Zettl, J. D., Barbour, S. L., Huang, M., Si, B. C. and Leskiw, L. A. 2011. Influence of textural layering on field capacity of coarse soils. Can. J. Soil Sci. 91: 133-147. The current method of designing reclamation covers for land disturbed by oil sands mining in northern Alberta, Canada, relies on an estimate of the field capacity (FC) of both natural soils and reclamation soil prescriptions. The objective of this research was to examine the influence of layered, textural heterogeneity on FC. Field testing was performed on seven natural sites with coarse-textured soils that support a range of ecosite classes. Double-ring infiltration and drainage tests with real time monitoring of water content were undertaken along with test pit excavation and detailed profile sampling. The measured water storage at FC following drainage demonstrated that higher water storage at FC values are associated with increased textural heterogeneity, and these sites reflected more productive ecosite class. Rigorous, physically based modeling illustrated that a texturally heterogeneous site can have water storage at FC within 1 m profile that is between 110 to 330 mm higher than a homogeneous profile with the same average texture. These higher values of water storage at FC in texturally heterogeneous sites could account for the differences in observed ecosite productivity. This work highlights the importance of textural layering in designing reclamation covers in coarse-textured soils to maximize FC.

Dyck, M. F. and Kachanoski, R. G. 2011. Scale-dependent covariance of soil physical properties above and below a soil horizon interface: Pedogenic versus anthropogenic influences on total porosity. Can. J. Soil Sci. 91: 149-159. The basic unit of soil - the pedon - is described as the minimum, three-dimensional unit of soil representative of the variability of soil horizon dimensions and morphology. Pedogenic processes responsible for soil horizon and soil profile formation are primarily hydrologic in nature. The spatially variable distribution of soil horizons (i.e., the variation among pedons within catenae or landscapes) is likely a reflection of the inherent variability of the soil parent material and the spatial variability of hydrological/pedogenic processes. This paper explores the spatial variability and spatially scale-dependent covariance between a basic soil property (porosity) above and below an A/B horizon interface under adjacent disturbed (cultivated) and undisturbed (forested) conditions. A combination of scale-dependent variance and Fourier-domain spectral analysis shows that the scale-dependent covariance of A and B horizon porosity varies significantly between the cultivated and forested sampling transects. The majority of these observed differences between the scale-dependent covariance of A and B horizon porosity under contrasting land uses is attributed to tillage. These results suggest that anthropogenic activities such as tillage may not only alter the surface horizons, but the nature of the spatial covariance between surface and underlying horizons which likely influences current soil hydrological processes.

Tallon, L. K., O'Kane, M. A., Chapman, D. E., Phillip, M. A., Shurniak, R. E. and Strunk, R. L. 2011. Unsaturated sloping layered soil cover system: Field investigation. Can. J. Soil Sci. 91: 161-168. Unsaturated soil cover systems are effective in minimizing the interaction of meteoric water with underlying mine waste. Studies detailing field-monitoring results of layered systems in sloping landscapes are scarce. The objective of this paper was to evaluate the field performance, defined as a reduction in percolation, of a sloping fine-over-coarse-layered cover system at a phosphate mine in the northwestern United States. Cover water content profiles were elevated in the underlying waste material during and after wet periods such as spring snow melt, suggesting that any layering effect of increasing storage capacity was lost. During dry periods, water content profiles suggested a slight benefit due to layering, as water contents were slightly elevated immediately above the cover/waste shale interface. Although there were incidental gains in performance due to layering, the majority of the infiltrating water was stored in the fine-textured layer. This layer was most responsible for limiting percolation into the underlying waste. There was little difference in performance due to slope position. The cover was sufficient in preventing net percolation into the underlying waste shale, and performance was at least partially improved by increased storage at layer interfaces.

