Over-seeded annual grasses and legumes, which can provide forage on dormant perennial warm-season grass pastures, serve as cover crops on fallow cropland. Although erosion control is not a typical need for pastures with perennial grass sod, cover crops functioning as catch crops to reduce cool-season nutrient loss or legumes for N fixation could contribute to reduced-cost warm-season pasture growth. Treatments of over-seeded cool-season species and management evaluating effects of cover crop removal as forage versus mulched as a N source were evaluated at three locations in 3 years. Cool-season legumes produced more biomass N than cool-season grasses, indicating biological N contributions of the legumes. Nitrogen limitation of the less productive, non-fertilized grasses indicates that readily available soil N had been depleted, limiting N leaching. Despite mulching of legume biomass with N amounts of 45-89 kg ha(-1), biomass production of bermudagrass [Cynodon dactylon (L) Pers.] in the following growing season was not increased. Lack of benefit of cover crop N contributions to subsequent bermudagrass forage production indicates that the availability of increased soil N was not synchronized with periods of efficient bermudagrass N uptake. These unanticipated results appear to be due to the effect of N mineralization-immobilization processes on N availability combined with variable rates of bermudagrass growth in response to periodic moisture limitations in this warm, humid, but uncertain environment.

Temperature is a fundamental factor influencing the processes of seed germination. Investigating the response of carinata to thermal stress and establishing a dependable and efficient method for screening thermotolerance will enhance breeding programs and model applications. We assessed the response of 12 carinata genotypes to a range of eight temperatures, spanning from 8 to 37 °C, throughout the germination process. A four-parameter Weibull function effectively characterized the seed germination time course across various temperatures and genotypes. Quadratic functions effectively characterize the maximum seed germination and the rate of seed germination as a function of temperature across various genotypes. The average cardinal temperatures recorded were -0.14, 20.41, and 40.70 °C for maximum seed germination, while the temperatures for seed germination rate were 5.30 °C, 24.51 °C, and 43.71 °C, corresponding to minimum, optimum, and maximum conditions, respectively. A notable variation was observed in maximum seed germination, seed germination rate, and cardinal temperatures across different genotypes. The specified parameters were employed to screen the genotypes for their thermotolerance capabilities. The analysis of principal components and the cumulative response indices effectively characterized carinata genotypes for high- and low-temperature tolerance exhibiting distinct characteristics. The AX17004 was identified as a genotype with significant tolerance to high temperatures, whereas AX17009 demonstrated remarkable tolerance to low temperatures. In contrast, AX17002 exhibited sensitivity to both high and low-temperature stress. According to the classification of breed types, both double haploid and hybrid groups revealed consistent thermotolerance responses during the germination phase. In contrast, the inbred group exhibited a wider response cluster to both minimum and maximum temperatures. The in vitro assay method presents a cost-effective approach for evaluating thermotolerance in carinata genotypes.

Carinata (Brassica carinata A. Braun) is an emerging oilseed crop with potential as a dual use winter cover/cash crop in the southeastern US region. Although carinata is historically cultivated as a spring crop in northern latitudes, incorporating carinata into southeastern US cropping systems can provide winter/cover ecosystem services and a bio-feedstock for a high value, renewable aviation fuel without displacing feed and food crops. In this study, our major objective was to quantify the agronomic performance and stability of selected carinata genotypes across several locations in the southeastern US. Extensive field evaluations of twelve, elite carinata genotypes, arranged in a randomized complete block design with four replications, were conducted from 2016 to 2019 across Mississippi, Alabama, Georgia, Florida, South Carolina, and North Carolina. Data was collected on days to 50% bolting, days to 50% flowering, plant height, grain yield, and test weight. Results demonstrated the ability to produce viable grain yields across the region, but also highlighted the impact of freezing temperatures on winter production. In total 20% of all environments were lost to mortality due to freezing temperatures. Overall, genotype 15 produced the highest grain yield across individual environments, topping the trial in 74% of all environments. However, both crossover and non-crossover genotype x environment interactions were detected for agronomic traits, with problematic crossover interactions more prevalent for days to 50% bolting and days to 50% flowering. Our results also suggest the southeastern US be separated into three mega environments to include 1) northern Georgia, South Carolina, and North Carolina, 2) southern and central Georgia and Alabama, and 3) northern Florida. Future efforts to identify advanced breeding lines and/or commercial seed products with adaptation to the region should consider field testing in each of these mega environments.

