Landform Elements Research Articles

Quantification of tillage and landscape effects on soil carbon in small Iowa watersheds

Knowledge of the long-term effects of tillage on soil organic carbon is important to our understanding of sustainable agricultural systems and global carbon cycles. In landscapes susceptible to erosion, tillage can exacerbate losses of soil and C by increasing erodibility and stimulating microbial respiration. We measured long-term changes in soil carbon and soil loss in three small watersheds located in southwest Iowa, USA. The following soil series were formed on deep loess hills: Ida and Dow (Typic Udorthents), Napier and Kennebec (Cumulic Hapludolls) and Monona (Typic Hapludolls). All watersheds were cropped to continuous corn ( Zea mays L.) and two were moldboard plowed and disk tilled while the third was ridge-tilled. The ridge-tillage system had greater C contents in the surface soil than the disk tillage soils, but ridge-tillage was not different from the conventional tillage in carbon retention over time. The ridge-tillage system, however, was more effective in retaining soil within the watershed. Microbial respiration by soil microorganisms accounted for 97% of the carbon loss in the ridge-tilled watershed compared to carbon loss in eroded sediment (3%). Terrain analysis was used to segment the landscape into landform elements. Less total carbon was present in the soil profiles of backslope elements than in footslope or toeslope elements, reflecting the combined effects of soil erosion and deposition within the watersheds. Profile C content was also positively correlated with the wetness index, a compound topographic attribute, that identifies areas of the landscape where runoff water and sediment accumulate.

Watershed-scale assessment of soil quality in the loess hills of southwest Iowa

Soil quality is a concept that integrates soil biological, chemical and physical factors into a framework for soil resource evaluation. Conventional tillage practices can result in a loss of soil organic matter and decreased soil quality. The potential for soil quality degradation with tillage may vary depending upon landscape position and the spatial distribution of critical soil properties. Information on how to accurately integrate soil spatial information across fields, landscapes and watersheds is lacking in the literature. The primary objective of this study was to evaluate the long-term effect of conventional and ridge-tillage on soil quality in three small watersheds at the Deep Loess Research Station near the town of Treynor in southwest Iowa. Soil types included Monona silt loams in summit positions, Ida or Dow silt loams in backslope positions, and Napier or Kennebec silt loams in footslope positions. We removed surface soil cores from transects placed along topographic gradients in each watershed and quantified total soil organic C (SOC), total soil N (TN), particulate organic matter C (POM-C) and N (POM-N), microbial biomass C (MB-C), N mineralization potential (PMIN-N), nitrate N, extractable P and K, pH, water-stable macroaggregates (WSA), and bulk density (BD). We used terrain analysis methods to group the data into landform element classes to evaluate the effect of topographic position on soil quality. Results indicate that soil quality is higher under long-term ridge-tillage compared with conventional tillage. Soil quality differences were consistently documented among the three watersheds by: (1) quantification of soil indicator variables, (2) calculation of soil quality index values, and (3) comparison of indicator variable and index results with independent assessments of soil function endpoints (i.e. sediment loss, water partitioning at the soil surface, and crop yield). Soil quality differences under ridge-till were found specifically for the backslope and shoulder landform elements, suggesting that soil quality increases on these landform elements are responsible for higher watershed-scale soil quality in the ridge-tilled watershed.

Computer-assisted discrimination of morphological units on north-central Crete (Greece) by applying multivariate statistics to local relief gradients

Traditional manual methods have been employed for decades to measure geomorphometric properties from topographic maps. Such measurement techniques tend to be tedious and time-consuming and the designated landform elements cannot be easily overlaid on any digital map and imagery for further applied research. This study deals with a new quantitative geomorphometric procedure, based on the multivariate statistical analysis of local topographic gradients within a part of north-central Crete. This method employs sets of computer algorithms that automatically extract and classify geomorphometric properties from Digital Elevation Models (DEMs). This was done by evaluating the morphological setting around each pixel of the DEM along the eight azimuth directions. ISODATA unsupervised classification was implemented to generate 10 morphometric classes showing the spatial distribution of areas with a similar geomorphic scenario. Results revealed that this approach permitted a quick estimation of the spatial distribution of morphologically homogeneous terrain units. It also demonstrated the ability of the delineated landform elements to be superimposed on any digital map and imagery for further investigation. This became apparent during the examination of the relationship between the geomorphological units and the land-cover/land-use types in the study area. Both relative association and the dominant land cover/land use types in relation to geomorphological units are presented.

