes in Lignocellulosic Polymers, Carbon, and Energy in Switchgrass for Bioenergy Production

Core Ideas Depending on the energy conversion method, switchgrass may be harvested over 2 months prior to killing frost. Drought may have caused a delay in the fall increase in C concentrations in switchgrass. Switchgrass cellulose, hemicellulose, lignin, and energy contents were unaffected by drought. Few studies have intensively monitored switchgrass chemical components during natural drought conditions. Switchgrass (Panicum virgatum L.) is a potential bioenergy crop recommended by the U.S. Department of Energy. To produce biofuel from switchgrass, high cellulose and low lignin concentrations are ideal for biochemical conversion while high lignin and energy content are desirable for thermochemical conversion. These values change during plant growth. The objective of this study was to identify the optimum harvest window using a one‐cut system. Thirteen and eight harvests were collected in 2011 and 2012, respectively, and analyzed for cellulose, hemicellulose, lignin, total C, and energy content. Generally, cellulose and hemicellulose concentrations increased through July, remained relatively constant for the remainder of the study period (through early November), and were unaffected by drought. Carbon concentrations increased significantly with plant growth then decreased significantly in July/August, presumably due to reproductive growth, followed by a significant increase in September or October of 2011 and 2012 due to senescence. Drought in early 2012 may have caused small changes in C concentration as compared to 2011. Energy content increased significantly early in the season, and remained similar between August and November while lignin concentrations increased. Both parameters, however, were relatively unaffected by the 2012 drought. It was concluded that switchgrass could be harvested as early as late August (earlier than the current recommended period of after 1 November or killing frost) depending on the requirements of the conversion method. More research is needed to determine whether early or delayed harvests have a greater economic impact on overall fuel yields in drought or normal years.

Switchgrass Harvest Progression in the North-Central USA

In the North-Central USA, switchgrass to be used as a biomass feedstock typically will be harvested in the autumn. The accumulated area harvested over the harvest season (defined here as the harvest progression) will influence the size of the machinery fleet and seasonal labor required to complete the majority of the harvest before the first lasting snow. A harvest progression model was developed that uses drying rate, mower and baler productivity, and weather conditions as major inputs. Ten years of weather data (2005–2014) from Wisconsin, Iowa, and Nebraska (WI, IA, NE) were used. Harvest progression was modeled for four harvest systems involving conventional and intensive conditioning both swathed and tedded (CC, IC, CCT, and ICT, respectively) and two dates at which harvest began (1 September and after a killing frost). To reduce risk of exposing crop to prolonged periods of inclement weather, mowers were idled when more than 80 ha were cut but not yet baled. For all sites, the harvest start date and the mower idled constraint had greater impact on harvest progression than the type of harvest system. Harvest progression was greatest when mowing started on 1 September and continued whenever weather permitted (i.e., no mower idled constraint). Compared to the harvest system used today (CC), using the IC system resulted in more area harvested with less crop exposed to rain after cutting and considerably less area left to be baled in the spring. Starting harvest on 1 September, using intensive conditioning, and not idling the mowers might be considered the system that best balances the desire for rapid harvest progression, small equipment fleet size, low-capital expenditures, and maximum labor utilization.

All Washed Out? Foliar Nutrient Resorption and Leaching in Senescing Switchgrass

Ideal bioenergy feedstocks are low in nutrients that act as anti-quality factors during conversion processes. Research has shown that delaying harvest of temperate perennial grasses until late winter reduces nutrient content, primarily due to end-season resorption, but also indicates a role for foliar nutrient leaching. While end-season resorption has been estimated, foliar nutrient leaching has not, and is a factor that could refine harvest recommendations. Additionally, establishing a baseline of mineral loss during switchgrass senescence will improve our understanding of leaf-level nutrient resorption. Therefore, we applied simulated rainfall to replicated (n = 5) plots within a previously established switchgrass stand to determine if heavy precipitation can induce nutrient leaching in senescing, unharvested foliage. Hour-long simulated rainfalls of ∼120 mm were applied every 2 weeks from early September to a killing frost in 2014 and 2015. Leaf samples were taken from the upper and lower canopy before and after simulated rainfalls and from no-rain controls and analyzed for elemental N, P, K, S, Mg, and Ca. Nutrient resorption estimates ranged from 33 to 82% in control plots. Comparison of rainfall plots to controls indicated that lower canopy leaves, upon reaching ≥50% senescence, were slightly susceptible to foliar nutrient leaching, with losses ranging from 0.3 to 2.8 g kg−1 dry matter for K, P, and Mg. Nitrogen, Ca, and S were not susceptible to foliar leaching. Although statistically significant (P ≤ 0.05), these values suggested that foliar leaching was not a strong driver of nutrient loss during senescence.

