Now showing items 1-20 of 21

    • Understory plant response to site preparation and fertilization of loblolly and shortleaf pine forests

      Brockway, D. G.; Wolters, G. L.; Pearson, H. A.; Thill, R. E.; Baldwin, V. C.; Martin, A. (Society for Range Management, 1998-01-01)
      In developing an improved understanding of the dynamics of understory plant composition and productivity in Coastal Plain forest ecosystems, we examined the influence of site preparation and phosphorus fertilization on the successional trends of shrubs and herbaceous plants growing on lands of widely ranging subsoil texture in Arkansas, Louisiana, and Texas which are managed for southern pine production. Burn-inject, chop-burn, chop-burn-disk, double-chop, shear-burn, shear-windrow, and shear-windrow-disk site preparation methods were applied in a completely randomized split-plot design to sites with subsoil textures consisting of loam, gravelly-clay, silt, silty-clay, and clay, both fertilized with 73.4 kg P/ha and unfertilized. Site preparation method, subsoil texture, and fertilization influenced production of paspalums and other forbs the first growing season following treatment, but no treatment combination affected plant groups in subsequent years. Total herbaceous production increased 24 to 35-fold over pretreatment levels the first growing season after treatment. While site preparation methods had little influence on herbaceous biomass, subsoil texture affected herbaceous production the first year after treatment, with loam subsoils being most productive. Although annual composites were the most abundant herbaceous group the first year after treatment, they were largely replaced by perennial grasses by the third post-treatment growing season. By the seventh growing season following treatment, herbaceous production declined on all subsoil textures with composition and yield approximating pretreatment estimates. Subsoil texture influenced shrub density only in the first and third growing seasons after treatment. During the first few years after site preparation, herbaceous production appeared inversely related to shrub density. In the first and third post-treatment growing seasons, fertilization significantly increased total herbaceous production and biomass of composites and legumes. But 7 years after application, total herbaceous production and biomass of bluestems, other grasses, and sedges was greater on unfertilized areas. The absence of differences among treatments by the seventh post-treatment growing season indicates an overall long-term similarity in the degree of disturbance caused by application of each method in this ecosystem.
    • Technical Note: Stream temperatures as related to subsurface waterflows originating from irrigation

      Stringham, T. K.; Buckhouse, J. C.; Krueger, W. C. (Society for Range Management, 1998-01-01)
      Continuous stream temperature data were collected from adjacent reaches of a third-order stream in eastern Oregon. The upstream reach was located within a non-irrigated meadow and the downstream reach was located within an irrigated meadow. Sensors were placed in the stream above a head-ditch irrigation diversion, in the irrigation ditch, in the subsurface (interflow) groundwater, and in the stream reach within the irrigated meadow. Daily maximum stream temperature in the reach located within the irrigated meadow was found to be 1 to 3 degrees C cooler than the non-irrigated reach. Daily minimum stream temperatures exhibited the opposite relationship with the reach within the irrigated meadow ranging from 0.5 to 1.7 degrees C warmer than the non-irrigated meadow reach.
    • Seedbank characteristics of a Nebraska sandhills prairie

