Tallgrass prairies provide an important source of hay and summer forage in eastern Nebraska. A study was conducted in 1989 and 1990 on 2 late seral tallgrass prairies near Lincoln and Virginia, Nebraska to determine if production of selected components of tallgrass prairie communities could be altered by burning (not burned, or burned in either early, mid-, or late spring)and applying fertilizer (0 and 67-23 kg N-P ha-1) and atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] (0 and 2.2 kg a.iha-1). Vegetation was harvested the year treatments were applied at about 30-day intervals starting in June and ending in August. Maximum big bluestem (Andropogon gerardii var. gerardii Vitman) accumulated standing crop (ASC) on unburned areas and areas burned in mid-spring occurred later in 1990 than in 1989. Burning in late spring 1989 maintained big bluestem ASC above 1,100 kg ha-1 through July, whereas big bluestem ASC declined below 840 kg ha-1 in July on areas where other burn treatments were applied. In 1990, big bluestem ASC exceeded 1,570 kg ha-1 in June on areas burned in early and midspring and exceeded 1,500 kg ha-1 in July on areas that were not burned or burned in mid- or late spring. From July to August 1990 big bluestem ASC declined below 730 kg ha-1 for all treatments except the late spring burn treatment where ASC was 1,340 kg ha-1. Burning in late spring reduced prairie dropseed [Sporobolus heterolepis (A. Gray) A. Gray] and tall dropseed [S. asper (Michx.) Kunth.] ASC by at least 67% in June 1990 compared to areas burned in early and mid-spring. Cool-season grass ASC at Virginia declined 86% in June when burned in late spring compared to areas that were not burned. Fertilization increased big bluestem ASC by about 23 and 29% in June and July. Vegetation response to atrazine was variable. Atrazine had a negligible effect on big bluestem ASC. Burning late seral tallgrass prairie in late spring increased big bluestem ASC later in the growing season and decreased cool-season grasses more effectively than burning earlier in the spring.

The use of standing dead biomass, during the winter that was produced by warm-season grasses in the previous growing season by pregnant beef cows may be an alternative to grazing systems in the semi-arid Pampean Region of Argentina. This study, conducted over 2 years, 1990 and 1991, compared the winter forage quality produced during the previous growing season for 4 warm-season grasses; switchgrass (Panicum virgatum L. cv. Pathfinder), kleingrass (Panicum coloratum L.), tetrachne (Tetrachne dregei Nees) and weeping lovegrass (Eragrostis curvula (Schrad), Nees cv. Tanganyka). Five harvests of the summer growth started after the first frost, and were spaced evenly throughout the winter period. Changes in the standing crop of dry matter were measured and subsamples of forage were divided into leaf and stem fractions. Forage quality analyses included: crude protein (CP), in vitro dry matter digestibility (IVDMD), effective rumen degradability (ED), neutral (NDF) and acid (ADF) detergent fiber and lignin. Tetrachne dregei produced forage with a higher leaf:stem ratio and of generally higher quality, than the other species, although the differences were not always significant. Its CP content was marginally below the maintenance requirements of cows. Dry matter yield of tetrachne was lower than that of weeping lovegrass, but differences were only significant in 1990. Kleingrass generally was high in quality and dry matter yield, although it was the lowest in percentage of leaves of the 4 species evaluated. Switchgrass was the least productive; the nutritive value of its forage was low, comparable or lower than that of weeping lovegrass. The first harvest date was higher in nutritive value. Although the nutritive value of leaves and stems were not compared statistically, the leaves tended to be higher than the stems. Tetrachne dregei, the best of the species evaluated in this study, is a very promising warm-season grass, which could provide nutritious forage for winter grazing systems in the semiarid Pampean Region of Argentina.