Huang, M., Barbour, S. L., Elshorbagy, A., Zettl, J. D. and Si, B. C. 2011. Infiltration and drainage processes in multi-layered coarse soils. Can. J. Soil Sci. 91: 169-183. Infiltration and drainage processes in multi-layered soils are complicated by contrasting hydraulic properties. The objective of this study was to evaluate the performances of the hysteretic and non-hysteretic models to simulate the infiltration and drainage processes from three different natural soil profiles containing as many as 20 texturally different layers. Hydraulic properties were estimated from soil textures using pedotransfer functions and were calibrated and validated using measured water contents during infiltration and drainage phases, respectively. The results supported the use of the Arya-Paris pedotransfer function to estimate the wetting curve when contact angles are incorporated. The unique Kozeny-Carmen equation parameter was evaluated by optimizing the estimated saturated hydraulic conductivity. The calibrated numerical model (Hydrus-1D) accurately simulated soil water content profiles and water volumes during the infiltration and drainage phases. The mean error of prediction (MEP) between the measured and estimated soil water contents varied from -0.030 to 0.010 cm³ cm^-3, and the standard deviation of prediction (SDP) from 0.003 to 0.057 cm³ cm^-3. The simulation was improved for more heterogeneous soil profiles when hysteresis was taken into account. The measured and simulated results indicated that the soil profile with vertical heterogeneity in soil texture can store more water than the similar textured vertically homogeneous soils under drained conditions.

Huang, M., Elshorbagy, A., Barbour, S. L., Zettl, J. D. and Si, B. C. 2011. System dynamics modeling of infiltration and drainage in layered coarse soil. Can. J. Soil Sci. 91: 185-197. A system dynamics (SD) model was developed to simulate transient infiltration and drainage processes in multilayered soils. STELLA Software was used as a stock-flow icon-based simulation environment. The developed SD model combined both physically based formulations and empirical assumptions to describe one-dimensional saturated-unsaturated water flow in the vadose zone. The model was successfully calibrated and validated using measured water contents during the infiltration and drainage phases, respectively, of a double-ring infiltration test. The simulation results were also compared with a finite element model of saturated/unsaturated flow (HYDRUS). The results showed that the SD model was capable of accurately simulating the various hydrological processes in multilayered soils, and could be a useful tool for designing reclamation covers. The simulated and measured results show that the presence of a finer sand layer overlying a coarse sand layer will increase the soil water storage at field capacity.

Huang, M., Barbour, S. L., Elshorbagy, A., Zettl, J. D. and Si, B. C. 2011. Water availability and forest growth in coarse-textured soils. Can. J. Soil Sci. 91: 199-210. A method of evaluating the influence of soil layering and climatic variability on plant available water for forest growth is presented. This method enables species-specific levels of maximum sustainable plant transpiration to be evaluated. A calibrated HYDRUS-1D model was used with a 60-yr meteorological record to simulate actual evapotransipration (ET_a) of dominant tree species with different values of leaf area index (LAI) for three sites in northern Alberta. A probability distribution of ET_a was developed for each case. The relationships between LAI, plant above-ground primary production (ANPP), and ET_a were used to estimate the minimum water demand to support plant growth at specific sites. The developed frequency curves of ET_a and the minimum water demand can be used to determine the maximum sustainable LAI and the risk associated with revegetating a particular site with a dominant tree species. The effect of different tree species on the minimum water demand and the maximum sustainable LAI was also illustrated. The results indicated that layering of coarse-textured soils can provide more plant available water and support a higher maximum sustainable LAI than homogeneous soils of a similar texture.

Kulasekera, P. B. and Parkin, G. W. 2011. Influence of the shape of inter-horizon boundary and size of soil tongues on preferential flow under shallow groundwater conditions: A simulation study. Can. J. Soil Sci. 91: 211-221. Detailed studies of the impact of soil tongues at soil horizon interfaces are very important in understanding preferential flow processes through layered soils and in improving the accuracy of models predicting water and solute transport through the vadose zone. The implication of having soil tongues of different shapes and sizes created at the soil horizon interface on solute transport through a layered soil horizon was studied by simulating water and solute transport using the VS2DI model. This 2-D simulation study reconfirmed that soil tongues facilitate preferential flow, and the level of activeness of tongues may depend on the number of soil tongues, their spacing and distribution. Also, the size of the soil tongues (length and diameter at the interface between the soil horizons) and their shape influence the rate of preferential flow. Increasing tongue length consistently resulted in an increase in solute velocity across the entire soil profile regardless of the tongue shape; for example, a soil tongue of 0.25 m length increased solute velocity by about 1.5 times over a soil profile without tongues, but this increase might be different for soil types and groundwater conditions other than those considered in this study. Narrowing of tongues increased solute velocity, whereas increasing the number of tongues in a wider soil profile decreased the solute-front's velocity. As tongue length increased, the area containing solutes at prescribed elapsed times decreased. An implication of this study is that soil horizon tongue shape and spacing reduce pollutant residence times, hence inter-horizon boundary morphology should be considered when modelling transport through the vadose zone. As well, since the solute velocity behaviours of a triangular- and a wider rectangular-shaped tongue were nearly identical, simply measuring solute velocity in the field will reveal little information on the shape of a soil tongue.

