Ghanbarian-Alavijeh, B., Millán, H. and Huang, G. 2011. A review of fractal, prefractal and pore-solid-fractal models for parameterizing the soil water retention curve. Can. J. Soil Sci. 91: 1-14. The soil water retention curve is an important hydraulic parameter for characterizing water flow and contaminant transport in porous media. Therefore, many empirical, semi physical, and physical models of the soil water retention curve have been proposed. Among them, fractal models appear to be a useful approach for modeling soil as a heterogeneous porous medium and its hydraulic characteristics. Fractal models are mathematically based, and their parameters have physical meanings. In this study, we review published fractal, prefractal and pore-solid-fractal models for soil water retention curves including Tyler and Wheatcraft, Rieu and Sposito, Perrier et al., Perfect, Bird et al., Millán and González-Posada, and Cihan et al. models. In the pore-solid fractal (PSF) approach the pore phase and matrix phase have a finite volume even for an infinite number of iterations. The results of fitting the PSF model to measured soil water retention data indicate that this model works well, particularly at lower water contents.

Dhief, A., Abdellaoui, R., Tarhouni, M., Belgacem, A. O., Smiti, S. A. and Neffati, M. 2011. Root and aboveground growth of rhizotron-grown seedlings of three Tunisian Desert Calligonum species under water deficit. Can. J. Soil Sci. 91: 15-27. In southern Tunisia, plants are subjected to severe drought and many human disturbances, causing the degradation of soils and plants. The study of wild plants and their response to water deficit can facilitate their conservation and help in ecosystem rehabilitation. In this context, the adaptive responses to water deficit of three desert Calligonum species (C. comosum L'Herit, C. azel Maire and C. arich Le Houerou), differing in their topographic location, were studied in rhizotrons under two water regimes. The objectives were to correlate the adaptive ability of these species, with several developmental traits, such as root architecture and growth, aerial growth and height, with environmental and soil properties, and to define which of the three Calligonum species is best adapted to water stress. Water deficit was applied when plants formed two green branches, and measurements were carried out over 8 mo. Under water deficit, all species increased their cumulative root length. In deeper soil layers, only treated C. arich plants developed secondary roots. Under drought, C. azel and C. arich increased their biomass production during the experiment. It seems that C. arich has adapted better to water deficit by developing a deep root system and the greatest root and aboveground biomass. Hence, C. arich is suggested as the best species for early dune stabilization and biomass production.

Huo, A., Chen, X., Li, H., Hou, M. and Hou, X. 2011. Development and testing of a remote sensing-based model for estimating groundwater levels in aeolian desert areas of China. Can. J. Soil Sci. 91: 29-37. Regional groundwater level is an important data set for understanding the relationships between groundwater resources and regional ecological environments. The decline in water table levels leads to vegetation degradation and thus affects the ecological environment. Such a negative effect is especially apparent in the desertification areas. In this study, a remote-sensing based method was proposed to predict the distribution of the regional groundwater level in an aeolian desert area in northern China. The study used the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data and field investigations. Based on field investigation of groundwater level, soil moisture, and other supporting information in the aeolian desert area, as well as the soil moisture distribution derived from the MODIS images, empirical equations describing the relationship between the soil moisture and groundwater level were obtained. The groundwater levels derived using the MODIS image data were verified by groundwater levels measured from 58 wells. The results show that the correlation coefficient between the measured groundwater levels and the remote sensing-based estimated water levels was 0.868, indicating that the error is small and the predictions closely reflect the real water levels. This model can be used to predict groundwater levels in aeolian desert areas based on remote sensing data sets.

