Till Landscape Research Articles

Riparian Lowlands in Clay Till Landscapes: Part I—Heterogeneity of Flow Paths and Water Balances

AbstractRiparian lowlands act as interfaces between the streams and upland areas. This study identified and quantified local flow paths in four transects of a 26 ha Danish riparian lowland in a glacial till landscape. The riparian lowland was fed by drain water from the upland agricultural drainage catchments. Precipitation, stream stage, and drainage discharge into the riparian lowland were measured continuously, while groundwater hydraulic heads were measured in piezometer pipes twice per month. A water balance model was developed to quantify water fluxes leaving the riparian lowland area via evapotranspiration, leakage to a deeper aquifer, and via groundwater flow, drain flow, and overland flow to the adjacent stream. Overland flow originating from the tile drains was the main flow path in all four transects, and also fluxes to the stream via groundwater or lowland tile drains were significant in some subareas. The presence of a secondary tile drainage network within parts of the riparian lowland reduced overland flow and increased interaction with the riparian lowland soils. Area‐normalized fluxes varied greatly between transects, largely reflecting variations in hydraulic loading rate (ratio of water input rate to the area of the receiving riparian lowland). This, combined with the significance of groundwater flow and riparian lowland tile drain flow in some of the investigated transects, revealed a heterogeneous distribution of flow paths within the small headwater lowland. The rate of overland flow was highly correlated to the hydraulic loading rate, which in turn was dominated by the drainage discharge rate at the hillslope boundary.

Riparian Lowlands in Clay Till Landscapes Part II: Nitrogen Reduction and Release Along Variable Flow Paths

AbstractRiparian lowlands are known to control catchment nitrogen (N) balances. This study examined the role of agricultural tile drainage systems, often present in clay till landscapes, on the transport, transformation, and mass balance of N species in four riparian peat lowland transects receiving agricultural tile drainage water. Monitoring of N speciation of drain, stream, and groundwater, combined with a previously established water balance, enabled the determination of N mass balances for different flow paths including groundwater, subsurface drain water, and overland flow for each piezometer transect. The type of overland flow largely affected nitrate‐N (NO3‐N) removal efficiency, as determined by the total N output from a transect relative to the NO3‐N loading (%). Infiltration and subsurface flow followed by exfiltration (short return flow) allowed an efficient removal of NO3‐N (71–94%), while direct overland flow strongly lowered NO3‐N removal (25%) in one transect. The hydraulic loading rate versus the lowland infiltration capacity determined the transport pathways and thus the resulting NO3‐N removal efficiency. For all transects there was a net export of organic N and/or ammonium, associated with in situ N release from peat decomposition, through overland flow and groundwater discharge. These exports partly counterbalanced NO3‐N removal and significantly reduced the overall total N removal for the riparian lowlands. However, the N removal efficiencies remained positive (1–56%). The study indicates that N budgets for riparian lowlands need to account for overland flow as a transport pathway for N.

Groundwater nitrate removal in riparian buffer zones: a review of research progress in the past 20 years

This review evaluates research in the past 20 years focusing on groundwater nitrate removal in the riparian zones of agricultural watersheds. Studies have reported a large range in the magnitude of groundwater and nitrate fluxes to buffers in different hydrogeologic settings. An earlier focus on buffers with shallow subsurface flow has expanded to include sites with deep flow paths and groundwater-fed overland flow. Nitrate removal efficiency and the width required for removal have been linked to riparian sediment texture and depth to an impervious layer. Denitrification has been identified as the dominant mechanism of nitrate removal based on evidence that this process occurs at depth in many buffers which contain buried organic-rich deposits. Several studies have assessed the cumulative effect of riparian buffers on nitrate removal at the watershed scale. Despite considerable research progress areas of uncertainty still remain. Buffers with coarse-textured sediments located in landscapes with upslope sand aquifers have received most attention. In contrast, few sites have been analysed in weathered bedrock and glacial till landscapes. Many studies have reported nitrate removal efficiency based on nitrate concentrations rather than measuring groundwater fluxes which assess the magnitude of nitrate removal. More information is needed on interactions between riparian hydrological flow paths and biogeochemical processes. Further research is recommended on the effect of riparian zone nitrate removal at the watershed scale and long-term monitoring with respect to buffer restoration, the ability to sustain nitrate removal and responses to land use and climate change.