Drainage Network Analysis for Regional Partitions of Alluvial Paddy‐Field Soils

Terrain data on floodplains might be a useful source of ancillary information about soil properties at a regional scale. However, terrain data are not believed to be suitable for obtaining information on paddy‐field soils on floodplains, because the contrast in the topography of floodplains is only slight. This study was conducted in the Tsuruoka area, a part of the Shonai Plain in the northern part of Japan, to evaluate whether a division of floodplain into landform elements can provide useful information on delineation of paddy‐field soils. As source data for the division, a digital elevation model (DEM) was constructed based on a closely spaced differential global positioning system (DGPS) survey and geostatistical interpolation. By using the DEM, drainage network analysis was performed to delineate the landform units. To evaluate correspondence of soil classification with the land division, soil chemical data from 154 soil samples were classified by using a set of numerical procedures. The numerical procedures included principal component analysis and unsupervised classification techniques. In the land partition map created, each landform unit could satisfactorily represent a separate soil group as characterized by soil chemical properties. A statistical analysis revealed that the regional partition map was better than the conventional soil map inasmuch as the partition map described more satisfactorily the spatial distribution of soil chemical properties. However, this conclusion depends largely on the spatial resolution and precision of the DEM. The useful regional partition map could not be produced by different DEM that has lower resolution and accuracy.

Terrain attributes, landform segmentation, and soil redistribution

The 137 Cs technique has greatly expanded our knowledge of the topography–soil redistribution relationship. For the technique to be useful in upscaling of process models and regional-scale conservation planning, we must be able to show that a consistent relationship exists between 137 Cs -derived soil redistribution rates and terrain attributes in a given region. In this paper, the association between 137 Cs -derived soil redistribution rates and quantitatively defined landform elements was examined at nine hummocky terrain sites in southern Saskatchewan, Canada. Shoulder (SH) elements with convex plan curvatures had the highest mean soil loss rates of 33 t ha −1 yr −1, followed closely by other SH and backslope (BS) elements. The erosional behavior of level elements (i.e. those with gradients less than 3°) was highly dependent on the specific dispersal area (SDA) of the element—elements with high dispersal areas were dominantly erosional (mean soil loss of 14 t ha −1 yr −1), whereas level elements with low dispersal areas were depositional (mean soil gain of 15 t ha −1 yr −1). Doubly concave footslope (FS) elements had mean soil gain of 10 t ha −1 yr −1. The dispersion of values across the nine sites was much greater for the depositional units than the erosional units, indicating a complex relationship between deposition and terrain attributes in the depositional units. The results clearly indicate that regional-scale patterns of soil redistribution can be developed using the 137 Cs technique.

Soil variation within a hummocky podzolic landscape under intensive potato production

