Switchgrass (Panicum virgatum L.) is a warm-season (C-4) perennial grass and a potential bioenergy crop. On-farm switchgrass field scale trials, which were initiated to obtain economic production information for switchgrass grown as a bioenergy crop in the northern Plains, provided information on establishment year stands and post-establishment year yields and stands both within and across fields and were used to determine if a stand threshold exists for switchgrass grown as a biomass energy crop. Switchgrass was seeded in 10 cropland fields, ranging in size from 3 to 9.5 ha, in Nebraska, South Dakota, and North Dakota in 2000 and 2001. The fields were selected to be representative of their region and eligible for the Conservation Reserve Program (CRP). Twelve sites within each field were geo-referenced, and switchgrass stand frequency was measured at each sample site. Biomass yields were estimated in late summer at the same within-field sites using a clipped quadrat. Fields with low initial switchgrass stand frequencies showed a linear relationship between initial switchgrass stands and second year stands and biomass yields. Results from the 10 field, three-state study indicated that establishment year stand frequency level of 40% or greater, determined by a frequency grid, can be considered an establishment year stand threshold for establishment success and subsequent post-planting year biomass yields for switchgrass. An establishment year stand frequency of 25% would be adequate for a switchgrass conservation planting in which no harvests would be planned for several years.

Quantifying root structure response to multiple defoliation events in a grazing situation is critical in developing management plans for warm‐season tallgrasses. A pasture experiment was conducted in 1999, 2000, and 2001 near Mead, NE. The objective of the experiment was to determine the effect of timing and frequency of grazing on big bluestem (Andropogon gerardii Vitman) etiolated tiller growth and root and rhizome structure. Paddocks were grazed at a stocking rate of 9.9 Animal Unit Month (AUM) ha−1 in two to four cycles from mid‐May to early‐September. In April 2002, five 6.6‐ × 132‐cm soil cores were extracted from each paddock. Soil cores were subsampled at 30‐cm depth increments for estimates of root mass, root surface area, and root volume. Etiolated tiller tents were used to estimate organic reserves of big bluestem in each paddock in spring 2002. Mean number and weight of etiolated tillers were reduced by up to 40% and 50%, respectively, in paddocks grazed in a sequence of June after internode elongation, early August, and early September. Root structure in the top 30 cm of the soil profile was affected most by multiple defoliation events with <40 d of recovery between grazing periods. Root mass decreased by 25%, while mean surface area and volume of roots declined 10 and 15%, respectively, in the upper 30 cm of the soil profile in paddocks grazed in the sequence of post‐internode elongation in June, early‐August, and early‐September. To maintain vigorous big bluestem pastures, grazing management should concentrate on the elongation and postelongation periods. Grazing at the elongation stage should be rotated among paddocks in successive years and the recovery period following grazing at internode elongation should be >40 d.

Buffalograss [Buchloe dactyloides (Nutt.) Engelm.] use as a turf in the northern USA is limited to a certain extent by its extended winter dormancy. A mixture of buffalograss with cool‐season turfgrasses might extend the turf's green appearance and enhance quality. Research was conducted to determine the effects of overseeding fine‐leaved fescue (Festuca spp.) in buffalograss turf on turfgrass color and quality and the effects of species, seeding rate and date, and core cultivation on fine‐leaved fescue establishment in buffalograss turf. Hard fescue (F. longifolia Thuill.), blue fescue (F. ovina L. var. glauca Lam.), and Chewings fescue (F. rubra L. ssp. commutata Gaud.); seeding rates (10, 20, and 30 g m−2); seeding dates (fall, spring, or split fall–spring); and core cultivation (single or double pass) were evaluated for species composition, turfgrass quality, color, and green cover at the John Seaton Anderson Turfgrass Research Facility located near Mead, NE. Buffalograss turf overseeded with blue fescue in fall had the highest turfgrass quality, color, and green cover ratings. Fall overseeding resulted in the highest shoot density values. Spring overseedings were below acceptable levels. Botanical composition of the mixtures overseeded in fall reached 75 to 80% fescue and 20 to 25% buffalograss after 2 yr. Seeding rate effect was linear with each increment between 10 g m−2 and 30 g m−2 increasing fine‐leaved fescue shoot density, turfgrass quality, color, and green cover. Blue fescue–buffalograss mixtures overseeded in the fall exhibited 80% green cover when buffalograss was dormant. Turfgrass green cover in the mixture was extended by 2 months when compared to buffalograss monostands growing in areas adjacent to the study. The results of this study support the use of fine‐leaved fescue and buffalograss mixtures to extend turfgrass green appearance and enhance quality.

