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A total of 344 soil cores were taken in annually cropped fields of Alberta, Saskatchewan, Manitoba, and Ontario from 2011 to 2013 in areas where the field shapes, or obstacles within fields, required the driving pattern of farm operations to overlap. Soil nitrate-N concentrations in overlapping areas were 60% greater, soil Olsen-P concentrations were 23% greater, and pH was 0.5 units greater at 0–15 cm depth compared with non-overlapping areas, suggesting smaller nutrient use efficiency and potential for greater nutrient loss.

No information exists on the susceptibility of arbuscular mycorrhizal fungal (AMF) communities in Canadian prairie agriculture soils to climate change. An experiment was initiated in mid-May 2011 in which replicated soil cores were transplanted reciprocally from four cultivated prairie sites in Saskatchewan, Canada, representing different regional climatic zones ranging from semiarid to subhumid regional climates, such that replicated (n = 4) soil cores from each site were present at all sites. Field pea was grown in all cores and at harvest in early-September 2011; soil samples were collected to analyze the changes of AMF communities over the cropping season. A total of 82 operational taxonomic units belonging to eight AMF genera were identified using 18S rRNA gene pyrosequencing. When soils were transplanted to new environments, the relative abundance of AMF changed considerably. Typically, Shannon diversity declined when soil cores were transplanted to new environments. We present evidence that with the altered climatic conditions following transplantation of soil cores, the relative abundance of AMF was significantly altered, and some taxa were enhanced, suppressed, or disappeared in the home-away soils compared with home-site soils. This study implies that the future climate change effects on AMF may impact specific phylogenetic taxa differently, such that rare species or those with low abundance may increase or decrease with unknown consequences. Understanding the potential responses of AMF communities to soil–climate interactions is important when considering the impacts of climate change on soil microbial communities.

Concerns about climate change have increased interest in ways to maximize carbon (C) storage in forests through the use of alternative forest management strategies. However, the influence of these strategies on soil C pools is unclear. The primary objective of this study was to test for differences in mineral soil C stocks among various silvicultural and harvesting treatments that were initiated in the 1950s and have been maintained since on the Penobscot Experimental Forest in central Maine, USA. Five mineral soil cores below the surface organic horizon to a depth of 1 m were collected from each replicate (n = 2) of selection, shelterwood, and commercial clearcut treatments. For these treatments, the mean mineral soil C stock was 47.7 ± 16.4 Mg ha−1 (mean ± SD). We found no significant differences in average mineral soil C stocks among treatments. However, a post hoc power analysis indicated that the probability of detecting a significant treatment effect was only 6%. We determined that 98 stands per treatment would be required to be 80% certain that the F test would detect a difference in average mineral soil C stocks whenever any pair of treatments had C stocks differing by more than 5 Mg ha−1.

Whalen, J. K., Han L. and Dutilleul, P. 2015. Burrow refilling behavior of Aporrectodea turgida (Eisen) and Lumbricus terrestris L. as revealed by X-ray computed tomography scanning: Graphical and quantitative analyses. Can. J. Soil Sci. 95: 231–235. Solute and gas transport through earthworm burrows is altered when burrows become refilled. Earthworm burrow refilling was evaluated with non-invasive X-ray computed tomography in undisturbed soil cores. Proportionally, Lumbricus terrestris refilled burrows had more air-filled space left around their perimeter than those of Aporrectodea turgida, which often were completely refilled.

Miller, J. J. and Chanasyk, A. S. 2015. Unsaturated water flux at mid and lower slope positions within an inclined landscape of the Dark Brown soil zone in southern Alberta. Can. J. Soil Sci. 95: 27–36. Little research has quantified vertical-unsaturated water flux below the root zone for mid and lower slope positions within inclined, low-relief, and longer-slope landscapes of the Dark Brown soil zone of the Canadian prairies. We measured soil moisture (0.23–1.22 m) in the field at mid and lower slope positions in southern Alberta from May to October in 1985 and 1986. Undisturbed soil cores were taken from soil horizons and saturated hydraulic conductivity and soil moisture retention were determined in the laboratory. Vertical-unsaturated water flux below the root zone was calculated between 1.07 and 1.22 m depths below ground surface using the hydraulic gradient method. Water fluxes for the 2 yr ranged from −11 to 10−10 m s−1 at the mid slope position, and from −11 m s−1 to 10−9 m s−1 at the lower slope position, and were consistent with some other studies. Cumulative water flux was dominantly downward (−2.2 to −3.4 mm) at the mid slope position and this flow direction was consistent with this Orthic Dark Brown Chernozemic soil that was located in a “recharge area”. Cumulative water flux was dominantly upward at the lower slope position in 1985 (1.4 mm) and dominantly downward but of very low magnitude in 1986 (−0.1 mm), and this flow direction was consistent with this saline Gleyed Regosol and “saline seep”. Cumulative water fluxes as a percentage of annual precipitation were 0.8 to 1.8% at the mid slope position and 0.3 to 0.5% at the lower slope position.

