Abstracts

Chan, D., Kodikara, J., et al. 2007, Data Analysis and Laboratory Investigation of the Behaviour of Pipes Buried in Reactive Clay, Common Ground: 10th Australia New Zealand Conference on Geomechanics, Brisbane, Carillon Conference Management Pty Ltd for the Australian Geomechanics Society. pp. 206-211.

Buried pipe failures due to ground movement is a common problem which leads to the loss of water or gas supply in urban areas. Statistical analysis of pipe asset data indicates that pipe failure is correlated to ground movement caused by the shrinking and swelling of reactive soils due to seasonal climatic variations. This problem was studied in a large scale laboratory experiment, where a two meter long polyethylene pipe is buried in a box filled with reactive clay soil. The clay soil was subjected to capillary wetting conditions by supplying water to the bottom of the box, simulating seasonal climatic change by increasing the soil moisture content. Deformation of the pipe during soil movement was measured by a series of strain gauges attached to the pipe. Soil temperature, moisture content and suction were measured using the thermocouples, theta probes and thermal matric sensors respectively. This paper reports the statistical analysis of field data and the experimental setup for studying buried pipe failures.

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Edwards, I., Gillespie, A., et al. 2005, 'Spatial Distribution of Ammonium and Calcium in Optimally Fertilized Pine Plantation Soils', Soil Science Society of America Journal, vol. 69, pp. 1813-1821.

Commercial timber production is increasingly reliant on long-term fertilization to maximize stand productivity, yet we do not understand the extent to which this practice homogenizes soil properties. The effects of 16 yr of optimal fertilization and optimal fertilization with irrigation (fertigation) on forest floor depth, pH, total organic carbon (TOC) and total nitrogen (TN) content, and concentrations of potentially plant available NH₄⁺, Ca²⁺, Mg²⁺, and Al³⁺ in the fine root zone of monoculture loblolly pine (Pinus taeda L.) stands in North Carolina were examined. Generally, optimal fertilization significantly increased forest floor depth and the concentrations of potentially plant available NH₄⁺, Ca²⁺, and Mg²⁺. No significant effects on TOC or TN were observed. However, differences were observed between optimally fertilized and fertigated treatments. Specifically, fertilization alone tended to retain more Ca²⁺ and Mg²⁺ in the root zone and to increase pH more than fertigation. Semivariogram analysis indicated optimal fertilization generally lead to a significant increase in the effective spatial autocorrelation ranges of NH₄⁺ and Ca²⁺ at the end of the growing season, from approximately 25 m in controls to more than 100 m. However, optimally fertilized and fertigated plots differed in terms of their NH₄⁺ and Ca²⁺ spatial autocorrelation ranges, with the ranges in fertigated plots being 1.5- to 2-fold greater. A comparison of kriged maps of NH₄⁺ and Ca²⁺ availability in fall 2000 and spring 2001 suggested that the spatial distribution of Ca²⁺, which has not been added to these soils for 6 yr, was stable, whereas the heterogeneity of NH₄⁺ distribution increased post fertilization.

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Kleinman, P.J.A., Srinivasan, M.S., et al. 2006, 'Role of Rainfall Intensity and Hydrology in Nutrient Transport via Surface Runoff', Journal of Environmental Quality, vol. 35, pp. 1248-1259.

Loss of soil nutrients in runoff accelerates eutrophication of surface waters. This study evaluated P and N in surface runoff in relation to rainfall intensity and hydrology for two soils along a single hillslope. Experiments were initiated on 1- by 2-m plots at foot-slope (6%) and mid-slope (30%) positions within an alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) field. Rain simulations (2.9 and 7.0 cm h^-1) were conducted under wet (spring) and dry (late-summer) conditions. Elevated, antecedent soil moisture at the foot-slope during the spring resulted in less rain required to generate runoff and greater runoff volumes, compared with runoff from the well-drained mid-slope in spring and at both landscape positions in late summer. Phosphorus in runoff was primarily in dissolved reactive form (DRP averaged 71% of total P), with DRP concentrations from the two soils corresponding with soil test P levels. Nitrogen in runoff was mainly nitrate (NO₃-N averaged 77% of total N). Site hydrology, not chemistry, was primarily responsible for variations in mass N and P losses with landscape position. Larger runoff volumes from the foot-slope produced higher losses of total P (0.08 kg ha^-1) and N (1.35 kg ha^-1) than did runoff from the mid-slope (0.05 total P kg ha^-1; 0.48 kg N ha^-1), particularly under wet, spring-time conditions. Nutrient losses were significantly greater under the high intensity rainfall due to larger runoff volumes. Results affirm the critical source area concept for both N and P: both nutrient availability and hydrology in combination control nutrient loss.

