Outwash Soils Research Articles

Effects of Biochar on Drought Tolerance of Pinus banksiana Seedlings

Drought is a major stressor of tree seedlings regarding both natural and artificial regeneration, especially in excessively drained, sandy outwash soils. While climate change is expected to cause an increase in the total annual precipitation in the Upper Midwest, USA, the timing of the precipitation is predicted to result in longer periods of drought during the growing season. Biochar, a material created through the pyrolysis of organic matter, such as wood waste, has been proposed as a soil amendment that may increase the water holding capacity of a soil. Biochar has mostly been studied in agricultural settings, and less is known about the impact of biochar on forest soils and tree seedlings. We used a greenhouse experiment to test the ability of biochar to improve the drought tolerance of jack pine (Pinus banksiana) seedlings via increased soil water holding capacity. The seedlings were planted in sandy soil treated with three levels of biochar (none, 3% by weight, and 6% by weight) in two experiments, one manipulating the timing of drought onset and the other controlling the amount of water that seedlings received. Our results showed no significant effects of biochar on seedling survival, growth, or physiology under drought conditions. While this outcome did not support the hypothesis that biochar would increase seedling performance, the biochar amendments did not negatively affect seedlings, indicating that biochar may be added to soil for carbon storage without having negative short-term impacts on tree seedlings.

Long-Term Ecosystem Nutrient Pool Status for Aspen Forest Harvest Simulations on Glacial Till and Sandy Outwash Soils

Sandy outwash and glacial till soils compose large amounts of public forestland due to historically poor agricultural yields. The outwash soils have low fertility, poor nutrient retention and are restricted from whole-tree harvesting (WTH) in some states, whereas the glacial till has medium nutrient retention and fertility, and is unrestricted from WTH. To assess the long-term sustainability of harvesting, a nutrient budget was constructed from field measurements, the National Cooperative Soil Survey (NCSS) database, and literature values for stem-only harvesting (SOH) and WTH at a 45-year rotation length and 11 rotations were simulated. The budgets showed that SOH and WTH recovery years, or the time necessary for the inputs to match outputs through leaching and one harvest, exceeded common rotation lengths for both soil types under all weathering scenarios, and the average WTH reduced the total available rotations by one harvest. The large variation in soil nutrient pools and harvest removals complicated the ability to identify the difference between SOH and WTH early in the model, but differences became apparent with sequential harvests. The recovery years were 2–20 times the 45-year rotation length under all weathering rates. Taken together, models in this study bridge the gap between short- and long-term studies and bring into question the sustainability of WTH and SOH practices on nutrient-poor soils.

Legacy effects of non-native Cytisus scoparius in glacial outwash soils: Potential impacts to forest soil productivity in western Washington

Scotch broom (Cytisus scoparius (L.) Link) is a highly competitive, nonnative, leguminous shrub species of major concern in coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) forests of the Pacific Northwest that has potential to impact long-term soil productivity. We conducted a bioassay to assess the potential for legacy effects on soils (e.g., soil nutrient effects, soil seedbank, etc.) following Scotch broom removal and the potential for recovery over time. The bioassay was conducted using glacial-outwash soils from an existing Long-Term Soil Productivity study near Matlock, WA, USA, where Scotch broom had been removed or kept out for 0 (broom present), 4, 10, or 14 years. Soils from each broom removal duration were combined with fertilizer treatments to assess mechanisms of response of three native plant species: yarrow (Achillea millefolium L.), Roemer’s fescue (Festuca idahoensis Elmer ssp. Roemeri), and coast Douglas-fir. There was evidence for negative soil legacy effects on Douglas-fir growth and biomass, which decreased with time since broom removal. Responses to the fertilizer treatments indicated the effect was not associated with reduced nutrient availability. In contrast, both yarrow and Roemer’s fescue had significantly greater biomass in soil from where broom was recently present, which decreased with time since broom removal. Responses to the fertilizer treatments indicated that this positive legacy effect is associated with nutrient availability, likely increased N. Soils from 0 and 4 years since broom removal were estimated as having the potential to produce over 578,500 Scotch broom germinants ha−1. Our results demonstrate the potential for both negative and positive soil legacy effects of broom depending on the responding plant species. Combined effects of negative soil legacies and a large and viable seed bank from Scotch broom create growing conditions likely to hinder long-term productivity of Douglas-fir.

