Abstracts

Azooz, R.H. and Arshad, M.A. 1995, 'Tillage Effects on Thermal Conductivity of Two Soils in Northern British Columbia', Soil Science Society of America Journal, vol. 59, pp. 1413-1423.

Tillage management practices may affect crop growth, in part by altering soil thermal properties. Effects of long-term conventional (CT), no tillage (NT), and modified no tillage (NTR: NT with surface residue pushed away from a 7.5-cm zone over the seed rows) systems on soil thermal conductivity (K) and water content (θ) were evaluated on Donnelly silt loam and sandy loam (Typic Cryoboralfs). Measured K (M1) was compared with calculated K using the McInnes equation (M2) and a modified McInnes equation (M3, which included additional soil properties). The K in both soils increased with an increase in soil θ; the differences among the tillage systems decreased as the soil dried. Soil K for the silt loam was 0.81 (θ = 0.13 m³ m^–3), 0.83 (θ = 0.14 m³ m^–3), and 0.84 W m^–1 K^–1 (θ = 0.15 m³ m^–3) in CT, NTR, and NT, respectively, at 25 d after planting in 1992 (a dry year). It was 1.13 (θ = 0.42 m³ m^–3), 1.53 (θ = 0.50 m³ m^–3) and 1.55 W m^–1 K^–1 (θ = 0.57 m³ m^–3) in CT, NTR, and NT, respectively, at 47 d after planting in 1993 (a wet year). Soil K for sandy loam was significantly lower than for silt loam. Soil K measured by M1 and calculated by both the M2 and M3 methods were highly correlated. However, the calculated K values were somewhat improved, although not significantly, with the M3. Mean K was lower by 0.133 W m^–1 K^–1 in M2 and by 0.045 W m^–1 K^–1 in M3 than in M1 under CT on silt loam. Increased soil water storage under long-term NT produced a greater thermal contact area and, consequently, a significantly greater K under NT and NTR than CT.

Request Information                              Back to Reference List

Azooz, R.H., Arshad, M.A., et al. 1996, 'Pore Size Distribution and Hydraulic Conductivity Affected by Tillage in Northwestern Canada', Soil Science Society of America Journal, vol. 60, no. 4, pp. 1197-1201.

Tillage management can affect crop growth, in part by altering the pore structure and hydraulic properties of soil. We hypothesized that water retention, pore size distribution, and unsaturated hydraulic conductivity (k) differed under conventional tillage (CT) and no tillage (NT). We evaluated this hypothesis on a Donnelly silt loam (fine-loamy, mixed, frigid Typic Cryoboralf) and a Donnelly sandy loam (coarseloamy, mixed, frigid Typic Cryoboralf) in northwestern Canada. Soil cores were collected from the 0- to 300-mm depth in 75-mm increments. Water retention was measured at 10 pressure levels from -2 to –400 kPa to calculate pore size distribution and k. Both soils retained 0.04 to 0.09 m³ m^–3 more water under NT than under CT. The volume fraction of total porosity with pores <7.5 µm in diameter (effective pores for retaining plant-available water) in the silt loam averaged 0.49 and 0.58 m³ m^–3 under CT and NT, respectively, and in the sandy loam averaged 0.39 and 0.51 m³ m^–3 under CT and NT, respectively. In contrast, the volume fraction of total porosity with pores >150 µm in diameter (pores draining freely with gravity) in the silt loam averaged 0.29 and 0.23 m³ m^–3 under CT and NT, respectively, and in the sandy loam averaged 0.35 and 0.24 m³ m^–3 under CT and NT, respectively. Conventional tillage appeared more likely to interrupt capillaries than NT, since large differences in k between tillage regimes were observed below a depth of 75 mm with increasing moisture deficit. Continuous NT management increased water storage of both silt loam and sandy loam soils in this cold, semiarid region.

Request Information                              Back to Reference List

Cresswell, H.P., Green, T.W., et al. 2008, 'The Adequacy of Pressure Plate Apparatus for Determining Soil Water Retention', Soil Science Society of America Journal, vol. 72, no. 1, pp. 41-49.

