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  • Cambridge University Press
  • 1990-1994  (527)
  • 1930-1934
  • 1
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    Winter cover crops to minimize nitrate losses in intensive lettuce production (1993)
    Cambridge University Press
    Details
    Publication Date: 1993-08-01
    Description: SUMMARYA 2-year study conducted in Salinas, California in 1989–91 showed that soil nitrate (NO3–N) concentrations were reduced by cover crops during a short winter fallow period and that this practice can be compatible with year-round vegetable crop production schedules by planting and incorporating cover crops directly on the beds into which the lettuce crop will be direct seeded in the early spring. Cover crops grown the first year were oilseed radish (Raphanus sativus cv. Renova), white senf mustard (Brassica hirta cv. Martigena), white mustard (Brassica alba), Phacelia (Phacelia tanacetifolia cv. Phaci), rye (Secale cereale cv. Merced) and annual ryegrass (Lolium multiflorum). Only phacelia and Merced rye were included in the second year. In both years, all of the cover crops depleted soil NO3-N and soil moisture relative to the fallow control. Estimates of cover crop root length, based on core sampling to 60 cm soil depth, averaged 18800 m/m2 after 17 weeks of growth the first year and 12500 m/m2 after 13 weeks of growth the second year. Above-ground dry matter production averaged 449 g/m2 (12·8 g N/m2) the first year and 161 g/m2 (61 g N/m2) during a shorter growing period and under the more adverse growing conditions of the second year. Following cover crop incorporation with a rotary tiller, soil ammonium (NH4-N), N03-N and net mineralizable N (anaerobic incubation) peaked after c. 1 week, then gradually declined for 1 month. Cover-cropped plots sustained higher net mineralizable N levels than the fallow control after incorporation. Nitrate concentrations after spring rains were lower in soils left fallow during winter. The subsequent lettuce crop was not affected by cover crop treatment.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 2
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    Uranium-Series Ages of Travertines and Timing of the Last Glaciation in the Northern Yellowstone Area, Wyoming-Montana (1994)
    Cambridge University Press
    Details
    Publication Date: 1994-05-01
    Description: Uranium-series age determinations by mass spectrometric methods were done for travertines and associated carbonate veins related to clastic deposits of the last glaciation (Pinedale) in the northern Yellowstone area. Dramatic variations in the hydrologic head are inferred from variations in the elevation of travertine deposition with time and are consistent with the expected hydrologic effects of glaciation. We determine the following chronology of the Pinedale Glaciation, with the key assumption that travertine deposits (and associated carbonate veins) perched high above present thermal springs were deposited when glaciers filled the valley below these perched deposits: (1) the early Pinedale outlet glacier advanced well downvalley between 47,000 and 34,000 yr B.P.; (2) the outlet glacier receded to an interstadial position between 34,000 and 30,000 yr B.P.; (3) an extensive Pinedale ice advance occurred between 30,000 and 22,500 yr B.P.; (4) a major recession occurred between 22,500 and 19,500 yr B.P.; (5) a minor readvance (Deckard Flats) culminated after 19,500 yr B.P.; and (6) recession from the Deckard Flats position was completed before 15,500 yr B.P. This chronology is consistent with the general trend of climatic changes in the northern hemisphere as revealed by recent high-resolution ice-core records from the Greenland ice sheet.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 3
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    Theoretical Correlations and Lateral Discontinuities in the Quaternary Aminostratigraphic Record of the U.S. Atlantic Coastal Plain (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-11-01
    Description: Aminostratigraphic correlations of emergent Quaternary deposits along the U.S. Atlantic Coastal Plain have employed independent radiometric data, regional temperature history models, and assumptions regarding the nature of the preserved late Quaternary sea-level record on this passive margin. A substantial “aminostratigraphic offset” is required if regional aminozones are rigorously constrained by all available Th/U data. New insights regarding the relation of this offset to subsurface stratigraphy in the Cape Fear region of southeastern North Carolina can explain these conflicts as consequences of the highly incomplete post-Cretaceous depositional record of the region. Southward projection of theoretical aminostratigraphic correlation trends suggests that stage 5 correlative marine units are rarely preserved on the emergent portion of the Coastal Plain between Cape Lookout and central South Carolina and that samples of this age would be most frequently found in this region only as fragmentary (and/or reworked) deposits on the inner shelf or in the subsurface of modern barrier islands. If this hypothesis is correct, then the accuracy of several Th/U coral dates from the South Carolina Coastal Plain must be questioned, along with sea-level, tectonic, and paleoclimatic conclusions derived from these dates.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 4