Switchgrass Biomass Quality as Affected by Nitrogen Rate, Harvest Time, and Storage

Core Ideas Switchgrass, being an efficient perennial biofuel crop, can be used as an alternative to fossil fuels and help in the sustainability of energy. Thus, it is important that we understand the effect of storing switchgrass for extended periods of time. Storing switchgrass for an extended period may have an impact on quality and yield. Storing switchgrass in bales or as a standing crop in the field are two storage methods assessed in this study. The purpose of this study was to assess the changes in switchgrass (Panicum virgatum L.) biomass quality as affected by N rate, harvest time, and storage. This research was conducted near Bristol, SD, in 2010 and 2011. Treatments included three N rates (0, 56, and 112 kg N ha−1) applied annually and each N rate replicated four times. After a killing frost, all of the plots were harvested and baled in large round bales in October 2010 and November 2011. An area of about 30 m2 from each plot was left unharvested to represent storage of standing switchgrass over the winter and to determine dry matter yields. Switchgrass was analyzed for hemicellulose, cellulose, lignin, mineral elements, N, and C. In the first season, storage of the fall harvested switchgrass bales numerically increased the concentrations of hemicellulose, lignin, and N. In the second season, they increased significantly. Mineral elements significantly increased in both sampling seasons. Delaying harvest until spring decreased lignin, N, and mineral elements concentration, and increased cellulose and hemicellulose concentrations, but also reduced biomass yield. Results from this study suggest that delaying the switchgrass harvest until spring increased the overall feedstock quality for ethanol production, but yield reductions must be considered to determine the overall economic impact of a delayed harvest.

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.

Extending the Fall Harvest Window of Switchgrass on the Basis of Phosphorus and Potassium Tissue Concentrations

It is hypothesized that switchgrass (Panicum virgatum L.) remobilizes phosphorus (P) and potassium (K) to belowground plant organs during maturation and senescence. Consequently, recommended biomass harvests occur after the first killing frost or early November, although field curing conditions at that time may be undesirable. Therefore, the objectives of this study were to determine i) if harvests can occur earlier based on removal of P and K (in leaves and stems) for two standard (‘Alamo’ and ‘Kanlow’) and eight new upland and lowland cultivars during the fall (i.e., mid‐September, mid‐October, late October, and early November) in Exp. 1, and ii) changes in P and K concentration in aboveground versus belowground biomass (roots, crowns, and shoots) in standard cultivars during mid‐September, late October, and mid‐November in Exp. 2. Both experiments were performed in a randomized complete design with three blocks at Knoxville and Springfield, TN, USA, in 2009 and 2010. Shoot P and K concentrations in cultivars did not decline from mid‐September to late October, nor did P and K in crowns and roots increase from mid‐September to mid‐November (P > 0.05). However, leaf concentrations of P (across locations and years) were greatest for OK NSL‐2001‐1 (lowland cultivar), which did not differ from Blackwell (upland cultivar). Cultivar Kanlow had the lowest P concentrations across all plant parts and cultivars. Similarly, stem P was greatest for the cultivar Blackwell. Harvest timing of upland and lowland switchgrass cultivars may therefore be extended to earlier in the fall (mid‐September) based on lack of attenuating declining trends of P and K in shoots of switchgrass cultivars in the Southeast.

Effects of chemical additives on the fermentation quality and N distribution of alfalfa silage in south of China.