Tenuta, M. and Sparling, B. 2011. A laboratory study of soil conditions affecting emissions of nitrous oxide from packed cores subjected to freezing and thawing. Can. J. Soil Sci. 91: 223-233. A series of laboratory experiments using a packed core soil assay was carried out to test several soil conditions affecting the emission of N₂O (nitrous oxide) during thawing of soil. The assay consisted of a sandy loam soil packed to 1.1 Mg m^-3, moistened to 80% water-filled pore space, and temperature treated to 4 or -20°C for 2.5 d; the emissions from thawing soil were then determined as the differences in N₂O release rates of the temperature-treated soils when placed at 15°C. Nitrate addition to surface soil (0-10 cm) enhanced thaw emission. Thaw emissions, averaged for deeper collected soil (10-30 and 30-60 cm), was 0.3% with NO₃^- treatment and 1.2% without NO₃^- treatment of that for surface soil treated similarly. Higher thaw emission for surface soil was related to greater organic matter and microbial biomass C contents and denitrifying enzyme activity than deeper collections of soil. Increasing the bulk density of soil from 1.1, 1.2, and 1.25 Mg m^-3 decreased thaw emission. A second freeze-thaw cycle of the highest compaction treatment resulted in an emission of 2.3% of the first freeze-thaw cycle. Acetylene increased thaw emission of N₂O and more so for NO₃^- untreated than treated soil. Using the acetylene inhibition method, the N₂O:N₂ ratio of gas produced was higher for frozen (0.17) than cold (0.07) treated soil, respectively, without the addition of NO₃^-. The addition of NO₃^- increased the N₂O:N₂ ratio of gas produced with the ratio being 2.45 and 0.53 for frozen and cold-treated soil. The results are consistent with biological denitrification being a source of N₂O with conditions promoting N₂O production rather than consumption enhancing thaw emissions.

Liu, G. and Si, B. C. 2011. Soil ice content measurement using a heat pulse probe method. Can. J. Soil Sci. 91: 235-246. Measuring the volume-based ice content (_i) and thermal conductivity (k) of frozen soil is important for modeling energy and water balance of the earth's surface. The objective of this study was to examine whether a heat pulse probe (HPP) method can be used to measure soil ice content. To minimize ice melting, a heat pulse of duration of 60 s and strength of q≈25 W m^-1 was used for a HPP in frozen sands at various temperatures (T). For a 60-s heating duration, we compared the infinite line source (ILS) solution and finite line source solution with the solution of finite sample size and finite line source through simulations. The simulation suggested that a 60-s heating duration for ILS can be used for long heater probes in infinite media, or short probes in finite size samples in containers made of thermally insulating materials. In this study, sands were packed in small containers with heat pulse probes and a 60-s heating duration, and ILS were used for ice content estimation. Our results suggest that the HPP method has limited use in frozen soil. For sands with a mean grain size of 0.41 mm and 2.13 mm, there were good agreements between the HPP measured and gravimetric _i values at temperature below -22°C and -18°C, respectively. However, above these temperatures, ice melting was significant and would lead to overestimation of _i. The higher the initial temperature, the larger the overestimation of _i.