      Pérez, C. J.; Waller, S. S.; Moser, L. E.; Stubbendieck, J. L.; Steuter, A. A. (Society for Range Management, 1998-01-01)
      Evaluating seedbank ecology is critical for understanding plant community development and successional patterns and for identifying factors regulating population dynamics. The relationships among seedbank composition, seedbank depth, seed dormancy, and vegetative expression were evaluated for a range site on a Valentine fine sand soil (mixed, mesic Typic Ustipsamments) in the Sandhills Prairie. Twenty soil samples were collected at each of 2 depths (0 to 5, 15 to 20 cm) in early June 1990 and 1991 from 12 macroplots (32 X 32 m) representing 3 range condition classes. A seed extraction and germination trial was conducted to determine the diversity, size, and germinability of the persistent seedbank. Seedling emergence was counted in a greenhouse, with and without a 14-day prechilling (3 to 5 degrees C) stratification treatment, to characterize seedbank dormancy. Fourteen grass species, 17 forb species, and Schweinitz flatsedge (Cyperus schweinitzii Torr.) were identified in the seed bank. Two additional genera (Carex and Euphorbia) also occurred in the seedbank. Only 10 species occurred in 8 or more macroplots in both years. Aboveground botanical composition was not correlated with (P > 0.10) seedbank species composition. More germinable seeds occurred in the 0 to 5 cm depth (P < 0.01) than the 15 to 20 cm depth. Also, the species diversity and seed number were greater in the shallower depth. Germination percentage was low for all types of vegetation. Lambsquarters (Chenopodium album L.) and annual eriogonum (Eriogonum annuum Nutt.) had the largest seedbanks, but germination was less than 6%. Sand dropseed [Sporobolus cryptandrus (Torr.) Gray] and sand lovegrass [Eragrostis trichodes (Nutt.) Wood] were the most abundant perennial grasses and accounted for about 60% of the germinated seeds. Prechilling increased seedling emergence of grasses (P < 0.01), forbs (P < 0.01), and grass-like species (P < 0.01). Perennial grasses emerged first, forbs later, and grasslike species exhibited a bimodal emergence pattern. Based on germination percentage and emergence data, sand dropseed has the potential to colonize openings in the Sandhills prairie, possibly to the exclusion of many annuals occurring in the seedbank.
    • Root and shoot responses of sand bluestem to defoliation

      Engel, R. K.; Nichols, J. T.; Dodd, J. L.; Brummer, J. E. (Society for Range Management, 1998-01-01)
      Knowledge of root response, as well as shoot response, to defoliation is needed to manage grasslands in environments where water and/or nutrients are limiting. The objective of this study was to document the response of sand bluestem (Andropogon hallii Hack.) roots and shoots to different times and frequencies of defoliation. Individual sand bluestem plants were grown in 15 X 100-cm polyvinyl chloride (PVC) containers which were placed in the plants' natural setting. Twelve plants (replications) were clipped to a 7-cm stubble height during mid-month for each of the following defoliation schedules: 1) June, July, and August; 2) June and August; 3) June; 4) July; 5) August; and 6) October. The October defoliation, after shoot senescence, served as the control. Multiple defoliations reduced (P < 0.05) root weight, root area, root length, and weight of total nonstructural carbohydrates (TNC) in roots by an average of 33, 42, 43, and 34%, respectively, compared to control plants. A single defoliation in June only reduced root weight, root area, root length, and weight of TNC in roots by 14, 19, 16, and 13%, respectively, compared to control plants. Defoliating plants during the growing season did not affect (P > 0.05) number of tillers, weight per tiller, above-ground weight, number of buds, weight of rhizomes, or weight of TNC in rhizomes. Grazing sand bluestem more than once during the growing season may reduce root growth and diminish its ability to compete for water and nutrients. Grazing during the dormant season or once during the early part of the growing season should be least detrimental to sand bluestem.
    • Regrowth and rest requirements of northern wheatgrass following defoliation

      Kowalenko, B. L.; Romo, J. T. (Society for Range Management, 1998-01-01)
      Degree-days required for standing crop and above-ground net primary production of northern wheatgrass (Agropyron dasystachyum [Hook.] Scribn., syn. Elymus lanceolatus [Scrib. &Smith] Gould) mowed to a 5-cm stubble to recover to levels similar to an unmowed control were determined in southwestern Saskatchewan. Nine, single mowing treatments and an unmowed control were established from early May through late August in 1991 and 1992 on a clayey range site at 2 locations. Green and dead phytomass and above-ground net primary production were determined for 2 to 3 years following mowing. Degree-days required for recovery of green and dead standing phytomass on mowed plots decreased linearly and were highly correlated (r2 = 0.64 to 0.99) with the number of days plots were mowed after 1 May. Regardless of mowing date, green phytomass did not recover to control levels the year of mowing. Each day mowing was delayed past 1 May reduced the number of degree-days required for total recovery of green phytomass on mowed plots by 15.7 in 1991 and 17.7 in 1992. Degree-days required for recovery of standing dead on mowed plots were reduced 17.6 in 1991 and 15.8 in 1992. Degree-days required for recovery of above-ground net primary production declined linearly (r2 = 0.67 and 0.99) as mowing was delayed after 1 May. More degree-days were required for the 1991 than 1992 plots. At least 2 and sometimes 3 growing seasons were required to accumulate enough degree-days to allow full recovery of green and standing dead phytomass and above-ground net primary production on mowed plots. For optimum sustained production, a grazing system should be used on northern wheatgrass-dominated rangeland with a 2 year rest period applied to paddocks after grazing.
    • Rainfall interception by selected plants in the Chihuahuan Desert