In order to better utilize the last cut alfalfa harvested before killing frost in a high moisture environment, the effects of chemical additives on the quality of alfalfa silage were studied in south of China. The alfalfa was freshly harvested at branching stage, and wilted by dry matter content of about 300 g/kg (fresh matter basis). Silage was prepared by using a small-scale silage fermentation system, where sucrose, potassium citrate, sodium carbonate, formic acid, acetic acid and propionic acid were used as silage additives, and no additives served as control. These silos were stored at ambient temperature (5-20°C), and the silage qualities were analyzed after 120 days of fermentation. All additive treatments affected the chemical composition and N distribution, increased the water-soluble content and crude protein contents, decreased non-protein nitrogen (NPN) content, and enhanced the in vitro ruminal dry matter digestibility (except for sodium carbonate). Silages treated with organic acids were preserved with significantly (P < 0.05) lower pH value, ethanol content and NPN content compared with control. When the fermentation quality, chemical composition and N distribution were considered, the treatment with sucrose or organic acids resulted in high quality of alfalfa silage ensiled before killing frost, with formic acid having the best effect.

1600 AD Huaynaputina Eruption (Peru), Abrupt Cooling, and Epidemics in China and Korea

The 1600 AD Huaynaputina eruption in Peru was one of the largest volcanic eruptions in history over the past 2000 years. This study operated on the hypothesis that this event dramatically affected the weather and environment in China and the Korean Peninsula. Over the course of this research the Chinese and Korean historical literatures as well as dendrochronology records were examined. The historical evidence points to the conclusion that the eruption was followed by an abrupt cooling period and epidemic outbreaks in 1601 AD within both China and the Korean Peninsula. These records manifested themselves in unseasonably cold weather resulting in severe killing frosts in northern China in the summer and autumn of 1601 AD. In southern China (Zhejiang and Anhui Provinces and Shanghai Municipality), July was abnormally cold with snow, with an autumn that saw anomalously hot weather. In addition, there was unseasonable snowfall that autumn within Yunnan Province. Widespread disease outbreaks occurred in August, September, and October in northern and southern China. In Korea, the spring and early summer of 1601 AD were unusually cold, and conditions led to further widespread epidemics occurring in August.

The Effects of Hybrid Relative Maturity on Corn Stover for Ethanol Production and Biomass Composition

Full‐season corn (Zea mays L.) hybrids take advantage of more of the growing season than shorter‐season hybrids often leading to greater grain and biomass yield. Many agronomic experiments aimed at corn stover production have been performed at forage harvest rather than later when stover is normally harvested for biofuel measurements. The objective of this research was to evaluate the influence of hybrid relative maturity (days RM) on stover ethanol production, ruminant digestibility, and biomass composition. Hybrids selected were high‐yielding commercial grain hybrids grown throughout Wisconsin and ranged from 85 to 115 d RM in 10 d RM increments during 2009, and in 5 d RM increments during 2010. Hybrids were harvested at physiological maturity or after a killing frost. Overall, stover and theoretical ethanol yields increased as RM increased at a linear rate of 0.211 Mg ha−1 RM−1 and 67.1 L ha−1 RM−1. Stover nutritional and biomass composition improved as RM increased, but yield variability was greater than nutritional and biomass compositional variability. Increasing ethanol yields will likely occur by increasing stover yields rather than by altering stover composition. Therefore, until price premiums for stover composition are made available to farmers for ethanol production, the adoption of full‐season or longer maturing hybrids should be implemented for increased stover and ethanol yields.

Autumnal leaf senescence in Miscanthus × giganteus and leaf [N] differ by stand age.