Fine and coarse root biomass, C, and N mass parameters were assessed by root size and soil depths from soil cores in plots of 32-year-old black spruce ( Picea mariana (Mill.) Britton, Sterns & Poggenb.) from four full-sib families studied previously for drought tolerance and differential productivity on a dry and wet site. All fine and coarse root size categories had greater root biomass on the dry than on the wet site. Most of the site differences resided in 0–20 cm soil depth. The wet site had greater root N concentration than the dry site, despite the same soil N; thus, virtually no differences were observed in total fine and coarse root N mass between sites. Root N concentration declined with increases in both soil depth and root size. Fine roots (

Miller, J. J., Beasley, B. W., Drury, C. F. and Zebarth, B. J. 2012. Denitrification during the growing season as influenced by long-term application of composted versus fresh feedlot manure. Can. J. Soil Sci. 92: 865–882. Application of composted (new practice) rather than fresh (current industry standard) feedlot manure to cropland is increasing in Alberta. We hypothesized that fall application of composted feedlot manure to cropland may lower growing season denitrification losses of nitrogen (N) to the atmosphere compared with fresh feedlot manure because of lower carbon (C) availability from labile C (water-soluble C, acetic acid) and total organic C. Treatments included soil amended with either fresh (FM) or composted manure (CM) containing straw bedding applied annually at 77 Mg ha−1 yr−1 from 1998 to 2009, as well as an unamended control. Surface soil denitrification was measured every 2 wk (May 20 to Sep. 25) for 4 yr (2007–2010) on undisturbed soil cores (0- to 10-cm depth) that were incubated in...

Wang, E., Cruse, R. M., Chen, X. and Daigh, A. 2012. Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability. Can. J. Soil Sci. 92: 529–536. Freeze/thaw cycles can affect soil aggregate stability, which in turn impacts wind and water erosion. The objectives of this laboratory study were: (1) to determine the effect of variable freeze/thaw cycles and soil water conditions on aggregate size distribution and stability; and (2) to evaluate differences in aggregate size distribution and stability between disturbed soil and undisturbed soil cores as affected by freeze/thaw cycles and soil water conditions. Surface soil was collected before freezing in late fall of 2009. Aggregates isolated from disturbed soil or intact soil cores were subjected to a factorial combination of 3 gravimetric water content treatments: 0.15 m3 m−3, 0.23 m3 m−3 or 0.30 m3 m−3, and 3 freeze/thaw treatments: 0, 3, or 9 cycles. A freeze/thaw cycle involved soil freezing at –10∘C for 24 h, followed by thawing at 5∘C for 24 h. Most aggregate size classes were affected significantly (P5 mm. Dry-sieved aggregates were relatively more sensitive to the freeze/thaw treatment than wet-sieved aggregates. The mean weight diameter (MWD) of dry-sieved aggregates was significantly (P3 m−3 than 0.15 m3 m−3 water content, but the opposite trend was observed for MWD of wet aggregates and aggregate stability. There was a significant (P

Volumetric water content (θv) was estimated from time domain reflectometry (TDR) measurementsof apparent dielectric permittivity (Ka) in an organic soil (Humisol). The goals of this study were: (i) to test the accuracy of existing θv-Ka relationships in this soil and if found insufficient (ii) to develop alternative θv-Ka relationships for this organic soil. The Ka values were measured over a wide range of θv in intact soil cores taken from three horizons (Ohp, Of, Oco). Empirical θv-Ka relationships found in the literature for organic porous media could not accurately describe the θv-Ka relationships of any horizon of this Humisol, probably because of the its very large organic matter content (> 75%) of this soil. New θv-Ka relationships for each horizon were consequently developed. Key words: Organic soil, TDR, coprogenic soil, volumetric water content, apparent dielectric permittivity

