ALBERT

Description: Critical soil water levels for soil microscale processes are difficult to determine because of variability in large soil volumes and lack of techniques for logging soil water contents in small soil volumes. This study tested nearinfrared (NIR) spectroscopy for soil water content determination. Five soil horizons with a range in soil texture, soil organic carbon, carbonates, pH and horizon depth, were tested at air-dry, field capacity and 0.1 MPa tension water content. Volumetric soil water content, determined using the standard method of oven-drying and soil bulk density, was compared to NIR absorbance in various combinations and wavelengths. The NIR spectra obtained with the probe in direct contact with the soil gave better results than when the probe was separated from the soil with a glass slide. The most reliable validation results were obtained using a multivariate partial least squares regression of the full spectrum with an r2 of 0.95 and RMSE of prediction of 6.4%. Smoothing and derivatives of the spectra did not improve the validation results. The relationships for absorbance at single wavelength segments, ratios, differences and area under the curve around the 1940 nm peak were good (r2 values near 0.85 ) but poorer than the results using the full spectra. The high correlation coefficients obtained with the wide variety of soils utilized in this study suggest that NIR absorbance is a practical method for determining volumetric soil water content for small soil volumes. Key words: Near-infrared spectroscopy, soil water, Near-infrared absorbance

Description: The stratigraphy and hydrology of saline soils were investigated at 15 sites in Saskatchewan, Canada. At five sites (Series A) nests of piezometers were installed and at 10 sites (Series B) a single piezometer was installed in or near an aquifer. Piezometric surface data from the nests showed the potential for upward movement in all Series A sites. The electrical conductivity (EC) of water from Series A piezometers increased from the deepest to shallowest and there was a general increase in soil EC towards the soil surface. Hydraulic conductivity of strata was measured at three sites and varied from 1.6 × 10−7 to 3.2 × 10−4 cm∙sec−1. It was calculated that observed salt loads for the three sites could accumulate by upward movement from the aquifer in from 500 to 5300 yr. For Series B sites the approximate sodium percentage (ASP) of the soil (Y) was related to the ASP of the aquifer (X) by the equation:[Formula: see text]For Series A and Series B sites combined the EC (dS∙m−1) of the 1:1 suspension of the stratum immediately above the aquifer (Y) was related to the EC of the aquifer (X) by the equation:[Formula: see text]Key words: Soil salinity, aquifers, stratigraphy, salt profiles

Description: The spatial and temporal variability of soil properties with depth in the profile and across landscape positions results in diverse patterns of water and solute distribution over the landscape. Vertical and lateral movement of soluble nutrients within the soil profile influences the availability of nutrients required for crop growth, and the entry of nutrients into groundwater and surface water systems. However, commonly used geomorphic concepts such as crest and depression are not rigorously, quantitatively defined. The objective of this study was to determine the influence of quantitative topographic variables and zones of relative surface flows on vertical and lateral redistribution of a bromide tracer under field conditions in a variable glacial till landscape under zero tillage agricultural management. Tracer plots were established on three representative soil-slope associations and digital terrain models (DTM) were produced for determining slope gradient (G), horizontal curvature (Kh), vertical curvature (Kv), mean curvature (H) and accumulation curvature (Ka). Models of accumulation, transit and dissipation (ATD) zones of surface flows were produced for each digital elevation model (DEM) using data on mean and accumulation curvatures. Topographic variables and soil properties had mixed ability to predict bromide redistribution parameters. Soil profile development indicators were negatively correlated with bromide recovery, indicating that increased profile development resulted in more redistribution and lower recovery rates. Pedogenic indicators were significantly different between ATD zones, with depth to calcium carbonate, A horizon thickness, solum thickness and profile development indicator all significantly greater at accumulation zones relative to dissipation or transit zones, indicating that profile development was greatest at accumulation zones. However, the concept of ATD zones did not correlate significantly with bromide redistribution parameters. The utility of ATD zones as a predictive tool for static soil properties is limited by differing hydrologic regime and pedogenic processes occurring at lower slope positions, as a result of near-surface, dynamic water tables. Previous research, however, has shown that topographic variables and concepts of landscape element complexes have some utility in determining spatial variability of deep solute percolation and determination of potential for groundwater impacts. This study indicates that increased N application in convergent portions of the landscape may result in higher rates of deep percolation and removal of N from the crop rooting zone, in areas of depression-focused recharge, when environmental conditions are favourable for such. Key words: Solute redistribution, bromide tracer, digital terrain model, topography, landscape