Poor first winter survival in Miscanthus × giganteus has been anecdotally attributed to incomplete first autumn senescence, but these assessments never paired first-year with older M. × giganteus in side-by-side trials to separate the effect of weather from stand age. Here CO2 assimilation rate (A), photosystem II efficiency (ΦPSII), and leaf N concentration ([N]) were used to directly compare senescence in first, second, and third-year stands of M. × giganteus. Three M. × giganteus fields were planted with eight plots, one field each in 2009, 2010, and 2011. To quantify autumnal leaf senescence of plants within each stand age, photosynthetic and leaf [N] measurements were made twice weekly from early September until a killing frost. Following chilling events (daily temperature averages below 10 °C), photosynthetic rates in first year plants rebounded to a greater degree than those in second- and third-year plants. By the end of the growing season, first-year M. × giganteus had A and ΦPSII rates up to 4 times greater than third-year M. × giganteus, while leaf [N] was up to 2.4 times greater. The increased photosynthetic capability and leaf N status in first-year M. × giganteus suggests that the photosynthetic apparatus was not dismantled before a killing frost, thus potentially limiting nutrient translocation, and may explain why young M. × giganteus stands do not survive winter when older stands do. Because previous senescence research has primarily focused on annual or woody species, our results suggest that M. × giganteus may be an interesting herbaceous perennial system to investigate the interactive effects of plant ageing and nutrient status on senescence and may highlight management strategies that could potentially increase winter survival rates in first-year stands.

Back to Basics: Breeding plants for organic agriculture

Back to Basics: Breeding plants for organic agriculture

Cropload Management of ‘Vidal blanc’ Improves Primary Bud Cold Hardiness and Maintains Berry Composition in the Lower Midwestern United States

Canopy architecture, yield components, berry composition, pruning weight, Ravaz Index, and midwinter primary bud cold hardiness of own-rooted ‘Vidal blanc’ (Vitis vinifera × Vitis rupestris) were measured in response to balanced pruning formula treatments of 20, 30, or 40 nodes retained for the first 454 g of dormant pruning weight and an additional 10 nodes for each additional 454 g and three cluster thinning levels of one, two, and two+ clusters per shoot in 2006 and 2007. Although the pruning formula affected the distance between shoots along the canopy, and the number of count shoots per hectare, the canopy leaf layer numbers were unaffected in either year. Application of the pruning formula did not affect components of yield in either year. However, the number of clusters and yield per vine were affected by cluster thinning treatments where they increased linearly with the decrease in its severity, explaining 73% and 77% of total variance in yield in 2006 and 2007, respectively. Pruning formula or cluster thinning did not affect berry composition substantially. Cluster thinning improved the percentage of mature nodes on shoots before a killing frost in both years. Cluster thinning to one or two clusters per shoot also improved the lethal temperature killing 50% of the primary buds compared with no cluster thinning in both years of the study. Mature wood weight and total pruning weight displayed a quadratic response to cluster thinning where two clusters per shoot had the greatest weight for both, whereas pruning formula had no effect on pruning weight. Optimum fruit weight–pruning weight ratio was achieved with the 30 + 10 pruning formula and two clusters per shoot cluster thinning treatments in both years of the study. The results of this study provide valuable information for growers of interspecific hybrids such as ‘Vidal blanc’ in the lower midwestern United States as well as in other regions with long, warm growing seasons. Balanced pruning to 30 nodes per 454 g of dormant prunings and cluster thinning to two clusters per shoots optimized yield, maintained fruit composition, improved primary bud cold hardiness, and achieved an optimum fruit weight-to-pruning weight ratio of 10.0 kg·kg–1. Thus, this approach should be used for ’Vidal blanc’ in the lower midwestern United States to sustain production.

Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict

AbstractWe present the first study of the global impacts of a regional nuclear war with an Earth system model including atmospheric chemistry, ocean dynamics, and interactive sea ice and land components. A limited, regional nuclear war between India and Pakistan in which each side detonates 50 15 kt weapons could produce about 5 Tg of black carbon (BC). This would self‐loft to the stratosphere, where it would spread globally, producing a sudden drop in surface temperatures and intense heating of the stratosphere. Using the Community Earth System Model with the Whole Atmosphere Community Climate Model, we calculate an e‐folding time of 8.7 years for stratospheric BC compared to 4–6.5 years for previous studies. Our calculations show that global ozone losses of 20%–50% over populated areas, levels unprecedented in human history, would accompany the coldest average surface temperatures in the last 1000 years. We calculate summer enhancements in UV indices of 30%–80% over midlatitudes, suggesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems. Killing frosts would reduce growing seasons by 10–40 days per year for 5 years. Surface temperatures would be reduced for more than 25 years due to thermal inertia and albedo effects in the ocean and expanded sea ice. The combined cooling and enhanced UV would put significant pressures on global food supplies and could trigger a global nuclear famine. Knowledge of the impacts of 100 small nuclear weapons should motivate the elimination of more than 17,000 nuclear weapons that exist today.