Knowing the amount of herbage on rangeland is basic to management decisions related to livestock grazing. However, the amount of herbage available for grazing changes seasonally. Therefore, changes in herbage biomass were examined in different communities of the fescue prairie. The study was conducted at 2 sites in southwestern Alberta. In the Porcupine Hills near Stavely, changes in herbage biomass components were examined in 3 communities: rough fescue (Festuca campestris Rydb.), Parry oat grass (Danthonia parryi Scribn.)-Kentucky bluegrass (Poa pratensis L.), and Kentucky bluegrass-sedge (Carex spp.) by sampling at monthly intervals from April or May to late September. Observed trends among the rough fescue, Parry oatgrass-Kentucky bluegrass, and Kentucky bluegrass-sedge communities were, for peak current year's standing production, 398, 305, and 226 g m-2, respectively; for spring current year's standing production as a percent of its peak, 73, 50, and 35%, respectively; and for percent losses of total herbage biomass, from fall to spring, 24, 43, and 56%, respectively. In the foothills near Pincher Creek, the standing crop of grasses and fortes was sampled using paired subplots. One subplot was harvested in October and the other in April. Dry matter losses over winter averaged 27 and 58% for grasses and fortes, respectively. Of the 3 communities examined, production on the rough fescue community was the greatest, least dependent on precipitation during the growing season, and least susceptible to weathering losses and, therefore, had the greatest forage values. The Kentucky bluegrass-sedge community had the lowest forage values.

The relation was studied between the applied stocking rates and the degree to which sheep grazed stems of various karoobush species. A rule of thumb exists amongst farmers and research workers in the Karoo, that sheep graze stems of karoobushes with a diameter of 2 mm or less. This hypothesis was examined over a period of 3 years. The meetly grazed off stems of Pentzia spinescens Less. (doringkaroo) and Rosenia humilis (Less.) Bremer (blou perdekaroo), the most abundant forage species, were measured by sliding Vernier callipers. Estimates of grazeable dry matter, as used in the estimate of the current grazing capacity, is based on the separation of clipped dry matter into grazeable and non-grazeable material. This separation is based on the 2 mm criterion. The hypothesis that sheep voluntarily graze stems with a diameter of up to 2 mm was rejected. The stems of less palatable species are seldom grazed at 2 mm diameter, while grazed stems of paintable species are often thicker than 5 mm. It was established that sheep graze stems of the less palatable karoo bushes to a mean diameter of 1.4 to 1.6 mm. This impacts directly on the method in which dry matter production is estimated for the purposes of determining grazing capacity. The long term grazing capacity norm for this area is 30 ha large stock unit-1. Based on gain ha-1 data obtained from stocking rate trials, the grazing capacity is 33.4 ha large stock unit-1. The stocking rate: grazed stem relation yields an optimum grazing capacity figure of 32.5 ha large stock unit-1. This indicates that monitoring the grazed stems of appropriate species can be used to set grazing capacity limits or adjust stocking rates.

Caldén (Prosopis caldenia) seeds not dispersed by animals sometimes constitute a considerable number of seeds to the seed bank which may contribute to the species' dissemination. The monthly change in the number of viable non-animal dispersed seeds was evaluated over a one-year period. We determined the percentage germination of seeds and the amount of predation by bruchid beetles to learn how these factors influence seed longevity. Forty eight bags containing 10 fruits were placed in 4 sites below caldén tree canopies at the time of shedding (March). To monitor seed losses we randomly removed 1 bag per site every 25-35 days during a year. At the time of shedding, fruits contained 29 seeds, 73 +/- 5.0% which were viable and 9 +/- 2.2% attacked by bruchids. Viability decreased to 33 +/- 22.3% one year later. Loss of viability was described by a polynomial quadratic (y = 70.12 + 0.0238 t-0.0004 t2 (r2= 0.62)). Bags with germinated seeds were observed beginning in November. Percentage germinated seed increased 4.8 +/- 3.7% in the last month of sampling. Consumption of seeds by bruchids also increased in November, but the effect was highly variable. In the last month of sampling (March in the following year), 35 +/- 18.0% of seeds were affected by bruchids. A predictive seed longevity model was developed considering climatic variables, but data were well described only until January (y = 81.50-0.097 time-3.94 precipitation (r2= 0.66)). Undispersed seeds had a high rate of decay and low germination. Longevity was strongly affected by bruchid attack.