Large soil monoliths (> 50 kg) are required to study and monitor soil energy and water budget, gas and liquid fluxes, and contaminant transport. This paper reviews the types of studies requiring large soil monoliths, design and material for the casing, and collection methods for vertically forced cylindrical and for block (orthorhombic) monoliths. Methods of extraction are described along with recommendations. Advantages and disadvantages of each method are discussed. Vertically pushed cylindrical monoliths are easier to sample, but compared with orthorhombic monoliths that are not pushed into the soil, the pushing process has the disadvantage of modifying certain soil physical properties. Key words: Large soil samples, intact soil cores, acrylic boxes, soil sampling

A laboratory experiment was done to identify the properties that make a substrate susceptible to frost heaving. Tests were carried out on nondisturbed soil cores (fresh and dry) of Ae and B horizons from sand, loamy sand, and sandy loam in a freezing cabinet (–3.5 °C). Cores were continuously supplied with water from below. Freezing tests were repeated after soil disturbance (V-shaped furrow, 50% increase in surface area). The effects of texture, horizon, drying, and disturbance on frost heaving were tested using repeated-measures analysis of variance with soil elements (organic Al, organic Fe, inorganic Al, inorganic Fe, C, and N) and soil fractions (clay, fine silt, coarse silt, fine sand, and coarse sand) as covariates. The effect of horizon was as important as that of texture, and soil disturbance increased frost heaving. Disturbed fresh B horizon from loamy sand and sandy loam heaved the most (soil expansion >5% in height), whereas nondisturbed dry Ae horizon, regardless of texture, and nondisturbed dry B horizon from sand heaved the least (soil expansion

Living retention trees are being used in managed forests to promote a variety of values, including the maintenance of biological diversity. Federal forest plans for the northwestern USA include guidelines that require the retention of a minimum of 15% basal area in harvest units, with the goal of facilitating the development of late-seral stand structure, which is an important habitat element for old-growth forest-dependent species. However, effective levels and patterns of green-tree retention are unknown. We present results of a treatment consisting of 15% basal area, evenly dispersed retention (15%D). We quantified changes in the ectomycorrhiza (EM) community after the 15%D treatment, both near and away from retention trees. Pretreatment samples were obtained between 1 and 24 months before tree harvest. Post-treatment samples were collected within 14–25 months of harvest. In areas 8–25 m from retention trees, there was a 50% decline in the number of EM types per soil core from before to after treatment. Soil cores taken >5 m from retention trees exhibited a shift in EM community structure. EM-type richness was positively correlated with fine-root-tip density. We demonstrate the potential for retention trees to act as refugia for recolonization of newly established seedlings by ectomycorrhizal fungi.

The effects of seasonal prescribed fire on the belowground ectomycorrhizal community and live fine root biomass were investigated before, 1 year after, and 2 years after prescribed underburning. Ectomycorrhizas were sampled from four replications of three treatments (fall underburning, spring underburning, and a nonburned control) in a randomized complete block design. Samples were separated in two subsamples representing the upper 5 cm and lower 5 cm of a soil core. Molecular tools were used to distinguish 140 restriction fragment length polymorphism (RFLP) species of fungi directly from the ectomycorrhizas. Prior to underburning, the number of RFLP species and amount of live root biomass were similar among treatment units and between upper and lower core samples. Fall underburning largely removed live root biomass to a depth of 10 cm and significantly reduced ectomycorrhizal species richness compared with spring underburning and the nonburned control for at least 2 years. RFLP species richness and live root biomass following spring underburning were generally similar to the nonburned treatment. The successful reintroduction of fire to the ecosystem to retain high species diversity of ectomycorrhizal fungi and achieve the desired future condition of large-tree ponderosa pine retention with low fuel loads may require more than underburning in a single season.

