Upslope Positions Research Articles

Spatial Distribution and Chemical Speciation of Soil Phosphorus in a Band Application

There is limited information on how manure and inorganic fertilizer application in a concentrated band impacts the solubility, mobility, and transformation of the phosphate compounds in Canadian prairie soils. A combination of resin membrane probes, sequential chemical extraction, and synchrotron based techniques were used to reveal the spatial distribution and chemical speciation of soil phosphorus (P) when inorganic fertilizer P or manure is placed in the soil in a band under field conditions. This study was performed at Central Butte and Dixon, SK, Canada. Monoammonium phosphate blended with urea was applied at a rate of 54 kg N ha−1 and 12 kg P ha−1 at Central Butte (Brown Chernozem) and solid cattle manure was applied at rate of 60 t ha−1 yr−1 at Dixon (Black Chernozem). Fertilizer application increased the total and labile P supply at the center of the band and was mainly confined to a relatively small area within about 5 cm of band regardless of slope position. The X‐ray absorption near edge structure (XANES) spectroscopy directly identified different forms of soil P, while chemical extraction results provided indirect support that there are differences in the forms of P in the band center as related to in the landscape position and fertilization type. The XANES analysis results showed that different P retention mechanisms take place depending on both landscape position and fertilizer type. For the inorganic fertilizer application made in calcareous upslope positions, a significant amount of apatite and adsorbed P species were observed at center and near‐band and only apatite was present at large distances from the band; adsorbed P species dominated at all distances from the band at downslope positions. The solid cattle manure applied soil contained dicalcium phosphate (DCP) and organic P at center and near‐band at both slope positions but adsorbed P and calcium phosphate further away at upslope positions and adsorbed P further away at downslope positions. The XANES results also indicated that the movement of organic P was limited as this species was always localized near the band.

Site-specific wild oat (Avena fatua L.) management

Beckie, H. J. and Shirriff, S. 2012. Site-specific wild oat ( Avena fatua L.) management. Can. J. Plant Sci. 92: 923–931. Variation in soil properties, such as soil moisture, across a hummocky landscape may influence wild oat emergence and growth. To evaluate wild oat emergence, growth, and management according to landscape position, a study was conducted from 2006 to 2010 in a hummocky field in the semiarid Moist Mixed Grassland ecoregion of Saskatchewan. The hypothesis tested was that wild oat emergence and growth would be greater in lower than upper slope positions under normal or dry early growing season conditions. Three herbicide treatments were imposed on the same plots each year of a 2-yr canola (Brassica napus L.) – wheat (Triticum aestivum L.) sequence: (1) nontreated (weedy) control; (2) herbicide application to upper and lower slope positions (i.e., full or blanket application); and (3) herbicide application to lower slope position only. Slope position affected crop and weed densities before in-crop herbicide application in years with dry spring growing conditions. Site-specific wild oat herbicide application in hummocky fields in semiarid regions may be justified based on results of wild oat control averaged across slope position. In year 2 of the crop sequence (wheat), overall (i.e., lower and upper slope) wild oat control based on density, biomass, and dockage (i.e., seed return) was similar between site-specific and full herbicide treatment in 2 of 3 yr. Because economic thresholds have not been widely adopted by growers in managing wild oat, site-specific treatment in years when conditions warrant may be an appropriate compromise between no application and blanket herbicide application.

Influence of tillage displaced soil on the productivity and yield components of barley in northwest Iran