The purpose of this study was to determine if relationships between landscape position and soil properties occurred on a podzolic landscape with hummocky meso-topography, which is under intensive potato production in New Brunswick, Canada. Elevation was measured on an approximately 5 m grid spacing and used to construct a digital elevation model. Selected soil textural, morphological and chemical properties were measured on a 7×17 grid with 25 m spacing. Landform segmentation was used to divide sampling locations into eight landform elements based on profile and plan curvature, slope gradient and specific dispersal area. Orthic Humic Regosols and Orthic Sombric Brunisols were predominant in upper slope positions, whereas gleyed subgroups of the main soil orders were commonly found in the concave, lower slope positions. Lower, concave slope positions generally had lesser sand and coarse fragment contents, greater silt, organic carbon and 137Cs contents, and greater depth to C horizon and to bedrock than upper, convex slope positions. In contrast, A horizon thickness, clay content, soil pH and soil test P showed little relationship to landscape position. Landform segmentation was effective in characterizing the spatial distribution of soil loss at the study site, as indicated based on 137Cs content, and of soil taxa. However, the resulting landform elements had generally small differences in parameters such as SOC, sand, silt and clay content, which are commonly considered important in agricultural production. The landscape examined in this study appears to be dominated by soil loss and the closely related homogenizing effects of intensive tillage for potato production. The properties that continue to show a clear relationship to landform position are largely remnant properties (e.g., depth to bedrock or to the C horizon), whose pattern reflects a stronger hydrological and/or pedological control. The results provide further evidence that human-induced changes in soil can fundamentally alter the natural pattern of soil distribution in the landscape, even over relatively short (i.e., 100 years) time scales.

Geoarchaeology of the Milfield Basin, northern England; towards an integrated archaeological prospection, research and management framework

AbstractThis paper presents the results of geoarchaeological investigations undertaken on the valley floor of the Milfield Basin in Northumberland, northern England. The area has a regionally and nationally important archaeological record, including a series of major neolithic and Anglian settlements, but has hitherto lacked archaeological assessment and management guidelines appropriate to the wide range of late‐glacial and post‐glacial environmental settings in the basin. This project has used geomorphological techniques to delimit and classify a total of nine valley floor landform elements in terms of their geomorphology and their known and potential archaeological and palaeoenvironmental associations.Terraced glaciodeltaic and glaciofluvial sand and gravel landforms comprise the oldest landform elements described here and have formed the primary regional focus for prehistoric and early historic settlement and associated subsistence and ritual activity. These landforms have experienced little post‐glacial geomorphological activity, but their multiperiod archaeological landscapes lie beneath a shallow soil cover and are vulnerable to land‐use activities that disturb terrace soils and underlying sediments. A second group of landform elements are of Holocene age and include localized surface peats, alluvial fans, colluvial deposits and extensive deposits of terraced alluvium. Archaeological landscapes in these environments may lie buried intact and unrecorded beneath protective covers of sediment although locally they may have been subject to erosion and reworking by fluvial and slope processes. Holocene alluviation may account, at least in part, for the paucity of recorded archaeology in these parts of the basin. However, peat and organic‐rich sedimentary sequences identified here (including four 14C dated peat sequences) offer an opportunity to elucidate the environmental context and land‐use histories of local prehistoric and early historic communities in the basin, and hence also should be regarded as an archaeological resource.Discussion of landform elements and their archaeological associations is followed by a brief outline of evaluation criteria developed with the aim of ensuring effective long‐term management of archaeological and palaeoenvironmental resources. It is concluded that geoarchaeological analysis of landform elements may be considered central to development of frameworks intended to underpin future programmes of archaeological research and the development of cultural resource management and evaluation strategies. Copyright © 2002 John Wiley & Sons, Ltd.