A Test of Two Spatial Frameworks for Representing Spatial Patterns of Wetness in a Glacial Drift Watershed

Core Ideas Soil moisture and water table position vary across ecosystems and parent materials. Ecosystem classifications and topographic wetness indices represent moisture status. Topographic wetness indices perform best in till rather than outwash soils. Including soil properties with topographic information improves moisture estimates. In forest ecosystems, soil water availability is an important indicator and driver of biogeochemical transformations, pedogenesis, and surface water–groundwater linkages. Given the importance of soil moisture and shallow groundwater to ecosystem processes, field measurements are critical. We investigated the spatial patterns and temporal dynamics of moisture conditions in a forested first‐order watershed in northern Michigan. We measured soil volumetric water content (VWC, %) and water table levels across a range of glacial parent materials and landforms. We also assessed the utility of using two different spatial frameworks (Landscape Ecosystem classification, Topographic Wetness Index) to represent spatial patterns of soil moisture and water table levels across the watershed. At the lowest landscape position (outwash‐lake plain swamp), saturation was perennial, with a median soil VWC of 53% and the water table 8 cm below ground surface. Among upland ecosystems, outwash landforms had consistently low VWC (16%) and showed no evidence of groundwater within 4 m of the surface; moraine ecosystems (till parent material) possessed mixed hydrologic conditions, with VWC ranging from 18 to 25% and water table levels 6 to 65 cm below the surface. In low‐variability dry or wet areas with relatively homogenous soils, larger ecosystem classification map units provide good representations of moisture conditions. In the more heterogeneous till soils, a finer‐scale spatial framework that accounts for local soil variation is optimal. A combination of both spatial frameworks is most appropriate for estimating moisture conditions in this glaciated landscape and can be used to identify biogeochemically important sites and to inform land management decisions.

Local‐scale and watershed‐scale determinants of summertime urban stream temperatures

AbstractThe influence of urbanization on the temperature of small streams is widely recognized, but these effects are confounded by the great natural variety of their contributing watersheds. To evaluate the relative importance of local‐scale and watershed‐scale factors on summer temperatures in urban streams, hundreds of near‐instantaneous temperature measurements throughout the central Puget Lowland, western Washington State, were collected during a single 2‐h period in August in each of the years 1998–2001. Stream temperatures ranged from 8.9 to 27.5 °C, averaging 15.4 °C. Pairwise correlation coefficients between stream temperature and four watershed variables (total watershed area and the watershed percentages of urban development, upstream lakes, and permeable glacial outwash soils as an indicator of groundwater exchange) were uniformly very low. Akaike's information criterion was applied to determine the best‐supported sets of watershed‐scale predictor variables for explaining the variability of stream temperatures. For the full four‐year dataset, the only well‐supported model was the global model (using all watershed variables); for the most voluminous single‐year (1999) data, Akaike's information criterion showed greatest support for per cent outwash (Akaike weight of 0.44), followed closely by per cent urban development + per cent outwash, per cent lake area only, and the global model. Upstream lakes resulted in downstream warming of up to 3 °C; variability in riparian shading imposed a similar temperature range. Watershed urbanization itself is not the most important determining factor for summer temperatures in this region; even the long‐recognized effects of riparian shading can be no more influential than those imposed by other local‐scale and watershed‐scale factors. Copyright © 2013 John Wiley & Sons, Ltd.

Enhanced containment of polycyclic aromatic hydrocarbons through organic modification of soils

A methodology to enhance the containment of polycyclic aromatic hydrocarbons (PAHs) in pervious pavement systems was developed through the chemical modification of a typical Rhode Island glacial outwash soil. In addition, the PAH‐retaining capacity of different structural components of pervious pavements was evaluated using column experiments in terms of PAH retention. Two methods were used for soil amendments. The first method was a direct modification of the porous matrix using quaternary ammonium cations through an ion exchange process. The second method involved blending the soil with a commercial organoclay (PM‐199; CETCO Oil Field Services). These amendments successfully increased the soil's fraction of organic carbon (foc) by at least 70%. To quantify the efficiency of these amended soils to sorb PAHs, a series of batch isotherms and column experiments were conducted on unmodified and modified soils. These studies demonstrated that, through the synthetic modification, the sorption of PAH was increased by up to 20‐fold. The Langmuir (α, β) and Freundlich (KF, n) isotherm coefficients calculated from batch studies were higher when compared with column experiments. Overall, the organoclay‐glacial outwash blend exhibited the greatest KF value of 114.2. Breakthrough curves obtained using HYDRUS 1D were compared with measured data. The column experiments conducted on porous concrete and aggregate demonstrated that these materials have a minimal contribution to the overall containment of PAH in pervious pavement systems. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 47–54, 2014