Ectomycorrhizal fungal communities of both seedlings and mature trees of Abies firma Sieb. et Zucc. were studied based on morphological and molecular analyses of ectomycorrhizal (ECM) roots. A total of 142 seedlings and 28 soil cores were collected from a 10 m × 30 m plot, and 37 morphotypes were recorded from seedlings and 23 from mature trees. A morphotype, type 21, formed by an unidentified fungus that is likely a Russula species, was dominant on both seedlings (30% of the total number of the ECM roots detected) and mature trees (56%) and overlapped them spatially, suggesting a hyphal linkage between mature trees and seedlings in the plot. A total of 12 morphotypes were recorded from soil blocks underneath fruiting bodies of undescribed Russula sp. 1, the dominant aboveground fruiting body in the plot, among which type 21 was the most abundant. The pattern of restriction fragment length polymorphism of this type was identical to that of the fruiting body of Russula sp. 1. These results indicate that Russula sp. 1 was the dominant ECM fungus associated with both mature trees and seedlings and would play an important role in the dynamics and maintenance of this Abies-dominated forest site.Key words: Abies firma, ectomycorrhizal fungal community, morphotype, PCR-RFLP analysis, tree age.

We investigated diversity of ectomycorrhizas associated with Quercus garryana Dougl. ex Hook. (Oregon white oak, or Garry oak) at Whetstone Savanna Preserve in southern Oregon. Based on morphotyping and DNA restriction fragments, we described 39 ectomycorrhizas. The most common five morphotypes were found in 5% or more of 160 soil cores. Cenococcum geophilum, the most abundant morphotype, occurred in 75% of soil cores. Another common morphotype yielded a restriction fragment length polymorphism (RFLP) pattern similar to that of Tuber species. Uncommon morphotypes were responsible for the majority of ectomycorrhizal diversity on Q. garryana. Morphotype diversity of seedlings was more similar to that of their parent tree than to seedlings under other trees. Internal transcribed spacer (ITS) – RFLP patterns of ectomycorrhizas found beneath sporocarps did not match those of the sporocarps fruiting above ground. An understanding of the diversity of the ectomycorrhizal community on Q. garryana will enable us to compare ectomycorrhizas on other oak species and habitats; determine seasonality of ectomycorrhizal growth; evaluate treatments such as fire, grazing, invasion by exotic plants, and other anthropogenic disturbances; and aid restoration protocols.Key words: biocomplexity, biodiversity, ectomycorrhizas, hypogeous fungi, morphotypes, Peziza infossa, Tuber.

An identification database for seeds in coastal habitats at La Pérouse Bay, Manitoba, Canada, was developed using the DELTA (DEscriptive Language for Taxonomy) format and the program INTKEY. The database should be applicable throughout the coastal lowlands of the Hudson Bay and James Bay regions as similar plant assemblages are present. The database, based upon morphological characteristics and also incorporating ecological information, was used to identify seed specimens found in soil cores and seed traps. The most useful characters for identifying seeds were seed length, seed width, and seed shape. The database is available on the World Wide Web at http://prod.library.utoronto.ca/polyclave/. The seed flora is also documented in the form of a checklist, the first one published for the La Pérouse Bay region; this checklist is also applicable to other coastal areas in the Hudson Bay lowlands.Key words: Arctic, DELTA, floristics, identification, seed morphology.

We investigated the soil seed bank in a subalpine ecosystem with patchy disturbance from camping. Soil cores were collected from three site types, heavily impacted, lightly impacted, and undisturbed, that differed in area of bare ground and depth of surface organic matter. We hypothesized that the density and composition of the seed bank would vary with depth of surface organic matter and distance from established vegetation. Seedling emergence was determined in the greenhouse. Seed density was significantly lower on disturbed sites, averaging 441 seeds/m2 on heavily impacted sites, 1495 seeds/m2 on lightly impacted sites, and 4188 seeds/m2 on undisturbed sites. Seed density declined exponentially with distance from established vegetation and increased with depth of surface organic matter. The number of species present did not vary across site types, but 10 species that occurred on lightly impacted and undisturbed sites were not present on heavily impacted sites. We concluded that disturbance that causes removal of surface organic matter can affect natural revegetation by lowering the density of propagules and affecting the species represented in the seed bank.Key words: seed bank, subalpine, patchy disturbance, recreation impacts.