Cultivation‐Induced Effects on Belowground Biomass and Organic Carbon

Land conversion and cultivation effects on belowground biomass and C were assessed at a fescue (Festuca altaica Trin. ssp. hallii) prairie site and an adjacent cultivated field seeded to spring wheat (Triticum aestivum L.). Belowground biomass and soil organic C (SOC) were measured in three landform element groups (upper level and convex shoulder elements [UL], low‐catchment‐area footslope elements [FS], and low‐elevation level and high‐catchment‐area footslope elements [LL]) at both sites. Upper level, FS, and LL landscape positions in the prairie had, respectively, eight, 12, and 13 times more belowground biomass in the top 60 cm of soil than their cultivated field counterparts. In the upper 1.8 m of soil, belowground biomass in the prairie grassland increased downslope (UL = 1849 ± 306, FS = 2533 ± 899, and LL = 3663 ± 1248 g m−1). In the cultivated field, LL landscape positions had higher levels of belowground biomass than either UL or FS positions (UL = 228 ± 54.5, FS = 200 ± 47.0, and LL = 294 ± 76.8 g m−2). Losses of C from belowground biomass accounted for 17.6% of total SOC losses in UL landscape positions, and 71.7% of losses in FS positions after cultivation. Lower level positions had the greatest loss of belowground plant C (−15.6 Mg ha−1) but overall the SOC had increased by 9.0 Mg ha−1 In these position the loss of belowground C was offset by significantly higher SOC additions to the surface through soil redistribution. On a whole landscape basis, the C loss because of changes in belowground biomass is a large part of the C change that occurs during the transition from native prairie to arable agriculture.

Cultivation-Induced Effects on Belowground Biomass and Organic Carbon

Land conversion and cultivation effects on belowground biomass and C were assessed at a fescue (Festuca altaica Trin. ssp. hallii) prairie site and an adjacent cultivated field seeded to spring wheat (Triticum aestivum L.). Belowground biomass and soil organic C (SOC) were measured in three landform element groups (upper level and convex shoulder elements [UL], low-catchment-area footslope elements [FS], and low-elevation level and high-catchment-area footslope elements [LL]) at both sites. Upper level, FS, and LL landscape positions in the prairie had, respectively, eight, 12, and 13 times more belowground biomass in the top 60 cm of soil than their cultivated field counterparts. In the upper 1.8 m of soil, belowground biomass in the prairie grassland increased downslope (UL = 1849 ± 306, FS = 2533 ± 899, and LL = 3663 ± 1248 g m−1). In the cultivated field, LL landscape positions had higher levels of belowground biomass than either UL or FS positions (UL = 228 ± 54.5, FS = 200 ± 47.0, and LL = 294 ± 76.8 g m−2). Losses of C from belowground biomass accounted for 17.6% of total SOC losses in UL landscape positions, and 71.7% of losses in FS positions after cultivation. Lower level positions had the greatest loss of belowground plant C (−15.6 Mg ha−1) but overall the SOC had increased by 9.0 Mg ha−1 In these position the loss of belowground C was offset by significantly higher SOC additions to the surface through soil redistribution. On a whole landscape basis, the C loss because of changes in belowground biomass is a large part of the C change that occurs during the transition from native prairie to arable agriculture.

Profile cone penetrometer data used to distinguish between soil materials

In young glaciated landscapes the variability of soil materials imparts a major control on crop growth and yield and environmental quality associated with production agriculture. Two common soil materials found on these glaciated landscapes are glacial till and reworked loess. Soil materials can be characterized by a combination of physical and morphological soil attributes. We hypothesized that penetration resistance is the response signal to a complex of multiple soil attributes and can be used as an integrating indicator to map soil materials. Our objective was to test the ability of a profile cone penetrometer to map soil materials at landscape-scale. The study site was located in southern Wisconsin, USA, on soils developed in reworked loess material overlying glacial till, which are classified as Typic or Mollic Hapludalfs and Typic Argiudolls. We collected a dense data set of cone index profiles from a 2.73 ha area on a 10 m grid up to depths of 1.3 m. Additionally, we collected soil cores randomly at 21 penetration locations and analyzed these by layer for texture, bulk density, and water content. We utilized point elevation data collected with a differential global positioning system to create a digital elevation model and derive slope and compound topographic index to subdivide the study area into landform element classes. We used expert knowledge to characterize soil materials and subsequently measured soil attributes to identify soil materials. A hierarchical cluster analysis was used to group cone index profiles. Combining the sparse soil material data with the dense cone index and landform element data resulted in soil material information covering the entire study area. The spatial distribution of soil materials was visualized using a three-dimensional soil layer model. The proposed method is associated with large uncertainties in some areas and can be recommended only for coarse mapping of contrasting soil materials such as glacial till and reworked loess at landscape-scale, when used in combination with landform element data.

