Agricultural land use can impact the sustainability of inherent soil quality by its influence on the extent, severity, and dynamics of soil salinity. To assess this impact, a salinity risk index was developed and applied to the agricultural region of the Canadian prairies, utilizing land-use data sets for 1981 and 1991. The analysis is presented in map form. The total extent of moderate or more severe salinity for the prairie region, as determined from a summation of each provincial map, is 1.4 million hectares. The risk assessment based on 1991 land-use data indicates that 62.2 percent of the farm land has little to no risk of a change in salinity, 27.9 percent has a moderate risk, and 9.9 percent of the land has a high risk. A comparison of the risk index classes for the 1981 and 1991 land-use data indicates that risk of salinity for the majority of the land (92 percent) hat not changed, whereas less than 7 percent of the land had a lower risk class, and approximately 0.5 percent had a higher risk class in 1991.

The use of discrete management units for variable-rate N fertilization requires that factors influencing grain yield response to N fertilizer are adequately characterized by delineating landscapes into such management units. The objective of this study was to compare the use of topographically derived landform element complexes (LEC) and the use of individual soil series as management units. Soil volumetric moisture content, nitrate-N, exchangeable ammonium-N, extractable phosphorus, exchangeable potassium, and sulphate-sulphur were studied in 10 intensively sampled transects in an undulating glacial till landscape near Miniota, Manitoba. The study site was delineated into upper, mid and lower LEC using a digital elevation model derived from relative elevation data. The LEC were useful in capturing gross variability at a manageable landscape scale. Among LEC there was a general trend of lower > mid > upper for median values of soil moisture, nitrate, phosphate, potassium and sulphate, as these attributes generally increased with convergent landscape character. Differences among LEC were often statistically significant, and relative distributions exhibited temporal persistence. The site was also stratified by soil series, including Newdale, Varcoe and Angusville soils (Black Chernozems), which were identified by examination of individual soil cores at each sample point. Stratifying the site into management units using soil genetic information, which is reflective of historical moisture conditions and biomass production, was expected to be superior. There was little advantage, however, in using soil series rather than LEC. Spatial distributions of the most agronomically relevant attributes (soil moisture and nitrate) were expressed at a landscape scale broader than that at which soil series occurred within the site. While there were important differences among soil series with respect to nutrients such as phosphate and sulphate, the site was better stratified by LEC with respect to soil moisture and nitrate.

Moderate to severe soil salinity currently affects the surface 60 cm of approximately 1 million ha within agricultural regions of the prairies. The subsoil (60–120 cm) is affected on about 3.5 million ha. The risk of soil salinization (RSS) indicator was developed to measure and monitor the change in risk of soil salinization in the Canadian Prairies as a function of changes in agricultural land use and management practices as reported in the Canadian Census of Agriculture. We have expressed the RSS indicator in five classes from very low to very high risk. In 1981, 18.4% of the land area in the agricultural regions of the prairies was rated as having a moderate or higher risk of salinization. By 2001 this had improved to less than 12% (8 million ha). Prairie-wide the land area at high and very high risk of salinization decreased from 6.2 to 4.4% of agricultural landscapes and the area at moderate risk decreased from 12.2 to 7.3%. We attribute this improvement largely to a reduction in summer fallow with a minor contribution from increased use of permanent cover. Although the risk of soil salinization is far from eliminated, the trend is towards greater agri-environmental sustainability. Key words: Risk of soil salinization, dryland salinity, land use, summer fallow, permanent cover

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

Soil salinisation is a typical problem for the Canadian prairies. At macro-topographic scale, build-up of salts occurs in depressions. However, this relationship is not displayed on existing small-scale maps of soil salinity. To improve these maps, one can use a concept of accumulation, transition and dissipation zones of the landsurface. The concept allows one to reveal depressions (topographically expressed accumulation zones) using digital models of horizontal and vertical curvatures, or accumulation and mean curvatures derived from a digital elevation model. We applied the concept of accumulation, transition and dissipation zones to improve an existing small-scale map of the salinity risk index for the prairies and adjacent areas. A comparison of the old and the improved maps demonstrated that once data on depressions have been taken into account, areas marked by salinity risk decreased significantly. We suggest that the method used may prevent an overestimation in predictions of soil cover degradation due to salinisation. The method used can also reveal saline areas linked with discharges of saline aquifers. This is because sites marked by high discharges of groundwater usually relate to sites of intensive fracturing of geological materials, which are closely associated with topographically expressed accumulation zones. Key words: Digital terrain models, topography, soil salinisation, mapping