      Wood, M. K.; Jones, T. L.; Vera-Cruz, M. T. (Society for Range Management, 1998-01-01)
      Water budget modeling usually requires quantification of all possible processes of the hydrologic cycle. This includes rainfall interception. The purpose of this study was to estimate the potential amounts of water transferred back to the atmosphere from interception for some common plants found in the Chihuahuan desert. Fifty plants of many sizes representing 10 common species of the Chihuahuan Desert were chosen for evaluation. Plants were submerged in a 2 X 2 m tank filled with water. After submersion, the plants were weighed, and the difference in weight was recorded as the maximum water storage capacity of the plant's canopy. Plants were also measured for maximum and minimum crown diameter (cm), height (cm), green weight (g) at time of submersion, and oven-dry weight (g). The forb, grass, and shrub species had different variables included in the prediction equations. Dry and green weight were the 2 variables which appear to have the strongest relationship with the amount of water intercepted for all species. Of the 7 grass species evaluated, dry and green weight were part of all equations, and height was included in only 2 equations.
    • Previous grazing or clipping affects seed of Indian ricegrass

      Orodho, A. B.; Cuany, R. L.; Trlica, M. J. (Society for Range Management, 1998-01-01)
      Previous heavy grazing for more than 50 years, compared with protection from livestock grazing, in the semi-arid area of Chaco Canyon in the southwestern United States did not result in any significant decrease in seed production potential of Indian ricegrass [Oryzopsis hymenoides (Roem. and Schult.) Ricker]. There also were no significant differences in seed production between grazed and ungrazed collections of Indian ricegrass from the Chaco Canyon study site when transplanted and grown in a common garden. This indicated that long-term protection from livestock grazing probably had not genetically (ecotypically) altered seed production potential. Both grazed and ungrazed transplants of Indian ricegrass differed in seed production from the cultivars 'Paloma' and 'Nezpar'. Nezpar produced the greatest seed yield (312 kg/ha), while Paloma had the lowest yield (78 kg/ha). Defoliation about 1 June over a 2-year period reduced seed production and nitrogen fertilization did not increase seed yield. Previous grazing history had little effect on seed germination, but there were significant differences in germination among some collections and cultivars of Indian ricegrass. Germination was less than 5% for all entries. A tetrazolium viability test showed that seed of native strains were more viable than those of Paloma. Dormancy is a troublesome, but desirable, trait of Indian ricegrass seed for use in droughty areas.
    • Late growing-season fire effects in mid-successional tallgrass prairies