Selection at the seedling stage in grass breeding would be useful if seedling traits were correlated to desired agronomic traits of mature plants. Objectives of this study were to determine if seedlings from big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) populations that differ genetically in seedling tiller number differ in mature plant (i) morphological characteristics, (ii) forage yield managed by a three‐cut harvest system or a single end‐of‐season harvest, and (iii) leaf elongation rate. Field experiments were conducted on a Kennebec silt loam soil (fine‐silty, mixed, superactive, mesic Cumulic Hapludolls). In addition, greenhouse studies were conducted in 1999 through 2001. Seedlings from big bluestem and switchgrass populations that differed for seedling tiller numbers were transplanted into spaced‐planted field nurseries and greenhouse pots for study. Leaf width, leaf length, plant height, number of tillers per plant, yield, and leaf elongation rate were measured. Mature plant morphological characteristics differed between multiple‐tiller and single‐tiller plant types for both big bluestem and switchgrass. There were no differences in forage yield for big bluestem plant types. Switchgrass single‐tiller plant types yielded 200 g plant−1 more than multiple‐tiller types when harvested only once. Leaf elongation rate was 22 and 28% greater for single‐tiller types vs. multiple‐tiller types for big bluestem and switchgrass, respectively. Selection at the seedling level for tiller number appears to be an effective method to develop genotypes differing in yield per tiller, which has been shown to affect herbage yield when grown in swards.

Selection at the seedling stage in forage grass breeding would be extremely useful if seedling traits are highly heritable and correlated to desired agronomic traits. Objectives of this study were to determine the response to selection for high shoot weight and divergent selection for seedling tiller number in big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) seedlings and obtain estimates of realized heritability for these traits. Base populations were breeding populations of 'Pawnee' big bluestem and 'Pathfinder' switchgrass. Divergent selection for single or multiple (three or more) tiller(s) 6 to 8 wk after planting in a greenhouse produced four populations [big bluestem high seedling weight, multiple tiller (BBMT); big bluestem high seedling weight, single tiller (BBST); switchgrass high seedling weight, multiple tiller (SWMT); and switchgrass high seedling weight, single tiller (SWST)], which were planted in isolated polycross nurseries. Seed from polycross nurseries was used to conduct a second cycle of selection. Populations were evaluated in greenhouse studies for fresh weight and tiller number of seedlings. Seedling fresh weight was increased in BBST and SWST Cycle 2 populations, and divergent selection for tiller number resulted in populations significantly different from the base population. Realized heritability estimates for seedling tiller number in big bluestem and switchgrass were 0.26 and 0.23, respectively. The effect of genetic modification of seedling tiller number and shoot weight on establishment under field conditions and on mature plant phenotypes will need to be determined.

Big bluestem (Andropogon gerardii Vitman) has a rapid growth phase that begins in early to mid‐June in eastern Nebraska. During this rapid growth phase, rate of biomass accumulation exceeds intake rate of grazing livestock, resulting in low levels of harvest efficiency. To delay the rapid growth phase, big bluestem pasture can be grazed in mid‐ to late May without affecting herbage yields for the remainder of the growing season. A pasture experiment was conducted in 1999, 2000, and 2001 near Mead, NE. The objective was to determine the effect of timing and frequency of grazing big bluestem pasture, following a May grazing period, on cumulative pregrazing yields, cumulative herbage disappearance, resulting harvest efficiency, leaf/stem ratio, and stand persistence. Yield and morphological characteristics were obtained immediately before and after each grazing period, and basal cover of big bluestem was estimated annually. May grazing had no effect (P < 0.1) on cumulative pregrazing yields and resulted in an increase of cumulative herbage disappearance (3638 vs. 2673 kg ha−1) and leaf/stem ratio (2.02 vs. 2.83) compared with paddocks with no May grazing. Grazing at the vegetative stage in June compared with the elongation stage resulted in an increase in cumulative pregrazing yields (10774 vs. 9510 kg ha−1), cumulative herbage disappearance (4116 vs. 3194 kg ha−1), and leaf/stem ratios (2.57 vs. 1.98). Grazing at the elongation stage in June followed by a grazing period in early August is not an advisable management strategy.