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Lagergren, F., Lankreijer, H., et al. 2008, 'Thinning Effects on Pine-spruce Forest Transpiration in Central Sweden', Forest Ecology and Management, vol. 255, pp. 2312-2323.

This study analyses the effects of thinning on stand transpiration in a typical mixed spruce and pine forest in the southern boreal zone. Studies of transpiration are important for models of water, energy and carbon exchange, and forest management, like thinning, would change those processes. Tree transpiration was measured by the tissue heat-balance sapflow technique, on a reference plot and a thinning plot situated in a 50-year-old stand in central Sweden. Sapflow was measured during one season (1998) on both plots before thinning, to establish reference values. In winter 1998/1999 24% of the basal area was removed from the thinning plot. Thinning was done so as to preserve the initial species composition and the size distribution. The measurements continued after thinning during the growing seasons of 1999 and 2000. The climate showed remarkable differences between the 3 years; 1998 was wet and cool, with frequent rain, and the soil-water content was high throughout the year. In contrast, 1999 was dry and warm, and the soil-water content decreased to very low values, ca. 5-6% by volume. In 2000, the weather was more normal, with variable conditions. Stand transpiration was similar on both plots during the year before thinning; the plot to be thinned transpired 6% more than the reference plot. After thinning, transpiration was initially ca. 40% lower on the thinned plot, but the difference diminished successively. When the following drought was at its worst, the thinned plot transpired up to seven times more than the reference plot. During the second season after thinning, the thinned plot transpired ca. 20% more than the reference plot. The increased transpiration of the thinned plot could not be attributed to environmental variables, but was most probably caused by changes in biological factors, such as a fertilization effect.

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López-Bellido, R.J., López-Bellido, L., et al. 2007, 'Tillage System, Preceding Crop, and Nitrogen Fertilizer in Wheat Crop: I. Soil Water Content', Agronomy Journal, vol. 99, pp. 59-65.

Under rainfed Mediterranean conditions, water economy must be based on a suitable choice of agronomic techniques. A 6-yr study was undertaken to determine the effects of tillage system, preceding crop, and N fertilizer on soil water at wheat (Triticum aestivum L.) planting and harvest in a Vertisol. Tillage treatments were no-tillage and conventional tillage. Preceding crops, in 2-yr rotations, were sunflower (Helianthus annuus L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), fallow, and continuous wheat. Nitrogen fertilizer rates were 0, 50, 100, and 150 kg N ha^-1 applied to wheat only. No-tillage did not provide more water at wheat planting for any of the rotations. Preceding crop effect on soil water content (SWC) at planting was as follows: fallow ≥ faba bean > wheat ≥ chickpea > sunflower. At harvest, SWC was higher in continuous wheat. Only at harvest were there differences among N fertilizer rates for SWC. Besides, measurement of SWC at harvest for sunflower, chickpea, faba bean, and fallow were performed to determine soil water storage and precipitation storage efficiency (PSE) for 2 yr. Soil water storage was higher for rotations with sunflower or fallow. Nevertheless, fallow PSE was the lowest (10%). The mean PSE was 29%. Under the conditions of this study, no-tillage is not more efficient than conventional tillage in soil water accumulation. Fallow is not a useful tool for increasing water availability.

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Salt, M., Jaksa, M., et al. 2007, Water Balance Modelling for Phytocovers and Conventional Final Covers at Landfill Closure, Common Ground: 10th Australia New Zealand Conference on Geomechanics, Brisbane, Carillon Conference Management Pty Ltd for the Australian Geomechanics Society. pp. 392-397.

At landfill completion, regulators require waste be covered to protect humans and the environment and minimise leachate. Cover criteria have become more stringent and prescriptive, with Australian regulators requiring a compacted clay barrier to prevent leaching. However, research overseas has shown that the compacted clay barrier is compromised over time. Research suggests alternative covers based on natural systems (whereby moisture is stored in the soil and lost by evapotranspiration) may be as protective as conventional covers.

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Schack-Kirchner, H., Schmid, T., et al. 2005, 'High-Resolution Monitoring of Surface-Flow Depth with Frequency-Domain Probes', Soil Science Society of America Journal, vol. 69, pp. 343-346.