This study evaluated the accuracy of pressure plate apparatus for measuring soil water retention at –0.5 and –1.5 MPa matric potential. Samples from 35 contrasting Australian soils were wetted with distilled water and drained on pressure plate apparatus at –0.5 and –1.5 MPa. The soil matric potential of each sample was then determined using a thermocouple psychrometer, and water content was measured. Water content at exactly –0.5 and –1.5 MPa matric potential was determined independently by interpolating between replicates of matric potential–water content data measured using a thermocouple psychrometer. Water content of the soil samples at apparent equilibrium on pressure plates was compared with these "target" water contents. The 35 samples on pressure plates at –1.5 MPa equilibrated, on average, to 0.3% (w/w) wetter than the target water content, with mean matric potential of –1.10 MPa. Fifteen samples were significantly wetter than the target values. Soil samples on pressure plates at –0.5 MPa equilibrated, on average, to 0.2% (w/w) wetter than the target water content, attaining a mean matric potential of –0.48 MPa. Mean error in water content at –1.5 MPa on pressure plates was reduced from >0.5 to <0.1% (w/w) in a subset of 10 samples prone to dispersion by wetting with 0.01 mol L^–1 CaCl₂. Water contents of samples equilibrated on pressure plates at –1.5 MPa were good estimates of "true" –1.5 MPa water content for the nonswelling soils tested, provided CaCl₂ was used to minimize dispersion. Vapor equilibrium measurement methods are recommended for swelling soils.

Request Information                              Back to Reference List

Duniway, M.C., Herricka, J.E., et al. 2007, 'The High Water-Holding Capacity of Petrocalcic Horizons', Soil Science Society of America Journal, vol. 71, pp. 812-819.

Petrocalcic soil horizons occur in most arid and semiarid ecosystems around the world, often within the plant rooting zone. Little is known, however, about the water-holding characteristic of soils indurated with CaCO₃. We conducted a replicated experiment to define the soil-water release curve (SWRC) for a range of petrocalcic horizon materials. Samples from both plugged and laminar zones of two Stage V petrocalcic horizons in southern New Mexico were characterized. Wetter soil-water potentials were measured using a pressure plate; more negative potentials (down to less than < –10 MPa) were measured using a chilled mirror water activity meter. Measured SWRC data were fitted to the van Genuchten equation. The SWRC methods used were found to be both reliable and repeatable. Plant-available water-holding capacity (AWHC) for desert species (with wilting point set at –4.0 MPa) ranged from 0.26 m³ m^–3 in plugged zones to 0.06 m³ m^–3 in some laminar zones in contrast to about 0.07 m³ m^–3 in the loamy sand parent material. Correlation analyses across morphologies of AWHC and soil properties resulted in significant statistical relationships only with bulk density and porosity. The AWHC and CaCO₃ content, however, were significantly negatively correlated within the laminar and positively correlated within the plugged petrocalcic horizon morphologies. Cementation by CaCO₃ dramatically alters the water-holding characteristics of soils and understanding these horizons is crucial to understand patterns of soil water in desert systems throughout the world.

Request Information                              Back to Reference List

Fuentes, J.P., Flury, M., et al. 2004, 'Hydraulic Properties in a Silt Loam Soil under Natural Prairie, Conventional Till, and No-Till', Soil Science Society of America Journal, vol. 68, pp. 1679–1688.

Tillage in the Palouse region of Washington State over the past 100 yr has influenced the soil physical and biological properties. In particular, hydraulic properties are significantly affected by soil cultivation. The objectives of this study were to assess the temporal patterns of soil hydraulic properties under three management systems,natural prairie (NP), conventional till (CT), and no-till (NT), and to compare hydraulic properties between these three systems. Saturated and near-saturated hydraulic conductivities (up to -15 cm-H₂O hydraulic head), and soil water retention curves were determined using intact soil cores taken from the top 10 cm of soil. Soils were sampled at six different times during a period of 1.5 yr from a NP, a long-term (>100 yr) CT, and a 27-yr-old NT system. The NP represented the original soil and natural vegetation of the area. Significant temporal variation in hydraulic conductivity was found. Temporal variation was most evident in the NP soil, where organic matter content was twice as large as under the CT and NT soils. Hydraulic conductivities in the NP were about one order of magnitude larger than in the cultivated soils. In NT, saturated hydraulic conductivities in the top 5 cm of soils were significantly larger than in CT. No-till and CT soils had similar near-saturated hydraulic conductivities, indicating that even 27 yr of continuous NT could not restore the original hydraulic properties of the soil. Restoration of original hydraulic properties in cultivated former prairie soils may take considerably longer.

