Olatuyi, S. O., Akinremi, O. O., Flaten, D. N. and Lobb, D. A. 2012. Solute transport in a hummocky landscape: I. Two-dimensional redistribution of bromide. Can. J. Soil Sci. 92: 609–629. Bromide has been widely used in field studies to estimate nitrate leaching in agricultural soils. This study examined the impacts of crop response to nitrogen fertilization on the vertical and lateral redistribution of bromide in the fall and spring seasons in a hummocky landscape. The study was carried out near Brandon, Manitoba, in 2007 and 2008, using two separate plots (Site-2007 and Site-2008). The plots were delineated into three landscape positions as upper (UPP), middle (MID) and lower (LOW) slope. A microplot at each landscape position received 15N labelled fertilizer (KNO3) at the rates of 0, 90 and 135 kg N ha−1, and KBr at the rate of 200 kg Br− ha−1. Site-2007 was seeded to canola while Site-2008 was seeded to winter wheat. Soil samples were taken within the microplot to a depth of 120 cm for vertical distribution, and up to 200 cm away from the microplot for lateral distribution of Br− in the top 20 cm depth. The downward movement of Br− in the soil was reduced under N fertilization. This resulted in the accumulation of Br− in fertilized plots, and a greater lateral movement of Br− in fertilized compared with unfertilized plots. The greatest vertical and lateral movement of Br− occurred at the LOW slope position. In the fall season following Br− application, 55 and 15% of the Br− applied were recovered in the vertical and lateral components of the landscape, respectively. Estimated loss of Br− due to vertical and lateral movement was 47% in the unfertilized treatment and 36% with N fertilization. The order of Br− loss in the two dimensions was: LOW (48%)>MID (40%)>UPP (37%). The study shows that crop response to N fertilization reduced the vertical movement of solute, thereby providing an experimental support for the “Campbell hypothesis” which states that N fertilization and proper rate of N application reduces nitrate leaching.

Olatuyi, S. O. and Leskiw, L. A. 2014. Long-term changes in soil salinity as influenced by subsoil thickness in a reclaimed coal mine in east-central Alberta. Can. J. Soil Sci. 94: 605–620. Elevated salinity and sodicity are major challenges to reclamation of surface-mined coal sites in the Alberta Plains region. Research plots were established in 1981 at the Battle River Coal Mine near Forestburg, AB, to determine an optimum depth of subsoil replacement over sodic mine spoil required to sustain agricultural capability. Subsoil thickness was varied at 0, 25, 65, 135, 165 and 335 cm, overlain with 15 cm topsoil. The plots were monitored annually from 1982 to 1986 and were seeded to forage from 1987. Plots were resampled in 2013 to examine long-term changes in soil quality by comparing the results with the historical means for the 1980s. Key soil parameters measured are pH, electrical conductivity (EC), total dissolved salts (TDS), sodium adsorption ratio (SAR) and soluble Na. The soil quality of the root zone (0–40 cm) improved over time in all treatments as EC, TDS, SAR and concentration of Na decreased significantly between the 1980s and 2013. Amounts of EC and soluble Na consistently increased with depth, suggesting salt accumulation was predominantly by downward leaching, but with contribution by upward migration of Na from the underlying spoil. Relative to the native soils in 2013, the root zone quality ratings for EC and SAR in the topsoil/spoil treatment were better than in the shallow-bedrock Solonetzic soil. Ratings for the 25-cm subsoil treatment were also comparable with the local Chernozemic soil, but better than the fine till Solonetzic soil. This study demonstrates that a minimum of 25 cm subsoil and 15 cm topsoil are required for mitigating salinity and sodicity in these reconstructed soils. The resampling in 2013 demonstrates that long-term monitoring is essential to obtain a better understanding of reclamation outcomes.