Nazmi, L., Asadi, H., Manukyan, R. and Naderi, H. 2012. Influence of tillage displaced soil on the productivity and yield components of barley in northwest Iran. Can. J. Soil Sci. 92: 665–672. In hilly landforms subject to long-term cultivation, erosion has denuded the upper slope positions of topsoil, and accumulated topsoil in the lower slope positions. Slope gradient and position effects aggregation processes, which in turn impact soil productivity. A field experiment was conducted to assess the tillage-induced soil displacement and its effects on the soil properties and barley (Hordeum vulgare var. Sahand) biomass production for three different landscapes. The study was conducted on a hill slope seeded with barley (1.4–10.1° slope) located in the Mollaahmad watershed of the Ardabil province in northwestern Iran. For this purpose, soil samples were collected from four slope positions in a grassland as well as an agricultural field (dryland). A field experiment was conducted to evaluate the effects of slope gradient and position on barley growth and soil quality. Soil generally had lower organic carbon, available phosphorus, calcium carbonate equivalent, soil water content and mean weight diameter of soil aggregates in the farmland than the grassland, and in the upper slope positions than in the lower slopes. Significantly higher barley growth indices were associated with lower slope positions. Agronomic productivity of the soil was lowest for landscapes with the highest slope gradient. The relationships between tillage erosion and yield components were found to be significant. Spike weight and slope position had the largest contribution for the explanatory capacity of canonical variables (tillage erosion and yield components) estimated when compared with other parameters (slope gradient, dry matter, spike number, grain yield and 1000-grain weight). The findings in this study can be used as a tool to assist farmers, soil and water conservationists, and other policymakers in decision making regarding the use of lands.

Relationships between Soil Compaction and Harvest Season, Soil Texture, and Landscape Position for Aspen Forests

Although a number of harvesting studies have assessed compaction, no study has considered the interacting relationships of harvest season, soil texture, and landscape position on soil bulk density and surface soil strength for harvests in the western Lake States. In 2005, we measured bulk density and surface soil strength in recent clearcuts of predominantly aspen stands (Populus grandidentata Michx. and Populus tremuloides Michx.) in the Chippewa National Forest in northern Minnesota. We stratified these clearcuts by the season harvested, soil texture, and topographic position. In nearly all cases, we observed higher bulk density and surface soil strength following harvesting compared with adjacent and similar but unharvested stands. Within harvested sites, fine-textured soils generally had higher surface soil strength (more compaction) than coarse-textured soils when harvested in the summer, and fine-textured sites harvested in the summer had higher surface soil strength than those harvested in the winter. Landscape position was an important factor only in fine-textured soils. Both summit and toeslope positions had higher surface soil strength following summer harvesting compared with winter harvesting. Overall, our results indicate that fine-textured soils located on both lower and upper slope positions and harvested during unfrozen soil conditions are most susceptible to compaction during logging.

Nitrogen dynamics in a feedlot soil

ABSTRACT The feedlot system (FL) generates a high input of sewage causing imbalances in the cycling process of nitrogen (N) as well as a potential negative impact on the environment. The objective of this study was to deepen into the dynamics of N in a FL´s soil so as to provide tools to reduce its environmental impact. The study was conducted in a FL, located in Balcarce County (Buenos Aires, Argentina). Soil samples were taken between November 2006 and May 2007 in a control Pasture, in the FL-High (Upper Slope position) and FL-Low (Lower Slope position) of the FL, and in the runoff area (RA). Urease activity and concentrations of Ammonium-N, Nitrate-N and urea-N were evaluated in the soil up to 60 cm depth. Urea-N values were always low (6 mg kg -1 ), due to the high urease activity measured (438 mg kg -1 ). Ammonium-N concentration was highest in FL-Low, reaching a value of 65.5 mg kg -1 at 40-60 cm soil depth. Nitrate-N concentration was highest in FL-High for all depths, with a maximum concentration of 97.4 mg kg

Agroforestry system reduces subsurface lateral flow and nitrate loss in Jiangxi Province, China