      Engle, D. M.; Mitchell, R. L.; Stevens, R. L. (Society for Range Management, 1998-01-01)
      Wildfire in the growing season is relatively frequent and interest is increasing in using growing-season fire in management of tallgrass prairie. However, the influence of fire in the growing season on forage production and species composition, especially in mid-successional tallgrass prairie, is largely unknown. Our objective was to compare vegetation composition and production on Loamy Prairie and Very Shallow ecological sites in mid-successional stages in response to late growing-season fire at different frequencies. We applied 4 burning treatments (no burn, or 1, 2, or 3 burns in 5 years) in the late growing season in southern Oklahoma during a series of years of above-average precipitation. The sites were dominated at the beginning of the study by early- and mid-successional species including prairie threeawn (Aristida oligantha (Michx)), a species indicating a disturbance history. After the initial burns in 1990, tallgrasses, little bluestem, and perennial grasses were reduced by burning on the Loamy site. Forbs were more productive on burned plots (1,980 kg ha-1) than on plots that were not burned (1,290 kg ha-1) averaged across sites. Total production was not reduced by burning in 1990. Growing-season burns in 2 consecutive years had little influence on species composition or production as compared to a single burn in 2 years. Warm-season perennial grasses other than tallgrasses and little bluestem increased on the Loamy site, but decreased on the Shallow site. Production of cool-season perennial grasses increased to almost 40% of total production on twice-burned plots averaged across sites. Other than the effect on cool-season perennial grasses, 2 burns over a two-year period had little effect beyond the first growing season after the second burn. Twice-burned plots and plots burned 3 times produced more forbs than either plots that were burned once or not burned. Production of perennial grasses was opposite that of forb production. Total production was not reduced on either site regardless of fire frequency. Results indicate managers may expect a short-term reduction in production of forage grasses and an increase in forbs following late growing-season fire in mid-successional tallgrass prairies.
    • Landscape heterogeneity and long-term animal production in Tierra del Fuego

      Cingolani, A. M.; Anchorena, J.; Collantes, M. B. (Society for Range Management, 1998-01-01)
      Grasslands of northern Tierra del Fuego sustain 1 sheep/ha and are very extensively managed, with flocks roaming freely in large paddocks (2,000-4,000 ha). This system requires knowledge of landscape-level constraints and influences upon production for decision making. On a typical sheep ranch we checked upland floristic gradients against 30-years records of animal production. Community types and landscape units were surveyed and mapped. Using gradient analysis techniques we obtained animal production differences at the landscape scale that were strongly related to a vegetation gradient associated with soil fertility. Extensive and strongly variable lithological mantles allowed expression of the fertility gradient at that scale. Landscapes with fertile soils and neutrophilous community types were best for sheep breeding. These landscapes produced a mean of 37% more lambs ha-1 yr-1 than lands with soils of intermediate fertility and slightly acidophilous community types, and 116% more lambs ha-1 yr-1 than lands with highly infertile soils and highly acidophilous vegetation. Contrarily, the soil moisture gradient, being mainly expressed at the topographic scale, was not related with sheep production records. A forage gradient which was identified behind the fertility gradient supported our findings. Poa spp., the main item in sheep diets, and other important forage species attained the highest covers in neutrophilous community types. With the range in proportion of lowlands present in this ranch (12 to 30%), no relationship was found between the percentage of hygrophitic vegetation in the landscape and animal production.
    • Improvement of dry tropical rangelands on Hainen Island, China. 3. Legume response to initial fertilizers

      Michalk, D. L.; Fu, N. P.; Zhu, C. M. (Society for Range Management, 1998-01-01)
      During 1981-83, we identified nutrient requirements and fertilizer strategies for the development of legume-based pastures in dry tropical rangelands of Hainan Island, China. Nutrient requirements for pastures grown on sandy and red loam soils were established using soil tests and missing element experiments with 3 test legumes. An acute P deficiency (< 5 mg kg-1 Bray P) was detected by soil tests on sandy soils, but no deficiencies were found on loam soil. The exclusion of P from a total fertilizer treatment reduced relative yield to 20% of potential on sandy soil. A factorial P rates experiment replicated in space and time showed a strong curvilinear response for stylo (Stylosanthes hamata L. Taub. cv. Verano) and siratro (Macroptilium atropurpureum (DC.) Urban) based pastures on sandy soil. No response was observed on loam soil. Given limited superphosphate supplies available for range improvement in south China, results from these studies showed no benefit from applying P fertilizer to stylo pastures grown on soils with available P > 20 mg kg-1. In contrast, application of P fertilizer proved both profitable and essential for development of legume-based pastures on P-deficient sandy soils. It is recommended that a rate of about 40 kg of P ha-1 should be applied at establishment of stylo pastures on sandy soil. At this rate both legume yield and P content of tops should be maintained at levels needed to sustain a beef production enterprise and return about 1.5 per dollar invested in fertilizer.
    • Improvement of dry tropical rangelands on Hainan Island, China: 4. Effect of seedbed on pasture establishment

