• Response of a mixed native warm-season grass planting to nitrogen fertilization

      Berg, W. A. (Society for Range Management, 1995-01-01)
      Plant available nitrogen limits production of native warm-season grasses on marginal farmland in the Southern Plains. In this western Oklahoma study, N was applied at 0, 35, 70, or 105 kg N ha-1 yr-1 to a mixed stand of blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths), sideoats grama (B. curtipendula (Michx.) Torr.), little bluestem (Schizachyrium scoparium (Michx.) Nash), sand bluestem (Andropogon hallii Hack.), switchgrass (Panicum virgatum L.) and indian grass (Sorghastrum nutans (L.) Nash). The grass was established on sandy loam soil farmed an estimated 90 years. With near-normal precipitation the first year, production of perennial grasses increased linearly with 26 kg herbage produced kg-1 N applied. In drouth conditions, the second and third years, production averaged 10 kg herbage kg-1 N applied. The fourth and fifth year the stand was not fertilized and residual effects measured. Herbage production increased 10 kg for each kg N applied over the previous 3 years. Blue Grama made up much of this increased herbage production along with warm-season annuals (Panicum capillare L. and Amaranthus retroflexus L.). With increasing N rates the residual N effect increased the proportion of blue grama and decreased the proportion of taller perennial grasses. Thus, N fertilization of mixed native warm-season grass stands established on marginal farmland, typical of stands established on sandier soils under the USDA Conservation Reserve Program, can result in substantial herbage yield increases, however, some of the increased yield may be from weedy species.
    • Bison selectivity and grazing response of little bluestem in tallgrass prairie

      Pfeiffer, K. E.; Hartnett, D. C. (Society for Range Management, 1995-01-01)
      The perennial bunchgrass little bluestem (Schizachyrium scoparium [Michx.] Nash) was examined in a 5-yr study on tallgrass prairie to determine how fire influences its use by bison and its responses to grazing. On unburned prairie, bison grazed only 5% of the available little bluestem, selecting it only 30% as frequently as big bluestem, the dominant co-occurring species. On burned prairie, grazing frequency of little bluestem was over 3-fold greater and equal to that of its dominant neighbor. Grazing frequency of little bluestem was affected by plant size (basal area). On burned sites, plants of intermediate size classes were least abundant (< 10% of total) but were grazed most frequently (> 50%). Small plants were most abundant but were grazed least frequently. Density, tiller numbers, and basal area of little bluestem were significantly greater in annually burned compared to infrequently burned sites but were decreased by > 50% in grazed compared to ungrazed sites. Grazing shifted the population size distribution toward higher frequencies of smaller individuals (< 5 0 cm2 basal area), whereas burning increased the frequency of large (> 200 cm2 basal area) individuals. In unburned prairie, little bluestem accumulates a persistent clump of standing dead tillers that appear to serve as a physical deterrent to grazing. Although burning enhances its growth, it also removes its canopy of dead tillers exposing the plant to grazers. The shift in population structure toward a high frequency of smaller (and perhaps less drought- or grazing-tolerant) individuals may contribute to the decline of little bluestem populations under persistent grazing. Thus, plant growth form, population size structure, and fire interact to influence bison grazing patterns and responses of little bluestem to grazing on tallgrass prairie.
    • Book Review: Goat Nutrition, P. Morand-Fehr

      Scarnecchia, D. L. (Society for Range Management, 1995-01-01)
    • Effects of buffer additions on fermentation of dormant range grasses