Temperature is a major abiotic stress factor limiting plant growth and development during the early developmental stage. Information on carinata (Brassica carinata A. Braun) traits response to low and high temperatures is necessary for breeding or selecting genotypes suited for specific ecoregions, which is limited. In the present study, 12 carinata genotypes were evaluated under low (17/09°C), optimum (22/14°C), and high (27/19°C) day/night temperatures at the early developmental stage. This study quantified temperature effects on several physiological and morphological characteristics of 12-advanced carinata lines. High-temperature plants decreased (15%) the accumulation of flavonoids and increased the nitrogen balance index by 25%. Low-temperature treatment significantly inhibited the aboveground (plant height, leaf area, number, and shoot weight) and root (length, surface area, and weight) traits. Across all genotypes, the shoot weight decreased by 55% and the root weight by 49% under low temperature. On the other hand, the maximum proportion of biomass was partitioned to roots under low temperature than at the high temperature. A poor relationship (r 2 = 0.09) was found between low- and high-temperature indices, indicating differences in trait responses and tolerance mechanisms. AX17004 and AX17009 with higher root to shoot ratios might be suitable for late planting windows or regions with low-temperature spells. The two genotypes (AX17015 and AX17005) accumulated higher biomass under low- and high-temperature treatments can be used for planting in later summer or early winter. The identified low- and high-temperature stress-tolerant carinata genotypes could be a valuable resource for increasing stress tolerance during the early developmental stage.

The goal of pasture design is to achieve a livestock distribution that positively affects pasture utilization, plant diversity, watershed function, and control of animal wastes and nutrient flows. This chapter describes plant responses to defoliation and the mechanisms underpinning them. It defines the key grazing management choices and their potential impact on a grazing system and reviews the elements of effective pasture design. A goal of grazing management is to achieve canopy conditions and forage productivity that result in optimal levels of animal performance. Manipulation of grazing intensity, stocking method, and timing of grazing are the primary means of achieving the desired canopy characteristics. Design of pastures depends on a number of factors, including landscape characteristics and intensity/complexity of grazing management. Pasture design is particularly important when considering responses that are affected by distribution of livestock across the landscape.

Over-seeding cool-season annual forages in pastures in the southeastern US provides increased grazing opportunities for livestock and reduces the amount of hay needed during winter. The constant presence of vegetation can benefit soil health, the biological aspect of which has only received cursory investigation to date. Since 2009, a commercial cattle grazing operation located in south Mississippi has been over-seeding a diverse mixture of oats (Avena sativa L.), triticale (X Triticosecale Wittmack), annual ryegrass (Lolium multiflorum Lam.), hairy vetch (Vicia villosa Roth), radish (Raphanus sativus L.), turnips (Brassica rapa L. subsp. rapa), red clover (Trifolium pratense L.), ball clover (Trifolium nigrescens Viv.), and crimson clover (Trifolium incarnatum L.) into pastures dominated by bahiagrass (Paspalum notatum Flugge). Soil health properties were assessed across a heterogeneous landscape from soils collected immediately prior to seeding and following increased spring productivity of cool-season annuals from 2015 to 2017. Samples were collected across a topographic sequence to a depth of 15 and 30 cm. Three samples per site were collected from summit, backslope, and footslope locations. Soil chemical assessments included macronutrients, pH, soil organic matter (SOM), total carbon (TC), and total nitrogen (TN). Fatty acid methyl ester analysis and enzyme assays were used to determine soil microbial community structure and activity. While TC and TN did not change with time (20.5 and 2.4 g kg(-1), respectively), SOM increased by 6% from 2015 to 2017. Nitrate-N decreased by 82% from 2015 to 2017. N-acetyl-beta-glucosaminidase activity increased by 32%, while beta-glucosidase remained constant. Total microbial abundance did not change with time; however, Gram positive bacteria and actinomycetes decreased by 51% and 43%, respectively, from fall to spring. Arbuscular mycorrhizal fungi increased from fall to spring by an average of 45%. This pasture management technique of over-seeding a diverse mix of winter annuals may have resulted in a steady state of TC and TN, while SOM increased and inorganic nitrogen decreased with time, and enhanced the total soil microbial community particularly fungi and their potential enzyme activity. Despite some biological indications of system stability, soil properties potentially limiting to plant growth were identified for some sites, but these limitations were not closely related to topographic position as expected.