Maximizing Land Use during Switchgrass Establishment in the North Central United States

Switchgrass (Panicum virgatum L.) grown under three differing establishment methods was evaluated for yield, quality, and potential ethanol production across seven environments in Wisconsin and Michigan. The three establishment methods included: (i) June seeding into fallow ground; (ii) June seeding following winter rye (Secale cereale L.) forage; and (iii) August seeding following winter wheat (Triticum aestivum L.). Planting switchgrass in June was successful following the rye forage crop, but planting in August after wheat resulted in complete stand loss. While harvested biomass in a two‐cut system was equal to or greater than that realized in a one‐cut system (6.9 vs. 6.8 Mg ha−1), biomass quality for ethanol production was highest following a killing frost (226 vs. 224 g ethanol kg−1 biomass). The higher overall biomass production in the two‐cut system generally compensated for this difference however, with ethanol yields similar between the two systems (1950 vs. 1970 L ethanol ha−1 for the two‐ and one‐cut system, respectively). In addition to ethanol production, we found that forage nutritive value in the first cut of the two‐cut system was of sufficient quality to satisfy the dietary needs of several classes of livestock. Harvesting established switchgrass for hay with an early season cutting in a two‐cut system provides producers with an alternative forage source while not affecting total seasonal biomass yield if harvested at the appropriate growth stage and cutting height to leave sufficient photosynthetic material for regrowth.

Short- and long-time effects of multispecies lactic acid bacteria inoculant on fermentation characteristics and aerobic stability of corn silages at different maturities and frost killed corn

The objective of this experiment was to evaluate the short- and long-time effects of a multispecies lactic acid bacteria (LAB) inoculant on biochemical characteristics of corn silages at hard dough (HD, 253.1 g DM kg−1), one-third milk line (ML, 293.7 g DM kg−1), and one-third milk line with a killing frost (FKML, 297.6 g DM kg−1) maturity stages. The crops were ensiled in laboratory silos with (1.5 × 105 cfu g−1 of fresh forage) or without Lactisil Maize. Concentrations of dry matter and neutral detergent fiber, value of pH, and population of fungi were higher in ML and FKML crops compared with HD (p < 0.01). In contrast, lower water-soluble carbohydrate and crude protein concentrations and lower populations of epiphytic LAB were measured in ML and FKML crops (p < 0.01). Frosting reduced population of LAB and increased yeast number (p < 0.01) but did not affect chemical composition. Preservation of ensilage for 160 days compared with 42 days increased concentration of lactic acid and ratio of lactic acid to acetic acid in HD silage. Extensive homolactic fermentation was occurred in response to inoculation in all treated silages at first period of ensiling (42 days). However, the current inoculant could dominate heterofermentative LAB over homofermentative LAB during the latter part of the ensiling period (160 days). Application of this inoculant for ensiling corn crop will improve fermentation characteristics but aerobic stability of inoculant-received silages will be improved after long-time preservation.

A Five-year Study on the Effect of Cluster Thinning and Harvest Date on Yield, Fruit Composition, and Cold-hardiness of ‘Vidal Blanc’ (Vitis spp.) for Ice Wine Production