Mineral N fertilizers may contribute to N gas emissions to the atmosphere. Soil cores were collected in 1993 and 1994, in a sandy loam and a sandy clay cropped with an early-maturing corn (Zea mays L.) hybrid and fertilized with ammonium nitrate at rates of 10, 60, 120 or 180 kg N ha−1. Denitrification and N1O production rates, air-filled porosity (AFP), water-soluble mineral N (WSMN) and water-soluble organic C (WSOC) were measured. Denitrification and N2O production rates were generally small, but values >2 µg N2O-N kg−1 h−1 were measured (i) when WSMN contents exceeded 5 mg kg−1, and (ii) when AFP was 2O production and denitrification rates increased with N fertilizer level. In 1993, AFP was relatively high and variable in soil cores, and regression analyses revealed that denitrification rates were closely related to AFP. In 1994, AFP was relatively low in soil cores, and regression analyses showed that denitrification and N2O production rates were positively related to WSMN and negatively to WSOC. It is suggested that provided AFP was low, N fertilization may have had either a direct effect on denitrification and N2O production rates by determining WSMN availability to microorganisms, or an indirect effect by affecting WSOC metabolism in soil. Depending on the year and soil type, mean denitrification rates were 40 to 130% greater in the soil with 180 than with 120 kg N ha−1. Corresponding N2O production rates were 50 to 200% higher in the 180 than in the 120 kg N ha−1 treatment. It appears that limiting N fertilizer to 120 kg ha−1, under early-maturing corn production, may prevent excessive gaseous N losses due to denitrification. Key words: Denitrification, nitrous oxide, N fertilizers, available N, grain corn

Nitrogen fixation was measured in different habitats in the area of Ny-Ålesund, Spitsbergen, using the acetylene reduction method on intact soil cores and Nostoc commune growing in macroscopic sheet communities. The samples were incubated both under constant conditions (19 °C and 200 μE∙m−2∙s−1) and under in situ conditions. Cyanobacteria were considered to be the major nitrogen-fixing organisms. The nitrogen fixation rates showed a seasonal variation during the growing season of 1994, with low activities just after the snow melt, increasing until the middle of August and showing a rapid decline after the snow fell on August 29. The soil temperature at the time of sampling showed a positive, linear correlation with the nitrogen fixation activities measured on intact soil cores, whereas the nitrogen fixation activities measured in situ of N. commune showed a positive, linear dependence on the moisture content in the sheets and the incubation temperatures inside the incubation vessels during the experiments. The optimal temperature of the nitrogen fixation activity was about 20 °C, both for N. commune and a Puccinellia salt marsh. The highest nitrogen fixation rate measured in situ was at a patterned ground, which had the highest pH, the highest concentrations of extractable calcium and magnesium, and the highest C:N ratio measured.Key words: nitrogen fixation, cyanobacteria, Nostoc commune, high arctic.

Piceaengelmannii Parry ex Engelm. becomes established after fire by dispersing seeds into a burn, not through the maintenance of a persistent soil seed bank. The objective here was to determine causes of spruce seed loss from the bank to understand its lack of a persistent seed bank. One hundred seeds placed in soil cores were enumerated for 2.5 years and divided into three treatments: (i) varying the amount of protection from predators, (ii) keeping litter intact or removing it, and (iii) placing seeds on top of litter or between litter and mineral soil. For all treatments, fewer than 5% of seeds remained at the end of the study. Predation caused the greatest loss to the seed bank, much greater than germination in all treatments. Removal of litter increased germination, but predation occurred at the same rate; therefore, the total rate of loss to the seed bank increased. Seeds placed between litter and mineral soil experienced greater germination and less predation than seeds placed above the litter layer. However, increased germination balanced the reduced predation so there was little difference in the total rate of loss to the seed bank from seeds placed in either location. Further, seeds appeared to lose viability within two seasons. Thus, there is no persistent seed bank because of high predation and a rapid loss of viability.

