• Importance of predation and germination on losses from the seed bank of calden (Prosopis caldenia)

      Lerner, P.; Peinetti, R. (Society for Range Management, 1996-03-01)
      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.
    • Interrelationships of forage and steer growth dynamics on wheat pasture

      Pinchak, W. E.; Worrall, W. D.; Caldwell, S. P.; Hunt, L. J.; Worrall, N. J.; Conoly, M. (Society for Range Management, 1996-03-01)
      Little information is available comparing animal performance or stocking stability for different wheat (Triticum aestivum L.) cultivars. Wheat is annually planted on 10 million ha in the Southern Great Plains. Our objective was to determine the effects of wheat cultivars with different forage production potentials on the seasonal and total productivity of steers. 'Lancota' and 'NK Pro 812'(NK 812) were planted in September 1987 and October 1988 at the W.T. Waggoner Ranch in north Texas. Hereford steers (Bos taurus L.), 220 to 233 kg. were grazed from November 1987 to May 1988 and December 1988 to April 1989. Seasonal and total forage production and disappearance were affected (p<0.05) by season and year. Cultivar did not affect forage production and disappearance. Steer average daily gain (ADG), gain head-1, and gain ha-1 were significantly affected by year, season, year x season, and cultivar x season interactions. Steer gain ha-1 was lower (P<0.10) in year 2 than year 1 for both cultivars. Both gain head-1 and gain ha-1 were lower (P<0.10) on NK 812 than Lancota in year 2. Season long gain ha-1 followed similar trends to gain head-1. A season x year interaction (P<0.05) occurred because NK 812 matured earlier and was less winter hardy than Lancota. Across years steer ADG increased with herbage allowance up to 27.3 kg 100 kg BW-1 Day-1 and further increases in herbage allowance had limited effect on steer ADG. Yearly variation in environmental conditions had greater effects on steer performance and forage production than cultivar.
    • Karoobush defoliation in the arid Karoo

      Du Toit, P. C. V. (Society for Range Management, 1996-03-01)
      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.
    • Productivity of Cenchrus ciliaris in relation to rain-fall and fertilization

      Rao, A. S.; Singh, K. C.; Wight, J. R. (Society for Range Management, 1996-03-01)
      Forage for livestock is always in short supply in the arid zone of India. Cenchrus ciliaris L. is one of the major forage grasses cultivated in this region. We studied its productivity in relation to rainfall and nitrogen (N) and phosphorus (P) fertilization in the Indian arid zone at Jodhpur during 1983 to 1992. Factorial combinations of 4 rates of N (0, 20, 40, and 60 kg ha-1) and 3 rates of P (0, 15, and 30 kg ha-1) were applied annually. Twenty kg N ha-1 was the most effective fertilizer treatment, increasing average annual forage yields from 942 to 1,785 kg ha-1 over the 10 year study with significant yield increases occurring in 7 of the 10 years. Yield responses to N rates greater than 20 kg ha-1 occurred only during the last 3 years of the study and then only at the 60 kg ha-1 rate with either 15 or 30 kg P ha-1. Yields reached maximum levels on both the nonfertilized and fertilized plots with between 180 and 250 mm of growing-season rainfall.
    • Seasonal changes of herbage biomass on the fescue prairie

      Willms, W. D.; Adams, B. W.; Dormaar, J. F. (Society for Range Management, 1996-03-01)
      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.
    • Seedbed and seeder options for old world bluestem establishment

      Berg, W. A.; Dewald, C. L.; Sims, P. L. (Society for Range Management, 1996-03-01)
      Seedbeds of graze-out wheatland and herbicide-killed wheat (Triticum aestivum L.) were evaluated as were use of a grass drill and the Woodward chaffy grass seeder for Old World bluestem (Bothriochloa ischaemum (L.) Keng) establishment. Seedings were made in 3 consecutive years in western Oklahoma. Steer grazing days on the seedbed treatments, seedling establishment, and second year grass herbage production were measured. Adequate stands were established in either seedbed. Economics favor the graze-out wheat seedbed treatment which produced an average of 189 steer grazing days ha-1 year-1. Adequate stands were established with either the grass drill or the Woodward seeder. Denser stands were usually established with the Woodward seeder—this was unexpected since it is a broadcast seeder. Results with the Woodward seeder are attributed to a requirement for very shallow planting of Old World bluestem and the protected environment of wheat drill furrows and wheat residue. Seedbeds of graze-out wheatland are recommended for Old World bluestem establishment in the Southern Plains.
    • Semi-arid warm-season grass yield and nutritive value in Argentina