Ramnarine, R., Voroney, R. P., Wagner-Riddle, C. and Dunfield. K. E. 2011. Carbonate removal by acid fumigation for measuring the d¹³C of soil organic carbon. Can. J. Soil Sci. 91: 247-250. Complete removal of carbonates from calcareous soil samples is critical for accurate measurement of the quantity and isotopic signature (d¹³C) of soil organic carbon (SOC). Carbonates confound SOC and d¹³C measurements because they have d¹³C values ranging from -10‰ to 2‰, whereas those of soil organic carbon range from -27‰ to -13‰, depending on the source of plant residues. Commonly used methods for removing carbonates involve treatment with acid followed by repeated water washings; however, these methods are time consuming, labour-intensive and lead to losses of acid- and water-soluble organic carbon. Fumigation of soil samples with HCl was evaluated as an alternative method, and the time required for complete carbonate removal was determined in this study. Moistened soil samples, taken from 0- to 10-cm and 30- to 50-cm depths, were exposed to HCl vapours for periods of 0, 6, 12, 24, 48, 72, and 96 h, followed by measurements of total C and d¹³C using coupled elemental analyzer-isotope ratio mass spectrometry. The minimum time required to remove all carbonates was ca. 30 h and 56 h for surface and subsurface soils containing 0.80 and 1.94% inorganic C, respectively. Therefore, the fumigation period required is dependent on the total carbonate content of the sample and the nature of the carbonate (pedogenic vs lithogenic). In our study, the rate of removal of inorganic carbon was 0.08-0.10 mg h^-1 for soil samples sizes with 2.4 to 5.8 mg of carbonate-C, a rate similar to previous studies on acid fumigation. A “correction factor” was used to account for a change in sample mass due to fumigation and is necessary for accurate determination of SOC concentration using our proposed methodology.

Li, S., Lobb, D. A., McConkey, B. G., MacMillan, R. A., Moulin, A. and Fraser, W. R. 2011. Extracting topographic characteristics of landforms typical of Canadian agricultural landscapes for agri-environmental modeling. I. Methodology. Can. J. Soil Sci. 91: 251-266. Soil and topographic information are key inputs for many agri-environmental models and there are linkages between soil and topography at the field scale. A major source of soil data is soil databases established based on field soil survey. Although both soil and topographic information are recorded in field soil surveys, the nominal nature of the topographic data has limited their use in agri-environmental models. In this study, we developed a methodology to extract various topographic derivatives and to classify the landscape into landform elements with distinctive topographic characteristics based on detailed analyses of fine resolution digital elevation models. Data obtained from these analyses were used to calculate a representative two-dimensional hillslope of five segments, each with a defined length and slope gradient. A set of modal hillslopes was developed to describe topographic variability. Additional topographic parameters, ratios and indices were calculated to reflect different aspects of topographic characteristics and also to build connections between different agri-environmental models. In particular, a topographic complexity index was developed as a quantitative measure of the degrees of divergence and convergence. This paper describes the methodology using one site as an example. Application of this methodology to other landforms in agricultural land of Canada is reported in a companion paper.

Ramírez-Ávila, J. R., Sotomayor-Ramírez, D., Martínez-Rodríguez, G. A. and Pérez-Alegría, L. R. 2011. Phosphorus in runoff from two highly weathered soils of the tropics. Can. J. Soil Sci. 91: 267-277. Agricultural fields with high soil phosphorus (P) content are important contributors to surface water degradation. Two consecutive simulated rainfall events were conducted on two Ultisols previously amended with inorganic P fertilizer or broiler litter. Soil test P (Bray 1 and Olsen) levels evaluated ranged from 1 to 350 mg kg^-1. Surface runoff concentrations of total P (TP) and dissolved P (DP) generated by a 30-min runoff event were quantified. Runoff DP concentrations ranged from 0.08 to 3.98 mg L^-1 in fertilizer P-amended soils and from 0.08 to 4.93 mg L^-1 in broiler litter-amended soils. A single exponential model adequately described the relationships between soil test P and DP concentrations in runoff. For each soil, the soil test P-DP concentration relationships were positively influenced by soil organic matter and negatively influenced by antecedent soil moisture (P<0.05). For both soils, the soil test P-DP concentration relationships were positively influenced by groundcover percentage and negatively influenced by slope. Environmental soil test P critical levels corresponding to a runoff threshold of 1 mg L^-1 DP, ranged between 176 and 296 mg kg^-1 (Olsen) and 143 to 276 mg kg^-1 (Bray 1) in soils amended with fertilizer-P. In broiler litter-amended soils, threshold values were 88 and 111 mg kg^-1 using Olsen and Bray 1, respectively. Differences in surface runoff-P concentrations due to amendment sources, antecedent soil moisture content, soil organic matter, groundcover and slope suggest that these factors need to be considered in P management decisions at the farm level.