A 5 year study was conducted during 1988-1992 to quantify the effects of grazing date and frequency on total organic reserves of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem (Andropogon hallii Hack.). Treatments consisted of mid-month grazing periods in (1) June, (2) July, (3) August, (4) October, (5) June and July, (6) June and August, (7) July and August, or (8) June, July, and August. Seasonal stocking rates were equal among treatments and divided equally over multiple grazing periods. Grazing treatments were applied to the same pastures during 4 consecutive years with yearling cattle and 4-7 day grazing periods. Mean tiller weight of etiolated initial-spring growth was used to estimate total organic reserves in the fifth year. Dormant season grazing in October was not different from 4 years of rest for either species. Total organic reserves in prairie sandreed decreased when paddocks were grazed in June or July regardless of the number of grazing periods per treatment. Reserves in sand bluestem were maintained by grazing once in June or August. Rotationally grazing pastures 2 or more times during June-August is least likely to maintain or increase total organic reserves in either species. Multiple grazing periods initiated in June reduced reserves by about 38% in prairie sandreed and 30% in sand bluestem. When stocking rates are similar to this study, deferment periods should be longer than 60 days after grazing in June to avoid measurable reductions in total organic reserves in both species. Periodic deferment of grazing until mid-August or later will be required to maintain simultaneously high levels of reserves in prairie sandreed and sand bluestem.

The objective of this study was to evaluate the potential of near infrared reflectance spectroscopy (NIRS) for estimating botanical composition of esophageal extrusa samples. Spectral data were collected on 361 samples from fistulated sheep and cattle grazing native tallgrass range. Principal components analysis was used to identify a subset of 73 samples with spectral dissimilarity. These samples were microhistologically analyzed to determine botanical composition and were considered 'actual' for regression and calibration purposes. Thirty-six species (12 grasses, 22 forbs, and 2 sedges) were identified in the microhistologically analyzed samples. However, most accounted for less than 5% of the total diet. Additional pure calibration samples were obtained by feeding individual species to confined fistulated sheep. Initial regression analyses and predictions were made on 13 major species or species groups. Satisfactory prediction equations could only be developed for big bluestem andropogon gerardii Vitman) (r2 =0.61), and the total grasses (r2= 0.79) and total forbs (r2 = 0.79) groups. Addition of spectra from pure samples into the calibration set was beneficial. In general, valid predictions could not be made for individual species that constituted less than 10% of the sample and/or had a low frequency of occurrence in the calibration samples. The NIRS method offered acceptable precision and accuracy in the prediction of major botanical components and it would be practical and efficient because it reduces the number of samples that would have to be microhistologically analyzed.

An inexpensive method of tree felling is needed to precondition dense stands of mature junipers (Juniperus spp.) for the effective use of prescribed burning. The purpose of this research was to determine draft requirements to fell individual juniper trees at different striking heights. These baseline data are necessary to design an elevated chaining technique. Sites in Oklahoma with single-stemmed Ashe juniper (Juniperus ashei Buchholz) (N=40) and Texas with multi-stemmed redberry juniper (Juniperus pinchotii Sudw.) (N=45) were selected for evaluation. A horizontal breaking bar was cabled to an instrumented tractor drawbar for draft force determinations. Data from the drawbar loadcell were stored in a laptop computer data acquisition system. Maximum force to fell junipers was determined at striking heights of 0, 0.6, 0.9, and 1.2 m in Oklahoma and striking heights of 0, 0.6, and 0.9 m in Texas. Force to fell Ashe juniper trees at striking heights of 0, 0.6, 0.9, and 1.2 m averaged 149, 78, 50, and 38 kN, respectively. Striking trees at 0.9 m compared to 0 m (ground level) reduced the felling force by 67% and still uprooted 50% and severed 50% at ground level. With redberry junipers, felling force at striking heights of 0, 0.6, and 0.9 m averaged 81, 14, and 12 kN, respectively. At the striking height of 0.6 m, required draft was reduced by 84% compared to ground level striking, and 67% of the trees were severed at ground level and the remainder were uprooted. To predict force to fell a given size tree, draft was regressed on basal stem diameter in Ashe juniper or total basal stem area in redberry juniper. Based on these data, we concluded an anchor chain modified for elevated striking heights could substantially reduce the tractor drawbar draft for preconditioning of dense stands of juniper by chaining.