Selection at the seedling stage in grass breeding would be extremely useful if seedling traits are correlated to desired agronomic traits. The objective of this study was to evaluate seedling morphological development, plant growth, and field establishment of big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) populations that were developed by divergent selection for seedling tiller number while selecting for high shoot weight. Six populations were evaluated: (i) 'Pawnee' big bluestem base, (ii) 'Pathfinder' switchgrass base, (iii) big bluestem multiple tiller, (iv) big bluestem single tiller, (v) switchgrass multiple tiller, and (vi) switchgrass single tiller. Field plots were seeded in spring 1999 and 2000 in a Kennebec silt loam (fine-silty, mixed, superactive, mesic Cumulic Hapludolls). Plants were excavated and evaluated during the growing season for shoot weight, root weight, and morphological stage of shoot and root systems. There were no major population differences in shoot weight, root weight, and morphological root stage. Shoot stage was higher for multiple tiller populations than single tiller populations 6 wk after emergence. Stand counts for all populations exceeded 10 seedlings per linear m of row, which is considered an acceptable stand density, and there were no consistent differences among populations. Populations divergently selected for seedling tiller number did not differ in ability to become established under field conditions because root systems apparently were not altered by the selection for seedling tiller number and weight. These results suggest that selection for high shoot weight did not improve seedling vigor in the field.

Soil moisture deficit is usually the major limiting factor for herbage production in the Sandhills of Nebraska. We examined inter-population and interspecific variability in stomatal characteristics and drought tolerance in sand bluestem (Andropogon hallii Vitman), little bluestem [Schizachyrium scoparium (Michx.) Nash], prairie sandreed [Calamovilfa longifolia (Hook) Scribn.], and switchgrass (Panicum virgatum L.). Ramets were collected during the dormant season across an aridity gradient from east to west (ranging from 560 mm to 340 mm average annual precipitation) in the Sandhills of Nebraska. Plants were grown in individual pots under greenhouse conditions. Once plants were well established, stomatal characteristics were determined and stomatal conductance (gs) was measured through a dry-down period of no watering. Populations did not differ in stomatal characteristics across the gradient, except for stomatal density on the adaxial leaf surface of prairie sandreed and the abaxial leaf surface of sand bluestem. Leaves of switchgrass and prairie sandreed were amphistomatic (stomata on both leaf surfaces), whereas leaves of little bluestem and sand bluestem were hypostomatic (stomata on the lower leaf surface). In the absence of drought, gs was 17 to 31% higher in little bluestem than in other species. Differences among species in gs were found mainly when watered and disappeared as the dry-down progressed. There was a positive relationship between stomatal density and gs in all species except prairie sandreed. Prairie sandreed maintained 35% of the initial relative water content of its leaves after 17 d of dry-down, compared to 23% for sand bluestem, 14% for switchgrass, and 9% for little bluestem. Variation in stomatal traits within species did not explain ecotypic adaptation to sites with a range of precipitation in the Nebraska Sandhills. Key words: Stomatal characteristics, water stress, warm season grasses, Nebraska Sandhills