Olatuyi, S. O., Akinremi, O. O. and Hao, X. 2012. Solute transport in a hummocky landscape: II. Vertical and seasonal redistribution of bromide and 15 N-labelled nitrate. Can. J. Soil Sci. 92: 631–643. Bromide (Br−) tracer is often used to estimate potential nitrate-nitrogen (NO3-N) leaching in soil. An alternative is to use 15N-labelled fertilizer to provide a direct measure of NO3-N leaching losses. We employed a dual application of Br− and 15N to estimate NO3-N leaching in a hummocky landscape. The study was carried out near Brandon, Manitoba, in 2007 and 2008, using two separate plots (Site-2007 and Site-2008). The plots were delineated into three landscape positions as upper (UPP), middle (MID) and lower (LOW) slope. A microplot at each landscape received KBr at the rate of 200 kg Br− ha−1, and 15N-labelled KNO3 fertilizer at the rates of 0, 90 and 135 kg N ha−1. Site-2007 and Site-2008 were seeded to canola and winter wheat, respectively. Soil samples were taken in the fall and spring. The soil samples for the 90 and 135 kg N ha−1 fertilization treatments were analyzed for vertical distribution of Br−, 15N, and NO3-N. The smallest amounts of Br−, nitrogen derived from 15N-labelled fertilizer (NDFF), and NO3-N were measured in the soil profile (0 to 120 cm) at the LOW slope position for both N fertilizer rates. The greatest amounts were at the MID slope, indicating that the downward movement of solute followed the order of: LOW>UPP>MID (P<0.05). Crop uptake of fertilizer N was 35 and 63% in canola and winter wheat, respectively, while Br− uptake was negligible. In the absence of crop uptake, Br− transport was similar to that of NDFF as 38% of each solute was lost between fall and spring in Site-2007 and 33% in Site-2008. Unlike Br− and NDFF, NO3-N distribution remained unchanged between fall and spring measurements, possibly due to its replenishment from native soil N sources. The dual tracer technique, as used in this study, showed the limitations of using soil profile NO3-N alone as an indicator of nitrate leaching and for making treatment comparisons.

Olatuyi, S. O. and Leskiw, L. A. 2015. Evaluation of soil reclamation techniques at the Key Lake uranium mine. Can. J. Soil Sci. 95: 153–176. Adequate soil nutrients and water supply are critical to vegetation establishment and creation of sustainable ecosystems in post-disturbed mining sites. This study investigated effects of various amendments and capping techniques on soil quality and moisture distribution on a reclaimed waste rock pile at the Key Lake uranium mine in northern Saskatchewan, Canada. Soil profiles were reconstructed in 2010 using locally available sandy glacial materials to create soil covers of 1 m thickness. The reclamation treatments consisted of a Control plot, commercial peat (Peat), a local lake sediment (Sediment), underlying flax straw (Straw), mulched forest floor and Ae (LFH), fertilizer (NPK), manure pellets (Pellets), and a demonstration plot (Demo) comprised of Sediment, LFH and Pellets. Soil amendments were applied by various techniques as broadcast, surface incorporation, below the surface or surface mounding. Annual plot monitoring was conducted from 2011 to 2013 and soil samples were analyzed for pH, electrical conductivity (EC), sodium adsorption ratio (SAR), available nutrients, cation exchange capacity (CEC), total organic carbon (TOC), total nitrogen (TN), and regulated metals. Volumetric moisture contents were measured periodically to examine soil moisture response to growing-season precipitation. In 2013, the topsoil of the Control plot was slightly acidic (pH of 6.3) while the Sediment and Demo plots had the lowest pH of 4.0. The EC and SAR values were below 1.0 in all treatment plots. The highest levels of available N, TN, TOC and CEC were in the Sediment and Demo plots, followed by the Peat. The concentration of arsenic exceeded the regulatory limit by 3.4- and 2.6-fold in the Sediment and Demo topsoil, respectively, while concentrations of other metals were below the limits in all treatment plots. The Sediment and Demo treatments were most effective in retaining water in the topsoil, while application of soil amendment by mounding enhanced infiltration and water transmission in the profile. In terms of soil fertility and moisture storage, the combination of organic amendments in multi-layers plus surface mounding, as in the Demo plot, is the most promising capping technique for restoring soil health, vegetative cover and ecosystem functions on the waste rock pile.