Selles, F., Campbell, C. A., Zentner, R. P., Curtin, D., James, D. C. and Basnyat, P. 2011. Phosphorus use efficiency and long-term trends in soil available phosphorus in wheat production systems with and without nitrogen fertilizer. Can. J. Soil Sci. 91: 39-52. Efficient use of phosphorus (P) in crop production is important for economic and environmental reasons, and to prolong the life of a limited resource. Short-term studies often show low recovery of fertilizer P, but P use efficiency may be underestimated because the value of residual P in the soil is ignored. Our objective was to determine fertilizer P use efficiency in two wheat production systems [continuous wheat (CW) and a 3-yr rotation of summer fallow-wheat-wheat (FWW)] using data from a 39-yr study (1967-2005) at Swift Current, SK. Each rotation received either P only (P) or nitrogen plus P (NP) fertilizer. Annual grain P removal was monitored (all straw was returned to the soil) and changes in soil available P (0- to 15-cm layer) were measured by the Olsen bicarbonate method. In 1993, subplots which received no additional P were established to evaluate the residual effect of P fertilizer applied in the preceding 27 yr. Where P was applied each year, grain P removal averaged 54 to 78% of fertilizer P, with values as high as 65 to 109% in 1994 to 2005, the period of lowest water deficit. The P-only treatments removed 13% less P in grain, on average, than NP treatments. In the P-nly systems, Olsen P content increased linearly with time, but in the NP systems it reached a maximum after 20-22 yr and then stabilized. The cumulative P balance (fertilizer P minus P removed in grain) accounted for 60% of the variability in Olsen P accumulation over the course of the experiment. In CW, Olsen P content increased by 0.15 kg ha^-1 for each kg ha^-1 of P added in excess of crop removal. The rate of Olsen P accumulation was greater (0.20 kg ha^-1 for each kg ha^-1 of excess fertilizer P) in the FWW rotation possibly due to P mineralization during the summer fallow year. When P was withheld between 1994 and 2005, total grain production in the CW rotation was reduced slightly (by 10%), but there was no significant effect on FWW. Crop P removal (1967-2005) where P was withheld in the final 12 yr was equivalent to 105 and 90% of fertilizer P added to the NP and P-only systems, respectively. We concluded that residual P in prairie soils is retained in forms that are available to plants; wheat crops may therefore recover close to 100% of applied fertilizer P given sufficient time.

Xie, H. T., Yang, X. M., Drury, C. F., Yang, J. Y. and Zhang, X. D. 2011. Predicting soil organic carbon and total nitrogen using mid- and near-infrared spectra for Brookston clay loam soil in Southwestern Ontario, Canada. Can. J. Soil Sci. 91: 53-63. Mid-infrared (MIR) and near-infrared (NIR) spectroscopy of soils have been tested to estimate soil organic carbon (SOC) and total N (TN) concentrations at local, regional and national scales. However, these methods have rarely been used to assess SOC and TN concentrations of the same soil under different management practices. The objective of this study was to determine if models developed from infrared spectra of Brookston clay loam soils under different management practices could be used to estimate SOC, and TN concentrations and the C:N ratio. Soils used for model calibration included 217 samples from a long-term fertilization and crop rotation study and a long-term compost study, whereas 78 soil samples from a long-term tillage study on the same soil type were used for model validation. Soil organic carbon and TN concentrations of all samples were also analyzed using dry combustion techniques. Soil samples were scanned from 4000 to 400 cm^-1 (2500-25 000 nm) for MIR spectra and from 8000 to 4000 cm^-1 (1250-2500 nm) for NIR spectra. Partial least squares regression (PLSR) analysis was used for the calibration dataset to build prediction models for SOC, TN and C:N ratio. The SOC and TN concentrations determined using dry combustion techniques were compared with the prediction from the models using the calibration datasets. The predictions of SOC and TN concentrations by the PLSR method using infrared spectra were statistically sound, with high coefficient of determination with the calibration dataset (R²_cal, SOC_MIR=0.99 and SOC_NIR=0.97, TN_MIR=0.98 and TN_NIR=0.97) and the validation dataset (R²_val, SOC_MIR=0.96 and SOC_NIR=0.95, TN_MIR=0.96 and TN_NIR=0.95) and low root mean square error (RMSEP_cal, SOC_MIR=0.93 and SOC_NIR=1.60, TN_MIR=0.08 and TN_NIR=0.12; RMSEP_val, SOC_MIR=1.40 and SOC_NIR=1.75, TN_MIR=0.11 and TN_NIR=0.12). The predictions of SOC and TN concentrations in the 5 to 30 cm depth were better than the predictions for either the surface (0 to 5 cm) soils or for soils from lower depths (>30 cm). The models could be used as an alternative method for determining SOC and TN concentrations of Brookston clay loam soils; however, larger sample populations and improved model algorithms could further improve predictions.