Request Information                              Back to Reference List

Giakoumakis, S.G. and Tsakiris, G.P. 1999, 'Quick Estimation of Hydraulic Conductivity in Unsaturated Sandy Loam Soil', Irrigation and Drainage Systems, vol. 13, pp. 349-359.

Laboratory experiments were conducted for determining hydraulic conductivity during infiltration in an unsaturated sandy loam soil, using both steady state and equilibrium methods. A constant head Guelph permeameter and a volumetric pressure plate extractor were used. Based on two ponded heights in the permeameter, the parameters of Gardner's equation expressing the unsaturated hydraulic conductivity as a function of pressure head (i.e. the saturated hydraulic conductivity K_s and the exponent α), were estimated simultaneously. Furthermore, it was found that the parameter α, could also be predicted from the soil-water retention curve based on equilibrium data obtained from the extractor. This indicated that, for the soil type studied, one-ponded height in the permeameter method could be sufficient for the determination of the exponent α, provided that the soil-water retention curve is known.

Request Information                              Back to Reference List

Katsura, S., Kosugi, K., et al. 2005, 'Saturated and Unsaturated Hydraulic Conductivities and Water Retention Characteristics of Weathered Granitic Bedrock', Vadose Zone Journal, vol. 5, pp. 35-47.

As a first step toward describing water flow processes in bedrock, we determined the hydraulic properties of three trimmed samples of weathered granitic bedrock (referred to as Samples A, B, and C, in order of size) in the laboratory. Silicone rubber was used to fill the space between each sample and the surrounding cylinder wall, ensuring accurate measurement of hydraulic properties of the samples. All samples showed similar saturated hydraulic conductivity values of 1 x 10^–4 cm s^–1, with the saturated water flow in all samples obeying Darcy's Law. Unsaturated hydraulic conductivity and water retention functions of Sample A were determined by means of a multistep outflow experiment. Parameters in both functions were optimized by comparing observed and computed cumulative outflow rates. The resulting computed cumulative outflow rates using the optimized parameters showed a good match to the observed cumulative outflow data. Moreover, the derived water retention function agreed closely with the function measured by the pressure plate method. We conclude that the methods proposed in this study are effective for determining the hydraulic properties of weathered bedrock. The bedrock water retention curve exhibited small changes in volumetric water content throughout the measurement range where the pressure head, ψ, was greater than –200 cm. The bedrock hydraulic conductivity function showed a small decrease in hydraulic conductivity in the very wet range of greater than –30 cm, and then declined gradually with decreasing ψ.

Request Information                              Back to Reference List

Luedeling, E., Nagieb, M., et al. 2005, 'Drainage, Salt Leaching and Physico-chemical Properties of Irrigated Man-made Terrace Soils in a Mountain Oasis of Northern Oman', Geoderma, vol. 125, pp. 273-285.

Little is known about the sustainability of irrigated oasis agriculture in northern Oman. The objective of this study therefore was to examine which factors allowed agricultural productivity to be apparently maintained during the two millenia of a mountain oasis' existence. Soil moisture and physico-chemical properties were measured in a typical flood-irrigated field sown to alfalfa (Medicago sativa L.). Particle size, organic (C_org) and inorganic carbon content, pH and electrical conductivity (EC) of the soil progile were analyzed at 0.15, 0.45 and 1.00 m. Saturated hydraulic conductivity and the soil's apparent bulk density and water potential were determined from undisturbed samples at 0.05, 0.25 and 0.60 m. During irrigation cycles of 6-9 days, volumetric water contents ranged from 30% to 13%. A tracer experiment with potassium bromide revealed that 52-56% of the irrigation water was stored in the upper 0.4 m of the soil. The rest of the water moved further down the profile, thus providing the necessary drainage to avoid the build-up of toxic salt concentrations. Due to differences in pore size, plant-available water in the topsoil amounted to 18.7% compared to 13% and 13.5% at 0.25- and 0.60-m depth, respectively. The aggregate structure in the upper 1.0 m of the profile is likely preserved by concentrations of calcium carbonate (CaCO₃) from 379 to 434 mg kg^-1 and C_org from 157 to 368 mg kg^-1 soil. The data indicate that the sustainability of this irrigated landuse system is due to high water quality with low sodium but high CaCO₃ concentration, the elaborate terrace structure and water management which allows adequate drainage.