Xing, Z., Chow, L., Rees, H. W., Meng, F., Monteith, J. and Stevens, L. 2011. A comparison of effects of one-pass and conventional potato hilling on water runoff and soil erosion under simulated rainfall. Can. J. Soil Sci. 91: 279-290. Hilling plays an important role in potato production, but is found to be inducing soil loss. An artificial rainfall simulation system was used to evaluate the differences between one-pass hilling (OPH, hilling performed when planting, or shortly after planting) and conventional hilling (CH, hilling performed approximately 35-45 d after planting) as well as their combination with a cover crop (ryegrass; _R) on runoff and soil loss. A three-replicate randomized block experimental design with constant rainfall intensity (120 mm h^-1) was used in this study. No significant differences in runoff were found between different hilling methods. The soil losses, however, showed significant differences both among treatments, among canopy cover classes, and among their interaction terms (all P<0.001). The mean soil loss for CH was significantly higher than that for OPH, by 40%, and the mean soil loss for CH_R was higher than that for OPH_R by 57%. On average, the CH treatments (CH and CH_R) induced greater soil loss than the OPH treatments (OPH and OPH_R) by 47%. Further, the effects can vary with different canopy cover percentages. The OPH treatments (OPH and OPH_R) induced more soil loss than CH treatments (CH and CH_R), by 4.4 to 12.8%, in the <30% canopy cover group, while soil loss in the CH treatments was greater than that in OPH treatments for both the 30-70% and >70% canopy cover groups by 21-94%. Irrespective of treatment, soil loss before canopy forming was 2.4 to 8.9 times higher than the soil loss for the partial to full canopy period. With a cover crop, the CH and OPH treatments can reduce soil loss by 37-55%. One-pass hilling initiated runoff earlier than CH. The water runoff and soil loss with respect to the elapsed time since initialization of water runoff and soil loss could be modeled by a three-parameter Sigmoid function with r²≥0.94. The information generated from this study could be used in landscape modeling to study the impacts of potato production on soil and stream water quality.

Guérin, J. É., Parent, L.-É. and Si, B. C. 2011. Spatial and seasonal variability of phosphorus risk indexes in cultivated organic soils. Can. J. Soil Sci. 91: 291-302. Many reports have attributed phosphorus (P) leaching from cultivated organic soils and the eutrophication of adjacent surface waters to P fertilization exceeding the P sorption capacity of the soil. The index of phosphorus saturation (IPS) using the Mehlich III method (M-III) has been proposed to define an agri-environmental threshold of P saturation in cultivated organic soils. The spatial and temporal variability of IPS_M-III must be documented and related to the risk of P pollution to recommend more efficient fertilization practices. The objective of this research was to measure spatial and seasonal variation patterns of P in cultivated organic soils and to evaluate the losses of soil test extractable P between autumn and the following spring. Composite soil samples were taken on a 25-× 25-m grid within 7-ha areas in three representative types of cultivated organic soils of southwestern Quebec in fall 2006 and spring 2007. Soil P, iron, and aluminum were extracted in duplicate using the M-III and the acid ammonium oxalate methods (OX). The spatial analysis of organic soils showed that the P_M-III and the IPS_M-III were spatially autocorrelated and that the experimental semivariograms can be described by linear to sill or spherical models with ranges of 68 to 168 m. There was a high seasonal variability among the P_M-III and the IPS_M-III values. The IPS_M-III values were generally higher than the environmental threshold of 0.05 across sites and sampling periods. Losses of M-III and OX extractable P averaged 41 kg P_M-III ha^-1 and 84 kg P_OX ha^-1, respectively, between fall and the following spring, suggesting substantial contribution of cultivated organic soils to the pollution of downstream surface waters.

Moulin, A., Tenuta, M., Lobb, D., Dunmola, A. and Yapa, P. 2011. Probability distribution functions for short-term daily nitrous oxide fluxes in a prairie pothole agricultural landscape in western Canada. Can. J. Soil Sci. 91: 303-307. Probability distributions of N₂O fluxes are often non-normal due to large temporal and spatial variability of environmental factors. The most common approaches to statistical analyses of these fluxes in the scientific literature are to transform data with a log function, or conduct non-parametric tests. Analysis of N₂O flux data for 128 sites within a 16-ha field, taken on 20 dates in 2005 and 2006 near Brandon, Manitoba, show that the Johnson Su and generalized log probability distributions provided the best fit for the majority of sample dates. The results of this research indicate that statistical analysis of N₂O fluxes with the Johnson Su probability function should be considered as an alternative to the lognormal function.