Multiple generations of rhizome-connected tillers stabilize soils and produce measurable amounts of herbage on sandy rangeland throughout the world. However, little is known about the dynamics of rhizome development in these clonal plant species. Seasonal relationships between foliar characteristics and rhizomes of prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] were examined on sands range sites at 30-day intervals from May through September 1989 and 1990 at the University of Nebraska, Panhandle Experimental Range near Scottsbluff. Quadrats were excavated each year from two, 5 x 5 Latin Square macroplots in each of 2 grazing histories, long-term rest or current-year deferment. Under dry conditions in 1989, a 65% reduction in the length of new rhizomes during July preceded a 64% reduction in live tillers in August. After which, rhizome length and live tiller density were unchanged and mean tiller weight increased during September. When average precipitation occurred in 1990, a 25% reduction in live tillers and concurrent increases in new rhizome length and mean tiller weight occurred during July. Rhizome bud densities increased throughout the growing season at different but predictable rates (R2 greater than or equal to 0.95) for grazing histories, regardless of precipitation. Length of new rhizomes was highly correlated (R2 = 0.91) with live herbage throughout the growing season. Measurable increases in total rhizome length did not occur until live herbage of prairie sandreed exceeded a threshold of about 50 g m(-2). Maximum increase in length of new rhizomes per unit of live herbage was about 10 cm g(-1) near 100 g m(-2). Given its dependence on vegetative reproduction and relatively high palatability to beef cattle, periodic or repeated years of full growing season deferment may be the only reliable method of obtaining measurable increases in prairie sandreed populations.

Recent advancements in describing morphological development of perennial grasses have provided a useful index for identifying dates to harvest hay or graze pasture. The objective of this study was to determine the relationship between big bluestem ( Andropogon gerardii Vitman) morphological developmental stage, days from 1 May, and accumulated growing degree days (GDD) and leaf/stem ratio, crude protein (CP), and neutral detergent fiber (NDF) in grazed and nongrazed swards. The grazing experiment was conducted in eastern Nebraska during 1997 and 1998. Six grazing treatments consisting of all combinations of two herbage allowances (22 or 66 kg of herbage dry matter per animal unit day) and three grazing dates (late May, early June, and mid‐June) were randomly assigned to seven paddocks (900 m 2 ) in each of four blocks along with a nongrazed control treatment. Random samples consisting of 50 or more tillers were hand‐clipped weekly at ground level in each paddock beginning in late May and ending in early August. Morphological developmental stage of the samples were determined, and a mean morphological stage based on shoot count [mean stage count (MSC)] was calculated. Samples were hand‐separated to determine leaf/stem ratio and analyzed for CP and NDF. Regression analysis showed that good relationships were found between MSC ( R 2 = 0.61–0.81), days from 1 May ( R 2 = 0.45–0.76), and GDD ( R 2 = 0.44–0.74) and leaf/stem ratio in nongrazed big bluestem and high herbage allowance swards. All three were adequate predictors of nutritive value and leafiness, but MSC may be more useful to researchers who want a more descriptive measure of plant morphological development, particularly when comparing cultivars or species.

Tiller recruitment is an essential process for ensuring the perenniality of grasses. The timing and extent of tiller recruitment and the role of biennial tillers must be documented for key range species. Prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] is an important grass in the Nebraska Sandhills for both ecological functioning and as a forage. The objective of this study was to document tiller recruitment patterns and the occurrence and contribution of current year and biennial tillers to biomass production in prairie sandreed at 2 locations in Nebraska. Tiller recruitment was monitored at 2-week periods throughout the growing season during a 2-year period. Newly emerged tillers were classified as intravaginal, extravaginal, or rhizomatous tillers and marked with colored wire. Prairie sandreed has an unimodal pattern of tiller recruitment and over 50% of the current year tillers emerged by mid-May and 80% by mid-June. Rate of tiller emergence and absolute number of emerged tillers were poorly correlated with short- and long-term precipitation totals (r < 0.3 P > 0.20). The year after new tillers were marked, biennial tillers and tillers initiated during the current-year were counted and clipped in September for biomass determination. Biennial tillers made up only 6 and 20% of the total tiller emergence at these locations and were generally only 30% as large as the new tillers. Extravaginal tillers composed over 78% of the biennial tiller population as a result of both their dominance in emerging populations and the higher percentage of tillers that survived the winter. Current year tillers contributed the most to prairie sandreed forage production and their emergence was largely completed by mid-June. The lack of a relationship between tiller recruitment and precipitation patterns, combined with previous studies of prairie sandreed, indicates that tiller recruitment involves a process that begins the previous growing season.