      Michalk, D. L.; Fu, N. P.; Zhu, C. M. (Society for Range Management, 1998-01-01)
      Seedbed requirements for the establishment of grasses and legumes were studied in 3 experiments conducted over 3 years (1981-83) on the sandy (< 5 mg kg-1 Bray P) and loam (> 20 mg kg-1 Bray P) ultisol soils found in the dry tropical rangelands of western Hainan Island, China. Density at the end of the wet season and production accumulated over the growing season (May-October) were the discriminative parameters used. Experiment 1 measured the effect of seedbed preparation (cultivated and uncultivated but heavily grass pasture) on the establishment of 2 grasses, buffel (Cenchrus ciliaris L. cv. Biloela) and sabi (Urochloa mosambicensis (Hack.) Dandy cv. Nixon), sown alone or mixed with 3 stylos (Stylosanthes guianensis (Aubl.) Sw. var. guianensis cv. Graham, S. hamata (L.) Taub. cv. Verano and S. scabra Vog. cv. Seca) on the 2 soil types. Biloela buffel established better and produced more in subsequent years than Nixon sabi grass when sown on a cultivated seedbed, but neither grass established when sown into undisturbed grassland. Companion stylos established on both seedbeds, but initial density and yield was lower on the uncultivated seedbed. However, in 3-year-old swards, stylo yield on uncultivated seedbeds equalled or exceeded yield on cultivated seedbeds. Seca was the most productive stylo, but Graham yielded more consistently between years. Soil type had no effect on sown grass production, but legumes grew better on the sandy soil. Experiment 2 measured the effect of 4 seedbeds (heavily grazed, 1 disking, sprayed with herbicide, and cultivated to fine tilth) on establishment on Verano and Seca stylos on sandy soil. Density of both stylos was highest where grass competition was minimized with herbicide and lowest where heavy grazing was imposed prior to seeding. Compared to herbicide, disking resulted in lower density and yield in the establishment year, but the difference disappeared with time. Burial of seed too deeply and subsequent competition from native species account for the poor performance of both stylos when drilled into a cultivated seedbed which was still evident in 3-year-old swards. Experiment 3 examined the interaction between seedbed type (heavily grazed, burnt, 1 disking, sprayed with herbicide) and superphosphate application. Superior establishment was measured on herbicide and disked treatments and production was still higher in 3-year-old swards than heavy grazing. Burning was more effective than heavy grazing. Increasing fertilizer input improved legume production on all seedbeds, but did not affect density. Reduction in legume yield between 2- and 3-year-old swards in the burnt and disked treatment due to grass competition highlights the need for appropriate grazing to maintain legume content of augmented grasslands. Overall we recommend rough disking as the most practical and cost-effective means to augment native grasslands with stylos. A fine seedbed is recommended to provide the disturbance required to establish grasses. There is no advantage gained by including grasses with legumes oversown into living grassland.
    • Harvest frequency and burning effects on vigor of native grasses