Paré, M. C. and Bedard-Haughn, A. 2011. Optimum liquid density in separation of the physically uncomplexed organic matter in Arctic soils. Can. J. Soil Sci. 91: 65-68. Using an appropriate density to separate the soil light fraction (LF) and heavy fraction (HF) is an important aspect of the density fractionation technique. The effect of liquid density when separating the physically uncomplexed Arctic soil organic matter (SOM) was tested on three Arctic sites: High-Arctic, Low-Arctic, and Sub-Arctic. Our results showed that selecting the right density to use for Arctic soils is not unequivocal. Nevertheless, based on these two criteria: (1) the difference between the C:N values of the LF and HF needs to be as large as possible, and (2) the C:N value of the whole soil needs to be different from the C:N values of the LF and HF, the optimum density for all of our Arctic sites was between 1.49 and 1.55 g mL^-1. We concluded that 1.55g mL^-1 was the conservative optimum liquid density to use to separate Arctic SOM light and heavy fractions.

Zhu, Y., Wang, Y., Shao, M. and Horton, R. 2011. Estimating soil water content from surface digital image gray level measurements under visible spectrum. Can. J. Soil Sci. 91: 69-76. Determining soil water content (SWC) is fundamental for soil science, ecology and hydrology. Many methods are put forward to measure SWC, such as drying soil samples, neutron probes, time domain reflectrometry (TDR) and remote sensing. Sampling and drying soil is time-consuming. A neutron probe cannot determine SWC of surface soil accurately because neutrons escape when they are emitted near soil surface and TDR is, to some extent, influenced by soil salinity and temperature. Remote sensing can obtain SWC over a large area across a range of temporal and spatial scales. Complicated terrain and atmospheric conditions often make remote sensing data unreliable. Determining SWC from surface gray level (GL) measurements in the visible spectrum may have advantages over other remote sensing techniques, because surface soil images can be easily acquired by digital cameras, even with complicated landforms and meteorological conditions. However, few studies use this method, and further work is required to develop the ability of visible spectrum digital images to accurately estimate SWC. In this study, 42 soil samples were collected to investigate the relationship between surface GL and SWC using computer processing of soil surface images acquired by a digital camera. After establishing an equation to describe this relationship, a simple calibrated model was developed. The calibrated model was validated by an independent set of 48 soil samples. The results indicate that surface GL was sensitive to SWC. There was a negative linear relationship between surface GL and the square of SWC for the 42 calibration soil samples (correlation coefficients >0.91). Based on this negative relationship, a model was established to estimate SWC from surface GL. The results of model validation showed the estimated SWCs by surface GL were very close to the measured SWCs (correlation coefficient=0.99 at a significant level of 0.01). Generally, SWC could be estimated from surface GL for a given soil, and the model could be used to quickly and accurately determineg SWC from surface GL measurements.

Hunter, A. E., Chau, H. W. and Si, B. C. 2011. Impact of tension infiltrometer disc size on measured soil water repellency index. Can. J. Soil Sci. 91: 77-81. Accurate measurement of soil water repellency (or hydrophobicity) is important for assessing the hydraulic properties of soils. Water repellency index (RI), a measure of soil water repellency, can be determined using the tension infiltrometer. Little is known about the effects of different infiltrometer disc sizes on measured RI. Furthermore, the impact of method selection in the context of site assessment is unknown. The objective of this study was to determine if the infiltrometer disc size affects the measured RI. Studies were conducted on seven sandy and one clay site in Western Canada in 2008 and 2009. Mini (disc 4.5 cm in diameter) and standard (disc 20 cm in diameter) tension infiltrometers were used to determine RI. There was strong spatial variability in RI values at all sites. Higher RI and greater variance were associated with the smaller disc size due to the smaller zone of influence. Water repellency index values obtained from the mini and standard tension infiltrometers were not statistically different in most cases. We conclude that the mini infiltrometer is an appropriate method for site assessment of RI. The mini infiltrometer RI values were compared with those from the standard infiltrometer, resulting in a 44% accuracy rate with a type I error in 33% of the cases and a type II error in 22% of the cases.