This 2-year grazing study carried out at Raymond, Mississippi, USA, evaluated animal performance and forage characteristics of a tetraploid ("Maximus") vs a diploid cultivar ("Marshall") of annual ryegrass at three stocking rates (SR; 3.5, 5.0 or 7.5 animals per ha). Angus cross-bred heifers (Bos taurus; initial body weight [BW] = 240 kg) were continuously stocked on pastures at set stocking rates for the duration of the study. Stocking rates and cultivars were arranged in a 3 x 2 factorial design that was completely randomized with two replications. There was no cultivar effect (p = .449) on average annual herbage mass (HM). However, HM decreased linearly with increasing SR (p = .001) from 3.8 to 2.5 t ha(-1) during Year 1 and 4.4 to 3.8 t ha(-1) during Year 2 (p = .028). In Year 2, there was a difference in water-soluble carbohydrates (WSC) between cultivars (p = .012; Marshall, 117.0 vs Ma x imus, 139.0 g/kg). There was no cultivar effect (p > .10) on average daily gain (ADG) in either year of the study. In both years, ADG decreased linearly with increasing SR (p = .001) from 1.22 to 0.98 kg/d during Year 1 and 1.31 to 1.08k g/d during Year 2. Across years, gain ha(-1) increased linearly (p < .001) with increasing SR. Our results showed no difference in animal performance and HM between the two cultivars. Producers' choice of annual ryegrass cultivar should be based on seeding cost and agronomic traits that allow for better adaptation of the forage.

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small‐scale and short‐term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy ( US DOE )/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long‐term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field‐scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm‐scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM ‐ ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country.

Harvest time (HT) and nutrient management may have an effect on switchgrass (Panicum virgatum L.) yield and nutrient cycling. Experimental objectives were to quantify HT and nitrogen (N) rate effects on dry matter yield (DMY), nutrient concentration, and N use. Alamo switchgrass was grown under four N rates (0, 40, 80, and 120kg ha(-1)) with six monthly HT (May to October) in a randomized complete block design experiment with a split-plot arrangement. Yield increased cubically and quadratically with HT in Years 1 and 2. Aftermath yield decreased linearly with HT in both years. N rate increased yield in Year 2 only with no yield benefit at rates >40kg N ha(-1). Nutrient concentration decreased from May to October, while its removal was determined by DMY. N use and recovery were greatest at 40kg N ha(-1) and declined with additional N inputs. Results indicate that harvesting post-frost-kill produced greater DMY with less nutrient concentration and removal.

Leaf stage-dependent defoliation is linked to the plant's physiological status and may be a more suitable criterion than time-based intervals for harvesting forage grasses, but no reports of research with annual ryegrass (Lolium multiflorum Lam. var. westerwoldicum) were found. To address this, a 2-year field study was carried out at Raymond, MS, on a Loring silt loam soil (fine-silty, mixed, thermic Typic Fragiudalfs). Forage production, morphological characteristics and nutritive value responses to defoliation based on leaf stage (2, 3 and 4 leaves per tiller) and two residual stubble heights (RSH; 5 and 10 cm) of a tetraploid ("Maximus") vs. a diploid ("Marshall") cultivar of annual ryegrass were quantified. Forage harvested, in 2011, increased linearly as leaf stage increased from 7.3 to 8.8 Mg/ha, but during 2012 was least (7.0 Mg/ha) at 3-leaf stage and similar at the other two leaf stages (7.6 Mg/ha). Tiller density was less for Maximus (1,191 tillers/m(2)) than for Marshall (1,383 tillers/m(2)). Leaf blade proportion decreased with increasing leaf stage and was greater by 9% for Maximus than for Marshall. Generally, forage nutritive value became less desirable with increasing leaf stage. There was a dichotomy in forage harvested and nutritive value responses, but maximum forage productivity was achieved when annual ryegrass was defoliated at the 4-leaf stage interval.