      Momont, P. A.; Pruitt, R. J.; Pritchard, R. H.; Johnson, P. S. (Society for Range Management, 1995-01-01)
      Replicated two-stage in vitro studies were conducted to determine the effects of single amino acid or branched-chain volatile fatty acid buffer additions on in vitro dry matter disappearance, neutral detergent fiber disappearance, and fermentation kinetics of dormant range grasses. Substrates consisted of separate samples of 2 cool season mid-grasses, western wheatgrass (Agropyron smithii Rydb.) and Japanese brome (Bromus japonicus Thunb.), and a mixture of warm season shortgrasses, buffalograss (Bunchloe dactyloids [Nutt.] Engelm.), and blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Steud.), hand clipped from standing forage in mid-March. Isonitrogenous treatments included buffer containing urea with or without amino acids, branched-chain volatile fatty acids, sodium sulfate, or starch. Urea increased (P < 0.05) in vitro dry matter disappearance and in vitro neutral detergent fiber disappearance of the cool season grasses over N free buffer. Methionine addition increased (P < 0.05) in vitro neutral detergent fiber disappearance and rate of fermentation of both cool season grasses and in vitro dry matter disappearance of Japanese brome over urea alone. Sodium sulfate increased (P < 0.05) in vitro neutral detergent fiber disappearance of Japanese brome compared to urea alone. None of the branched-chain volatile fatty acids tested increased dry matter disappearance, neutral detergent fiber disappearance, or rate of fermentation of the dormant range grasses. Addition of urea or amino acids did not increase in vitro dry matter disappearance or in vitro neutral detergent fiber disappearance of the shortgrass mixture. In vitro screening of amino acid and branched-chain volatile fatty acid buffer additions to dormant range grasses showed that methionine supplementation with urea offers the greatest potential, among the supplements evaluated, for improving digestibility and rate of fermentation of cool season grasses. None of the buffer supplements improved fermentation of the warm season grasses.
    • Effects of grazing management on standing crop dynamics in tallgrass prairie

      Cassels, D. M.; Gillen, R. L.; McCollum, F. T.; Tate, K. W.; Hodges, M. E. (Society for Range Management, 1995-01-01)
      Grazing system and stocking rate effects on forage standing crop of tallgrass prairies in north-central Oklahoma were evaluated from 1989 to 1993. Twelve experimental units, consisting of pastures dominated by big bluestem [Andropogon gerardi Vitman], little bluestem [Schizachyrium scoparium (Michx. Nash], indiangrass [Sorghastrum nutans (L.) Nash], and switch grass [Panicum virgatum L.], were arranged in a completely randomized design with either a short duration rotation or continuous grazing system and stocking rates ranging from 127 kg animal live-weight/ha to 222 kg live-weight/ha. Yearling steers grazed the units from late April to late September. Herbage standing crop was sampled in July and September. Total, live, and dead standing crops did not differ significantly between the 2 grazing systems in July. Total standing crop was significantly higher in the rotation units in September (3,600 versus 3,020 kg/ha, P < 0.05). Dead standing crop was also higher in the rotation units in September (1,950 versus 1,570 kg/ha, P < 0.05). Evidence suggests the difference in standing crop between systems is due, in part, to reduced forage intake by the livestock. Grazing system did not interact with either stocking rate or year. Stocking rate had significant effects on total, live and dead standing crops at both sample dates. The slope of the total standing crop-stocking rate relationship varied over years and ranged from -12 to -36 kg/ha per kg live-weight/ha in July and from -12 to -27 kg/ha per kg live-weight/ha in September. Higher standing crop at the end of the grazing season in the rotation units would mean greater soil protection and higher fuel loading for prescribed burning, and would suggest a lower impact on plant vigor. However, if the higher standing crop is a result of lower forage intake, we would expect livestock weight gains to decline.
    • Climatic effects on buffelgrass productivity in the Sonoran Desert

      Martin, M. H.; Cox, J. R.; Ibarra-F, F. (Society for Range Management, 1995-01-01)
      Buffelgrass (Cenchrus cilaris L.), a perennial bunchgrass from northcentral Kenya has been successfully seeded on 400,000 ha in northwest Mexico. To determine if carrying capacity increased after buffelgrass introduction we measured live, recent-dead standing, old-dead standing and litter at 2-week intervals for three years. Live biomass was produced throughout the year but peak production, over the 3 years was in August. Peak live biomass production varied from 46S kg/ha in a summer of below-average precipitation to 3,045 kg/ha in a summer of above-average precipitation. Recent- and old-dead standing quantities were highly variable among years and transfers among components were dependent on temperature and precipitation. Buffelgrass annually produces about 3 times more green forage than native grasses.
    • Grazing influences on watering point vegetation in the Chihuahuan desert