Spatial Distribution of Carbon in the Subsurface of Riparian Zones

Soil C supplies vary spatially within and among riparian wetlands. Understanding this variability is essential to assessments of C‐dependent riparian wetland functions such as water quality enhancement and C storage. In this study, we examined the distribution of C with depth across the riparian landscape. Our objectives were to describe the spatial distribution of various C forms in the subsurface of riparian wetlands, and to identify the watershed, landscape, and soil characteristics that govern the distribution of these forms. Twenty‐two riparian sites, mapped as alluvial or outwash soils, were examined along first‐ through fourth‐order streams. Soils were described from pits and auger borings along transects established perpendicular to the stream. Roots and buried A horizons represent the majority of C in the subsurface, representing an important source of C for riparian zone functions. Buried A horizons and C‐rich lenses, indicative of alluvial soils, were identified in 21 of the 22 sites. Higher order riparian zones tended to have greater quantities of alluvium. Roots were generally distributed to the greatest depths close to the streams where alluvial deposits were thickest. All first‐, second‐, and third‐order riparian zones were mapped as outwash soils on county‐scale soil surveys. These sites, however, contained predominantly alluvial soils, suggesting that soil surveys at the 1:15,840 scale are inadequate for identifying alluvial soils along lower order streams. To assess the best predictors of alluvium distribution within riparian zones, 11 watershed characteristics were examined. A forward stepwise regression revealed that watershed size and floodplain width are two of the most important indicators of the quantity, width, and depth of alluvium, and subsequently subsurface C, within glaciated riparian zones.

Manure placement depth impacts on crop yields and N retained in soil

The objective of this study was to determine the impact of manure placement depth on crop yield and N retention in soil. Experimental treatments were deep manure injection (45 cm), shallow manure injection (15 cm), and conventional fertilizer-based management with at least three replications per site. Water infiltration, and changes in soil N and P amounts were measured for up to 30 months and crop yield monitored for three seasons following initial treatment. Deep and shallow manure injections differed in soil inorganic N distributions. For example, in the manure slot the spring following application, NO3-N in the surface 60 cm was higher (p < .01) when injected 15 cm (21.4 μ g/g) into the soil than 45 cm (11.7 μ g/g), whereas NH4-N had opposite results with shallow injection having less (p = 0.045) NH4-N (102 μ g/g) than deep (133 μ g/g) injection. In the fall one year after the manure was applied, NO3-N and NH4-N were lower (p = 0.001) in the shallow injection than the deep injection. The net impact of manure placement on total N was that deep injection had 31, 59, and 44 more kg N ha− 1 than the shallow injection treatment 12, 18, and 30 months after application, respectively. Deep manure injection did not impact soybean (Glycine max L.) yield, however corn (Zea mays L.) yield increased if N was limiting. The higher corn yield in the deep injected treatment was attributed to increased N use efficiency. Higher inorganic N amounts in the deep injection treatment were attributed to reduced N losses through ammonia volatilization, leaching, or denitrification. Results suggest that deep manure placement in glacial till soil may be considered a technique to increase energy, N use efficiency, and maintain surface and ground water quality. However, this technique may not work in glacial outwash soils due to the inability to inject into a rocky subsurface.

