Till Landscape Research Articles

Effect of agriculture and of clear-cut forest harvest on landscape-scale soil organic carbon storage in Saskatchewan

The development of sound management approaches to reduce soil organic carbon (SOC) losses presupposes that we thoroughly understand the sources of these losses. We used a landscape-scale research design to estimate human-induced SOC losses by comparing SOC storage in undisturbed landscapes with comparable landscapes disturbed by clear-cutting of forests in the Mixedwood/Gray Luvisolic zone of central Saskatchewan and by agricultural activity in the Black soil zone. A 14.0% decrease in soil organic carbon storage in the upper 45 cm of the soil (from 57.1 Mg ha−1 in mature Mixedwood sites to 49.1 Mg ha−1 in clear-cut landscapes) occurred due to clear cutting at the research sites in the Mixedwood forest. The dominant soil type at these sites, Gray Luvisolic soils developed in glacial till, experienced a 11% loss in SOC storage; higher losses (36% loss) occurred from sandy Brunisolic inclusions in the sites. Changes in SOC storage at the research sites in the Black soil zone landscapes varied with texture and parent material: sandy glacio-fluvial landscapes experienced slight gains of SOC (from 54.1 to 60.1 Mg ha−1); silt and clay glacio-lacustrine landscapes experienced a 15.3% decrease in SOC (from 145.2 to 122.9 Mg ha−1); and loamy glacial till landscapes underwent a major decrease in SOC storage (from 116.2 to 75.2 Mg ha−1) Our results indicate that attempts to increase SOC storage in Saskatchewan soils should concentrate on agricultural landscapes, especially those dominated by glacial till. Key words: Landscape, soil organic carbon, Chernozemic, Mollisol

Landscape Evolution and Shallow Groundwater Hydrology of a Till Landscape in Central Iowa

AbstractDeciphering the effects of land use on environmental quality requires detailed knowledge of the processes governing soil and landscape genesis. The objective of this study was to describe the landscape evolution and shallow groundwater hydrology of a glaciated landscape in Iowa and to relate the soil color pattern to water table fluctuations. Stratigraphic and geomorphic maps and cross sections were prepared using characterization data from 128 soil cores collected from a 32‐ha site. One transect crossing several hillslopes was instrumented with 47 piezometers to determine groundwater flow direction. Three strata of surficial sediments overlying till were identified. The upper two strata were slope alluvium deposited after 4300 YBP, which limits the age of the soils to the late Holocene or younger. The lower sediment resembled alluvium and may be supraglacial sediment draped on the till and later eroded from adjacent hillslopes. The hydrology was characterized by recharge under topographic highs, lateral groundwater flow on sideslopes and discharge in swales. During dry periods, however, portions of higher swales acted as recharge areas and groundwater flow was directed between swales. Morphologic indicators of wetness are better expressed and shallower in soils at footslope and toeslope positions, but some of these features are relict because of the lowering of the water table by artificial drainage.

Cesium-137-measured erosion rates for soils of five parent-material groups in southwestern Saskatchewan

Despite the wide-spread perception that the soils of southwestern Saskatchewan are particularly erosion prone, few observations have been made on soil loss in this area. We used 137Cs redistribution to examine rates of soil loss associated with five parent-material groups in this area. Five sites were sampled in each parent-material group: one uncultivated site and four cultivated sites. Ten samples were taken at each site from landscape positions that have been shown in previous studies to have the highest rates of soil loss. The highest rates (median soil loss of −30 t ha−1 yr−1) were associated with glacial till landscapes; medium (−21 t ha−1 yr−1) but highly variable rates of loss, with coarse sandy glaciofluvial–lacustrine landscapes; and lower and consistent losses of around −12 t ha−1 yr−1, with silty glaciolacustrine and aeolian landscapes and with fine sandy glaciofluvial–lacustrine landscapes. The observed rates of loss can be used to calibrate models of geomorphic instability for this area. Key words: Soil erosion, soil quality, landscape-scale analysis, soil organic matter

Landscape-scale changes in indicators of soil quality due to cultivation in Saskatchewan, Canada

Quantitative assessments of the impact of agricultural practises on soil quality have been hindered by the lack of basic spatial units for designing landscape-scale research projects. This paper builds on the relationship which has been demonstrated to exist between small (5 m by 5 m) slope segments and soil distribution in order to define larger landform element complexes in till landscapes of southern Saskatchewan, Canada. Distinctive pedogenic regimes are associated with these complexes. These complexes were then used to stratify the landscape at four conterminous sites with different cultivation histories and to assess changes in indicators of soil quality. Soil redistribution (as assessed by 137Cs redistribution) has had a major impact on these landscapes. The shoulder and level summit complexes have experienced continued high rates of soil loss. The shoulder complexes have lost 55% of their original soil organic carbon (a loss of 64 mg ha −1) over 80 years and 70% of this loss is attributable to net soil export from these positions. The portions of the footslope complexes dominated by Orthic Black Chernozemic soils initially act as sediment deposition sites in the first 22 years of cultivation, but ultimately this soil is removed from these positions and a moderate decline in soil quality occurs. The Gleysolic-dominated portions of the footslopes and the level depressional complexes occupy 15% of the landscape and are the major long-term sediment depositional sites; the biochemical indicators of soil quality (soil organic carbon and total soil nitrogen) show a major and beneficial increase in these positions.