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 (165.8L•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.

Switchgrass (Panicum virgatum L.) chemical composition dynamics must be evaluated if dual‐purpose use as both forage and feedstock is to be considered. This 2‐year study, conducted at the Brown Loam Branch Experiment Station, Raymond, MS, quantified first harvest timing (HT) and nitrogen (N) rate effects on forage nutritive value, feedstock chemical composition, and ethanol yield of both primary and aftermath harvests of ‘Alamo’ switchgrass. Treatments were factorial combinations of six HT (monthly intervals from May to October) and four N application rates (0, 35.7, 71.2, and 107.1 lb/acre) in a randomized complete block design. Aftermath was harvested in November. In both years, first harvest acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin, cellulose, and hemicellulose concentrations of aboveground biomass, stems, and leaves increased with HT from May to October while aftermath harvest concentrations decreased with shorter regrowth after the first harvest. Stems had greater concentrations than leaf. Crude protein (CP) and in vitro dry matter digestibility (IVDMD) decreased with plant maturity and were greatest in the leaf component. Concentrations of major sugars increased with maturity and were greatest in the most mature stand in the aftermath. Ethanol yield was greatest in the least mature stands; however, ethanol production increased with maturity, largely because of greater biomass harvested. Nitrogen rate had no effect on forage nutritive value or feedstock composition in either the primary or aftermath harvests. These results provide information that can guide potential utilization of switchgrass as forage in early season and harvesting for biofuel feedstock at the end of the season.

ABSTRACTDetermination of animal preference in the early stages of the evaluation process of new forages may provide insights into potential animal performance as well as plant responses to grazing. A 2‐yr study was conducted at Raymond, MS, to determine grazing preference of cattle between tetraploid and diploid annual ryegrass (Lolium multiflorum Lam.) cultivars and its relationship with morphological and chemical characteristics. Treatments were two tetraploid cultivars, Maximus and Nelson, and two diploid cultivars, Marshall and Gulf, arranged in a 4 × 4 Latin square design experiment. Eight Angus crossbred yearling steers (Bos taurus) (initial body weight of 320 ± 19 kg) were used to determine grazing preference based on herbage disappearance, the Chesson–Manly (CM) index, and amount of time spent grazing. In both years, herbage disappearance was greater for the tetraploid (1380 kg ha−1) than diploid cultivars (895 kg ha−1), with greater CM index for the tetraploid than for the diploid cultivars (8.1 vs. 5.8% in Year 1 and 6.9 vs. 5.5% in Year 2). Also, animals spent about 10% greater time grazing the tetraploid than diploid cultivars during both years. During the first year, the tetraploid cultivars had less neutral detergent fiber (NDF) (556 vs. 589 g kg−1) and less acid detergent fiber (ADF) (341 vs. 359 vs. g kg−1) than the diploid cultivars and Nelson had greater water‐soluble carbohydrate (WSC) concentration (184 g kg−1) than the other three cultivars (152 g kg−1). In the second year, NDF, ADF, and WSC were not different among cultivars. Tetraploid cultivars had a greater proportion of leaf than diploid cultivars. The results indicate that cattle showed greater preference for tetraploid cultivars, which appeared to be linked mainly with pregraze herbage mass and the proportion of leaf.