Importance of geological information for assessing drain flow in a Danish till landscape

AbstractThere has, in recent years, been an increasing interest in developing nutrient load mitigation measures focussing on tile drains. To plan the location of such tile drain measures, it is important to know where in the landscape drain flow is generated and to understand the key factors governing drain flow dynamics. In the present study, we test two approaches to assess spatial patterns in drain flow generation and thereby assess the importance of including geological information. The approaches are the widely used topographical wetness index (TWI), based solely on elevation data, and hydrological models that include the subsurface geology. We set‐up an ensemble of 20 hydrological models based on 20 stochastically generated geological models to predict drain flow dynamics in the clay till Norsminde catchment in Denmark and test the results against TWI. We find that the hydrological models predict observed daily drain flow reasonably well. High drain flow volumes were found in stream valleys and in wetlands and lower drain flow volumes in the more hilly parts of the catchment. In spite of the apparent connection to the landscape, there was no statistically significant correlation between TWI and drain flow at grid scale (100 × 100 m). TWI was therefore not found to be a sufficient index on its own to assess where drain flow is generated, especially in the highlands of the catchment. The geology below 3 m was found to have a large impact on the drain flow, and correlations between sand percentage in the subsurface geology and drain flow volume were found to be statistically significant. Geological uncertainty therefore give rise to uncertainty on simulated drain flow, and this uncertainty was found to be high at the model grid scale but decreasing with increasing scale.

Persistence of high elevation fens in the Southern Rocky Mountains, on Grand Mesa, Colorado, U.S.A.

Small headwater fens at high elevations exist in the dry climatic regime of western Colorado, despite increasing demands for water development since the 1800’s. Fens on Grand Mesa have accumulated plant material as peat for thousands of years due to cold temperatures and consistently saturated soils. The peatlands maintain unique plant communities, wildlife habitat, biodiversity, and carbon storage. We located and differentiated 88 fens from 15 wet meadows and 2 marshes on Grand Mesa. Field work included determining vegetation, soils, moisture regimes, and impacts from human activities. All fens were groundwater-supported systems that occurred in depressions and slopes within sedimentary landslide and volcanic glacial till landscapes. Fens occupied 400 ha or less than 1 % of the 46,845 ha research area and ranged in size from 1 to 46 ha. Peat water pH in undisturbed sites ranged from 4.3 to 7.1. Most fens had plant communities dominated by sedges (Carex) with an understory of brown mosses. Variation in vegetation was controlled by stand wetness, water table level, organic C, conductivity (EC), and temperature °C. Fen soils ranged from 13.6 to 44.1 % organic C with a mean of 30.3 %. Species diversity in fens was restricted by cold short growing seasons, stressful anaerobic conditions, and disturbance. Multivariate analysis was used to analyze relationships between vegetation, environmental, and impact variables. Stand wetness, water table level, OC, electrical conductivity (EC), and temperature were used to analyze vegetation variance in undisturbed fens, wet meadows, and marshes. Vegetation composition in impacted fens was influenced by flooding, sedimentation, stand wetness, water table level, OC, EC, and temperature. Hydrologically modified fens supported 58 plant species compared to 101 species in undisturbed fens. Analysis of historical 1936–2007 aerial photographs and condition scalars helped quantify impacts of human activities in fens as well as vegetation changes. Fourteen fens had evidence of peat subsidence, from organic soil collapse, blocks of peat in the margins, soil instability, and differences in surface peat height between the fen soil surface and the annually flooded soil surface. Of 374 ha of fens in the Grand Mesa study area, 294 ha (79 %) have been impacted by human activities such as ditching, drainage, flooding, or vehicular rutting. Many fens had little restoration potential due to severe hydrological and peat mass impacts, water rights, or the cost of restoration.

Impact of sampling strategy on stream load estimates in till landscape of the Midwest

Accurately estimating various solute loads in streams during storms is critical to accurately determine maximum daily loads for regulatory purposes. This study investigates the impact of sampling strategy on solute load estimates in streams in the US Midwest. Three different solute types (nitrate, magnesium, and dissolved organic carbon (DOC)) and three sampling strategies are assessed. Regardless of the method, the average error on nitrate loads is higher than for magnesium or DOC loads, and all three methods generally underestimate DOC loads and overestimate magnesium loads. Increasing sampling frequency only slightly improves the accuracy of solute load estimates but generally improves the precision of load calculations. This type of investigation is critical for water management and environmental assessment so error on solute load calculations can be taken into account by landscape managers, and sampling strategies optimized as a function of monitoring objectives.

