Now showing items 15777-15796 of 20719

    • Rudjer Bošković Institute Radiocarbon Measurements XVII

      Horvatinčić, Nada; Krajcar Bronić, Ines; Obelić, Bogomil; Barešić, Jadranka (Department of Geosciences, The University of Arizona, 2012-05-04)
      This paper presents dating results of geological (speleothems, tufa, soil, and sediment), biological (mollusks and botanical), as well as hydrogeological samples from Croatia, Slovenia, Bosnia and Herzegovina, Turkey, and China. Included are results of samples measured by gas proportional counting (GPC) in the Zagreb lab until abandonment of this technique in 2007, as well as results of several series measured by both GPC and liquid scintillation counting (LSC) methods.
    • Rules of Origin in International Trade Treaties: Toward the FTAA [Article]

      Silveira, Mariana C. (The University of Arizona James E. Rogers College of Law (Tucson, AZ), 1997)
    • Rules of Origin: Considerations for Investment and Trade in North America [Article]

      Sandstrom, Mark R. (The University of Arizona James E. Rogers College of Law (Tucson, AZ), 1999)
    • Rumen Digestive Capability of Zebu Steers in Wet and Dry Seasons

      Hansen, R. M. (Society for Range Management, 1986-03-01)
      Most authors have suggested that the rumen's capability to digest foodstuff is influenced by the conditions resulting from microbial populations which are regulated by composition of the diets. Presumably the greatest ecological differences within the rumens of cattle grazing tropical semiarid range plants would be during wet and dry seasons. Rumen dry matter digestion indexes were determined by the nylon bag technique during wet and dry seasons for 4 different plant materials at the National Range Research Station near Kiboko, Kenya. The rumen digestive capability of 3 Zebu steers was not different between wet and dry seasons when these rumen fistulates selected their own foods from natural range vegetation.
    • Ruminal Digestion Consistency of Zebu Cattle

      Hansen, R. M.; Whittington, D. L.; Child, R. D.; Wanyama, J. M. (Society for Range Management, 1984-05-01)
    • Rumuruti chondrites: Noble gases, exposure ages, pairing, and parent body history

      Schultz, L.; Weber, H. W.; Franke, L. (The Meteoritical Society, 2005-01-01)
      In this paper, we present concentration and isotopic composition of the light noble gases He, Ne, and Ar as well as of 84Kr, 132Xe, and 129Xe in bulk samples of 33 Rumuruti (R) chondrites. Together with previously published data of six R chondrites, exposure ages are calculated and compared with those of ordinary chondrites. A number of pairings, especially between those from Northwest Africa (NWA), are suggested, so that only 23 individual falls are represented by the 39 R chondrites discussed here. Eleven of these meteorites, or almost 50%, contain solar gases and are thus regolithic breccias. This percentage is higher than that of ordinary chondrites, howardites, or aubrites. This may imply that the parent body of R chondrites has a relatively thick regolith. Concentrations of heavy noble gases, especially of Kr, are affected by the terrestrial atmospheric component, which resides in weathering products. Compared to ordinary chondrites, 129Xe/132Xe ratios of R chondrites are high.
    • Runoff and Erosion After Cutting Western Juniper

      Pierson, Fredrick B.; Bates, Jon D.; Svejcar, Tony C.; Hardegree, Stuart P. (Society for Range Management, 2007-05-01)
      Western juniper (Juniperus occidentalis spp. occidentalis Hook.) has encroached on and now dominates millions of acres of sagebrush/bunchgrass rangeland in the Great Basin and interior Pacific Northwest. On many sites western juniper has significantly increased exposure of the soil surface by reducing density of understory species and surface litter. We used rainfall and rill simulation techniques to evaluate infiltration, runoff, and erosion on cut and uncut field treatments 10 years after juniper removal. Juniper-dominated hillslopes had significantly lower surface soil cover of herbaceous plants and litter and produced rapid runoff from low-intensity rainfall events of the type that would be expected to occur every 2 years. Direct exposure of the soil to rainfall impacts resulted in high levels of sheet erosion (295 kg ha-1) in juniper-dominated plots. Large interconnected patches of bare ground concentrated runoff into rills with much higher flow velocity and erosive force resulting in rill erosion rates that were over 15 times higher on juniper-dominated plots. Cutting juniper stimulated herbaceous plant recovery, improved infiltration capacity, and protected the soil surface from even large thunderstorms. Juniper-free plots could only be induced to produce runoff from high-intensity events that would be expected to occur once every 50 years. Runoff events from these higher-intensity simulations produced negligible levels of both sheet and rill erosion. While specific inferences drawn from the current study are limited to juniper-affected sites in the Intermountain sagebrush steppe, the scope of ecosystem impacts are consistent with woody-plant invasion in other ecosystems around the world. 
    • Runoff and erosion in intercanopy zones of pinyon-juniper woodlands