The aim of this 5-year study was to investigate the influence of cluster thinning (CT) and harvest date on yield components, fruit composition, and bud cold-hardiness in ‘Vidal blanc’ (Vitis spp.) grapevines grown in northern Ohio. It is unknown whether delaying harvest of ‘Vidal blanc’ for ice wine production would impact negatively winter-hardiness. ‘Vidal blanc’ grapevines were cluster-thinned at post-fruit set [Eichhorn-Lorenz (EL) Stage 31] to two crop levels by retaining 40 (CT40) and 60 (CT60) clusters per vine. Each crop level was harvested at three dates: normal harvest (HD1), fall harvest (HD2) after the first killing frost, and winter harvest (HD3) corresponding to the typical commercial harvest for ice wine. Generally, and as expected, the high crop level CT60 increased crop weight and cropload and decreased total soluble solids and pH. Delayed harvest decreased crop weight, cluster weight, berry weight, and titratable acidity but increased total soluble solids and pH. Bud cold-hardiness, determined by thermal analysis and after two freezing events, was not different among all treatments. It was concluded that CT40 produced optimum vine size and cropload thus balanced vines. Furthermore, delaying fruit harvest in ‘Vidal blanc’ for ice wine production in the northeastern United States and Canada improves fruit composition but has no adverse influence on bud cold-hardiness.

Natural variation of biomass yield and nutrient dynamics in Miscanthus

Miscanthus has been rated as one of the most promising bioenergy crops due to its potential for biomass production. The sustainable production of Miscanthus for bioenergy feedstock partly depends on the varieties that are efficient in terms of nutrient use for the production of biomass. In this study, 23 Miscanthus accessions, collected from wide range of geographic regions, were established early in March 2010 in Wuhan, China. The feedstock was sampled for nutrient concentration determination late in November 2010 and 2011 (at physiological maturity), and harvested early in February 2011 and 2012 (after a killing frost) to evaluate the biomass yield, nutrient concentration and removal. Across these two years, the biomass yield was negatively related to the latitude of the original collection sites. A significant increase in biomass production was observed in the second growth year relative to that in the first growth year among almost all of the Miscanthus accessions. The accessions of MS267 and MS321 only yielded 1.32 and 1.91tonha−1 in 2010, respectively, but the biomass yield increased dramatically to 11.23 and 22.76tonha−1 in 2011, leading to greater nutrient removal by the final harvest and thus the requirement of much more fertilizer in the following years. The accessions MS92, MS145, MS262, MS436 and MS438 established poor biomass yields, averaging <1tonha−1 in the first two years, which suggests that they may be unsuitable for planting in the present environment. Significant differences between accessions were found for the nutrient concentration at maturity and after frost. Notable differences in the nutrient concentration after frost and nutrient removal were presented among the Miscanthus accessions. In addition, the significant difference conferred the possibility of achieving a desirable cultivar with significant biomass yield and relative nutrient removal by harvest. The accessions MS434, MS461 and MS296 had consistently high biomass yield and relatively low nutrient removal, demonstrating desirable characteristics as a low-input bioenergy crop. The results are important for guiding the agronomical practices of nutrient management and genetic improvement for nutrient-use efficiency to increase biomass production with low fertilizer input.

Ensiling corn silage with different levels of a multi-species lactic acid bacteria inoculant

A multi-species lactic acid bacterial inoculant (Lactisil maize, LM) was applied to whole-crop corn at different maturities in laboratory silos, to evaluate its effects on biochemical characteristics and aerobic stability. The corn crop was harvested at hard dough (HD, 253.1 g/DM kg), one-third milkline (ML, 293.7 g/DM kg) and one-third milkline with a killing frost (MLF, 297.6 g/DM kg). Crops were chopped to a 2.5-cm theoretical cut length, subsampled and treated with two levels of inoculant (LB1 = 1.5 × 105 cfu/g forage, LB2 = 3 × 105 cfu/g forage) or untreated (WO). The chemical composition of MLF crops was very similar to that of ML crops. However, lower (P &lt; 0.01) numbers of lactic acid bacteria and higher numbers of yeast were enumerated in MLF than in ML crops. Higher percentages of DM and neutral detergent fibre and higher pH, but lower (P &lt; 0.01) concentrations of water soluble carbohydrate and crude protein were measured in ML and MLF crops than in HD crops. Application of the inoculant increased (P &lt; 0.01) concentrations of volatile fatty acids, neutral detergent fibre and acid detergent fibre in silages. Lactic acid concentration increased (P &lt; 0.01) in HD treatments with an increasing level of inoculant. In contrast, the highest (P &lt; 0.01) lactic acid concentration was measured in LB1 treatment compared with WO and LB2 in ML and MLF silages. Silages prepared from ML and MLF crops had higher (P &lt; 0.01) lactic and acetic acid concentrations but lower (P &lt; 0.01) butyric acid concentrations than did those prepared from HD. The pH in LB1 and LB2 silages was higher (P &lt; 0.01) than that measured in WO silages. Aerobic stability was not influenced by inoculant treatment but low-DM silages were more (P &lt; 0.01) resistant to spoilage. Frost-killed corn crops had a good potential to produce well fermented silage. Using LM resulted in silages with slightly higher fermentation products but it failed to improve aerobic stability of silage after 120 days of ensiling. These results indicated that inoculation of corn crops with LM for a short-duration ensilage period cannot enhance aerobic stability of silages due to insufficient acetic acid production from lactic acid conversion.