Harvest frequency (HF) and fertilizer effects on biomass production, nutrient removal, and ethanol yield must be understood to help guide management decisions in switchgrass (Panicum virgatum L.) production. This 4‐yr study quantified yield and chemical composition responses of Alamo switchgrass to factorial combinations (4 × 2) of four HFs (harvesting one, two, three, or six times annually) and two N application rates (80 and 160 kg N ha−1) in a randomized complete block design experiment with three replications. In all years, yields decreased linearly with HF. In the one‐cut HF, yield increased from 8.8 in Year 1 to 14.7 Mg ha−1 in Year 3 and plateaued thereafter. For the two‐cut HF, yield was similar across years, averaging 10 Mg ha−1, but for the three‐ and six‐cut HFs, yield increased from Year 1 to Year 2 and declined by Year 4. Nutrient concentration increased with HF, while nutrient removal responses fluctuated among elements. Acid detergent fiber, neutral detergent fiber, hemicellulose, cellulose, and lignin concentrations decreased with increasing HF, but there was no effect of N rate. In Years 1 and 2, theoretical ethanol production (TEP) was similar between the one‐ (3.7 kL ha−1) and two‐cut HFs (4.2 kL ha−1) but decreased as the HF increased to three (2.6–3.4 kL ha−1) and six cuts (1.4– 2.5 kL ha−1). In Years 3 and 4, TEP decreased linearly with increasing HF. Greater HF resulted in reduced feedstock yield, quality, ethanol yield, and production, but N application rate did not have any effect.

Sorghum [Sorghum bicolor (L.) Moench] is one of four herbaceous dedicated bioenergy crops the U.S. Department of Energy identified as critical to annually produce one billion tons of dry biomass. Of these four crops, sorghum is unique as it is a drought-tolerant, annual crop established from seed that is readily tractable to genetic improvement. The purpose of this study was to assess the yield potential and stability of sorghums grown across diverse production environments in the USA. For this study, six sorghum genotypes (one cultivar, five hybrids) were grown in yield trials in seven locations in six states for 5 years (2008–2012). Variation in dry and fresh yield was attributable to not only genotypes, but also to the effects of year, location, and year × location. Even with the highest yielding genotype, environmental conditions were a major factor in determining the yield in a given year. This variability affects the consistency of the biomass supply for ethanol production. In general, the southeastern USA had the highest mean yields for fresh weight and dry weight, indicating that this area may be the most reliable for biomass production. A significant variation was detected among genotypes for fresh weight, dry weight, moisture content, and brix, revealing that sufficient variation within sorghum exists for continued improvement and that certain hybrids are more tractable for biomass/bioenergy production. With dedicated bioenergy sorghum germplasm and proper production environments, sorghum will be a valuable tool in the goal of the sustainable production of one billion tons of dry biomass each year in the USA.

ABSTRACTStudying grazing behavior of ruminants may help increase the understanding of the use of forage systems of varying forage types and composition. This study was conducted during 2008 at Raymond, MS, to evaluate grazing time by ruminants on various forage systems to examine any relationship with pasture composition and stocking rate (SR). Annual ryegrass (Lolium multiflorum Lam. ‘Marshall’) and white clover (Trifolium repens L. ‘Durana’) were used to create forage system treatments of either monoculture grass (MG) or monoculture legume (ML), a binary mixture of grass and legume (MIX), or a spatial system of adjacent grass and legume monocultures in a 50:50 land area ratio within the same paddock (SS). Two levels of SR (3 or 6 steers [Bos taurus] ha−1) were imposed on each of the four forage systems to give a 4 × 2 factorial arrangement of treatments with two replicate paddocks of each treatment combination in a completely randomized design experiment. Two Angus crossbred yearling beef steers (236 ± 24 kg initial body weight [BW]) were randomly assigned to each of the 16 paddocks. Time spent grazing per animal on continuously stocked pastures was recorded for 10 d selected randomly during the months of April and May, with each day of observation lasting for 14 h (0615 to 2015 h). Forage system had an effect (P < 0.001) on time spent grazing daily. Animals grazing MG and MIX spent similar time grazing (mean = 442 min per animal), which was greater than daily grazing time on SS (380 min per animal). Grazing time was least on ML (341 min per animal). Also, SR had an effect (P < 0.001) on daily grazing time. Animals on high SR (431 min per animal) spent greater time grazing than those on low SR (371 min per animal). There was no difference in time spent grazing on each component of the adjacent monocultures of grass and legume within the SS (P = 0.23; 197 [the monoculture legume component of a SS] vs. 182 min per animal [monoculture grass component of a SS]). Less grazing time by animal on SS than MG and MIX may have implications for performance of animals grazing such a system because of expected lesser energy expenditure for grazing.