      Fusco, M.; Holechek, J.; Tembo, A.; Daniel, A.; Cardenas, M. (Society for Range Management, 1995-01-01)
      Long-term influences of livestock grazing on vegetation around watering points was studied on 2 upland Chihuahuan desert ranges in southcentral New Mexico using regression analysis. One range had been conservatives stocked since the 1950's while the other was more heavily stocked. About 45% of the climax vegetation occurred on the heavily stocked range compared to 70% on the conservatively stocked range. During 3 years of study, both ranges were stocked conservatively so annual utilization of the key forage grasses was 30-35%. Regression analyses showed black grama (Boueteloua eriopoda Torr.), mesa dropseed (Sporobolus flexuosus Thurb, Rybd.), threeawn (Aristida sp.), and total perennial grass standing crop increased as distance from water increased on the good condition range (P < 0.05). However, black grama and threeawn standing crop showed no association with distance from water on the fair condition range. Broom snakeweed (Xanthocephalum sarothrae Pursh.), the primary poisonous plant found on both ranges, was associated (r2 = 0.35) with distance from water only on the good condition range in April. Poisonous plants other than broom snakeweed decreased as distance from water increased with the exception of the fair condition range in October. No livestock losses from poisonous plants were noted on either range over the 3 years. We attribute this to the present conservative stocking rates. Our study supports the recommendation that downward stocking rate adjustments be made for the zone more than 1,600 m from water.
    • Predicting buffelgrass survival across a geographical and environmental gradient

      Ibarra-F, F. A.; Cox, J. R.; Martin-R, M. H.; Crowl, T. A.; Call, C. A. (Society for Range Management, 1995-01-01)
      This research was designed to identify relationships between T4464 buffelgrass (Cenchrus ciliaris L.) survival and climatic and soil characteristics. At 167 buffelgrass seeding sites in North America we collected climatic and soils data where the grass: 1) persisted over time and increased in area covered (spreads), 2) persisted over time but does not increase in area covered (persists), and 3) declined over time and all plants eventually died (dies). At 30 sites in Kenya we collected climatic and soils data in the area where T4464 seed was originally collected. Only total soil nitrogen and organic carbon differed among survival regimes. Total soil nitrogen and organic carbon concentrations were least where buffelgrass spreads, intermediate where the grass persists and greatest where the grass dies. To predict buffelgrass survival among the 3 survival regimes, and between areas where the grass spreads or dies, we used discriminant function analyses. A model including organic carbon, total soil nitrogen, sand, clay, potassium and cation exchange capacity correctly classified 78% (r2=0.8) of the seeding sites in the 3 survival regimes. A model including sand, total soil nitrogen, calcium, mean minimum temperature in the coldest month, annual precipitation and winter precipitation correctly classified 88% (r2 = 0.8) of the seedling sites between spreads and dies. Survival regime selection prior to brush control, seedbed preparation and sowing will reduce planting failure probabilities, soil erosion and economic losses, and enhance long-term beef production.
    • Technical Note: A total urine collection apparatus for female bison and cattle

      Deliberto, T. J.; Urness, P. J. (Society for Range Management, 1995-01-01)
      A urinary collection device is described for use in metabolism studies on female bison (Bison bison) and cattle. Separating urine from feces, and collecting all urine produced by female animals in metabolism stalls present difficulties. Catheters are usually used on animals in confinement, but often with varying degrees of success. Thus, an external device designed to divert urine into collection receptacles was developed. The urine collection apparatus was used successfully in six 8-day metabolism trials conducted during 1991 and 1992.
    • Water budget for south Texas rangelands

      Weltz, M. A.; Blackburn, W. H. (Society for Range Management, 1995-01-01)
      Understanding hydrologic processes is essential to determine if water yield augmentation is possible through vegetation manipulation. Nine large non-weighing lysimeters, each 35 m2, were installed on the La Copita Research Area, 20 km south of Alice, in the eastern Rio Grande Plain of Texas. The non-weighing lysimeters were used to test the hypothesis that honey mesquite (Prosopis glandulosa var glandulosa Torr.) shrub clusters have greater evapotranspiration rates than grass interspaces. Annual evapotranspiration rates of shrub clusters and grass interspaces were found to be similar, and both were significantly greater than evaporative losses from bare soil. Surface runoff and deep drainage of water (> 2 m) from the bare soil were significantly greater than from the grass interspaces and shrub clusters. There was no drainage of water below 2 m from the shrub clusters. A total of 22 mm of water percolated below 2 m from the grass interspace during the 18 month study period. These results indicate that no net change in the water budget would occur if shrub clusters were replaced with grasses in years with below average or normal rainfall. Increasing water yield from converting shrub-dominated rangelands to grass-dominated rangelands in south Texas is marginal in this area and limited to years when winter and spring rainfall exceeds potential evapotranspiration. There is little evidence to suggest that the minimal (non-significant difference) increase in percolation and surface runoff from the grass interspaces could be reliably captured and dependably made available off-site.
    • Vegetation and soil response to grazing simulation on riparian meadows