Subsurface lateral flow is an important pathway responsible for agricultural non-point source pollution and may be affected by land use. An agroforestry system, citrus ( Citrus reticulata) tree intercropped with peanut ( Arachis hypogaea) crop and a mono peanut cropping system were compared over the period from 2003 to 2005 in Jiangxi Province, China. The objectives of this study were (i) to identify subsurface lateral flow by monitoring soil matric potential and NO 3-N concentration in soil water, and (ii) to estimate subsurface lateral flow and associated NO 3-N loss by modelling the water budget using Hydrus-2D. The dynamics of soil water, either during a particular storm or on an annual basis, demonstrated that subsurface lateral flow generated along the slopes under the two systems. The agroforestry system had a larger domain and a longer resident time of water saturation in the deeper soil layers than the mono cropping system, suggesting that the agroforestry system may have increased water retention capacity of subsurface soil due to its deeper root system. The simulated annual water budget showed that, compared with the mono cropping system, the agroforestry system reduced subsurface lateral flow by 9.2% of annual rainfall, which was equivalent to the amount of precipitation predicted to be reduced by interception. The two cropping systems received the similar amount of organic and inorganic N fertilizers (160.0–170.0 kg N ha −1 a −1), the total amount of N inputs in agroforestry system was smaller as it may have received less biological fixed N by about 0 to 70 kg N ha −1 a −1 due to the smaller effective area occupied by peanut crops. NO 3-N concentration measured in soil water in the agroforestry system was low within the soil profile (0.6–7.6 mg L −1) and had little seasonal variation. However, in the mono cropping system the NO 3-N concentration had two peaks in a year, which ranged from 14 to 52 mg L −1 at all soil depths between 0.20 and 0.85 m, and was higher on the lower slope than on the upper slope position. The estimated NO 3-N loss associated with subsurface lateral flow ranged from 45 to 64 kg ha −1 a −1 in the mono cropping system and from 16 to 48 kg ha −1 a −1 in the agroforestry system. The smaller NO 3-N loss in the agroforestry system was probably attributed to the smaller total N inputs and/or to the reduced subsurface lateral flow. However, the underlying mechanisms and the effectiveness of agroforestry systems need further study.

Effect of land use and topography on soil properties and agronomic productivity on calcareous soils of a semiarid region, Iran

ABSTRACTIn this research, the effects of land use and slope position on soil properties and its agronomic productivity were studied in a greenhouse experiment. The study also covered the effects of water stress, fertilizer treatment and their interactions. Eight soil samples were collected from four slope positions along hill slopes from two adjacent land use types of rangeland and dry farmland in a semiarid region of Iran. Soil samples were analyzed for their physical and chemical properties and yield and yield components of wheat were measured as indices of soil agronomic productivity in a replicated pot experiment. Soils of the dry farmland showed higher fertility and better quality than the soils from the adjacent degraded rangeland, especially at the upper slope positions. The results indicated that yield components of wheat were all higher for the dry farming land compared to the degraded rangeland, and at the bottom of slopes compared to the top. The effect of land use and slope position on agronomic productivity of soil was influenced by water supply. The actual impact on soil productivity of soil degradation, induced by land use and slope position, was overshadowed by the dominating effect of water stress. While both chemical fertilizer and fertilizer + manure treatments enhanced the agronomic productivity of all soils, their effects were much more pronounced on the degraded soils of the rangeland. Water stress reduced fertilizer efficiency on all the soils used in this study. Copyright © 2011 John Wiley & Sons, Ltd.

Soil characteristics in relation to groundwater for selected Dark Brown Chernozems in southern Alberta

Limited information exists on soil characteristics in relation to groundwater for undulating morainal landscapes of the Dark Brown soil zone in western Canada. A 4-yr (1985-1988) field study was conducted in southern Alberta to investigate these relationships for selected Dark Brown Chernozems. Soil morphology, physical and chemical properties of the soil horizons, water fluxes in the saturated zone, and tritium content of shallow groundwater were determined at nine sites. Three Orthic Dark Brown Chernozemic soils occurred in groundwater recharge areas with water tables ≥1.81 m, indicating that leaching of carbonates from the B horizons was consistent with downward groundwater flow. The other three Orthic soils occurred in groundwater discharge areas, and they may have developed because of deeper (≥2.60 m) water tables. High water-soluble Na in these latter three Orthic soils suggested a sodic influence from a shallower water table sometime in the recent past. The two Calcareous Dark Brown Chernozems, and saline Calcareous Dark Brown Chernozem occurred in groundwater recharge areas. One calcareous soil at a lower slope position had a shallow (0.84-2.02 m) water table, suggesting carbonates were brought upward into the Cca horizon from the groundwater. The other calcareous soil at the upper slope position had a deeper (>6.62 m) water table, suggesting carbonates were leached downward and precipitated in the Cca horizon. The saline Calcareous Dark Brown Chernozem was located in an area of groundwater recharge with a deeper (4-9 m) water table, suggesting that salinization likely occurred sometime in the past. Groundwater flow conditions during this study could not explain the genesis of some soils in this study area, suggesting that past groundwater, climatic, and environmental conditions need to be considered to explain the genesis of some relict soils.