      Cuomo, G. J.; Anderson, B. E.; Young, L. J. (Society for Range Management, 1998-01-01)
      Burning and harvest frequency can affect the vigor of switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and indiangrass [Sorghastrum nutans (L.) Nash]. A field study was established in 1986 and from 1988 to 1991 treatments were applied with burning in March, April, or May with unburned controls. Forage was harvested from plots 1 (June), 2 (June and July), or 3 (June, July, and August) times with unharvested control plots included. Treatments were applied to the same plots annually and were arranged in a split-split plot, randomized complete block design. The main plot was species, the subplot was burning, and the sub-subplot was harvest frequency. Big bluestem produced 147 and 122% more etiolated biomass in spring than did switchgrass or indiangrass, respectively. Effects of harvest management on plant vigor occurred after 1 growing-season, but changed little during the remainder of the study. Etiolated biomass declined more as harvest frequency increased from 2 to 3 harvests than from 1 to 2 harvests (213, 205, and 162 g m-2 for 1, 2, and 3 harvests per summer, respectively). Big bluestem produced 95 and 33 % more tillers than switchgrass and indiangrass, respectively, and burning stimulated tillering an average of 32% across all species and harvest treatments. Harvest frequency increased tiller density. However, plant vigor as measured by etiolated growth decreased as harvest frequency increased. This suggests that with these species tillering may occur at the expense of energy storage with frequent defoliation. Vigorous spring etiolated growth and high tillering potential may partially explain the dominance of big bluestem in the tallgrass prairie.
    • Grazing management affects nutrient intake by steers grazing tallgrass prairie

      McCollum, F. T.; Gillen, R. L. (Society for Range Management, 1998-01-01)
      Indicators of nutrient intake were compared for beef steers grazing tallgrass prairie managed with continuous grazing or 8-paddock short-duration grazing. Two replicates of each grazing system were evaluated during the 2 year study. Stocking rates for the grazing systems were similar in both years. Within each treatment replicate, 3 steers fitted with ruminal and duodenal cannulae grazed for the entire grazing season (late April through late September) with larger groups of intact steers. Rest periods for the 8-paddock cells were lengthened as the season progressed and forage accumulation rate slowed. Trials occurred in early June and early August in year 1 and early July and early September in year 2. Flow of organic matter and nitrogen at the duodenum, fecal nitrogen concentration, and fecal output were used as indicators of nutritional status. Chromic oxide was used as a flow marker. Flow of organic matter, total nitrogen, and microbial nitrogen at the duodenum in addition to fecal output were lower (P < 0.04) with short-duration grazing and indicate that forage intake and digestible organic matter intake were depressed in steers on the short-duration grazing treatment. Forage digestible organic matter intake, estimated from microbial protein flow, was 19.3% lower (P < 0.03) on short-duration grazing. Fecal nitrogen concentration was higher (P < 0.03) for steers under continuous grazing. Diet crude protein estimated from fecal nitrogen was 24.4 g kg-1 organic matter higher for continuous grazing. These results suggest that both diet nutrient composition and intake were depressed in steers in the short-duration grazing treatment. These observations partially explain the lower weight gains and higher end-of-season residual standing vegetation noted with short-duration grazing in concurrent grazing trials on these rangelands.
    • Energy cost of cattle walking on the level and on a gradient

      Di Marco, O. N.; Aello, M. S. (Society for Range Management, 1998-01-01)
      The effect of walking on cattle energy expenditure was assessed by monitoring the CO2 production of cattle with the 14C-entry rate technique. Seven Angus steers (298 +/- 38 kg BW) were peritoneally infused with a solution of NaH14CO3 for 72 hours using portable peristaltic pumps. The steers were forced to walk after 24 hours of infusion, on 2 consecutive days. On the first day, walking was at a constant speed of 2 km.hour-1, divided in 4 periods of 0.5 hours (1 km), first on the level ground, second and third ascending and descending a 6% grade, and finally on the level surface on the way back to corrals. On the second day, cattle walked 1 km at 1 km hour-1, and thereafter walked 4 km at 4 km hour-1 on the level. Saliva samples were collected for periods of 0.5 hours before and during different periods of walking and at rest at 2 and 4 hours after the activity. Concentration and specific activity of CO2 were measured in saliva samples to estimate the rate of CO2 production [ml.hour-1.(BW0.75)-1] as the ratio between the rate of infusion (microCi.hour-1) and the specific activity of CO2 (microCi.liter-1 of CO2). The production of CO2 was converted to heat production using an energy equivalent of 5.26 kcal.liter-1. Average energy expenditure (EE) in corrals in both days before the activity was 82.6 +/- 3.1 kcal hour-1.100 kg BW-1 [650 ml CO2.hour-1.(BW0.75)-1]. The cost of walking on the level surface and on the 6% grade was 9.0 +/- 1.14 and 16.4 +/- 2.18 BW-1, respectively. There was a small nonsignificant residual effect of walking that disappeared a few hours after exercise. It was concluded that the cost of walking can only have a minor effect on the energy requirement of grazing cattle.
    • Elk forage utilization within rested units of rest-rotation grazing systems