Bromide redistribution as influenced by landscape morphology and pedogenic properties in a variable glacial till landscape: A quantitative examination

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

Bromide redistribution as influenced by landscape morphology and pedogenic properties in a variable glacial till landscape: A qualitative examination

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

Unrestricted cattle access to streams and water quality in till landscape of the Midwest

Unrestricted cattle access to streams in traditionally pastoral regions has been linked to increased concentrations of bacteria, suspended sediments and associated contaminants in streams. However, there is a dearth of data available regarding the impact of cattle access to streams in poorly drained landscapes of the Midwest. In this study, we investigate changes in water quality on a 1005 m long stream section impacted by cattle grazing on the upper 130 m. We monitor discharge, water quality [nitrate, ammonium, total Kjeldahl nitrogen (TKN), total phosphorus (TP), total suspended sediments (TSS), turbidity, Escherichia coli] and chloride, atrazine, silica and major cation concentrations over a 12-month period. Cattle access to the stream does not significantly affect nitrate concentration but leads to large increases in TKN (fourfold increase), TP (fivefold increase), ammonium (fourfold increase), TSS (11-fold increase), turbidity (13-fold increase) and E. coli (36-fold increase) in the summer/fall period. In particular, E. coli concentration in the stream in the summer/fall period exceeds 235 colony forming unit (CFU)/100 ml 64% of the time upstream from the section impacted by cattle, but exceeds this same threshold 89% of the time immediately downstream. Despite the negative impact of cattle access to the stream on water quality, data indicate that dilution, in-stream processes, and natural stream geometry downstream from the impacted section help mitigate this pollution. We expect that this study will be an incentive for policy makers to promote stream rehabilitation and develop more stringent guidelines limiting cattle access to streams in many Midwestern states and other regions with poorly drained soils where the impact of cattle access to streams on water quality is often ignored.

Long-term solute redistribution in relation to landscape m orphology and soil distribution in a variable glacial till landscape

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

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat ( Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha −1 year −1 were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing ∼19 g kg −1 of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha −1 year −1 exhibited thick sola with low inorganic carbon content (mean 3 g kg −1) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.

Mapping hydrological pathways of phosphorus transfer in apparently homogeneous landscapes using a high-resolution DEM

Agriculture is a significant contributor to the diffuse loading of phophorus (P) in fresh water systems. At the landscape level, source areas and targeted surface waters are connected through different hydrological pathways. One of these pathways, P removal through surface runoff, may increase in relative importance when storm events occur and in wet seasons. With Digital Elevation Models (DEMs) it is possible to identify dominant surface pathways in the landscape although resolution of available DEMs is often not detailed enough for areas with low relief or for more detailed landscape-field studies. New high-resolution DEMs that do combine a high resolution with substantial spatial coverage provide the opportunity to develop site-specific management alternatives for sensitive or critical source areas at the landscape level. The objective of this paper is to map hydrological pathways of P for a relatively flat glacial till landscape in the Northern part of the Netherlands and to compare two strategies (A and B) in this landscape for minimizing P loading of surface waters following different scenarios. Strategy A assumes equal lowering of phosphate input rates for all fields and strategy B takes into account the relative sensitivity of fields for removal through overland flow. Available soil data, which did not allow to geo-reference individual fields, showed high soil P levels in about 5% of all fields. Data on field inputs of total phosphate (P 2O 5) were available for 29 farms and showed that fertilized fields received on average 124 kg ha − 1 in the year 2000. Transfer potential of each individual field was evaluated on the basis of two characteristics in a 5 × 5 m resolution DEM: 1) the degree of internal drainage through re-distribution and 2) the degree of external drainage, which indicates the overland flow potential. Almost every field was characterised by sinks (98%) and external drainage into along-field ditches (99%). In addition, almost half of the fields showed drainage directly into surface waters (47%). Applying a classification scheme to rank the sensitivity for losses through overland flow provided a framework to distribute catchment inputs of phosphate at field level (strategy B). Comparing the strategy of distributed phosphate inputs (B) with generic phosphate inputs (A) showed that catchment input-to-output ratios are higher for strategy B for three out of four of the applied scenarios.