Request Information                              Back to Reference List

Mecke, M., Westman, C.J., et al. 2002, 'Water Retention Capacity in Coarse Podzol Profiles Predicted from Measured Soil Properties', Soil Science Society of America Journal, vol. 66, no. 1, pp. 1-11.

Fennoscandian podzols consist of coarse parent materials with a strongly developed secondary structure in the Spodic B-horizons. For such materials, predictive standard water retention models developed for soils with a wide range of texture, including fine clay-rich soils, do not give estimates of water retention capacity with high enough precision. In this study we describe an approach to predict water content of coarse podzolic soils separately at seven potentials using multiple linear regression approach and stepwise regression analysis (Rawls et al., 1982, 1983). One model is constructed using only the easily measurable soil texture and dry bulk density data. To include the effects of secondary structure, two other models are constructed by using several measured soil physical and chemical properties for all horizons, or for all horizons excluding the eluvial horizons. These models explain between 90 and 95% of variation in water content (i.e., R² = 0.90–0.95) at potentials -3.2 to -100 kPa and at saturation, but not at the -1585 kPa potential. The validity of the models is tested on soils from four different sites covering a large range of soil properties of Fennoscandian podzols. Two of the models give accurate estimates of water content with errors ≤0.02 ± 0.03 m³ m^-3 at potentials of -10 kPa, -100 kPa, and at saturation. Results show that podzolization processes, including formation of secondary structure by enriched Al and Fe, affect soil water retention, but estimates based on oxalate extractable Al and Fe content cannot be generalized to other soils using the same model calibration.

Request Information                              Back to Reference List

Roels, S., Sermijn, J., et al. 2002, Modelling Unsaturated Moisture Transport in Autoclaved Aerated Concrete: a Microstructural Approach, Building Physics 2002: 6th Nordic Symposium, Trondheim, Norway. 17-19 June pp. 167-174.

Request Information                              Back to Reference List

Young, M.H., Albright, W., et al. 2006, 'Incorporating Parametric Uncertainty in the Design of Alternative Landfill Covers in Arid Regions', Vadose Zone Journal, vol. 5, pp. 742-750.

Monte Carlo simulations and a combination of site-specific data (e.g., soil properties, climatic conditions, and native vegetation) were used to design alternative (evapotranspiration) landfill covers at Edwards Air Force Base, located near Lancaster, CA. Laboratory analyses of site soils indicated the presence of three distinct surface soils, from which statistical distributions were generated. A 10-yr climate sequence (precipitation and potential evapotranspiration) was used for the upper boundary. Potential evapotranspiration was partitioned into potential evaporation and potential transpiration using the phenology of a Mojave Desert plant community. Nearly 1000 realizations were run for each of 72 different combinations of soil type, cover thickness, and plant cover percentage. The results indicate that threshold design parameters, needed to limit deep flux to <0.5 cm yr^–1, differ based on the relationship between the K_s (saturated hydraulic conductivity) of the surface soil, cover thickness, and plant cover percentage. In the lower conductivity soils (mean K_s = 20 cm d^–1), deep flux was 0.2 cm yr^–1 for a cover thickness >80 cm with a plant cover >10%. Higher conductivity soils (K_s = 250 cm d^–1) required thicker soils covers (>100 cm) and greater plant cover (>20%) to achieve similar fluxes. In all cases, variations in both cover thickness and plant cover percentage indicated threshold values, above which incremental additions added little to cover performance. The methods developed here could be implemented at other sites where conditions are known. Designs can account for uncertainties in site parameters and contribute to improved decision making.

Request Information                              Back to Reference List