Currently, chemical control of fairy ring caused by Marasmius oreades is not feasible, in part because colonized soil is very repellent to pesticidal solutions. Fungicidal control, however, might be successful if a surfactant was used to increase soil wettability. Of 13 surfactants screened for ability to enhance solution uptake by infested soil cores, the organosilicone, Silwet L-77, was most effective, followed by Citowett Plus and Agsurf. In a second, similar experiment, Silwet L-77 was more effective than the other two surfactants in increasing water uptake by both infested and uninfested soil cores. Silwet L-77 concentrations of 0.98–3% were equally effective in increasing grass production, relative to the water control, on colonized and uncolonized turf, under greenhouse conditions. At concentrations of 2% or higher, but not at concentrations of 0.016% to 1.0%, Silwet L-77, Citowett Plus, and Agsurf prevented M. oreades growth in liquid culture. Silwet L-77, and perhaps other organosilicone surfactants, seemingly have considerable potential for the management of fairy ring by improving uptake of water, or as carriers of biological or chemical control agents. Key words: Wetting agents, Silwet L-77

A top loading balance can be used to monitor and record drainage from a soil core. Possible applications of the apparatus are discussed. Key words: Tension apparatus, real-time weight loss, soil core

Seed traps were installed in 10 summer fallow sites across Saskatchewan to monitor annual additions to buried seed populations. Soil cores (7.5 cm deep) were also collected at these sites and tested for viable seeds through seedling emergence under greenhouse conditions. Seedlings of 33 forb species, 5 grass species, and 3 tree species emerged from the traps, whereas seedlings of 28 forb species, 4 grass species, and 1 tree species emerged from the cores. Although the nature of seed input for agricultural sites in different parts of Saskatchewan was highly variable, the annual seed rain onto fallow represented an important supplement to the buried seed reserves and would be an influence on subsequent weed communities in cultivated fields.

A core sampling technique was used for the investigation of root numbers in a 42-year-old red pine (Pinusresinosa Ait.) irrigation – K fertilization experimental area of a K deficient sandy outwash plain in the southeastern Adirondack Mountain Region of New York. Soil cores were collected from plots, 6 years after initiation of treatments, at 0–15 and 15–30 cm depths, using a 5.2 cm diameter corer. Roots were separated from soil cores by a sieving technique. Root tips, including each tip of mycorrhizal structures, were counted by classes established on the basis of morphological characteristics. Numbers of root tips were greater under nonfertilized than fertilized plots, and greater under irrigated than nonirrigated plots. This response pattern did not follow that of wood volume increment, which was greatest in fertilized plots, but was similar to the previously reported pattern in soil microarthropod numbers. The great natural variation observed suggests that root tip numbers may be highly sensitive to changes in soil conditions. Calculated sampling intensity, based on the variance estimates, and specific levels of probabilities (α and β) and allowable sampling error (ε), indicated the need for high numbers of samples.

Seed banks were examined in four plant communities in a high-elevation sphagnum bog in West Virginia, U.S.A. A germination assay was used to detect germinable seed densities. Vertical depth distributions were determined for one community in which the soil cores were transported intact to the greenhouse. Seed densities ranged from 12 874 in a Sphagnum-dominated community to 377 041 seeds m−2 in a sedge-dominated community. The seed bank in all communities was dominated numerically by Juncus effusus, although this species comprised a minor part of the aboveground vegetation. Three types of depth profiles were observed, including one distribution showing a simple decline in seed numbers with depth, another showing a unimodal peak below the soil surface, and a third with two distinct peaks at depth. A matrix model of seed burial was devised to account for the different depth profiles. By assuming that soil compression occurred and that the rate of compression declined with time, the model showed that either of the first two depth profiles could be produced with no need to invoke a historical change in the seed rain. The model was unable to account for the bimodal depth profile with the assumption of a constant seed rain. However, the fact that the model of seed burial could explain a unimodal peak in the depth profile suggests that simple historical interpretations of past abundance using a buried seed profile are difficult.

A tubular drill has been designed to extract a frozen soil core 12–15 cm in diameter and 15–40 cm in length with the roots and collars of intact plants. A snow cylinder is used to clear the sampling spot, causing minimum disturbance to the snow cover. This equipment makes possible a large scale study of vegetation during the cold season.

A soil coring device consisting of a frame, probe, probe-driver and hydraulic system was constructed. It was mounted on a motor grader which provided mobility and sufficient weight to achieve penetration to 122 cm. A technique using the device to isolate cores 15 cm in diameter × 122 cm deep is described. Each core was isolated in 7 min using a crew of four. Only slight compaction of the core was observed. The cost of materials for the coring device was approximately $600.00.