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    14C Dating of Laser-Oxidized Organics (1993)
    Cambridge University Press
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    Publication Date: 1993-01-01
    Description: We used a continuous krypton ion laser to rapidly oxidize milligram-sized fragments of coniferous driftwood of known ages, and dated the resulting carbon dioxide by accelerator mass spectrometry (AMS). AMS 14C ages of non-pretreated young wood from different parts of two logs were within 10% of the ages of conventionally determined alkaline insoluble fractions. The age of the oldest whole wood measured after laser oxidation was within the error ranges of conventional values.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 5
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    Accelerator Mass Spectrometry of 14C at the Australian National University (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-01-01
    Description: A 14C measurement capability has been developed on the 14UD accelerator at the Australian National University. At present, this system operates on a medium-precision, low-throughput basis with slow cycling between isotopes. We describe unusual features of the system, and review preliminary experience with this mode of operation, in sample preparation, and with a recently installed injection system.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 6
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    Reaction in a scalar mixing layer (1991)
    Cambridge University Press
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    Publication Date: 1991-12-01
    Description: Reaction in a scalar mixing layer in grid-generated turbulence is studied experimentally by doping half of the flow with nitric oxide and the other half with ozone. The flow conditions and concentrations are such that the chemical reaction is passive and the flow and chemical timescales are of the same order. Conserved scalar theory for such flows is outlined and further developed; it is used as a basis for presentation of the experimental results. Continuous measurements of concentration are limited in their spatial and temporal resolution but capture sufficient of their spectra for adequate second-order correlations to be made. Two components of velocity have been measured simultaneously with hot-wire anemometry. Conserved scalar mixing results, deduced from reacting and non-reacting measurements of concentration, show the independence of concentration level and concentration ratio expected for passive reacting flow. The results are subject to several limitations due to the necessary experimental compromises, but they agree generally with measurements made in thermal mixing layers. Reactive scalar statistics are consistent with the realizability constraints obtainable from conserved scalar theory where such constraints apply, and otherwise are generally found to lie between the conserved scalar theory limits for frozen and very fast chemistry. It is suggested that Toor's (1969) closure for the mean chemical reaction rate could be improved by interpolating between the frozen and equilibrium values for the covariance. The turbulent fluxes of the reactive scalars are found to approximately obey the gradient model but the value of the diffusivity is found to depend on the Damköhler number. © 1991, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 7
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    Westlothiana lizziae from the Viséan of East Kirkton, West Lothian, Scotland, and the amniote stem (1993)
    Cambridge University Press
    Details
    Publication Date: 1993-01-01
    Description: Westlothiana lizziae is known from the Brigantian of East Kirkton, Scotland. The skull resembles that of later amniotes in the large size of the parietal, the apparent loss of the intertemporal, and the absence of a squamosal notch, palatal fangs and labyrinthine infolding of the marginal teeth, but is primitive in the absence of a transverse flange of the pterygoid. The individual trunk vertebrae resemble those of amniotes; large intercentra are retained, but the neural arch is fused to the centrum. A surprising feature is the presence of 36 presacral vertebrae, as is the relative size of the very small but highly ossified limbs. The humerus is much shorter than the femur, but similar in configuration to that of early amniotes. There are three proximal tarsals as in primitive tetrapods, but an amniote phalangeal count. The presence of massive dorsal as well as ventral scales is a more primitive feature than that of most anthracosaurs.Westlothiana is ‘reptiliomorph’, and is judged to be a stem-group amniote on features of the skull roof, the absence of an otic notch, the gastrocentrous vertebrae and the pedal phalangeal formula. It has not, however, reached the amniote condition in the structure of the tarsus, and the palate is more primitive than that of both early amniotes and the ‘diadectomorphs’.