Genotype and slope position control on the availability of soil soluble organic nitrogen in tea plantations

Soluble organic nitrogen (SON) plays a vital role in ecosystem N cycling processes and is controlled by a number of biotic and abiotic factors. We compared soil SON availability, microbial biomass, protease and asparaginase activities and phospholipids fatty acid (PLFA) profiles at the 0–15 and 15–30 cm layers in 10 year old tea plantations of two genotypes—Oolong tea (Camellia sinensis (L.) O. Kuntze cv. Huangjingui) (designated as ‘OT’) and Green tea (C. sinensis (L.) O. Kuntze cv. Fuyun 6) (designated as ‘GT’)—established at different slope positions. Concentrations of soil SON measured by the 2 M KCl extraction under the OT plantation were greater than under the GT plantation, while concentrations of soil SON were greater in the middle slope (MS) and lower slope (LS) positions than in the upper slope (US) position. Trends in soil microbial biomass C and N and protease and asparaginase activities between the two genotypes and across the slope positions were similar to the SON pools. The fungal-to-bacterial ratios were higher in the US position than in the MS and LS positions and higher under the GT plantation than under the OT plantation. Results from this study support that the genotype and the slope position are key factors controlling the availability of soil SON in tea plantations and also imply the importance of plant traits (e.g. litter quantity and chemistry) and soil texture in determining overall soil N availability and transformation processes and microbial community composition at the landscape level.

Mineral weathering and elemental transport during hillslope evolution at the Susquehanna/Shale Hills Critical Zone Observatory

Located in the uplands of the Valley and Ridge physiographic province of Pennsylvania, the Susquehanna/Shale Hills Critical Zone Observatory (SSHO) is a tectonically quiescent, first-order catchment developed on shales of the Silurian Rose Hill Formation. We used soil cores augered at the highest point of the watershed and along a subsurface water flowline on a planar hillslope to investigate mineral transformations and physical/chemical weathering fluxes. About 25 m of bedrock was also drilled to estimate parent composition. Depletion of carbonate at tens of meters of depth in bedrock may delineate a deep carbonate-weathering front. Overlying this, extending from ∼6 m below the bedrock–soil interface up into the soil, is the feldspar dissolution front. In the soils, depletion profiles for K, Mg, Si, Fe, and Al relative to the bedrock define the illite and chlorite reaction fronts. When combined with a cosmogenic nuclide-derived erosion rate on watershed sediments, these depletion profiles are consistent with dissolution rates that are several orders of magnitudes slower for chlorite (1–5 × 10 −17 mol m −2 s −1) and illite (2–9 × 10 −17 mol m −2 s −1) than observed in the laboratory. Mineral reactions result in formation of vermiculite, hydroxy-interlayered vermiculite, and minor kaolinite. During weathering, exchangeable divalent cations are replaced by Al as soil pH decreases. The losses of Mg and K in the soils occur largely as solute fluxes; in contrast, losses of Al and Fe are mostly as downslope transport of fine particles. Physical erosion of bulk soils also occurs: results from a steady-state model demonstrate that physical erosion accounts for about half of the total denudation at the ridgetop and midslope positions. Chemical weathering losses of Mg, Na, and K are higher in the upslope positions likely because of the higher degree of chemical undersaturation in porewaters. Chemical weathering slows down in the valley floor and Al and Si even show net accumulation. The simplest model for the hillslope that is consistent with all observations is a steady-state, clay weathering-limited system where soil production rates decrease with increasing soil thickness.