Evaluating the use of digital terrain modelling for quantifying the spatial variability of 2,4-D sorption by soil within agricultural landscapes

The most sensitive input parameter in many herbicide fate and transport models is the sorption-partitioning coefficient (Kd), a measure of herbicide sorption by soil. Spatial analyses of Kd are traditionally performed using geostatistics, but this approach requires intensive soil sampling and herbicide analysis. This study examined the use of digital terrain modelling as an alternative tool for quantifying the distribution of herbicide sorption within agricultural fields. Soil samples from a conventional-till (CT) and zero-till (ZT) field were analysed for soil organic carbon (SOC), soil pH, clay content, and the 2,4-D ([(2,4-dichlorophenoxy)acetic acid]) soil-water partitioning coefficient. Digital terrain models were used to calculate topographical variables (elevation, slope gradient, slope aspect, horizontal curvature, vertical curvature, mean curvature, specific catchment area, topographic index and stream power index) for each sampling point. Results indicated that topographic variables were adequate predictors of all soil properties in ZT (R2 ranging from 0.64 to 0.76), and of SOC in CT (R2= 0.65, P < 0.001). For CT, 2,4-D sorption by soil was very well predicted with soil properties alone (R2= 0.82, P < 0.001) and with soil properties in combination with topographic variables (R2= 0.85, P < 0.001), but was less predicted by topographic variables alone (R2= 0.50, P < 0.001). For ZT, the level of prediction of 2,4-D sorption by soil was weak with soil properties alone (R2= 0.53, P < 0.001) or when topographical variables alone (R2= 0.56, P < 0.001) were used, but a substantial increase in the level of prediction was achieved when both soil properties and topographic variables were used (R2= 0.73, P < 0.001). We conclude that digital terrain modelling, in combination with soil properties data, is an appropriate approach for predicting the spatial distribution of 2,4-D sorption within undulating-to-hummocky glacial till landscapes in western Canada. Key words: herbicide sorption, topography, zero-tillage, conventional-tillage, digital terrain modelling.

Use of the Geonics EM-38 to Delineate Soils in a Loess over Till Landscape, Southwestern Iowa

Use of the Geonics EM-38 to Delineate Soils in a Loess over Till Landscape, Southwestern Iowa

Relationships Between Soil Nitrogen Availability Indices, Yield, and Nitrogen Accumulation of Wheat

The success of variable rate N fertilizer application rests on our ability to predict the contribution of soil N to growing crops. We assessed relationships between soil N availability indices (SNAIs), yield, and total N accumulation of wheat (Triticum aestivum L.) grown in a typical glacial till landscape in Saskatchewan, Canada. Soil samples were collected at 3‐m intervals along a 300‐m transect comprised of low (LCFS) and high catchment footslopes (HCFS), and low (LCSH) and high catchment shoulders (HCSH). Total soil N and C, organic C, mineral N, depth of A horizon, spring soil moisture, grain yield, and total plant N were measured. Soil N availability indices used in this study included: (i) cumulative N released during a 2‐wk aerobic incubation (NMIN); (ii) potentially mineralizable N estimated using a 16‐wk aerobic incubation (N0); (iii) NO3 sorbed on anion‐exchange membranes (NO3AEM); (iv) N extracted with hot KCl (NKCl); and (v) N hydrolyzed with hot KCl (NHYDR). Although all SNAIs were significantly correlated to yield and, with the exception of N0, total plant N when analyzed across the transect, typically <40% of the yield variability was explained. Forward stepwise regression revealed that most SNAIs failed to explain more variability in crop N accumulation than did basic soil properties or relative elevation. Although these results do not invalidate the use of SNAIs for soil testing purposes, it is clear that SNAIs must be combined with additional information about field scale variability for predicting fertilizer N requirements. Without this information, grid sampling as a means of assessing N requirements remains ill‐advised for glacial till semi‐arid landscapes.

Spring wheat (Triticum aestivum) yield and grain protein responses to N fertilizer in topographically defined landscape positions

A 3-yr field study was initiated in 1996 to examine the different grain yield and grain protein responses of wheat to varied N fertilizer rates in a typical glacial till landscape in Saskatchewan, Canada. Our objective was to assess the agronomic and economic feasibility of variable rate fertilizer (VRF) N application for wheat. Results suggest that spring soil water status largely determined the yield and the protein content of wheat both within different years of the study and between different landscape positions within a given year. Although grain yield was strongly related to spring soil water and was predictable on that basis, the grain yield response of wheat to fertilizer N additions was highly variable due, in part, to the dual role that N played in determining both grain yield and grain protein content. As a consequence of the unpredictable nature of the varied response of wheat to N fertilizer additions, there was little economic rationale for using VRF strategies in the 3 yr of this study. However, in the long-term, we believe that VRF N application strategies can be employed to manage N inputs from the perspective of managing and replacing harvested N. Key words: Variable rate fertilizer application, precision farming, nitrogen application, N fertilizer, Saskatchewan