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

Wheat yield and grain protein variation within an undulating soil landscape

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

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

Development and application of landform segmentation procedures

Landscape-scale approaches to research in soil science are explicitly focused on transfers of components within and between landscapes. Despite wide-spread recognition of the importance of these transfers, the application of landscape-scale approaches has been hindered by the lack of clear, reproducible research designs. Landform segmentation is used to divide natural and human-influenced landscapes into functionally distinct units. A specific type of landform segmentation, landform element classification, was used in a comparative mensurative design to compare the effects of cultivation on soil distribution and soil organic carbon (SOC) storage and in a manipulative design to determine the relationship between N 2O emissions and fertilizer rate in a hummocky till geomorphic surface in southern Saskatchewan. Significant transfers of SOC and surface soil from convex shoulder units to lower slope positions occurred over the past 90 years, resulting in a change in the type of soils that occupy these positions at two research sites. The observed pattern is consistent with a tillage translocation dominated surface. The dominant control on N 2O emissions in the landscape are spatial differences in water-filled pore space (WFPS) that are strongly controlled by water redistribution. Emissions from drier, shoulder landform element complexes are consistently low throughout the year, whereas a strong positive relationship between N fertilizer rate and N 2O emissions occur in the wettest, level depressional elements.

Error Analysis Bayse' a Posteriori Probability Error Propagated from Data Error.

Bayesian estimation is often applied in pattern recognition problems. We formulate estimation errors of a posteriori Bayesian probabilities to be propagated from observation. Next, we apply the scheme of the formulation to a practical image recognition problem : based on a posteriori probabilities, sectionalized regions in outdoor-scene images are classified into five categories of landform elements, i, e., asphalt, concrete, sand/soil, gravel, and grass. The errors originate from RGB pixel values, and propagate to the a posteriori probabilities via intermediary HIS color measures within a region. We concretely clarify a mechanism of the propagation for all steps, and show an effectiveness of the scheme by adducing changeovers between a posteriori probabilities with two kinds of landform elements.

A generic procedure for automatically segmenting landforms into landform elements using DEMs, heuristic rules and fuzzy logic

A robust new approach for describing and segmenting landforms which is directly applicable to precision farming has been developed in Alberta. The model uses derivatives computed from DEMs and a fuzzy rule base to identify up to 15 morphologically defined landform facets. The procedure adds several measures of relative landform position to the previous classification of Pennock et al. (Geoderma 40 (1987) 297–315; 64 (1994) 1–19). The original 15 facets can be grouped to reflect differences in complexity of the area or scale of application. Research testing suggests that a consolidation from 15 to 3 or 4 units provides practical, relevant separations at a farm field scale. These units are related to movement and accumulation of water in the landscape and are significantly different in terms of soil characteristics and crop yields. The units provide a base for benchmark soil testing, for applying biological models and for developing agronomic prescriptions and management options.

1020 データ誤差に基づくベイズ事後確率の伝搬誤差の解析

Bayesian estimation is often applied in pattern recognition problems. We formulate estimation errors of a posteriori Bayesian probabilities to be propagated from observation. Next, we apply the scheme of the formulation to a practical image recognition problem : based on a posteriori probabilities, sectionalized regions in outdoor-scene images are classified into five categories of landform elements, i.e., asphalt, concrete, sand/soil, gravel, and grass. The errors originate from RGB pixel values within a region, and propagate to the a posteriori probabilities via intermediary HIS color measures. We concretely clarify a mechanism of the propagation for all steps, and show an effectiveness of the scheme by adducing changeovers between a posteriori probabilities with two kinds of landform elements.

