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  • 1
    Electronic Resource
    Electronic Resource
    Seasonal differences in the soil water balance under perennial and annual pastures on an acid Sodosol in southeastern Australia (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Replacement of native deep-rooted grasses by shallow-rooted ones has resulted in greater losses of water and nitrogen by drainage. To counter this effect we have tested the hypothesis that liming, and the conversion of annual grass pastures to perennial grass pastures, could improve the sustainability of grazing systems in the high rainfall zone (〉 600 mm per annum) in southeastern Australia, through better use of water and nitrogen. A field experiment consisting of sixteen 0.135 ha (30 m × 45 m) grazed paddocks representing four pasture combinations (annual pasture (mainly Lolium rigidum) without lime (AP–); annual pasture with lime (AP+); perennial pasture (mainly Phalaris aquatica) without lime (PP–), and perennial pasture with lime (PP+)) was carried out from 1994 to 1997 on an acid Sodosol (Aquic Hapludalf) in southern New South Wales, Australia. Measurements were made of surface runoff, subsurface flow (on top of the B horizon) and soil water content. The results showed that perennial grass pastures, especially PP+, extracted approximately 40 mm more soil water each year than the annual grass pastures. As a result, surface runoff, subsurface flow and deep drainage were at least 40 mm less from the perennial pastures. These measurements were further supported by a simulation of soil water deficit and deep drainage for AP– and PP+ paddocks, using 10 years' past meteorological records. Overall, the results suggested that well-grown, phalaris-based pastures could reduce recharge to groundwater and make pastoral systems more sustainable in the high rainfall zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2001.00386.x
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Mineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)-based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl2) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO3– concentrations.The soil contained more mineral N in autumn (64–133 kg N ha−1 to 120 cm) than in spring (51–96 kg N ha−1), with NO3– comprising 70–77%. No NO3– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l−1 as NO3– initially but 〈 1 mg N l−1 by spring. Nitrate-N concentrations at 120 cm ranged between 2 and 22 mg N l−1 during winter. Losses of NO3– were small in surface runoff (0–2 kg N ha−1 year−1). In 1995, 9–19 kg N ha−1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha−1 in 1995 and 4–10 kg N ha−1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha−1 year−1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha−1 year−1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha−1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2001.00387.x
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  • 3
    Electronic Resource
    Electronic Resource
    Multichannel estimation of frequency-department Q from VSP data (1997)
    Oxford, U.K. and Cambridge, USA : Blackwell Science Ltd
    Geophysical prospecting 45 (1997), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A Method of estimating attenauation from the first arrivals of VSP data is presented. The motivation is the desire to investigate the effects of scattering on wave propagation, and particularly the apparent attenuation and associated phase delay due to fine layering (the O'Doherty-Anstey effect).In order to take account of the frequency dependence of the predicted scattering attenuation, and to provide robust statistics for the estimates, a beam-forming method is used to measure the attenuation. This simularaneously estimates the slowness and polarization angle of the different wave modes, and results in attenuation measurements which are largely free of interference from reflected and mode-converted energy. By working in the frequency domain and measuring amplitude decay with depth, the frequency dependence of the attenuation is also accounted for. The beam-forming algorithm works in two passes, the first of which estimates slownesses and polarization angles over a small depth range, while the second uses the information from the first pass over a larger depth range to estimate attenuation.An approximate error analysis of the method shows that the standard variance of the estimated Q values is proportional to Q2 and the data quality (measured by its spectral coherence), and inversely proportional to the square of the analysis depth range and the square of the frequency. Hence the depth resolution is traded against the stability of the results.The method is applied to a zero-offset three-component VSP. The data are of good quality, with a bandwidth ranging from 180 Hz in the shallow part to 100 Hz in the deepest part. Stable results were obtained using a 450 m depth range. Above about 50 Hz, there is little evidence of frequency dependence in the attenuation. There is a clear division in depth into layers of higher and lower attenuation, with values of Q typically between 50 and 200. Below 50 Hz, however, attenuation increases rapidly with decreasing frequency throughout the depth range, with values of Q of less than 10 at 15 Hz. This behaviour appears anomalous since on physical grounds we expect very high values of Q at low frequency, and we have no explanation for these observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1997.tb02272.x
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  • 4
    Electronic Resource
    Electronic Resource
    The utility of Burns’s equation to describe solute movement through soil under various boundary and initial conditions (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Burns’s equation for describing solute movement through soil is attractive because it is simple and predicts adequately in many instances. However, the assumptions implicit in it are not inconsistent with preferential solute flow. We have explored the consequences of this by leaching initially resident chloride and surface-applied tritium and nitrate through 250-mm-long intact cores of a silt loam soil. The applied flow rates of 3 and 5 mm h−1 (realistic rainfall intensities) produced unsaturated soil conditions, except near the base where free water dripped out. Burns’s equation described the movement of the three solutes fairly successfully with the water content parameter having values between 0.29 and 0.48, similar to the actual volumetric water content of 0.47.The leaching of resident chloride to 450-mm-deep mole drains in the field was also successfully simulated using Burns’s equation. However, simulation of the leaching of bromide applied to the soil surface as a solid salt was problematic. This resulted from uncertainty as to whether to treat the application as a pulse input to the flux or resident concentration. The observed behaviour fell about midway between the simulations for these contrasting initial conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1999.00262.x
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