Effects of climate change on killing frost in the Canadian prairies

Killing frost is a significant factor that governs agricultural production on the Cana- dian prairies across Alberta, Saskatchewan and Manitoba. The objective of this study was to assess the potential changes in the spatial distribution of killing frosts for spring wheat Triticum aestivum L. on the Canadian prairies under projected future climates. To accomplish this, (1) daily climate data (from 1961�1990) at 60 weather stations across the agricultural regions of the Cana- dian prairies were obtained; (2) 3 climate scenarios were developed for the period 2040�2069; (3) killing frost indices for spring wheat were calculated for both the baseline and the 3 climate change scenarios for all weather stations, and (4) geostatistical methods were used to interpolate the indices from the stations to fine grids covering the whole agricultural regions on the Canadian prairies. Results show that under baseline conditions — with the exception of some pockets in all 3 provinces — areas with the earliest mean dates of last spring killing frost (LSKF) (April 12 to April 14) are located in Alberta and west-central Saskatchewan; while the earliest mean first fall killing frost (FFKF) (September 16 to September 20) occurs mainly in southwest Saskatchewan. The 3 climate change scenarios projected an earlier LSKF (April 6 or earlier compared to April 14) and a later FFKF (October 3 or later compared to September 27). As a result, there was a longer killing frost free period (KFFP), which increased under all scenarios by ≥14 d compared to the baseline climate. Although the changes differed among the climate change scenarios, the major characteristics were fairly consistent. The results from this study will help formulate strategies to address climate change across the Canadian prairies, such as seeding earlier and choosing culti- vars with later maturity dates and longer growing periods.

Switchgrass, Big Bluestem, and Indiangrass Monocultures and Their Two- and Three-Way Mixtures for Bioenergy in the Northern Great Plains

High yielding, native warm-season grasses could be used as renewable bioenergy feedstocks. The objectives of this study were to determine the effect of warm season grass monocultures and mixtures on yield and chemical characteristics of harvested biomass and to evaluate the effect of initial seeding mixture on botanical composition over time. Switchgrass (Panicum virgatum L.), indiangrass [Sorghastrum nutans (L.) Nash], and big bluestem (Andropogon gerardii Vitman) were planted as monocultures and in all possible two- and three-way mixtures at three USA locations (Brookings and Pierre, SD and Morris, MN) during May 2002. Biomass at each location was harvested after a killing frost once annually from 2003 to 2005. Total biomass yield significantly increased with year at all locations. Switchgrass monocultures or mixtures containing switchgrass generally out-yielded big bluestem or indiangrass in monocultures or the binary mixture. Cellulose and hemicellulose concentrations were higher in 2004 and 2005 compared with 2003. Switchgrass or mixtures containing switchgrass tended to have less cellulose than either big bluestem or indiangrass. Results were more variable for total N, lignin, and ash. Switchgrass was the dominant component of all mixtures in which it was present while big bluestem was dominant when mixed with indiangrass. Indiangrass was maintained only in monocultures and declined over years when grown in mixtures at all locations. Our results indicated if biomass yield in the northern Great Plains is a primary objective, switchgrass should be a component of binary or tertiary mixtures that also contain big bluestem and/or indiangrass.