Pedogenesis of a catena of the Farmdale–Sangamon Geosol complex in the north central United States

The Farmdale–Sangamon Geosol pedocomplex consists of the Sangamon Geosol and the overlying Farmdale Geosol, which form the most extensive terrestrial record of the last interglacial to glacial transition in the Midwest United States. The geosol complex formed for upwards of 100 ka, extending from the end of MIS 6 through 4 for the Sangamon Geosol, then the Farmdale Geosol for during a brief episode at the end of MIS 3 following slow accumulation and pedogenic modification of eolian silt deposited on top of the Sangamon Geosol. Our study site consists of a buried paleo-hillslope transect that forms a catena, enabling evaluation of slope effects on interglacial-scale soil formation. The Sangamon Geosol is formed in calcareous and illitic glaciogenic sediment. Along the catena the Sangamon Geosol profiles display some morphological changes, namely in terms of colors that we interpret as indicators of differences in drainage. Most thickness and horizonation characteristics are similar all along the transect, with intact upper sola horizons (AE and E horizons) that overlie clay-enriched Bt horizons. The Bt horizons contain abundant clay that exists as illuvial clay coatings, matrix infills, and as mosaic-speckled domains. The clay originated both by in situ weathering and through illuviation from the clay depleted upper sola. Slope does not appear to affect Bt characteristics beyond redder hues of the matrix and clay coatings in the upper slope position. With depth, effects of carbonate leaching and infilling of clay in the matrix decrease and clay coatings are restricted to walls of voids adjacent to aggregates. Clay mineralogy shows illite depletion, but no interstratified kaolinite-expandable minerals, indicating the degree of weathering is not as great as is typical of Sangamon Geosol profiles formed in loess or in glaciogenic sediment of the central Illinois type area. Clay mineralogy is also stratified with depth, coincident with particle size, which probably indicates sorting of layers of illitic dolomite and shale. Variation of horizon and profile characteristics appears to largely be a function of particle size variability and stratification than topographic position in the catena. The influence of hillslope position on soil redistribution during formation of the Sangamon Geosol appears negligible given the uniformity of upper solum horizon thickness and sandy particle size characteristics, so we conclude that a bioturbation and rainwash origin of the upper solum and the texture contrast in these profiles is not the best process model explanation. We suggest that the base-rich nature of these soils led to ecosystem characteristics that discouraged erosion and encouraged infiltration and a lessivage-type origin of the texture contrast. No convincing evidence of MIS 6 through MIS 4 loess occurs at this site. The Farmdale Geosol formed in the Robein Silt, which is Roxana Silt (MIS 3 loess) that was redistributed downslope. The Robein Silt is thicker and finer in the topographic low and indicates the cooler and forested environmental conditions during MIS 3 were conducive to downslope movement of soil and also produced greater differences in drainage-induced soil morphological changes in the Farmdale Geosol.

Land Use/Cover Changes between 1966 and 1996 in Chirokella Micro-watershed, Southeastern Ethiopia

Keywords: Land Cover; Dynamic; Expansion; Exposed Land; ReductionTwo periods of panchromatic aerial photographs taken in 1966 and 1996 were analyzed to determine spatial and temporal land cover changes occurring in Chirokella micro-watershed, Southeastern Ethiopia. Theresults of the analysis were digitized with Arc View GIS 3.3 software to produce land use/cover maps for 1966 and 1996. Five land use/cover categories, namely dense forest, moderately disturbed forest, bush, degraded and cultivated and settlement were identified. The result indicated an increase in an area of cultivated and settlement, bush and degraded and a decline in forest land cover categories over the 30 year period. The dense forest land cover decreased by over 80%, giving an average decreasing rate of 32 ha (-2.9%) per year. The moderately disturbed forest land was completely transformed to other land cover systems between 1966 and 1996. Cultivated and settlement land increased by 62.8%, giving an annual average expansion rate of 33.3 ha (+2.1%) over the analysis period. Bush and degraded land cover categories showed increasing patterns of 49.9% and 100%, respectively. Transformation of forest land cover to others could explain an increasing demand for more arable and settlement land and timber resources associated with a population increase and a decline in land productivity due to degradation. This expansion largely took place onto steeper and upper slope positions, which resulted in increasing the area prone to land degradation, and further implicates adapting of more forest to cultivated and settlement land use/cover categories. Thus, it seems that, in the micro-watershed land, cover changes resulted from combinations of physical (e.g. land degradation) and socioeconomic (e.g. demand for more land resources) factors.