Release of Oregon White Oak from Overtopping Douglas-fir: Effects on Soil Water and Microclimate

Many former Oregon white oak (Quercus garryana) woodland and savanna stands in the coastal Pacific Northwest have been invaded by Douglas-fir (Pseudotsuga menziesii) during the past century as a result of fire suppression. Douglas-fir overtop and suppress the shade-intolerant oak, causing its eventual mortality. Removal of Douglas-fir is necessary for restoration of these oak ecosystems, but such action will influence belowground and near-ground conditions, affecting residual trees and understory communities. In a three-year study on a glacial outwash soil near Olympia, Washington, we compared soil and microclimate conditions near overtopped and released oak trees to determine how soil water content (SWC), throughfall, soil and air temperature, and vapor pressure deficit (VPD) are affected when oak is released from overtopping Douglas-fir. In each year, volumetric SWC near all trees declined from ~0.25 m3 m−3 to ~0.10 m3 m−3 during the growing season, but this decline was delayed approximately one month i...

Nitrogen fixation and growth response of Alnus Rubra following fertiliztion with urea or biosolids

Nitrogen fertilization of forests using biosolids offers a potentially environmentally friendly means to accelerate tree growth. This field study was designed to analyze the effects of nitrogen fertilization on the symbiotic, nitrogen (N)-fixing relationship between Alnus rubra Bong. (red alder) and Frankia. Anaerobically digested, class B biosolids and synthetic urea (46% N) were applied at rates of 140, 280 and 560 kg ha-1 available N to a well-drained, sandy, glacial outwash soil in the Indianola series (mixed, mesic Dystric Xeropsamments). Plots were planted with A. rubra seedlings. At the end of each of two growing seasons trees were harvested and analyzed for the rate of N fixation (as acetylene reduction activity), biomass and foliar N. At year 1, there was no N fixation for trees grown with urea amendments, but control (17 µmol C2H4 g-1 hr-1) and biosolids (26-45 µmol C2H4 g-1 hr-1) trees were fixing N. At the end of year 2, all trees in all treatments were fixing N (7 µmol C2H4 g-1 hr-1, 4-16 µmol C2H4 g-1 hr-1, and 20-29 µmol C2H4 g-1 hr-1 for control, urea and biosolids respectively). Trees grown with biosolids amendments were larger overall (year 1 shoot biomass 10 g, 5 g, and 23 g for control, urea, and biosolids respectively, year 2 shoot biomass 50 g, 51 g, and 190 g for control, urea, and biosolids respectively) with higher concentrations of foliar N for both years of the study (year 1 foliar N 26 g kg-1, 27 g kg-1, and 40 g kg-1 for control, urea, and biosolids respectively, year 2 foliar N 17 g kg-1, 19 g kg-1, and 23 g kg-1 for control, urea, and biosolids respectively). Trees grown with urea amendments appeared to use the urea N over Frankia supplied N, whereas the biosolids trees appeared to be able to use both N in biosolids and N from Frankia. The results from this study indicated that the greater growth of A. rubra may have been responsible for the observed higher N demand. Biosolids may have supplied other nutrients to the trees to support this accelerated growth.

Nitrogen-fertilization impacts on carbon sequestration and flux in managed coastal Douglas-fir stands of the Pacific Northwest

We examined whether N-fertilization and soil origin of Douglas-fir [ Psuedotsuga menziesii (Mirb.) Franco] stands in western Washington state could affect C sequestration in both the tree biomass and in soils, as well as the flux of dissolved organic carbon (DOC) through the soil profile. This study utilized four forest sites that were initially established between 1972 and 1980 as part of Regional Forest Nutrition Research Project (RFNRP). Two of the soils were derived from coarse-textured glacial outwash and two from finer-textured volcanic-source material, primarily tephra, both common soil types for forestry in the region. Between 1972 and 1996 fertilized sites received either three or four additions of 224 kg N ha −1 as urea (672–896 kg N ha −1 total). Due to enhanced tree growth, the N-fertilized sites (161 Mg C ha −1) had an average of 20% more C in the tree biomass compared to unfertilized sites (135 Mg C ha −1). Overall, N-fertilized soils (260 Mg C ha −1) had 48% more soil C compared to unfertilized soils (175 Mg C ha −1). The finer-textured volcanic-origin soils (348 Mg C ha −1) had 299% more C than glacial outwash soils (87.2 Mg C ha −1), independent of N-fertilization. Soil-solution DOC collected by lysimeters also appeared to be higher in N-fertilized, upper soil horizons compared to unfertilized controls but it was unclear what fraction of the difference was lost from decomposition or contributed to deep-profile soil C by leaching and adsorption. When soil, understory vegetation and live-tree C compartments are pooled and compared by treatment, N-fertilized plots had an average of 110 Mg C ha −1 more than unfertilized controls. These results indicate these sites generally responded to N-fertilization with increased C sequestration, but differences in stand and soil response to N-fertilization might be partially explained by soil origin and texture.