      Werner, S. J.; Urness, P. J. (Society for Range Management, 1998-01-01)
      Elk (Cervus elaphus) have been repeatedly observed to prefer rested units within rest-rotation grazing systems. Given the logistical and financial investments associated with the maintenance of these systems, elk herbivory within rested units is a potential source of conflict. Elk forage utilization was determined during the summers of 1994 and 1995 at the forest-grassland ecotone of 3 rest-rotation grazing allotments in south-central Utah's Fishlake National Forest. Average phytomass within areas protected from and subjected to elk herbivory was not statistically different in June and August 1994. Average phytomass within caged areas was greater (P < 0.20) than that within areas subjected to elk use in 2 of 3 rested units in June-July 1995 (14.1 and 35.6% utilization) and August 1995 (34.7 and 42.0% utilization). June-to-August forage regrowth, however, was 31.3 and 33.0% greater in 1995 than in 1994 within caged and uncaged areas, respectively.
    • Effect of forty-four years of grazing on fescue grassland soils

      Dormaar, J. F.; Willms, W. D. (Society for Range Management, 1998-01-01)
      A grazing study was initiated in the foothills of southwestern Alberta on the rough fescue grasslands (Festuca campestris (Rydb.) in 1949 comparing various grazing intensities. In 1992, soil samples were obtained from the Ah horizon of paddocks grazed at 1.2 (light), 2.4 (heavy), and 4.8 (very heavy) animal unit month ha-1 and from an ungrazed exclosure (control). The thickness of the Ah horizon of the control averaged 22 cm while that of the lightly, heavily and very heavily grazed paddocks averaged 18, 12, and 8 cm, respectively. Soil color changed from 10YR 2/1 (black) to 10YR 4/3 (dark brown to brown) in response to very heavy grazing. Grazing pressures decreased the mean-weight diameter of water-stable aggregates, total C and P, monosaccharide content and the galactose + mannose/xylose + arabinose ratio, while it increased bulk density, pH-CaCl2, and total N. The loss of P must be viewed with concern. Treatment effects on most soil parameters were most pronounced at the two heavier grazing pressures. Particularly, the heavy grazing pressure jeopardized the sustainability of the ecosystem by reducing fertility and water-holding capacity.
    • Defoliation and cold-hardiness of northern wheatgrass

      Kowalenko, B. L.; Romo, J. T. (Society for Range Management, 1998-01-01)
      Freezing temperatures in winter were hypothesized to be a major cause of mortality of tillers following defoliation of northern wheatgrass (Agropyron dasystachyum [Hook.] Scribn., syn. Elymus lanceolatus [Scribn. & Smith] Gould). Cold-hardiness of northern wheatgrass tillers was determined following a single mowing to a 5-cm stubble height in late May, June, July, or August in 1992 or 1993 in southwestern Saskatchewan. An unmowed control was also included. Cold-hardiness was determined in early and late winter immediately following mowing by: 1) exposing tillers to controlled temperatures ranging from -3 to -36 degrees C, or; 2) exposing them to -15 degrees C for 0 to 15 days. The LT50 (temperature at which 50% of tillers died) of northern wheatgrass tillers in early winter ranged from -29.5 to < -36.0 degrees C in 1992-93, and averaged -24.0 degrees C in 1993-94. In late winter LT50 ranged from -18.1 to -22.6 degrees C in 1992-1993, and it averaged -22.0 degrees C in 1993-1994. The LDur50 (duration at which 50% of tillers died) of tillers exposed to -15 degrees C for 0 to 15 days ranged from 8.0 to 13.1 days in early winter, and 2.7 to 4.7 days in late winter. Unexpectedly mowed tillers were generally more cold-hardy than those from control. In early winter LT50 was 1.5 to 10 degrees C lower for mowed than control tillers. The hypothesis that defoliation reduces cold-hardiness of northern wheatgrass was rejected. The degree or duration of cold stress in the field is generally insufficient to reduce tiller survival in northern wheatgrass. Late winter through early spring is a critical period for tiller survival of northern wheatgrass because cold-hardiness declines this time of the year. Maintaining insulating cover can moderate soil temperatures and reduce damage to plants from freezing temperatures.
    • Best linear unbiased prediction of herbivore preferences