Characterization of relationships between grazing and vegetation responses is difficult. Rapid and accurate measurement of pasture canopy characteristics would help clarify these relationships if canopy changes are directly related to grazing variables. The objectives of this study were (1) to evaluate use of the LI-COR LAI-2000 for quantification of changes in canopy density and architecture in response to defoliation by cattle, (2) to determine if changes in leaf area index (LAI) measured with the LAI-2000 are related to stocking rate, and (3) to determine advantages and drawbacks of the LAI-2000 for monitoring grazing impacts on canopy density and architecture. Leaf area index and mean foliage tilt angle were measured before and after defoliation by cattle (Bos taurus L.) in June, July, and August under 9 grazing treatments on Nebraska Sandhills range. Differences in LAI could be attributed to certain grazing treatments at various points throughout the season. Grazing treatment had little impact on mean foliage tilt angle. Change in LAI (delta LAI) had a significant negative relationship with stocking rate (P < or = 0.0001). The relationship detected for delta LAI versus stocking rate predicted LAI reductions of between 0.14 and 0.40 for the range of stocking rates studied; stocking rate accounted for 62% of the decrease in LAI caused by grazing. When configured for the Sandhills canopy, the LAI-2000 provided a rapid and precise method for quantification of the degree of defoliation associated with grazing.

Seed size has been associated with early seedling vigor (i.e., germination rate, emergence rate, and growth) in grasses. This study was conducted to compare seedling development over a 60-d period in the field as affected by heavy seed (HS) (0.19 to 0.21 g 100 seed(-1)) and light seed (LS) (0.13 to 0.16 g 100 seed(-1)) of 'Blackwell' and 'Trailblazer' switchgrass (Panicum virgatum L.). The experiment was conducted in 1995 and 1996 at Lincoln, NE, on a Kennebec silt loam (fine-silty, mixed, superactive, mesic Cumulic Hapludolls). The experimental design was a randomized complete block with four replicates. Seed was separated into two sizes using a South Dakota seed blower. Seed was planted into rows at a rate of 100 pure live seed per meter of row. Plants were excavated and evaluated for shoot weight, leaf area, and root weight. Shoot and root systems were morphologically staged four times during the summer. Seed size differences in switchgrass appeared to produce only slight differences in morphological development of shoot and root systems, leaf area, shoot weight, and adventitious root weight from seedling emergence to 6 wk of growth. Adventitious roots formed more quickly on seedlings from heavier than lighter seed, but the advantage to seedling establishment was minimal even when soil moisture appeared to be lacking. By 8 to 10 wk after emergence, growth and development of LS seedlings were similar to HS seedlings. Once seedlings formed two or more adventitious roots, seed size no longer affected establishment and growth. Seed size in switchgrass appears to have a minimal long-term effect on growth and development of seedlings.

A study on Conservation Reserve Program (CRP) land was established in southeastern Nebraska to determine the effect of dormant-season management on subsequent-year growth rates and yields of tallgrasses. The purpose of the management practices was removal of standing dead material and litter that negatively impact plant growth and grazing efficiency. Treatments consisted of a control with no residue manipulation and 5 residue manipulation practices including (1) October shredding and leaving residue; (2) October haying; (3) October intensive grazing; (4) March intensive grazing; and (5) spring prescribed buming. The study was conducted in 1994195 and 1995/96 on a switchgrass