The effects of N and S fertilization on nitrate reductase activity (NRA) and N fractions were studied in timothy (Phleum pratense L.) and switch grass (Panicum virgatum L.). Soil cores of timothy and switch grass plants were obtained from a marginally S-deficient area at Madison, Wisconsin. The cores were placed in growth chambers maintained near the optimal temperature for each species. Three rates of N (0, 224, 448 kg N/ha as Ca(NO3)2) and three rates of S (0, 11.2, and 22.4 kg S/ha as CaSO4) were applied in all possible combinations. Plants were harvested at anthesis and NRA in the leaves (blades) was determined. Total N, reduced N, nitrate-N (NO−3-N), and free α-amino N concentrations (concns.) were measured in leaves and stems (culms, leaf sheaths, and inflorescences). Fertilization with S had little effect on the concn. of any N fraction or on NRA in either species. Switch grass and timothy were not S-deficient as indicated by tissue S concn. Total N, NO−3-N, and free α-amino N concns. increased significantly in all plant fractions of both species with each increment of N fertilization. "Toxic" concns. of NO−3-N accumulated in timothy leaves when N was applied. Switch grass leaf NO−3-N concn. was less than one-half that found in timothy. NRA and concn. of reduced N in timothy leaves increased significantly only with the first increment of N fertilization. NRA and concn. of reduced N in switch grass leaves increased significantly with each increment of N fertilization. NRA was significantly correlated (0.01 level) with the concn. of every N fraction in the leaves of both species.

Three indices of nitrogen (N) availability were compared in the field over a 1-year period in an old-growth and a young-growth mixed-conifer forest. The indices utilized were ion exchange resin (IER) bags, buried bags, and a core-IER method employing intact soil cores enclosed in tubes capped at both ends by IER bags. The results from all three methods indicated that in the surface mineral soil, N availability was higher in the young-growth stand than in the old-growth stand. However, seasonal patterns of N availability were generally not well correlated among the methods (correlation coefficients ranged from 0.32 to 0.62). For a given amount of net N mineralized in buried bags, more N accumulated on IER bags placed in the young-growth stand than in those placed in the old-growth stand. This was the result of greater net nitrification in the young-growth stand coupled with the greater mobility of [Formula: see text] relative to [Formula: see text] in soil. Ten-month estimates of net N mineralization measured by the core-IER and buried-bag methods were similar in the young-growth stand (about 42 mg•kg soil−1), but the core-IER estimate was almost twice that of the buried-bag estimate in the old-growth stand (31.7 and 16.8 mg•kg soil−1, respectively). The different sensitivities of the core-IER and buried-bag methods to changes in soil moisture and leaching probably account for much of the difference in their N availability estimates. Results from the core-IER method did reflect the effects of leaching; however, soil water content within the core did not follow changes in soil water content effectively. Because of the greater labor involved in using the core-IER method, its use may be most efficacious in high-precipitation environments, or when in-field soil incubations must be conducted for extended periods of time.

The effects of heavy thinning (60% reduction in basal area) on fine (−1•year−1 in the control and thinned treatment, respectively, and mortality was estimated at 2.1 and 2.0 Mg•ha−1•ear−1 in the control and thinned treatment, respectively. Thinning shortened mean fine-root longevity from 6.2 to 2.5 months. With respect to total dry matter production, fine-root production remained a minor component following a heavy thinning. It accounted for only 4.6 and 6.1% of the stand total in the control and thinned treatments, respectively. These results indicate that on a fertile site with a mild climate the opportunity to shift production from fine roots to another component, such as stem wood, is likely to be small.

The acetylene reduction method was used to measure nitrogen fixation in soil cores of 16 cm diameter and 16 cm depth that included A and B horizon soil, roots, and decaying litter. Forty-three combinations of location and associated tree species were sampled. The rate of nitrogen fixation for most soil cores was 1 g N ha−1 day−1 or less, which extrapolates to less than 0.2 kg N ha−1 year−1. The highest rates, with values of up to 23 g N ha−1 day−1, were observed in old fields being invaded by trees. The time course of acetylene reduction was usually linear for a 24-h period, most of the activity was in the upper 15 cm of soil, and the maximum rates were observed in midsummer. No significant nitrogen fixation was observed in preliminary measurements of decaying woody litter or of aerial surfaces of trees and rocks. It is suggested that nitrogen fixation is not a significant input of nitrogen for the forests studied. If so, there may be significant unrecognized nitrogen inputs to forests, such as dry absorption of ammonia from the atmosphere.