Macro‐ and Micromorphology of Subsurface Carbon in Riparian Zone Soils

Soil organic matter (SOM) contains fractions that range from very active to passive, relative to microbial‐driven ecosystem processes and functions. A classification system is needed that can test the hypothesis that SOM can be separated by morphology into functionally meaningful fractions. The objectives of this study were to use macro‐ and micromorphological techniques to classify the various C forms present in saturated (or seasonally saturated) subsurface horizons of hydric riparian soils, and to increase our understanding of their genesis. Nine soils formed in outwash or alluvium, located in Rhode Island riparian wetlands, were described and sampled up to depths of over 3 m. The majority of these soils had seasonally high water table levels at or above the soil surface. Thirty‐four thin sections were constructed from undisturbed samples collected from subsurface horizons for micromorphological investigation. Six C forms (roots, fragmental organic matter [FOM], lenses, infillings, masses, and horizon C) and five root‐decomposition classes were identified. All C forms were more abundant in the subsurface of alluvial soils than in the subsurface of outwash soils. Masses and roots were the most abundant C form identified. Most masses have likely formed from dispersion of C associated with decomposed roots. Alluvial deposition has resulted in considerable C in subsurface riparian zone soils in the form of buried A and O horizons, lenses, and FOM. Illuvial‐horizon C was found primarily in sandy horizons having outwash parent materials. Carbon dating suggested that many of these C forms persist for thousands of years in the riparian subsurface. The variety of C forms that exist in riparian zone subsoils suggests that understanding C morphology, and how these forms are related, may prove useful for developing functionally different morphologic classes of soil C.

Phosphorus Leaching in Sandy Outwash Soils following Potato‐Processing Wastewater Application

Land application of wastewater presents potential for ground water pollution if not properly managed. In situ breakthrough tests were conducted using potato (Solanum tuberosum L.)-processing wastewater and a Br tracer to characterize P leaching in seasonally frozen sandy outwash soils. In the first test, P and Br breakthrough were measured in a 7-m deep well following wastewater [2.94 mg L(-1) total P (TP); 280 mg L(-1) Br] application at the site that had 13.1 mg water-extractable P (WEP) kg(-1)and 94.4 mg Bray-1 P kg(-1). Bromide was detected in the well after approximately 0.4 pore volumes, but there was no P break-through after 7 pore volumes. In the second breakthrough test, wastewater containing 3.6 mg L(-1) TP and 259 mg L(-1) Br was applied on 1.5-m deep lysimeters at low (0.8 mg WEP kg(-1); 12.1 mg Bray-1 P kg(-1)) and high soil test P sites (104 mg WEP kg(-1); 585 mg Bray-1 P kg(-1)). Leachate TP concentration during the test remained constant (0.04 mg L(-1)) at the low P sites but increased from approximately 3.5 to 5.6 mg L(-1) at the high P sites. These results indicate no P leaching in low P soils, but leaching in high P soils, thus suggesting that most of the P leached at the high P sites was mainly due to desorption and dissolution of weakly adsorbed P from prior P applications. This was consistent with P transport simulations using the convective-dispersive equation. We conclude that P concentration in land-applied wastewater should be regulated based on soil test-P level plus wastewater P loading.