Application of hog (Sus domesticus) manure to agricultural land converts waste to fertilizer. Nevertheless, matching nutrients in highly variable manure to soil or crop needs requires analytical capability that is ideally field portable and cost-effective. This study explored using rapid nondestructive near-infrared spectroscopy (NIRS) to analyze nutrients in hog manure and receiving soil. Spectral data in the visible and near-infrared (NIR) region (400-2500 nm) from manure samples were correlated with chemical analytical data from the same samples using multiple linear regression statistics to develop calibrations for the prediction of future unknown samples. For 64 manure samples from seven manure storage facilities, r(2) between NIR-predicted values and chemically measured values was 0.93 to 0.99 for NH4-N, total dissolved N (TDN), suspended N, soluble reactive P (SRP), total dissolved P (TDP), suspended P, suspended C, Na, and Mg. For K, Ca, conductivity, and pH, r(2) was >0.80. Subsequent analysis of 75 samples from 25 facilities gave similar or slightly less successful results. Soil samples collected before and following application of manure were scanned in a field-moist state and after drying. For field-moist soil, r(2) for N, organic matter, Mg+ and moisture was >0.84; for SO4-S was 0.7. For dry soil, results were similar for N and better for Mg SO4-S, Ca, and K. Near-infrared spectroscopy has potential to predict sonic nutrient and salt concentrations in manure rapidly and without sample preparation. It can determine moisture, organic matter, total N, and Mg in field-moist or dry soil and SO4-S, Ca, and possibly K in dry soil.

We investigated two approaches for large-scale analysis and prediction of the spatial distribution of soil properties in an agricultural landscape in the Canadian prairies. The first approach was based on the implementation of nine types of digital terrain models (DTMs) and regression analysis of soil and topographic data. The second approach used a concept of accumulation, transit, and dissipation zones of the landsurface. Soil properties were soil moisture, residual phosphorus, solum thickness, depth to calcium carbonate, and organic carbon content. The dependence of soil properties on topography was supported by correlations for the upper soil layer. However, topographic control of soil moisture and residual phosphorus decreased with depth. Also, correlation coefficients and regression equations describing topographic control of soil moisture and residual phosphorus differed among seasons. This imposes limitations on regression-based predictions of the spatial distribution of soil properties. The prediction of soil property distribution with the concept of accumulation, transit and dissipation zones can be more successful and appropriate than the prediction based on linear regression. The variability in relationships between soil and topographic characteristics with depth may stem from spatial variability in the rate of decline of hydraulic conductivity with depth. Temporal variability in soil–topography relationships occurs because soil properties result from interactions of a variety of pedogenetic factors and processes marked by different temporal variability. In soil studies with digital terrain modelling, there is a need to take into account four types of variability in relations between soil and relief: regional, temporal, depth, and scale.

The objective of this study was to compare landform element complexes (LEC) and soil series as discrete management units for variable rate N fertilizer application. Crop response attributes including grain yield, and grain protein concentration were studied in ten intensively sampled transects in an undulating glacial till soil-landscape near Miniota, Manitoba. In 1997, a year with growing season precipitation 37% below average, median grain yield tended to increase with both N fertilizer and with convergent character in the landscape (upper < mid < lower). Varcoe soils, located predominantly within the lower LEC, were generally more productive than Newdale soils. Grain protein concentration increased with N fertilizer, but tended to decrease with convergent character in the landscape (upper > mid > lower), and was lowest in the Varcoe series. In 1998, growing season precipitation was 62% above average. Grain yield responses to N fertilizer were greater, due in part to declining N fertility in the check and 45 kg ha–1 treatments. Trends among LEC were opposite to those in 1997, as median grain yield estimates tended to decrease with convergent character in the landscape (upper > mid > lower). Grain yield was modeled as a function of estimated plant-available N supply within each LEC and soil series. Modeled 1997 grain yield maxima were 2077, 2261 and 2485 kg ha–1 in the upper, mid and lower LEC. Estimated plant-available N supply at the yield maxima were 89, 130 and 130 kg N ha–1, respectively. In 1998, the relative order of modeled maxima among LEC was reversed. Grain yield of 2501, 2355 and 2227 kg ha–1 were predicted in the upper, mid and lower LEC. Estimated plant-available N supply at the yield maxima were 146, 142 and 154 kg N ha–1, correspondingly. In 1997, plateau yields were 2379, 2495 and 2325 kg ha–1 for Newdale, Varcoe and Angusville series, respectively, where the Varcoe series responded most strongly to estimated plant-available N supply. The corresponding estimated plant-available N supply values at the modeled maxima were 195, 139 and 110 kg ha–1. In 1998, plateau yields were 2343, 2253 and 2285 kg ha–1 for Newdale, Varcoe and Angusville series, respectively. The corresponding estimated plant-available N supply values at the modeled maxima were 136, 148 and 155 kg ha–1. Successful variable-rate fertilization by LEC or soil series will require long-term empirical study to establish risk-based grain yield-N relationships, and to determine if an economic advantage over conventional fertilization practices exists. Key words: Variable-rate fertilization, nitrogen, wheat yield, grain protein concentration, soil-landscape