      Stritzler, N. P.; Pagella, J. H.; Jouve, V. V.; Ferri, C. M. (Society for Range Management, 1996-03-01)
      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.
    • Soil nutrients and salinity after long-term grazing exclusion in a flooding Pampa grassland

      Chaneton, E. J.; Lavado, R. S. (Society for Range Management, 1996-03-01)
      Soil organic C, total N, extractable P, and salinity were evaluated after 12-16 years of protection from grazing in 2 native grassland sites which differed in frequency of soil waterlogging in the Flooding Pampa of Argentina. We tested the hypothesis that flooding regime would affect the impact of grazing on soil chemical properties. We sampled soil to 10-cm depth in adjacent grazed and ungrazed plots in each site, and assessed the percentage dissimilarity (PD) in vegetation composition among pastures. Grazing condition significantly interacted with site (p<0.001) in affecting topsoil C, N, and salinity. Soil C and N were higher in grazed grassland (C = 4.8%; N = 0.42%) than in long-term exclosure (C = 3.7%; N = 0.35%) for the more frequently flooded, lowland site, hut did not vary between grassland plots in the upland site (C = 3.1%; N = 0.29%). Soil electrical conductivity (E.C.) was low in both ungrazed plots (< 2 dS/m), yet in grazed condition salinization was higher in the upland (E.C.= 6.85 dS/m) than in the lowland site (3.88 dS/m). Soil extractable P did not change in any consistent way with grazing treatment. Grazing apparently amplified differences in soil chemistry between lowland and upland sites, while differences in botanical composition between topographical positions were smaller for grazed (PD = 44 %) than for ungrazed (64 %) grassland. Moreover, contrasting responses between sites occurred for various soil parameters, whereas compositional differences between grazed and ungrazed plots were similar in each site (PD = 65%). Thus, soil-vegetation changes in response to grazing appeared to be loosely coupled in this rangeland ecosystem
    • Tallgrass prairie vegetation response to spring burning dates, fertilizer, and atrazine

      Mitchell, R. B.; Masters, R. A.; Waller, S. S.; Moore, K. J.; Young, L. J. (Society for Range Management, 1996-03-01)
      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.
    • Viewpoint: Sustaining rangeland landscapes: a social and ecological process

      Huntsinger, L.; Hopkinson, P. (Society for Range Management, 1996-03-01)
      Sustaining rangeland ecosystems is as much a social process as an ecological one. It requires application of many of the same principles as those used in planning for wildlife reserves, but the tenets of conservation biology need to be applied to conserve social as well as ecological structural elements and processes. For some rangelands, a crucial element in a sustainable, culturally meaningful, and ecologically rich landscape is ranching, which is at once a collection of ecological processes and interactions, and an expression of human community. Results of several surveys and studies are used to highlight the "culture clashes" that occur at the ecological and social edges of landscape elements. Unfortunately, differing expectations of what conserved areas should be like has hindered the creation of alliances between environmentalists and ranchers that might prevent the degradation of the landscape by uncontrolled residential and urban development. In one California case, successful planning and alliance building led to the conservation of ranchlands. Zoning, conservation easements, political and financial support for the livestock industry, community leadership, and recognition of the heritage value of rural lifeways all played a part in this success. Similar patterns have been noted in other parts of the West. To conserve some of the most productive and biodiverse rangeland landscapes, ranching must not just be tolerated as a means to an environmental end, but valued and planned for, ecologically, socially, and economically. Rangeland professionals have an important role to play in the development of sustainable social relationships that support sustainable rangelands.