Developing grazing systems requires basic information on the growth and development of adapted species. The objective of this field study was to determine seasonal tiller demographics and leaf area index (LAI) of intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey], smooth bromegrass (Bromus inermis Leyss.), switchgrass (Panicum virgatum L.), and big bluestem (Andropogon gerardii Vitman) tiller populations. This study was conducted in 1992 and 1993 near Mead, NE, on a silty clay loam soil (Typic Argiudoll) as a randomized complete block. Monocultures were harvested six times each year for tiller demographics. Additionally, mean stage count (MSC), a quantified estimate of tiller population maturity, was determined at each harvest. The LAI was indirectly measured using a canopy analyzer at 7- to 14-d intervals. Tiller density for all species generally declined as MSC increased. Tiller demographics were highly variable by year for intermediate wheatgrass and smooth bromegrass, which indicates that grazing management should be based on current tiller populations. Density of vegetative tillers declined most rapidly for smooth bromegrass, followed by intermediate wheatgrass, switchgrass, and big bluestem. Switchgrass and big bluestem tiller demographics were more uniform and predictable across years than intermediate wheatgrass and smooth bromegrass. The LAI for all species increased as MSC increased. Maximum LAI for intermediate wheatgrass, smooth bromegrass, switchgrass, and big bluestem in 1992 was 4.7, 5.1, 4.9, and 5.8, respectively. Integrating tiller demographics and LAI suggests that initial grazing readiness starts with smooth bromegrass in early spring, followed by intermediate wheatgrass in about 2 wk, switchgrass in late spring, and big bluestem in early summer.

Morphological development of grasses has numerous implications to rangeland management including the timing and amount of herbivory. The objective of this study was to quantify the developmental morphology of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern.] tiller populations. Tiller populations of these 2 grasses were studied for 2 years in the Nebraska Sandhills. Plant development was evaluated using a growth staging system which quantifies the development of tiller populations. A morphological growth index for each species was calculated from either the weighted average of tiller numbers reported as mean stage count (MSC) or tiller weight reported as mean stage weight (MSW) and correlated with the independent variables of growing degree days (GDD) and day of year (DOY). Correlation coefficients with the independent variables were greater than 0.97 for MSC and MSW within years and greater than 0.90 between years. Greater rainfall and warmer temperatures in 1991 increased the number of tillers in the more advanced morphological stages in prairie sandreed, but tiller weight rather than tiller number increased in more advanced stages of sand bluestem. A majority of the harvested tillers were vegetative throughout the sampling period but by the end of the growing season, a wide range of morphological stages were present. The use of grazing to prevent the formation of culmed tillers in these grasses may be unnecessary because of the high proportion of vegetative tillers and the wide range of morphological stages available for selection by livestock.

Leaf:stem ratio of grass stands is an important factor affecting diet selection, quality, and forage intake. Estimates of leaf:stem ratios commonly are based on a labor intensive process of hand separating leaf and stem fractions. Near infrared reflectance spectroscopy (NIRS) has been used successfully to predict forage quality and botanical composition of vegetation samples. The objective of this study was to evaluate the use of NIRS to predict leaf:stem ratios in big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.), and smooth bromegrass (Bromus inermis Leyss.). A total of 72 hand-clipped samples of each species was taken from seeded monocultures in eastern Nebraska throughout the 1992, 1993, and 1994 growing seasons. Leaf:stem ratio was determined first for each sample and then the entire sample was ground. Samples were scanned by a Perstorp model 6500 near infrared scanning monochromator. Three calibration equations were developed based on using 18, 36, and 54 (1/4, 1/2, and 3/4 of total samples, respectively) samples. These 3 calibration equations were used to determine the number of samples necessary to achieve an r2 of 0.70 or higher for each data set. Big bluestem and switchgrass had coefficients of determination (r2) of less than or greater than 0.69 for all calibration equations except for the equation using only 18 samples of big bluestem r2 = 0.60). Smooth bromegrass had a r2 ranging from only 0.06 to 0.14 for the calibration equations regardless of the number of samples used. Near infrared reflectance spectroscopy was a rapid means of estimating leaf:stem ratios in monocultures of big bluestem and switchgrass but it was not suitable for smooth bromegrass.