The role of climate and local regolith–landscape processes in determining the pedological characteristics of æolian dust deposits across south-eastern Australia

Fine-grained æolian sediments are an important component of many loessic soil–landscape systems across south-eastern Australia. These loessic soils are commonly related to the deposition of ‘parna’, a red, clayey, calcareous material proposed to have been transported predominantly as silt-sized pellets and companion silt grains. However, it is apparent that loessic soils of south-eastern Australia do not necessarily exhibit or retain the morphological features regarded as typical of parna. This may be due to variations in post-depositional pedogenic processes operating over long periods of time. It is important to understand this inconsistency in loessic soil expression because the physico-chemical and structural attributes of these profiles may significantly affect catchment-wide processes such as salinisation and erosion. In this paper, the pedological features of a range of previously identified loessic profiles occurring across south-eastern Australia are examined to assess the relative importance of climate and local landscape processes on profile characteristics. Most of the sampling sites occur in mid- to upper-slope positions, while the annual average rainfall of the sites ranges from 440 mm to 650 mm. The deepest profiles in the driest locations tend to yield whole-coloured, slightly alkaline, slightly saline and sodic subsoils with moderate cation exchange capacities. Profiles in the wettest locations are generally characterised by smaller cation exchange capacities, are acidic, non-saline and non-sodic, and feature prominent mottling and sesquioxide nodules. Measurements and predictions of the structural attributes of the profiles indicate that all topsoils are quite stable to wetting, whereas subsoils exhibit variable stabilities, depending on physico-chemical properties. These results appear to demonstrate a broad climosequence effect on loessic soil attributes. The climosequence effect was compared to the changes in loessic profile characteristics down a case study toposequence in southern New South Wales. The toposequence indicates that local landscape features such as slope and drainage have also been important in determining the properties of these materials, as has re-working by colluvial processes. We conclude that to explain adequately the current characteristics of profiles containing fine-grained æolian sediments, particularly their salinisation potential and stability to erosion, it is critical to consider both the past and present climate and the local soil-forming processes.

Coarse root growth of Veronese poplar trees varies with position on an erodible slope in New Zealand

Poplars are commonly planted on moist, unstable pastoral hill country to prevent or reduce soil erosion, thereby maintaining hillslope integrity and pasture production. Mechanical reinforcement by poplar root systems aids slope stabilisation, particularly when the roots are anchored into the fragipan or underlying rock. Total root length, mass and distribution of coarse roots (≥2 mm diameter) were determined for three Populus deltoides × nigra ‘Veronese’ trees in their 12th growing season after being planted as 3 m poles at upper slope (TU), mid-slope (TM) and lower slope (TL) positions on an erodible hillslope near Palmerston North in the southern North Island. Most of the roots were distributed in the top 40 cm of soil. Depth of penetration of vertical roots was dependent on slope position and limited by the available depth of the soil above a fragipan (0.35 m at the upper slope to 1.4 m at the lower slope). Roots penetrated the fragipan at the upper slope position where the soil depth was shallowest, and at the mid-slope, but not the lower slope position. Total coarse root length was 287.9 m for TU, 1,131.3 m for TM and 1,611.3 m for TL, and total coarse root dry mass (excluding root crown) was 8.15 kg for TU, 38.77 kg for TM and 81.35 kg for TL.