Daviel, E., Sanborn, P., Tarnocai, C. and Smith, C. A. S. 2011. Clay mineralogy and chemical properties of argillic horizons in central Yukon paleosols. Can. J. Soil Sci. 91: 83-93. Wounded Moose paleosols occur on Middle Pleistocene and older glacial deposits in central Yukon, and exhibit thick sola with distinctive reddish brown argillic (Bt) horizons. Extensive field investigations in the mid-1980s documented the distribution, morphology, and standard physical and chemical properties of these paleosols, but paleoenvironmental interpretations of their clay mineralogy relied on analyses of only two pedons. New analyses of archived B horizon samples from 15 paleosol pedons demonstrate that these exhibit the highest degree of mineral weathering documented in Yukon soils and surficial materials, as expressed by Chemical Index of Alteration values that can exceed 80. This strong weathering is accompanied by ∼90% conversion of pedogenic iron oxides to crystalline forms. Clay mineral assemblages in this larger set of argillic horizons confirm a consistent and widespread presence of pedogenic smectite and interstratified minerals in central Yukon paleosols as initially detected in the limited earlier work.

Venner, K. H, Preston, C. M. and Prescott, C. E. 2011. Characteristics of wood wastes in British Columbia and their potential suitability as soil amendments and seedling growth media. Can. J. Soil Sci. 91: 95-106. In British Columbia, alternative uses for poor-quality wood-waste fines (approximately 50 mm or less) are being sought to replace traditional methods of disposal, including landfilling and burning without energy recovery. As a complement to associated field trials to assess the potential suitability of woody wastes as soil amendments, we determined chemical, physical and spectroscopic characteristics of a variety of wood wastes, co-composts and wood chips and carried out a plant (Betula papyrifera) bioassay. Chemical properties and ¹³C NMR spectra indicated similarity to other woody wastes, and suitability for site rehabilitation if applied under conditions to avoid excessive leachate. Seedlings grew poorly in the wood waste materials (final height <4 cm), except for co-composts prepared with municipal biosolids (final height 93 cm). Seedlings also grew poorly in wood chips unless fertilizer was added, indicating that nutrient deficiencies were the primary cause of the poor growth in wood chips. Even with nutrient addition, seedling growth was low in the finest wood chips (<10 mm), probably as a consequence of retention of excessive moisture. This problem could be overcome by applying larger particles or by incorporating the wood chips into soil rather than leaving them as a surface mulch. In conjunction with results from field trials, these results support the application of woody wastes for site rehabilitation, where in situ mixing with mineral soil should reduce bulk density and improve water-holding capacity, and fertilization can compensate for N immobilization by wastes with high C:N ratios.

Yang, J. Y., Huffman, E. C., Drury, C. F., Yang, X. M. and De Jong, R. 2011. Estimating the impact of manure nitrogen losses on total nitrogen application on agricultural land in Canada. Can. J. Soil Sci. 91: 107-122. About 1 million tonnes (1 Tg=10¹² g) of livestock manure N are applied to farmland in Canada each year. Comprehensive information on manure N production and losses from manure during on-farm storage, handling and field application is scarce, especially at a regional scale. However, manure N losses during storage and land application are of considerable concern with respect to nitrogen use efficiency and environmental pollution of air, soil and water. In this paper, manure N production, manure N losses during storage and land application and manure N mineralization from organic manure and the resultant manure N available for annual crops were estimated using the Census of Agriculture database, Farm Environmental Management Survey data and manure N loss factors obtained from the literature. A database of fertilizer N application rates for field crops was developed at the regional scale based on recommendations provided in agronomic extension bulletins and fertilizer N sales. Fertilizer N and available manure N (i.e., total manure N produced minus N losses plus N mineralized from manure applied in previous years) were allocated to each of 24 crops at the regional scale from 1981 to 2006.

The amount of manure N produced in Canada increased by 18.7% from 0.928 Tg in 1981 to 1.102 Tg in 2006. We estimated that 35.6% of the manure N produced was immediately available to crops, 25.6% was lost during storage and land application and 38.8% was carried over to the next year as organic N. The amount of fertilizer N applied to crops increased dramatically from 0.928 Tg in 1981 to a peak level of 1.68 Tg in 2000. There were significant changes in manure N production and application to farmland both on a regional and a temporal basis.

Karamanos, R. E. and Puurveen, D. 2011. Evaluation of a polymer treatment as enhancer of phosphorus fertilizer efficiency in wheat. Can. J. Soil Sci. 91: 123-125. The effectiveness of Avail® was assessed in two 3-yr trials that included an unfertilized control and three rates of seed-placed P (6.5, 13 and 19.5 kg P ha^-1) applied as monoammonium phosphate (MAP) with or without Avail®, and arranged in a randomized complete block design with six replications. Neither a significant effect of treating MAP with Avail® nor a significant interaction between Avail® treatment and rate of P on the yield of wheat and P uptake was observed.