Relationships between topographically expressed zones of flow accumulation and sites of fault intersection: analysis by means of digital terrain modelling

Topographically expressed zones of flow accumulation often coincide with fault intersections because of increased rock fracturing. We have conducted a study of the interrelationships between topographically expressed accumulation zones and fault intersections, and the function of these sites in landscape evolution. The investigation has been performed with the use of digital terrain models, geological and soil data for the Crimean Peninsula. First, we carried out an analysis of associations of sites of fault intersections, intensive rock fracturing and abnormally high discharges of springs and boreholes, relating to fault intersections, with three types of landform element (zones of flow accumulation, transit and dissipation). We found that all phenomena under study are closely associated with topographically expressed accumulation zones. This has demonstrated that, within these zones, the soil moisture is influenced both by upward transport of deep-seated groundwater and by accumulation of overland lateral flows. Second, we predicted the effect of topography on irrigation-induced changes in the salt regime of soils and the groundwater level, assuming that topographically expressed accumulation zones can be marked by properties of fault intersections. We found that water leaking out of the North Crimean Canal can result in secondary salinisation of soils and a considerable rise of the watertable within some accumulation zones located downslope. Salts collected in the accumulation zones, and their slow movement through rock fractures, can lead to salinisation of the aquifers. We believe that topographically expressed accumulation zones are areas of contact and substance exchange between overland lateral and deep flows.

Nivation forms and processes in unconsolidated sediments, NE Greenland

In the periglacial unconsolidated sediment landscape of Zackenberg in High Arctic NE Greenland, perennial and seasonal snowpatches dominate the geomorphological development in large areas and control the distribution of the vegetation. The existence and distribution of snowpatches and their associated landforms are mainly controlled by the dominating winter wind direction and the amount of snow precipitation, with aspect exerting much less influence. This makes them an important source of information on past environmental change, and knowledge of the combination of geomorphological processes and forms that result from their existence is thus essential. The main nivation processes are backwall failure, sliding and flow, niveo-aeolian sediment transport, supra- and ennival sediment flows, niveo-fluvial erosion, development of pronival stone pavements, accumulation of alluvial fans and basins, and pronival solifluction. The importance of failure, sliding and flow in the continuous retrogressive extension of nivation hollows and niches is emphasized under the term backwall failure. A morphological assemblage of landforms clearly demonstrates the direct nival sediment transfer link between the eroded nivation hollows, their associated meltwater eroded channels and the pronival alluvial fans or basins. All landform elements and their formative processes are integrated into a comprehensive model. © 1998 John Wiley & Sons, Ltd.

A Landscape‐Scale Study of Soil Quality in Three Prairie Farming Systems

AbstractThe relationship between farming practices and the quality or function of agricultural soils is difficult to characterize because of the complexity of soils and spatial variability within the landscape. This study in Saskatchewan, Canada, tested the hypothesis that soil quality differed among farming systems that varied in fallow intensity (crop‐fallow [fallow every second year], extended rotation [fallow every 3–5 yr], and continuous cropping [no fallow]) and that differences could be assessed using soil properties as indicators of soil quality. In 20 fields with coarse to fine loamy, glaciolacustrine soils (Typic Haploborolls), major landform elements were sampled. As years of continuous cropping and related fertilizer inputs increased, increases in organic C (by weight [Cw] 22%, by volume [Cv] 3%), aggregate size (24%) and stability (45%), microbial biomass (50%), resin‐sorbed N (503%) and P (227%), and nitrification potential (≈25%), decreases in bulk density (8%) and infiltration time (19%), and greater solum thickness (26%) were measured. We postulate that the changes in soil properties indicate an improvement in soil quality under the continuous cropping system and that the observed changes were caused by more frequent additions of crop residues (organic C), especially near the soil surface, which resulted in lower bulk density, more microbial biomass, and greater soil aggregation. It seems that the annual inputs of crop residues in conjunction with nutrients, such as N and P, resulted in the formation of an active and labile soil organic matter, increased availability of soil N and P, and a comparatively large pool of microbial C.