Quantifying Deep‐Soil and Coarse‐Soil Fractions

Forest soils are often deep and/or coarse‐textured, which does not always lend itself to easy unbiased sampling. Two important Pacific Northwest (PNW) forest soil series that are deep and coarse‐textured were studied to evaluate methods of estimating soil C: (i) a loamy sand glacial outwash soil (Indianola series, mixed, mesic Dystric Xeropsamments) and (ii) a very gravelly sandy loam glacial outwash soil (Everett series, sandy‐skeletal, isotic, mesic Vitrandic Dystroxerepts). Four methods were compared for estimating soil C, including: (i) large pit (0.5 m2) excavation, (ii) dug pit with 54‐mm hammer‐core bulk‐density sampling, (iii) 31‐mm soil push sampler, and (iv) clod method. Coarse (&gt;2 mm) fragments were also collected, processed, and analyzed for soil C. Extending soil sampling deeper than 15 cm increased soil C estimates by as much as 120%. The pit excavation method with sand‐displacement volume measurements, which is by far the most labor‐intensive and time‐consuming, was considered the “standard” by which other methods were compared, as it didn't contain any obvious biases. Soil core methods overestimated the &lt;2‐mm soil fraction (samples taken between large rocks). Biased methods are often accepted as the “best available” due to the high time requirement of pit excavation. The 31‐ or 54‐mm soil core methods often didn't work due to the high rock content (&gt;50%) of the Everett soil. Including C analysis of the &gt;2‐mm soil fraction increased soil C estimates by 170% for the Everett series soil (due to organic C contained in the rocks; there were no carbonates) but did not substantially increase the estimate in the Indianola series soil.

Evaluation of Nitrate Leaching Potential in Minnesota Glacial Outwash Soils using the CERES‐Maize Model

AbstractThis study examined how the CERES‐Maize model could be used to identify N and irrigation management practices that minimize nitrate leaching as well as provide economical corn (Zea mays L.) yield in glacial outwash soils of Minnesota. The model was validated against 2 yr of experimental data on corn grain yield, N uptake, and nitrate leaching for control and three N fertilizer application rates under two irrigation schedules on a sandy loam soil at Staples, MN. Simulated values were close to the measured corn yield, and were within the range of differences for similar comparisons. Simulations using 31 yr of climatic data showed that an irrigation trigger deficit as low as 30% had little impact on corn yield but significant impact on reduced percolation and nitrate leaching. A procedure was developed to characterize the potential of nitrate leaching in outwash soils using the output from the CERES‐Maize model. We used this procedure to characterize nitrate leaching from soils in Wadena County, MN. As expected, the high risk soils had the lowest water holding capacity and the highest drainage coefficient. The factors affecting the risk of nitrate leaching are: irrigation schedule &gt; climatic variability = N application rate. Linking a validated simulation model with a soil survey data base provides a valuable tool in site specific assessment and prescription of best irrigation and N management practices for the glacial outwash soils of the North Central region.

History of aPinus strobus‐dominated stand in northern New York

Abstract.Pollen, plant macrofossils and charcoal from a small forest hollow were analyzed to determine the formation and dynamics of aPinus strobus‐dominatedforest stand on outwash soil in northern New York.P. strobus, Betula papyriferaandAbies balsameacolonized the upland surrounding the hollow following a major disturbance that occurred ca. 360 yr ago. Pre‐disturbance vegetation consisted of shade‐tolerantTsuga canadensis, Fagus grandifoliaandPicea ruhens. The size‐class distribution of modern vegetation suggests continuing recruitment ofA. balsameaandAcer rubrumat the site. The status ofP. strobusandB. papyriferain the stand is uncertain, but there is no evidence for recolonization ofT. canadensis, F. grandifoliaorP. rubens. Frequent windthrow has probably played a role in stand dynamics since ca. 310 yr BP due to the high wind‐susceptibility of overstory and understory tree taxa in the modern forest patch.Vegetation change that occurred following fire(s) ca. 310 yr BP was recorded by plant macrofossils but not by pollen, indicating that the pollen assemblage was insensitive to vegetation change within at least 30 m (and potentially 60 m) of the hollow. The apparent insensitivity of this small‐hollow pollen assemblage to local vegetation change may be related to the relatively large size of the hollow (75 m2) and/or to its close proximity to a 0.24 ha kettle pond.