Description: Redistribution of water and associated solutes in undulating to hummocky landscapes affects crop yield via losses of valuable nutrients and negatively impacts groundwater quality. The objective of this study was to determine the influence of qualitative soil-landscape complexes on vertical and lateral redistribution of solutes in a variable glacial till landscape under zero tillage agricultural management by employing a bromide tracer. Tracer plots were established in the fall of 1999 within three sites comprising three representative soil-slope associations. Values of soil development indicators (A horizon thickness, solum thickness, depth to CaCO3, profile development index and organic carbon) generally increased from crest to midslope to depression. Further to this, the occurrence and thickness of eluvial and illuvial horizons increased from crest to midslope to depression. Well-developed, clay-coated blocky Bt horizons with vertical cracking and overlying Ae horizons in depressions appeared to have favoured rapid, downward vertical bromide redistribution. Crest positions were the least anisotropic and vertical redistribution was more important than lateral redistribution at this position. A combination of topographic and pedologic factors resulted in more lateral redistribution at the midslope position relative to crests and depressions. Bromide recovery rates in the top 60 cm of the soil profile indicated that most of the recovered bromide remained within that depth following spring runoff, but had mostly leached below that depth after the growing season, particularly at the depression position. Low bromide recovery rates in the top 30 cm following spring runoff, indicated that reduced availability of fall-applied nutrients for early crop growth could be expected at crest and depression positions following spring runoff. Bromide redistribution was important during both spring recharge and over the growing season at the depression position. Bromide movement below crop rooting depths and into shallow groundwater sources provides evidence that fall-applied nutrients can enter groundwater following both spring melt and growing season runoff in depressional landscape positions, especially in recharge areas. Management practices to reduce over-application of soluble nutrients and surface water accumulation, or both, in depressional areas may be an effective means to lower the risk of groundwater contamination with soluble nutrients without jeopardizing crop yield potential across the majority of the landscape positions in undulating to hummocky glacial till terrain. Key words: Solute redistribution, bromide tracer, soil properties, topography, landscape

Description: Soil spatial heterogeneity poses a challenge to accurate soil moisture determination. Remote sensing, in particular, using sensors that acquire data at microwave frequencies, is being used to overcome this challenge. In situ soil moisture monitoring can be used to validate remotely sensed surface soil moisture estimates and as inputs for agronomic and hydrologic models. Nine in situ soil moisture stations were established in Manitoba (Canada) and instrumented with Stevens Hydra Probes. The sensors were installed in triplicate with vertical orientation at the surface and with horizontal orientation at the 5-, 20-, 50-, and 100-cm depths. To ensure accuracy of the measured soil moisture, both laboratory and field calibrations were conducted. These calibrated soil moisture values were compared with the probe default values and those generated using published calibrations. Overall, the results showed that the field calibration was superior (coefficient of determination r 2 of 0.95) to the laboratory calibration ( r 2 of 0.89). In addition, coarse-textured sites generally performed better than the fine-textured, high cation exchange capacity (CEC) sites. At the Kelburn site with high clay and CEC, the use of field calibration reduced the root mean square error from 0.188 to 0.026 m 3 m –3 . However, at the low clay and CEC Treherne site, gains in accuracy were minimal, about 0.005 m 3 m –3 . The laboratory calibration consistently underestimated soil moisture at all the evaluation sites, whereas both Topp and Logsdon calibrations overestimated soil moisture.

Description: Landscape delineation based on soilslope associations with similar patterns of solute redistribution would allow for better agro-environmental land management. Long-term redistribution of solutes was examined in relation to topographic variables and static soil properties in a glacial till landscape near Miniota, Manitoba. Static soil properties that were the best predictors of solute redistribution included CO3, Ahor, Solum and OrgC. Temporal variability overshadowed the influence of topographic variables and static soil properties on dynamic solute redistribution within the crop rooting zone (i.e., 120 cm). Topographic variables (relative elevation, topographic index, contributing area) and static soil properties (A horizon depth, solum depth, A horizon organic carbon) were correlated to SO42- and NO3− redistribution. An unexpected result was that more statistically significant relationships were found between these parameters and solute redistribution below 120cm rather than within the root zone. Very low NO3− concentrations were found in the rooting zone at most sample positions, indicating that crop demand during recent growing seasons matched or exceeded supply. Accumulations of NO3− below the rooting zone indicated that deep percolation of NO3− has been an important process over the longer term throughout the upper and mid slope positions of this landscape. A lack of NO3− accumulation in one lower-toe position and the depression indicated that excess NO3− in these profiles may have been leached into the groundwater and/or removed via denitrification or simply may not have accumulated. There appears to be utility in using static soil properties and topographic variables as indicators of dynamic processes of solute redistribution, however, a priori knowledge of soil-landscape relationships and an understanding of associated pedogenic processes and hydrologic regimes are required to achieve sensible results. Key words: solute redistribution; soil properties; topography; landscape; nitrate, sulfate; chloride