      Clary, W. P. (Society for Range Management, 1995-01-01)
      Riparian areas have not responded consistently to grazing systems, suggesting that more knowledge is needed to explain how different areas respond to specific stresses. Several studies were conducted to determine herbaceous plant response to simulated grazing on riparian areas. One low-elevation redtop (Agrostis stolonifera L.) site in Oregon and 2 high-elevation sedge (Carex spp. L.) sites in Idaho were studied for 3 years. Several combinations of defoliation, compaction, nutrient return, and season of use were examined. The redtop community responded to spring, fall, or spring-fall defoliations by maintaining or increasing the following year's aboveground biomass production. The sedge communities maintained or decreased the following years's biomass production after spring, mid summer, or late summer defoliations. An increase in forbs occurred in 1 sedge community following spring defoliations to 1- or 5-cm residual stubble heights. The most consistent plant response among areas was reduction in height growth and biomass production following compaction treatments. When both defoliation and compaction are considered, it appears that spring, fall, or spring and fall grazing to a 5-cm stubble height on the redtop site would not decrease riparian herbage production. In contrast, when defoliation, compaction, and nutrient return effects are considered in the mountain meadow sedge-dominated communities, grazing once annually during the growing season to a 5-cm stubble height in the spring, or to a 10-cm stubble height in late summer, or at a utilization rate exceeding 30% of the total annual biomass production can reduce herbage production significantly. Results suggest that many of the land management agency riparian guidelines would maintain biomass productivity in these sedge-dominated communities.
    • Intermountain West lightning-caused fires: Climatic predictors of area burned

      Knapp, P. A. (Society for Range Management, 1995-01-01)
      An increase in continuous fine fuels promoted by the expansion of aggressive annual exotic grasses in the Intermountain West has altered the region's fire regimes, with both ecologic and economic ramifications. I examine the predictive nature of seasonal climatic variables, seasonal precipitation and temperature data up to 2 years before the actual summer fire season, to forecast the area burned by lightning-caused fires during the 13 fire seasons (1980-1992). Five climatically-distinct regions in the shadscale, sagebrush-steppe, sagebrush-semidesert, and open pine with grass communities of California, Idaho, Nevada, Oregon, and Utah were included in the analysis. The amount of associated variance ranged from 43 to 62% between area burned and seasonal climatic variables. Results show that the seasonal climate that promotes fue is distinctly regional, even in areas of similar vegetation. However, the area burned increases primarily when the climate favors the growth of annual grasses over perennial species, or promotes either cooler or wetter conditions during the previous summer (fire) seasons. These results provide land managers with additional information for making decisions on presuppression activities.
    • How much sagebrush is too much: An economic threshold analysis

      Bastian, C. T.; Jacobs, J. J.; Smith, M. A. (Society for Range Management, 1995-01-01)
      Much research concerning sagebrush control methods and forage response after control has been conducted due to the importance of sagebrush-grass dominated rangelands for livestock and wildlife in the western United States. Very little research has addressed the economic feasibility of sagebrush control at various levels of abundance. This study estimates the economic thmhold abundance of sagebrush based on forage response data from a sagebrush control experiment in Carbon County, Wyo. Forage response data are based on the difference in herbage between treated and untreated experimental units from sites ranging in initial sagebrush canopy cover from 4 to 40%. Breakeven returns per AUM were estimated for each sagebrush canopy cover level assuming 2,4-D (2,4-dichlorophenoxyacetic acid) or burning (for 28 to 40% canopy cover) as a control method with lives of control at 1S, 20, and 25 years. These breakeven returns were compared to a net lease rate of S6.13/AUM. Results indicate the economic threshold abundance of sagebrush is 12% assuming, 2,4-D as the control method and a control longevity of 25 years, but the feasible sagebrush abundance increases as longevity of control decreases. If the longevity of the control only lasts 20 years, the sagebrush abundance must be at least 20% before treating sagebrush becomes economically feasible. If the longevity of control is only 15 years, sagebrush abundance must be at least 24% canopy cover before treatment is economically viable. Given estimates of the cost of burning are almost half that of spraying with 2,4-D, all the scenarios which had enough biomass to sustain a burn (28% to 40%) indicated sagebrush controJ by fire was economically viable.
    • Optimization of rangelands management strategies under rainfall and price risks