Factors influencing surface runoff generation from two agricultural hillslopes in central Pennsylvania

AbstractThe variable source area (VSA) concept provides the underlying paradigm for managing phosphorus losses in runoff in the north‐eastern USA. This study sought to elucidate factors controlling runoff along two hillslopes with contrasting soils, including characterizing runoff generation mechanisms and hydrological connectivity. Runoff monitoring plots (2 m × 1 m) were established in various landscape positions. Footslope positions were characterized by the presence of a fragipan that contributed to seasonally perched water tables. In upslope positions without a fragipan, runoff was generated primarily via the infiltration‐excess (IE) mechanism (96% of events) and was largely disconnected from downslope runoff. Roughly 80% of total runoff originated from the north footslope landscape position via saturation‐excess (SE) (46% of events; 62% of runoff) and IE (54% of events; 38% of runoff) mechanisms. Runoff from the north hillslope was substantially greater than the south hillslope despite their proximity, and apparently was a function of the extent of fragipan representation. Results demonstrate the influence of subsurface soil properties (e.g. fragipan) on surface runoff generation in variable source area hydrology settings, which could be useful for improving the accuracy of existing runoff prediction tools. Published in 2009 by John Wiley & Sons, Ltd.

Soil Profile Properties in Relation to Soil Redistribution by Intense Tillage on a Steep Hillslope

Little is known about soil redistribution by tillage and its impact on the properties of soil profiles with thin soil layers on hillslopes. In this study, consecutive tillage by hoeing was performed 5 and 15 times on an Orthic Regosol within a steep hillslope landscape of the Sichuan Basin, China, to simulate the impact of short‐ and long‐term tillage on soil profile properties at different slope positions. After intense tillage, significant changes in 137Cs inventories of the soil occurred in the summit and toeslope positions. The soil profile (originally ≤0.3 m in depth) disappeared on the slope summit due to intense soil downslope translocation, and the soil profile was truncated in upper slope positions in the proximity of the summit, while a thickened soil profile was present in toeslope positions, where the original soil profile was buried. The summit was characterized by an exposure of bedrock corresponding to areas of 4.77 and 10.0% of the experimental plot for 5 and 15 tillage operations, respectively. Soil organic C (SOC) and P were completely depleted with the disappearance of soil profiles at the summit position, while a substantial increase in SOC and extractable P inventories of the post‐tillage soil profile was found in the toeslope position. Intense tillage caused remarkable soil redistribution within the landscape of the steep slope, resulting in net soil loss and gain close to the upslope and downslope boundaries of the field, respectively. Tillage results in an intense transformation of soil profiles and the variation in soil properties in steeply sloping fields.

Distribuição e formas de ocorrência de zinco em solos no município de Vazante - MG

A contaminação de solos é um problema atual que requer investigação detalhada no sentido de estabelecer critérios para a distinção entre anomalias naturais e contribuição antrópica. O trabalho foi desenvolvido com o objetivo de avaliar a distribuição e as formas de ocorrência de Zn para identificar a origem de valores anômalos em solos adjacentes a áreas de mineração no município de Vazante-MG. Foram coletadas amostras de perfis de solos em remanescentes sobre a área minerada e em posições a jusante e a montante desta, nas camadas de 0-2, 2-5, 5-10, 10-20, 20-50, 50-100, e 100-150 cm. Um estudo de extração seqüencial avaliou os teores de Zn nas formas: (a) solúvel; (b) trocável; (c) associada a carbonatos; (d) associada a óxidos amorfos; (e) associada a óxidos cristalinos; (f) associada à matéria orgânica; (g) residual; e (h) total. Verificou-se que os teores de Zn, de modo geral, são mais elevados nas áreas localizadas sobre a zona de mineralização, com solos mais jovens (Cambissolos e Neossolos), em relação aos solos mais intemperizados (Latossolos e Argissolos), localizados tanto a montante quanto a jusante da área minerada. Os teores totais foram muito altos. Mesmo considerando apenas as formas solúvel e trocável, mais lábeis, em alguns perfis os valores foram superiores aos teores totais encontrados naturalmente em solos. Verificou-se um padrão decrescente dos teores com a profundidade nos perfis localizados fora da área minerada. Por outro lado, os teores de Zn aumentaram com a profundidade em um Cambissolo localizado na área minerada. Não houve diferença significativa entre os teores de Zn das áreas a montante e a jusante em todas as formas químicas avaliadas, sugerindo que não se pode presumir efeito antrópico na dispersão do Zn em áreas adjacentes à zona de mineralização.