Sodic Soil Toposequence Related to Focused Water Flow

AbstractPresent concepts of sodic soil formation do not adequately account for observed variability of sodic soil properties on many landscapes in North Dakota. A conceptual model was developed to explain sodic soil genesis related to water and salt movement on a coarse‐loamy till landscape in central North Dakota. The relationship between subsurface water flow and sodic soils was determined by monitoring soil water using neutron attenuation and water wells at three contiguous landform positions. Electrical conductivity, major ions, and water‐dispersible clay were determined on extracts from selected soil samples from each landform position. Typic Argiaquolls, characterized by low salinity (electrical conductivity [EC] < 2.0 dS/m), occurred at the wetland position and were areas of recharge to groundwater. Typic Natraquolls also occurred at the wetland position but were characterized by high salinity (EC > 5.0 dS/m) and were areas of groundwater discharge. Udic and Leptic Natriborolls were areas of groundwater discharge at the intermediate and upland positions. Udic Haploborolls were hydrologically inactive areas at the upland position. Variations in sodic soil development were attributed to the concentration of water flow (focused flow) into specific areas of groundwater discharge or recharge. The most important factors that affected the direction and intensity of focused flow were stratigraphy and landform position.

Sodic Soil Spatial Variability and Classification in Coarse-Loamy Till of Central North Dakota

This study focuses on differences in the soil water regime in a coarse-loamy, closed, till landscape with sodic soils. Problems of classification of sodic soils are difficult to resolve in the field. Our basic hypothesis was that greater emphasis on soil water regime would improve classification of sodic soils. Three landscape positions were studied that reflect internal drainage differences: (i) a well-drained upland position; (ii) somewhat poorly drained intermediate position; and (iii) a poorly drained seasonal wetland. We classified and studied more than 50 profiles at each position. Six pedons were selected from trenches for detailed study. Pedons were analyzed for extractable ions, electrical conductivity (EC), pH, exchangeable sodium percentage (ESP), dispersible clay, and particle size. The upland position had soils with Na-induced clay illuviation Natriborolls. They lacked glossic morphology. The nonsodic soils at the upland position were Haploborolls. The soils at the intermediate and wetland positions were classified as Natriborolls and Natraquolls, respectively. A shallow water table exerted a stronger influence on soil development at the two positions than at the upland position. Field or laboratory evidence does not justify using the Glossic Udic Natriboroll taxon at the upland position. B-horizon structure and substrata colors and mottling are better criteria to recognize that the upland sodic soils are different. Sodic soils at the intermediate position should be recognized in a new subgroup, Aquic Natriborolls. The aquic subgroup would effectively discriminate between the moderately well-drained upland soils and the somewhat poorly drained intermediate soils. Sodic soils with high-surface salinity were an integral part of the sodic soils complex at all three landscape positions. The Leptic subgroup recognizes these soils; however, it does not differentiate between sodic soils with different soil water regimes. We suggest that sodic soils with high-surface salinity be differentiated as saline phases of soil series rather than a separate subgroup.

Hydrogeology of two Saskatchewan tills, I. Fractures, bulk permeability, and spatial variability of downward flow

Groundwater flow patterns were compared and contrasted in two deposits of clayey till of different thicknesses, both of which overlie regional aquifers in a flat upland recharge area. Analysis of 67 field and laboratory hydraulic conductivity determinations indicated that conductive fractures in the unoxidized zone of the thinner till (Dalmeny site) give rise to an isotropic bulk permeability of approximately 5 × 10 −9 ms −1, which is two orders of magnitude greater than the bulk permeability of unoxidized till in the thicker deposit (Warman site). Vertical pore water velocities, estimated using hydraulic and isotopic evidence, vary greatly at Dalmeny and appear to be of the order of 8 m in 10,000 yr at Warman. The association of vertical groundwater flux, depth to water table, and depth of oxidized zone at a given location is referred to as the flow regime there. Spatially detailed water-level monitoring and test drilling indicated substantial variation of the flow regime at Dalmeny on a horizontal scale of tens of meters. No such variation exists at Warman. The differentiation of the flow regime at Dalmeny is due to higher till permeability, which permits a spatially-variable response to microtopographically-focussed infiltration of surface water. Recognition of the causes and symptoms of flow regime variability beneath flat till landscapes has implications for environmental assessment procedures, agricultural practices, wetland management, and waste disposal.

NATURE AND DISTRIBUTION OF SECONDARY SOIL CARBONATES WITHIN LANDSCAPES IN RELATION TO SOLUBLE Mg++/Ca++ RATIOS

The presence of magnesium-bearing calcites in secondary carbonate accumulation layers of soils is shown to be associated with soluble Mg++/Ca++ ratios of one or greater in the attendant or underlying layers. The dissolution of both calcite and dolomite within the solum and the precipitation of only calcite in the developing Cca leads to a buildup of Mg++ in the soil solution. If leaching depth is considerably below the Cca horizon, the secondary calcite is Mg free. If leaching is restricted to relatively shallow depths (2–4 m), the buildup of soluble salts and the increased soluble Mg++/Ca++ ratio which result are conducive to the precipitation of Mg-bearing calcites. Soluble salt distribution within a glacial till landscape suggests that surface runoff waters and snow accumulation in depressions are more important aspects of water distribution in such landscapes than is lateral movement within the soil itself. The accumulation of soluble salts in the 2 to 4-m zone of upland soils and the complete lack of salts to greater depths in depressions ties in well with the presence or absence of Mg-bearing calcites. The implications of the nature of the carbonates to soil salinization processes are indicated.