As soil properties influence productivity, it is of interest to characterize their distribution for the purpose of intensified agricultural management in variable landscapes. Soil properties (soil organic C content, soil pH, A horizon thickness, solum thickness and depth to carbonates) were studied in 10 intensively sampled transects in a gently undulating glacial till landscape near Miniota, Manitoba. Using a landform description model, the study site was delineated into upper, mid and lower elevation landform element complexes (LEC). The program used a digital elevation model created from relative elevation data collected on a 10-m grid. Sample points were also stratified by soil series; Newdale (Orthic Black Chernozem), Varcoe (Gleyed Rego Black Chernozem) and Angusville (Gleyed Eluviated Black Chernozem) soils of the Newdale association were identified. Landform element complexes were ranked lower > mid > upper with respect to convergent landscape character. The eluviated Angusville profiles occurred under more convergent landscape character than the Newdale or Varcoe series. There was a consistent rank of lower > mid > upper with respect to depth to carbonates, A horizon thickness, solum thickness and soil organic C content. Relative ranking of the pH in the Ap horizon was the opposite. In all cases, the lower LEC emerged as most clearly distinct. There was substantial variability in soil profile development, and, therefore, soil series membership, within individual LEC. This indicated that the scale at which LEC are delineated is broader than that at which soil series variability occurs. Nonetheless, LEC were useful in capturing gross variability in soil properties within the landscape at a scale that would allow unique agricultural management practices. Key words: Soil-landscape, solum thickness, depth to carbonates, organic carbon, soil pH

The chemical and mineralogical characteristics of a Gleyed Sombric Brunisol (Keld Series) of the Grandview area of Manitoba were analyzed in detail to determine the influence of acid sulfate weathering. The Keld soil has developed in till derived from underlying soft Cretaceous pyrite-containing shale of the Ashville Formation. The major chemical features of this soil are low pH (3.3) and high amounts of exchangeable Al (15 cmol(+) kg−1) of the Cg and Bg horizons. In addition, amounts of As are high (18–25 mg kg−1) throughout the profile. This element seems to be associated with iron oxides but not with jarosite-type minerals. Pyrite and gypsum were found in the IICkg horizon but jarosite-type minerals, consisting mainly of natrojarosite with ≈ 40% jarosite, were detected in the Cg horizon only. Aluminium-substituted goethite is present in the Bmgj horizon. Smectite, which is partly beidellitic and has an average layer charge density of 0.32 equivalents per formula unit, is the dominant clay mineral in the soil profile and is inherited from the underlying shale along with associated kaolinite and mica. The oxidation and decomposition of pyrite and the formation of sulfuric acid, jarosite-type minerals and aluminum substituted goethite are typical of acid sulfate weathering reactions. The dominant effect of acid sulfate weathering on the clay minerals is their extensive structural breakdown towards the surface of the profile. This is also indicated by the high amounts of Si and Al extracted from weathered mineral residues in the surface horizons. The IICkg horizon of the keld profile is in the pre-sulfuricization stage, the Cg horizon expresses the active sulfuricization stage, and the Bg, Bmgj, and Ah horizons represent the postsulfuricization stage. Key words: Keld series, acid sulfate weathering, natrojarosite, As levels