    Print ISSN: 1755-6910
    Electronic ISSN: 1755-6929
    Topics: Geosciences
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  • 8
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    Apex and ear development in relation to the number of grains on the main-stem ears in spring barley (Hordeum distichon) (1991)
    Cambridge University Press
    Details
    Publication Date: 1991-08-01
    Description: SUMMARYApex and ear development in nine spring barley genotypes were studied at two sites in southern Spain in 1988. The genotypes were grouped into medium and early types, depending on the time from sowing to anthesis. Medium genotypes had significantly more spikelet primordia than early ones at both sites. Spikelet mortality was similar between genotypes and sites, resulting in a higher final number of grains/ear in the medium than the early genotypes.There was a positive correlation between the maximum number of spikelet primordia and the duration of three stages of apical development: lemma-, stamen- and awn-primordia. Negative correlations were observed between spikelet mortality and the duration of certain developmental phases of the ear.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 9
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    Simplified rotational grazing management of dairy cows: effects of rates of stocking and concentrate (1991)
    Cambridge University Press
    Details
    Publication Date: 1991-06-01
    Description: SUMMARYAn experiment was carried out in Normandy between 1986 and 1988 over c. 6 months in each year, using a simplified rotational grazing technique (two paddocks in spring, four in autumn) with a total of 162 high-yielding cows (mean milk yield of 30·0 kg/day at turn-out). Three stocking rates, designated control (C: 2·3 cows/ha over the total area of the system), moderate (M: 2·6 cows/ha = 115% of C) and high (H: 3·0 cows/ha = 130% of C), were compared at two rates of concentrate supplement, 3·7 kg/cow per day and 0·5 kg/cow per day. Individual milk yield differed by a non-significant 5% between the extreme stocking rates (21·3 v. 20·3 kg fat-corrected milk (FCM) for treatments C and H, respectively). Milk production/ha was 23% greater in the H treatment (9816 v. 7970 kg FCM for H and C, respectively). Concentrate supplementation led, on average, to a 9% milk yield improvement (21·8 v. 20·0 kg FCM for high and low rates, respectively), i.e. a mean efficiency of 0·6 kg FCM/kg supplement. This response tended to be greater in the higher-yielding cows and for the high stocking rate. The sward measurements contributed to a better understanding of herbage utilization by the cows.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 10
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    PCB congeners, DDTs and hexachlorobenzene in Antarctic fish from Terra Nova Bay (Ross Sea) (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-06-01
    Description: Chlorinated hydrocarbons were measured in seven species of Antarctic fish (Pagothenia bernacchii, P. hansoni, Trematomus centronotus, T. newnesi, Chionodraco hamatus, Cygnodraco mawsoni, and Gymnodraco acuticeps) from in the Ross Sea near Terra Nova Bay (74°40'S 164°10'E). Hexachlorobenzene (HCB), pp' DDT and its derivatives DDE and DDD, and about 20 congeners of polychlorinated biphenyls (PCBs)were found in muscle and liver. Levels of pp′ DDE were positively correlated with body length in P. bernacchii and the plot of concentrations showed higher values in males than females of the same body weight class. The results confirm the presence of these chlorinated hydrocarbons in the Antarctic marine food chain and an increase of PCBs with respect to DDTs. The “fingerprint” of C. hamatus is different from that of other Antarctic organisms and of fish from other parts of the world, suggesting possible metabolic differences.
    Print ISSN: 0954-1020
    Electronic ISSN: 1365-2079
    Topics: Biology , Geography , Geosciences
    Published by Cambridge University Press
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