      Carande, V. G.; Barlett, E. T.; Gutierrez, P. H. (Society for Range Management, 1995-01-01)
      Dynamic programming was used to obtain optimal management and marketing policies for stocker operations in Southeastern Colorado under different stocking rates, rainfall, and price scenarios. Simulated steer liveweights at low, moderate, and high stocking rates were incorporated with simulated steer prices to maximize the present value of net returns from the sale of 0, 50, and 100% of the steer inventory in July, August, September, or October. Two low-risk, 1 moderate-risk, and 2 high-risk scenarios were considered. The 2 low-risk scenarios were favorable rainfall-optimistic price and favorable rainfall-pessimistic price. The moderate-risk scenario was average rainfall average price. The 2 high-risk scenarios were unfavorable rainfall-optimistic price and unfavorable rainfall-pessimistic price. The highest net returns from the low-risk and moderate-risk scenarios were obtained at the high stocking rate with sales in September and October. The highest net returns from the highrisk scenarios were obtained at the moderate stocking rate with sales in September and October. Risk-averse operators who are not prepared to handle sales before October will be better off using a low stocking rate. Risk-taker operators will obtain higher net returns than risk-averse operators using a high stocking rate providing they are prepared to sell half of the herd in July if cumulative rainfall up to June is below 149 mm. If this high stocking rate is maintained beyond July, operators should sell in September independently of the amount of rainfall or the level of prices in August.
    • Postingestive feedback as an elementary determinant of food preference and intake in ruminants

      Provenza, F. D. (Society for Range Management, 1995-01-01)
      Ruminants select nutritious diets from a diverse array of plant species that vary in kinds and concentrations of nutrients and toxins, and meet their nutritional requirements that vary with age, physiological state. and environmental conditions. Thus, ruminants possess a degree of nutritional wisdom in the sense that they generally select foods that meet nutritional needs and avoid foods that cause toxicosis. There is little reason to believe that nutritional wisdom occurs because animals can directly taste or smell either nutrients or toxins in foods. Instead, there is increasing evidence that neurally mediated interactions between the senses (i.e., taste and smell) and the viscera enable ruminants to sense the consequences of food ingestion, and these interactions operate in subtle but profound ways to affect food selection and intake, as well as the hedonic value of food. The sensation of being satisfied to the full (i.e., satiety) occurs when animals ingest adequate kinds and amounts of nutritious foods, and animals acquire preferences (mild to strong) for foods that cause satiety. Unpleasant feelings of physical discomfort (i.e., malaise) are caused by excesses of nutrients and toxins and by nutrient deficits, and animals acquire aversions (mild to strong) to foods that cause malaise. What constitutes excesses and deficits depends on each animal's morphology, physiology, and nutritional requirements. This does not mean that ruminants must maximize (optimize) intake of any particular nutrient or mix of nutrients within each meal or even on a daily basis, given that they can withstand departures from the normal average intake of nutrients (i.e., energy-rich substances, nitrogen, various minerals, and vitamins). Rather, hemostatic regulation needs only some increasing tendency, as a result of a gradually worsening deficit of some nutrient or of an excess of toxins or nutrients, to generate behavior to correct the disorder. Extreme states should cause herbivores to increase diet breadth and to acquire preferences for foods that rectify maladies. From an evolutionary standpoint, mechanisms that enable animals to experience feedback, sensations such as satiety and malaise, should be highly correlated with nutritional well being, toxicosis, and nutritional deficiencies, which are directly related with survival and reproduction.