Pasture legumes for the drought-prone, outwash soils of the southern Mackenzie Basin

The persistence of lucerne (Medicugo sativa L.), red clover (Trifofiumpratense L.), birdsfoot trefoil (Lotus cornicufatus L.) and perennial lupin (Lupinuspolyphyks Lindley), overdrilled with and without companion grasses, was compared at a site representative of dry, acidic, outwash soils in the southern Mackenzie Basin, South Island. Plant populations were monitored for 9 years and legume seedling regeneration and stand recruitment were examined over three consecutive years under grazing by sheep and cattle. Pcrcnnial lupin was the best adapted legume species. Stand density increased by re-seeding. In contrast, few seedlings of birdsfoot trefoil developed as a result of reseeding, and survival of birdsfoot trefoil was generally restricted to the more favourable areas of the mosaic of soil. Red clover did not persist, and the few plants of lucerne that survived lacked vigour. Tall oat grass and cocksfoot showed good vigour and persistence across the mosaic of soil; smooth brome performed well and spread within the more favourable areas. From these results, _p_erennial.lupin,-tall-oat-grass-and-cocksfoot~a~~ to be the best species available for the future development of sustainable pastoral systems in drought-prone outwash landscapes in the Mackenzie Basin. Keywords: dryland, establishment, Lotus corniculatus, Lupinus po&amp;phyflus, outwash soils, pasture legumes, persistence, seedling recruitment

Lamellae Morphology in a Sandy Outwash Soil of East-Central Minnesota

Lamellae Morphology in a Sandy Outwash Soil of East-Central Minnesota

Characterization of the weathering status of feldspar minerals in sandy soils of Minnesota using SEM and EDX

Scanning electron microscopy was used to assess the weathering status of plagioclase and alkali feldspar grains isolated from sandy outwash soils located under three vegetation communities: mixed red and white pine, maple-basswood, and white cedar. Feldspars were selected for this study because they were the most common weatherable minerals in these sandy soils. A morphological weathering index, based on the percent of the surface of the feldspar grains covered with etch pits, was used to evaluate weathering intensity. Results revealed that significant pedogenic weathering has occurred in the surface and subsurface horizons of these soils compared to the parent material. Plagioclases were found to be much more weathered than alkali feldspars. Within the plagioclase solid solution series, the weathering index increased linearly with increasing Ca content as determined by energy dispersive X-ray analysis. Comparisons among the three sites showed that weathering environments under the pine and maple-basswood communities were relatively similar, being only slightly more intense under pine. The most intense weathering occurred under the white cedar community, particularly in the E horizon. Linear regression analyses showed that the weathering index for alkali feldspars was significantly related to soil pH ( r 2 = 0.30, p < 0.001). In the case of plagioclases, multiple linear regression analyses showed that the weathering index was significantly dependent on both Ca ( Ca + Na) molar ratio and pH ( r2 = 0.83, p < 0.001) , with 64% weight effect due to Ca ( Ca + Na) ratio, and 19% due to pH.

Long-term effects of heavy applications of biosolids on organic matter and nutrient content of a coarse-textured forest soil

Long-term changes in soil properties due to a single heavy application of municipal biosolids (municipal sewage sludge) on a coarse-textured glacial outwash soil were evaluated. Study sites, located at the University of Washington's Pack Experimental Forest, 100 km south of Seattle, were clearcut, cleared, fertilized with 500 Mg ha −1 of municipal biosolids and planted a variety of tree species in 1975. Soil samples were taken in 1990 from three biosolids-amended forest stands and adjacent unamended control sites by horizon to a depth of 185 cm. Biosolids-amended samples had higher C (139 vs. 67 mg g −1), N (12 vs. 3.4 mg g −1), P (14 vs. 2.2 mg g −1) and S (2.5 vs. 0.4 mg g −1) contents in 0–7 cm mineral soil and other surface soil horizons compared with adjacent unamended soil horizons, but showed no significant differences below 25 cm. Soil pH ranged from 0.4 to 1.0 units lower in biosolids-amended vs. unamended soil throughout the sampled soil horizon. Soil cation exchange capacity was higher in the surface soil horizons (30 vs. 18 mmol ckg −1 in 0–7 cm soil), but there were no significant differences below 50 cm. Biosolids-amended samples had higher total Ca (13 vs. 6.1 mg g −1 in 0–7 cm soil) and K (1.9 vs. 1.5 mg g −1 in 0–7 cm soil) throughout the sampled soil profile. Total Mg was relatively constant (2.0–3.0 mg g −1) throughout the sampled soil profile. Study results indicate that one of the primary objectives of the original biosolids application (increasing total nutrients in the rooting zone of the forest soil) extended at least 15 years from the application date.