Many rhizosphere microorganisms enhance nutrient uptake and plant growth, but their effectiveness can vary with host species and with genotype within species. This study evaluated the effectiveness of rhizosphere microflora indigenous to the rhizosphere of switchgrass (Panicum virgatum L.) for enhancing seedling yield and nutrient uptake. Switchgrass roots and rhizosphere soil were collected from native prairies and seeded stands in Nebraska, Kansas, Iowa, Missouri, Virginia, and North Carolina. Seedlings of four switchgrass cultivars were inoculated with root fragments and rhizosphere soil from each collection, fertilized with a nutrient solution, and grown in steamed sand for 12 wk in a greenhouse. Seedlings inoculated with rhizosphere microflora produced up to 15-fold greater shoot and root yields, and recovered up to 6-fold more N and 36-fold more P than seedlings inoculated with rhizosphere bacteria only. These responses were consistent for all four switchgrass cultivars and were probably due to arbuscular mycorrhizal fungi. Switchgrass rhizosphere populations were highly variable in their ability to recover N and P and stimulate seedling shoot and root yields. Seedlings inoculated with rhizosphere populations from seeded switchgrass stands averaged 1.5-fold greater shoot and root yields than seedlings inoculated with rhizosphere populations from native prairies. Rhizosphere populations that stimulated the greatest N uptake differed from populations that resulted in the greatest P uptake. Highly effective microbial populations appear to develop in the rhizosphere of seeded switchgrass stands.

The objective of this research was to determine the relationships between the morphological development and in situ ruminally degradable protein (RDP), ruminally undegradable protein (RUP), and microbial protein of two cool season grasses (intermediate wheatgrass and smooth bromegrass) and two warm season grasses (switchgrass and big bluestem). The initial growth of grass tillers grown near Mead, Nebraska was clipped at ground level six times during the 1992 growing season and morphologically classified. Mean stage was calculated. Forage was ground to pass a 2-mm screen and was incubated in ruminally fistulated steers for 16 h. The RUP was adjusted for microbial protein and acid detergent insoluble N. The mean stage of cool season grasses was higher than that of warm season grasses throughout the growing season. The RDP decreased as plant maturity increased for all species. The RUP expressed as a percentage of crude protein for the cool season grasses was lower than that for warm season grasses. The RUP for intermediate wheatgrass, smooth bromegrass, and switchgrass remained constant across maturities, but RUP for big bluestem decreased as maturity increased. Microbial augmentation of RUP decreased as crude protein decreased in all species. The RUP corrected for acid detergent insoluble N and microbial protein was relatively constant across plant maturities. The quantification of RUP across a range of plant maturities provided information for incorporating RUP content of forage grasses into the diets of animals.

Late-spring and early-summer plantings of warm-season grasses often fail, due to dry soil conditions and competition from annual grass and broadleaf weeds. The objective of this study was to compare the morphological development of switchgrass (Panicum virgatum L.) planted in early, mid, and late spring in eastern Nebraska, This study was conducted in 1994 and 1995 at Lincoln, NE, on a Kennebec silt loam (fine-silty, mixed, mesic Cumulic Hapludolls), 'Blackwell' and 'Trailblazer' switchgrass were planted in mid-March, late April, and late May using a single-row, precision grass-seed cone planter to a depth of 0.6 to 1.3 cm at 98 pure live seed per linear meter of row in a split-plot design, Twenty seedlings from each plot were excavated to a depth of 20 cm with a spade. Seedling morphological parameters measured were mean stage count root (MSCR) and shoot (MSCS), leaf area, shoot weight, and primary and adventitious root weight. Plots were sampled every 10 d following the first sample date, In 1994, seedlings from the March planting date were more advanced morphologically in MSCR and MSCS, had accumulated 2.5 times more leaf area, and about 3 times more shoot and adventitious root mass than the April planting date when sampled from late May to late June, In 1995, seedlings from the March planting date generally were more advanced morphologically in root and shoot development, had accumulated 2 to 12 times more leaf area, had 2 to 10 times more shoot mass, and had 2 to 33 times more adventitious root mass than the April or May planting dates at the sample periods from early June to mid-July. We suggest that switchgrass should be planted in early spring instead of in late April and May, as suggested by previous research.