ABSTRACTSpatially separated monoculture grasses and legumes within the same paddock (SS) may help alleviate constraints to the widespread adoption of legumes in pastures. A grazing study conducted during the winter–spring seasons of 2008 (steers, initial body weight [BW] = 236 ± 24 kg) and 2009 (heifers, initial BW = 245 ± 40 kg) at Raymond, MS, evaluated four forage systems (FS) at two stocking rates (SR; 3 or 6 animals ha−1). Using ‘Marshall’ annual ryegrass (Lolium multiflorum Lam.) and ‘Durana’ white clover (Trifolium repens L.), FS treatments were SS, monoculture grass (MG), monoculture legume (ML), and a binary mixture of grass and legume (MIX). Herbage mass was similar among FS at the high SR (1.9 Mg ha−1), but herbage mass at low SR was greater in MG, MIX, and the grass component of SS than ML and the legume component of SS (2.9 vs. 2.0 Mg ha−1). Among legume plots, SR did not affect herbage mass (1.9 Mg ha−1), but on grass plots, herbage mass was greater at low than high SR (2.9 vs. 2.0 Mg ha−1). Herbage accumulation was greater on grass than on legume plots (32 vs.13 kg ha−1 d−1), but there was no difference among FS within these two forage species. Low SR had greater herbage accumulation (27 kg ha−1 d−1) than high SR (21 kg ha−1 d−1). Average daily gain was greater on SS (1.12 kg) than on ML (0.97 kg), but neither was different from MG (1.08 kg) or MIX (1.00 kg), and greater on low SR than on high SR (1.09 vs. 0.99 kg). These results suggest that a SS system may be an option to enhance adoption of legumes in pastures.

Prairie bromegrass ( Bromus spp.) is a cool-season perennial bunchgrass with potential as a valuable forage crop in the southeastern USA. This 2-year study, conducted at Mississippi State, MS, compared dry matter production, persistence, plant morphology, and nutritive value of two experimental lines [BP101 ( B. parodii Covas & Itria) and BW103 ( B. wildenowii Kunth)] and a commercial entry ( B. willdenowii Kunth cv. Matua) of prairie bromegrass. No differences in nutritive value (mean crude protein = 128, ADF = 318, NDF = 591, in vitro dry matter digestibility = 644 g/kg, respectively) were seen among entries ( P = 0.11). The BP101 line had the least herbage mass (3,790 vs. 6,180 and 5,627 kg/ha, respectively, for Matua and BW103) at the first grazing event in 2006 ( P < 0.05), and did not persist as well as BW103 or Matua ( P < 0.01) (27.5, 80.0, and 83.8% stand 586 days after establishment for BP101, Matua, and BW103, respectively). Leaf blade, sheath, and reproductive tiller length differences ( P < 0.10) suggest variations in physiological traits among bromegrass entries. Neither of the experimental lines of prairie bromegrass outperformed Matua for the traits studied in northern Mississippi.