Soil moisture and nutrient variation within an undulating Manitoba landscape

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. Key words: Soil-landscape, soil series, soil moisture, soil residual nitrate, extractable phosphorus

Topographic influence on the variability of soil properties within an undulating Manitoba 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

LATE PLEISTOCENE ICE-FLOW DIRECTIONS AND THE AGE OF GLACIAL LANDSCAPES IN NORTHERN LOWER MICHIGAN

Lineation (alignment) of certain landscape features, most of which are glacigenic, and till-fabric data were mapped and used to indicate glacier flow directions in northern lower Michigan. I also reexamine the limit of the Greatlakean (ca. 11,850 14C yr B.P.) ice advance in northern Michigan. My study assumes that reddish-brown (7.5YR and redder) till in the region was deposited by the last ice advance, the Greatlakean, since this color till covers uplands immediately down ice from an established Greatlakean stratigraphic marker bed. Landscape linearity and till-fabric data within the reddish-brown till landscapes of northwestern lower Michigan both show strong northwest-southeast alignment, indicating that Greatlakean ice advanced out of the Lake Michigan basin. Earlier (Port Huron, ca. 13,000 14C yr B.P.) ice deposited brown till of 10YR hue, as evidenced at a borrow pit where reddish-brown Greatlakean till overlies brown drift. Thus, the “7.5YR and redder” vs 10YR hue limit is interpreted as the outer limit of the Greatlakean advance in northern lower Michigan. By mapping this limit only a few tens of km southeast of its only stratigraphically confirmed position at the Cheboygan bryophyte bed, I imply that Greatlakean ice did not advance as far into northeastern lower Michigan as others previously have suggested. Port Huron landforms in brown till show similar alignment and till fabrics to Greatlakean landforms in red till, suggesting that Port Huron ice in northern Michigan (also) advanced primarily out of the Lake Michigan basin. As it advanced from the northwest, flowlines and till fabrics suggest that the Port Huron ice gradually curved, eventually flowing north-to-south in northeastern lower Michigan, nearer the Saginaw Lobe. [Key words: glacial geology, drumlins, landscape fabric, Greatlakean advance, Port Huron advance, till fabric, glacial dynamics.]

Saturated hydraulic conductivity and soil water retention properties across a soil‐slope transition

The hydraulic properties of soil and their spatial structures are important for understanding soil moisture dynamics, land surface and subsurface hydrology, and contaminant transport. We investigated whether landscape features, including relative position on a slope, contribute to the variability of soil hydraulic properties in a complex terrain of a glacial till material. Using 396 undisturbed soil cores collected along two orthogonal transects, we measured saturated hydraulic conductivity (Ksat) and soil water retention functions at two (15 and 30 cm) depths across a glacial till landscape in central Iowa that encompassed two soil types (Nicollet loam with 1–3% slope on the hilltop position and Clarion loam with 2–5% slope on the shoulder position). The van Genuchten‐Mualem model was fitted to the experimental data using the RETC optimization computer code. At the 15 cm depth a statistical comparison indicated significant differences in Ksat, saturated water content (θs), water content at permanent wilting point (θ15,000) and van Genuchten fitting parameters (α and n) between soil types and landscape positions. At the 30 cm depth, θs, θ15,000, and residual water content (θr) were found to be significantly different across the soil‐slope transition. Available water content (θ333–15,000) did not show any significant difference across the soil‐slope transition for either depth. No clear directional trend was observed, with some exceptions for Ksat, θs, and α on specific transect limbs and depths. Drifts in the soil hydraulic parameters due to soil‐slope transition were removed using a mean‐polishing approach. Geostatistical analyses of these parameters showed several important characteristics including the following: (1) The spatial correlation lengths and semivariogram patterns of the independently measured (or estimated) loge Ksat and θs at 30‐cm depth matched extremely well; (2) better spatial structures with large correlation lengths were observed for (macro and micro) porosity‐related loge Ksat, θs, and loge α than for texture‐related loge θ333–15,000, loge θ15,000, θr and loge n at 30‐cm depth; and (3) a higher nugget effect at 15‐cm depth was evident for most soil hydraulic parameters, indicating tillage and other surface disturbances. These novel findings may prove to be critical for modeling and interpreting field‐scale or larger‐scale soil moisture dynamics, surface and subsurface flow, and solute transport.