      Rodríguez Iglesias, R. M.; Kothmann, M. M. (Society for Range Management, 1998-01-01)
      Generalized linear mixed models were used to obtain best linear unbiased predictions (BLUP's) of herbivore preferences for range plant species from expert knowledge contained in range site descriptions produced by the USDA Soil Conservation Service (currently Natural Resources Conservation Service). A total of 4,558 assessments of preference for cattle, deer, goats, and sheep on 167 plant species were available from 55 range site descriptions for the Edwards Plateau (Texas). Consistency of predicted preferences was evaluated through intraclass correlation estimated by restricted maximum likelihood. Predictions in observed (3-level ordinal) and logit scales were very similar; rank correlations between predictions in different scales ranged from 0.994 (P < 0.0001) for cattle to 0.998 (P < 0.0001) for sheep. Estimated intraclass correlations were also high (0.74 to 0.84 in observed scale and 0.82 to 0.92 in logit scale) suggesting consistent rankings of plant species across range sites. Metric multidimensional scaling and principal components analysis showed distinct patterns among the 4 herbivores. Grasses and browse were the most informative forage classes for discriminating preferences among herbivores. Deer and cattle exhibited the least similar diet preferences. Sheep and goats were intermediate, with sheep closer to cattle and goats most similar to deer. The pair deer-goat showed the most similar pattern of preferences. BLUP's of plant species preferences showed good agreement with published research on both individual plant species and forage classes. Optimal properties of mixed model procedures can be exploited to predict animal preferences at the range site scale from standardized expert opinion. These estimated preferences may be useful for modeling grazing effects at spatial scales compatible with management decisions.
    • Association of food quality and locations by cattle

      Bailey, D. W.; Sims, P. L. (Society for Range Management, 1998-01-01)
      Twelve yearling steers were observed in an 8-arm radial maze to determine the strength of the association between food quality and spatial locations following a 0- or 30-day delay. The study was conducted using 3 qualities of feed, low (straw), medium (alfalfa pellets), and high (grain). During phase 1, all 8 arms contained dehydrated alfalfa pellets. In phase 2, steers were fed either grain or wheat straw, in 2 arms (key arms). The remaining 6 arms contained alfalfa pellets. Six steers received straw in key arms, and 6 received grain. Key arms varied among steers and were selected so a change in arm selection patterns between phases would clearly be associated with corresponding changes in food quality. Straw was placed in arms that steers selected first during phase 1, and grain was placed in arms that were selected last in phase 1. Phase 3 began after a 0- or 30-day delay following phase 2. In this phase, all arms contained alfalfa. Steers rarely reentered a previously entered arm indicating an accurate spatial memory for food location. The sequence of arm selections in phase 2 changed (P < 0.05) from the pattern established in phase 1, which demonstrated that cattle can associate food quality with spatial locations. The delay between phase 2 and 3 did not affect (P > 0.05) the selection patterns of steers that had grain in key arms, but did appear to affect the number and sequence of arm entries for steers receiving low quality food in key arms during phase 2. With no delay, steers that received straw in phase 2 did not enter key arms on the first day of phase 3, but after 30 days animals entered and consumed food in key arms. Steers with no delay entered key arms fewer (P = 0.03) times during phase 3 than steers that began 30 days later. This suggests that strength of the association between food quality and spatial locations can decline over time.