The need exists for a measurement technique to accurately determine the depth of surface runoff on natural soil surfaces. The objective of this note was to determine the sensitivity to the immersion depth of commercially available frequency-domain probes. Within the range of 0 to 25 mm, measurement accuracies better than 0.5 mm were reached. Interestingly, soiling of the rods or droplets did not influence the results significantly. The influence of the electrical conductivity of the water or internal characteristics of different probes did not lead to a bias of more than 1 mm. A field test with grid-like mounted frequency-domain probes showed a stable output signal and a high sensitivity to hydrograph changes. We concluded that frequency-domain probes were well suited for tracking shallow depths of surface runoff in field studies and allow high spatial and time resolution. They provide higher accuracy than alternative systems in the water-level range <5 mm. However, when the measurement precision must be higher than 0.5 mm, an individual calibration of the probes is necessary as well as a correction for salinity.

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Szumigalski, A.R. and Van Acker, R.C. 2008, 'Land Equivalent Ratios, Light Interception, and Water Use in Annual Intercrops in the Presence or Absence of In-Crop Herbicides', Agronomy Journal, vol. 100, no. 4, pp. 1145-1154.

Increased crop production (overyielding) often observed in intercrops compared to sole crops has been attributed to enhanced resource use. The objective of this study was to investigate intercropping complementarity of wheat (Triticum aestivum L.), canola (Brassica napus L.), and field pea (Pisum arvense L.) for light and water use. Sole crop and intercrop combinations were evaluated for effects on land equivalent ratios (LERs), canopy light interception, soil moisture, water use (WU), and water use efficiency (WUE), with or without in-crop herbicides at two field sites in Manitoba, Canada. The mean LER was 1.1, but LERs varied greatly between site-years and herbicide treatments, and were significantly greater than one in 22% of the site-year-treatment combinations. The wheat-canola-pea and canola-pea intercrops showed the greatest frequency of overyielding for dry matter (50%) and grain yield (38%), respectively. Peak light interception tended to occur earlier with canola than with field pea, thus increasing the potential for light use complementarity between these crops. There was a positive correlation between LER and light interception in half of the site-years with applied herbicides and a negative correlation between LER and weed biomass at most site-years without herbicides. Although crop treatments used water differently within the soil profile, there were no differences in WU, but some differences in WUE, between crop treatments; however, WUE generally was not greater in intercrops compared to sole crops. In this study, overyielding in intercrops was inconsistent, and seemed to be related more to light interception than to water utilization.

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Verhoef, A., Fernández-Gálvez, J., et al. 2006, 'The Diurnal Course of Soil Moisture as Measured by Various Dielectric Sensors: Effects of Soil Temperature and the Implications for Evaporation Estimates', Journal of Hydrology, vol. 321, pp. 147-162.

Soil moisture content, θ, of a bare and vegetated UK gravelly sandy loam soil (in situ and repacked in small lysimeters) was measured using various dielectric instruments (single-sensor ThetaProbes, multi-sensor Profile Probes, and Aquaflex Sensors), at depths ranging between 0.03 and 1 m, during the summers of 2001 (in situ soil) and 2002 (mini-lysimeters). Half-hourly values of evaporation, E, were calculated from diurnal changes in total soil profile water content, using the soil water balance equation.

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Whitely, R., Zeppel, M., et al. 2008, 'A Modified Jarvis-Stewart Model for Predicting Stand-scale Transpiration of an Australian Native Forest', Plant and Soil, vol. 305, pp. 35-47.

Rates of water uptake by individual trees in a native Australian forest were measured on the Liverpool Plains, New South Wales, Australia, using sapflow sensors. These rates were up-scaled to stand transpiration rate (expressed per unit ground area) using sapwood area as the scalar, and these estimates were compared with modelled stand transpiration. A modified Jarvis-Stewart modelling approach (Jarvis 1976), previously used to calculate canopy conductance, was used to calculate stand transpiration rate. Three environmental variables, namely solar radiation, vapour pressure deficit and soil moisture content, plus leaf area index, were used to calculate stand transpiration, using measured rates of tree water use to parameterise the model. Functional forms for the model were derived by use of a weighted non-linear least squares fitting procedure. The model was able to give comparable estimates of stand transpiration to those derived from a second set of sapflow measurements. It is suggested that short-term, intensive field campaigns where sapflow, weather and soil water content variables are measured could be used to estimate annual patterns of stand transpiration using daily variation in these three environmental variables. Such a methodology will find application in the forestry, mining and water resource management industries where long-term intensive data sets are frequently unavailable.

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