      Wilcox, B. P. (Society for Range Management, 1994-07-01)
      In semiarid pinyon-juniper environments, the principal mechanisms of redistribution of water, sediments, nutrients, and contaminants are runoff and erosion. To study the phenomena underlying these mechanisms, we established six 30-m2 plots, in intercanopy zones, for monitoring over a 2-yr period (1991-1993). Two of the plots were severely disturbed; 4 were undisturbed. We measured the most runoff from these plots during mid summer (generated by intense thunderstorms) and late winter (from snowmelt and/or rain-on-snow). Runoff accounted for 10 to 28% of the water budget over the 2-yr period—a higher proportion than that observed in most other pinyon-juniper woodlands, which is probably explained by the smaller scale as well as the higher elevation of our study area. Runoff accounted for 16% of the summer water budget the first year, with above-average precipitation (and thereby higher soil moisture content) and 3% the second year, when precipitation was about average. Winter runoff was substantial both years as measured on the small scale of our study (no winter runoff was observed in the nearby stream channel). Interestingly, even though precipitation was lower the first winter, runoff was higher. This may be because snowmelt set in about 20 days earlier that year—while the soils were still thoroughly frozen, inhibiting infiltration. Differences between disturbed and undisturbed plots were most evident in the summer: both runoff and erosion were substantially higher from the disturbed plots. On the basis of our observations during this study, we suggest that the following hypotheses proposed about runoff and erosion in other semiarid landscapes are also true of pinyon-juniper woodlands: (1) Runoff amounts vary with scale: runoff decreases as the size of the contributing ares increases and provides wore opportunities for infiltration. (2) The infiltration capacity of soils is dynamic; it is closely tied to soil moisture content and/or sod frost conditions and is a major determinant of runoff amounts. (3) Soil erodibility follows an annual cycle; it is highest at the end of the freeze-thaw period of late winter and lowest at the end of the summer rainy season, when soils have been compacted by repeated rainfall.
    • Runoff and Reservoir Quality for Livestock Use in Southeastern Montana

      Soiseth, R. J. (Society for Range Management, 1975-09-01)
      Runoff and reservoir waters from the Pierre Shale Plains in southeastern Montana were fresh (< 1,000 mg/liter of TDS) to slightly saline (1,000 to 3,000 mg/liter of TDS) and were rated good to fair for livestock use. However, as water levels drop, mainly through evaporation, waters in some reservoirs could become moderately saline (3,000 to 10,000 mg/liter of TDS) and should not be used if other waters are available.
    • Runoff and Sediment Yields from Runoff Plots on Chained Pinyon-Juniper Sites in Utah

      Gifford, G. F. (Society for Range Management, 1973-11-01)
      Runoff and sediment production from a chained pinyon-juniper site in both southeastern and southwestern Utah was measured from about June 6 to October 1 over a 5-year period (1968-1972) using .04-hectare (0.11 acre) runoff plots. Treatments evaluated included chained-with-debris-windrowed, chained-with-debris-in-place, and natural woodland. All treatments were fenced to exclude livestock. Runoff events occurred at both sites during only 2 years (1968, 1970) of the study. Results indicate that chained-with-windrowing plots yield from 1.2 to 5 times more water during a runoff event than respective woodland plots. Runoff from debris-in-place plots was equal to or less than that measured from the natural woodland for all storms. Runoff data and sediment indexes indicate that when runoff exceeds about 0.1 cm from the woodland, from 1.6 to 6 times more sediment can be expected from windrowed sites than from adjacent woodland. Sediment yields from debris-in-place sites were similar to those from adjacent unchained woodland for all storms during this study.
    • Runoff and soil loss in undisturbed and roller-seeded shrublands of semiarid Argentina

      Aguilera, M. O.; Steinaker, D. F.; Demaria, M. R. (Society for Range Management, 2003-05-01)
      Vegetation influences runoff and soil losses in semiarid environments. In shrublands of Central Argentina, grazing has resulted in a reduction of plant cover, an increase in the proportion of bare soil, and eroded soils. Patterns of runoff and soil losses affected by seeding cultivated grasses were evaluated. We investigated the effects of roller-seeding of Cenchrus ciliaris L and the influence of microsite cover-type on the dynamics of water erosion. Evaluated cover-types were: bare soil, shortgrass cover, and tallgrass cover. Evaluations were performed 2 growing seasons after roller-seeding. The experimental design was a split-plot, replicated 3 times using a portable rainfall simulator. After simulation runs of 45 min at an average rate of 110 mm hour-1, runoff of tallgrass cover was the least, whereas bare soil and shortgrass cover had similar values (ca. 60%). However, both types of grass cover reduced soil splash compared to the bare soil cover-type. An exponential function between runoff and soil loss suggested that increasing runoff beyond 60% produced an abrupt rising of sediment loss. Roller-seeding did not influence runoff or sediment loss at the microsite-scale. Nevertheless, roller-seeding reduced the proportion of area covered by microsites prone to erosion (bare soil and shortgrass cover-types) at the whole plot level. We propose that any management tool that promotes the replacement of bare soil and shortgrasses by tallgrasses should reduce runoff and increase forage productivity via amelioration of hydrologic conditions of the rangeland site. Conversely, overgrazing will result in more bare soil, increasing runoff, and further intensifying the loss of sediments by detachment.
    • Runoff Farming