Anisotropy of Soil Hydraulic Properties Along Arable Slopes

The spatial variations of the soil hydraulic properties were mainly considered in vertical direction. The objectives of this study were to measure water-retention curves, θ(ψ), and unsaturated hydraulic conductivity functions, K(ψ), of the soils sampled at difierent slope positions in three directions, namely, in vertical direction, along the slope and along the contour, and to determine the efiects of sampling direction and slope position of two soil catenas. At the upper slope positions, the surface soils (0–10 cm) sampled in the vertical direction had a lower soil water content, θ, at a certain soil water potential (−1 500 kPa < ψ < −10 kPa) and had the greatest unsaturated hydraulic conductivity, K, at ψ > −10 kPa. At the lower slope positions, K at ψ > −10 kPa was smaller in the vertical direction than in the direction along the slope. The deep soils (100–110 cm) had similar soil hydraulic properties in all the three directions. The anisotropic variations of the hydraulic properties of the surface soils were ascribed to the efiects of natural wetting and drying cycles on the structural heterogeneity. These results suggested that the anisotropy of soil hydraulic properties might be signiflcant in influencing soil water movement along the slope and need to be considered in modeling.

Nitrate in Tile Drainage of the Semiarid Palouse Basin

Topographically heterogeneous agricultural landscapes can complicate and accelerate agrochemical contamination of streams due to rapid transport of water and chemicals to poorly drained lower-landscape positions and shallow ground water. In the semiarid Palouse region, large parts of these landscapes have been tile drained to enhance crop yield. From 2000-2004 we monitored the discharge of a tile drain (TD) and a nearby profile of soil water for nitrate concentration ([NO(3)]), electrical conductivity level (EC), and water content to develop a conceptual framework describing soil nitrate occurrence and loss via subsurface pathways. Tile-drain baseflow [NO(3)] was consistently 4 mg N L(-1) and baseflow EC was 200 to 300 microS cm(-1). Each year sudden synoptic increases in TD discharge and [NO(3)] occurred in early winter following approximately 150 mm of fall precipitation, which saturated the soil and mobilized high-[NO(3)] soil water throughout the profile. The greatest TD [NO(3)] (20-30 mg N L(-1)) occurred approximately contemporaneous with greatest TD discharges. The EC decrease each year (to approximately 100 microS cm(-1)) during high discharge, a dilution effect, lagged approximately 1 mo behind the first appearance of high [NO(3)] and was consistent with advective transport of low-EC water from the shallow profile under saturated conditions. Water-budget considerations and temporal [NO(3)] patterns suggest that these processes deliver water to the TD from both lower- and upper-slope positions, the latter via lateral flow during the high-flow season. Management practices that reduce the fall reservoir of soil nitrate might be effective in reducing N loading to streams and shallow ground water in this region.

Controls on the spatial distribution of soil moisture and solute transport in a sloping reclamation cover

A detailed field study was conducted to map the spatial distribution of soil moisture and salt transport within a sloping clay-rich reclamation cover overlying a saline-sodic shale overburden landform. The soil moisture data suggest that: lower-slope positions are wetter in spring due to the down-slope movement of surface run-off; infiltration occurs via preferential flow paths while the ground is frozen; and, interflow occurs along the cover–shale surface when the ground thaws. Soil moisture conditions also remain wetter in lower-slope positions throughout the summer and fall. Salt transport from the shale into the overlying cover is affected predominantly by soil moisture conditions and lateral groundwater flux. Quasi one-dimensional modelling of in situ profiles of pore-water Na+ concentration demonstrate that: (i) increased soil moisture conditions in lower-slope positions accelerate salt transport into the cover through diffusion; (ii) snow melt infiltration water bypasses the soil matrix higher in the cover profile; (iii) drier conditions in the mid- and upper-slope positions limit salt transport through diffusion; (iv) advection accelerates upward salt transport in lower-slope positions; and, (v) interflow and (or) deep percolation are key mechanisms mitigating vertical salt movement in lower- and upper-slope positions.