Cool-season annual forages provide high-quality herbage for up to 5 mo in the US Gulf Coast states, but their management in pasture-based dairy systems has received little attention. Objectives of this study were to evaluate pasture and animal responses when lactating Holstein cows (n=32, mean DIM=184±21) grazed either N-fertilized rye (Secale cereale L.)-annual ryegrass (Lolium multiflorum Lam.) mixed pastures or rye-annual ryegrass-crimson clover (Trifolium incarnatum L.)-red clover (Trifolium pratense L.) pastures at 2 stocking rates (5 vs. 2.5 cows/ha) and 2 rates of concentrate supplementation [0.29 or 0.40 kg of supplement (as is)/kg of daily milk production]. Two cows paired by parity (one multiparous and one primiparous) were assigned randomly to each pasture. The 2 × 2 × 2 factorial arrangement of treatments was replicated twice in a completely randomized design. Forage mixture and supplementation rate did not affect milk production during three 28-d periods. Greater milk production occurred at the low (19.7 kg/d) than the high (14.7 kg/d) stocking rate during periods 2 and 3, but production was similar during period 1. Despite lower production per cow, milk production per hectare was generally greater at the high stocking rate (81.6 vs. 49.5 kg/ha). Generally, greater pregraze herbage mass on pastures at the lower stocking rate (1,400 vs. 1,150 kg/ha) accounted for greater herbage allowance. Both forage (8.0 vs. 5.9 kg/d) and total (14.1 vs. 11.6) organic matter intake were greater at the low stocking rate. Cows fed less supplement had greater forage organic matter intake (8.0 vs. 6.1 kg/d). Greater herbage mass was associated with the greater intake and subsequent greater milk production. Differences in forage nutritive value, blood metabolites and milk composition, although showing some response to treatments, may not be of sufficient magnitude to affect choice of pasture species or other management practices. Animal performance was not improved by adding clovers to mixed cool-season grass pastures like those in this study. Stocking rate had a major effect on pasture and animal performance. During the cool season, supplementation with concentrates should be planned based on estimated energy intake from forages to achieve optimum milk production and ensure maintenance of body condition.

Cardinal temperatures for plant processes have been used for thermotolerance screening of geNotypes, geoclimatic adaptability determination and pheNological prediction. Current simulation models for switchgrass (Panicum virga-tum L.) utilize single cardinal temperatures across geNotypes for both vegetative and reproductive processes although intra-specific variation exists among geNotypes. An experiment was conducted to estimate the cardinal temperatures for seed germination of 14 diverse switchgrass geNotypes and to classify geNotypes for temperature tolerance. Strati-fied seeds of each geNotype were germinated at eight constant temperatures from 10oC to 45oC under a constant light intensity of 35 µmol m-2 s-1 for 12 h d-1. Germination was recorded at 6-h intervals in all treatments. Maximum seed germination (MSG) and germination rate (GR), estimated by fitting Sigmoidal function to germination-time series data, varied among geNotypes. Quadratic and bilinear models best described the MSG and GR responses to temperature, respectively. The mean cardinal temperatures, Tmin, Topt and Tmax, were 8.1, 26.6, and 45.1oC for MSG and 11.1, 33.1, and 46.0oC for GR, respectively. Cardinal temperatures for MSG and GR; however, varied significantly among geNotypes. GeNotypes were classified as sensitive (‘Cave-in-rock’, ‘Dacotah’, ‘Expresso’, ‘Forestburg’, ‘Kanlow’, ‘Sunburst’, ‘Trailblazer’, and ‘Warrior’), intermediate (‘Alamo’, ‘Blackwell’, ‘Carthage’, ‘Shawnee’, and ‘Shelter’) and tolerant (‘Summer’) to high temperature based on cumulative temperature response index (CTRI) estimated by summing individual response indices estimated from the MSG and GR cardinal temperatures. Similarly, geNotypes were also classified as sensitive (Alamo, Blackwell, Carthage, Dacotah, Shawnee, Shelter, and Summer), moderately sensitive (Cave-in-rock, Forestburg, Kanlow, Sunburst, and Warrior), moderately tolerant (Trailblazer), and tolerant (Expresso) to low temperatures. The cardinal temperature estimates would be useful to improve switchgrass models for field applications. Additionally, the identified cold- and heat-tolerant geNotypes can be selected for niche environments and in switchgrass breeding programs to develop new geNotypes for low and high temperature environments.