      Fink, Dwayne H.; Ehrler, William L. (Society for Range Management, 1986-04-01)
    • Runoff from simulated rainfall in 2 montane riparian communities

      Frasier, G. W.; Trlica, M. J.; Leininger, W. C.; Pearce, R. A.; Fernald, A. (Society for Range Management, 1998-05-01)
      Riparian ecosystems are the final terrestrial zone before runoff water enters a stream. They provide the last opportunity to decrease non-point source pollution delivery to streams by removing sediments from overland water flow from uplands and roads. To quantify processes of sediment transport, filtration and deposition, it is necessary to determine runoff characteristics for the area. A rotating boom rainfall simulator was used to evaluate the effects of 3 vegetation height treatments (control, 10-cm stubble height, and clipped to the soil surface) in 2 montane riparian plant communities (grass and sedge) on runoff characteristics. Each rainfall simulation event consisted of 2 phases, a dry run of about 60 min followed by a wet run approximately 30 min later. There were no differences in time to runoff initiation for either dry or wet runs that could be attributed to vegetation height treatments for either plant community. It usually required more time for runoff to be initiated in the sedge community compared to the grass community. Generally, there were lower equilibrium runoff percentages from dry runs in the sedge community compared with the grass community. These differences were less during wet runs. Several runoff parameters had characteristics of runoff from water repellent soils. The organic layer on the soil surface exhibited signs of water repellency that reduced the water infiltration rate during the initial stages of a rainfall simulation. These results indicate that runoff and infiltration processes in the surface organic horizon of riparian zones may not respond in the classical manner. This characteristic has important implications if criteria developed in areas with less organic matter on the soil surface are used to manage overland flow in the zone. Additional studies are needed to fully describe infiltration and runoff processes in riparian plant communities.
    • Runoff from Small Desert Watersheds

      Woolhiser, D. A.; Schwalen, H. C.; Agricultural Engineering Department; Agricultural Engineering Department (College of Agriculture, University of Arizona (Tucson, AZ), 1957)
    • Runoff prediction from sagebrush rangelands using water erosion prediction project (WEPP) technology

      Wilcox, B. P.; Sbaa, M.; Blackburn, W. H.; Milligan, J. H. (Society for Range Management, 1992-09-01)
      Runoff prediction is an important component of any process-based soil erosion model. In this paper we evaluate the runoff prediction capabilities of a new soil erosion model, WEPP, on sagebrush rangelands. Particular attention was given to the parameter estimation techniques used in WEPP to predict infiltration. Runoff volume predicted by WEPP is based on the Green and Ampt infiltration equation. Predicted runoff was compared to observed runoff from 90 large plot rainfall simulation experiments on sagebrush rangelands. There was a poor correlation between predicted and observed runoff when the Green and Ampt parameters were estimated using the parameter estimation techniques. Runoff prediction was improved when parameters were determined from field measurements. Additional refinement of the Green and Ampt parameterization techniques is needed for continued improvement of WEPP.
    • Runoff Water Quality from Varying Land Uses in Southeastern Arizona

      Schreiber, H. A.; Renard, K. G. (Society for Range Management, 1978-07-01)
      Surface runoff waters from three kinds of activity on rangeland were examined for suspended solids and some indicator chemical constituents. We compared ungrazed brush-covered rangeland with recently subdivided rangeland, originally and still partly brush-covered, but whose surface was disturbed by man's urbanizing influence. Water quality indicators showed the urbanized watersheds had poorer water quality. Comparisons between the two brush-covered watersheds and a third-grass-covered and grazed-were made only on the runoff water's dissolved constituents. Despite the grazing activity, the waters were of better quality. A contrast in the geology between the grass and brush areas suggested that mineral sources affected qualitative changes in the dissolved solids. Calcareous soils produced waters higher in Ca and total dissolved solids and lower in other cations. Phosphate in runoff averaged higher from the grass-covered, noncalcareous area than from the brush-covered calcareous watershed. We hypothesize now that the phosphate originated from soil sources, rather than from grazing activity. Nitrate levels were comparable in runoff from all the nonurban areas, but increased in runoff from the semiurban area. Thus, the nonagricultural complex of activities associated with a housing development was more detrimental to water quality than those from undisturbed or grazed rangelands.
    • Rural & Urban Residents... Differ in their Knowledge & Attitudes about the use of Insecticides

      Ryan, J.; Stoller, R.; Moore, L.; Soils, Water and Engineering Department; Agricultural Education; Department of Entomology (College of Agriculture, University of Arizona (Tucson, AZ), 1974)
    • Rural Homemakers Plan Programs

      Stewart, Jean M. (College of Agriculture, University of Arizona (Tucson, AZ), 1950)
    • Rural Poverty in Arizona

      Ayer, Harry; Weidman, Joe; Anderson, Terry; Department of Agricultural Economics; Urban Planning Department; Department of Agricultural Economics (College of Agriculture, University of Arizona (Tucson, AZ), 1972)