We, as well as others, have observed that nitrous oxide (N2O) fluxes increased markedly during soil thaw in early spring. This phenomenon was examined further by determining nitrous oxide concentrations in the soil profile and N2O fluxes from the soil surface during the winter-spring period and evaluating physical release and microbial production of N2O on thawing of frozen soil cores in the laboratory. In mid-winter, soil profile N2O concentrations were close to ambient and surface N2O fluxes were low. At thawing, high N2O concentrations (ranging from 1082 to 2066 mg∙m−3) were found at 10–30 cm in the soil profiles of a coniferous forest, and in manure- and straw-treated plots. Concurrently, N2O flux increased markedly and reached some of the highest values observed during the entire season. When thawing was complete, soil profile N2O concentrations and N2O flux declined. Soil cores were taken from frozen soil, warmed in the laboratory, and N2O release measured. Nitrous oxide was released on warming, and cores treated with CHCl3 had a slower release rate. The results indicate that some of the N2O flux occurring at thawing is due in part to physical release of N2O, and that additional N2O is likely produced by denitrification. Key words: Nitrous oxide, denitrification, frozen soils, nitrogen loss

Evaporation rates beneath maize canopies were measured using an intact soil core technique. Early in the growing season evaporation rates were periodically high (4.0 mm∙day−1) following rain, but declined rapidly. At full crop cover, when energy supply normally limits evaporation, significant differences in evaporation were detected between canopies with leaf area indices of 3.0 and 4.0. Key words: Evaporation measurement, energy supply, Zea mays L., leaf area, soil evaporimeter, lysimeter

The saturated hydraulic conductivity, Ks, was measured on a loamy sand, a fine sandy loam, a silt loam and a clay at four 100-m2-area sites in southern Ontario. Twenty measurements of Ks were obtained by each of three different measurement techniques at each of the four sites. The techniques included: (1) the air-entry permeameter method; (2) the constant head well permeameter method using the Guelph Permeameter; and (3) the falling-head permeameter method applied to small soil cores. The Ks data were found to be better described by the log-normal frequency distribution than by the normal frequency distribution. Statistical comparison of the mean Ks values [Formula: see text] indicated significant differences between some or all of the methods within each site. This site-method interaction was interpreted in terms of the influence of macropores and air entrapment on each of the measurement techniques. The measured Ks values ranged over an order of magnitude on the sand, one to two orders of magnitude on the loams, and three orders of magnitude on the clay. The [Formula: see text] estimates averaged over the three methods were: 3 × 10−5 m∙s−1 for the sand; 2 × 10−6 m∙s−1 for the loams and 1 × 10−7 m∙s−1 for the clay. Although all techniques were able to discriminate between the three soil types, the best choice of method for any particular situation appears dependent on the required type and accuracy of the Ks measurement, soil type, and the various practical constraints on the investigation. Key words: Air-entry permeameter, Guelph Permeameter, falling-head permeameter, spatial variability, macropores, entrapped air

Soil cores to a depth of 10 cm taken from native prairie and three adjacent agricultural sites were tested for the presence of buried viable propagules by stimulating germination from the samples in the laboratory. A total of 739 individuals per square metre emerged from the native prairie samples with 476 individuals per square metre from the grazed pasture, 520 individuals per square metre from the wheat stubble, and 1667 individuals per square metre from the summer fallow site. In addition, vegetative regeneration, mostly for grasses and sedges, was important in the native prairie and grazed pasture sites, giving rise to 694 and 2154 individuals per square metre, respectively. Nongerminating seeds were recovered at rates, per square metre, of 19 for native prairie, 387 for grazed pasture, 685 for wheat stubble, and 1007 for summer fallow. It is concluded that various cultural and chemical practices have altered the natural buried propagule complement of the region with the populations of weed seeds building up in the soil as cultivation continues.

Root distribution of tomatoes was measured by injecting P-32 into the stem and by taking soil cores after an equilibration period of 2 days. The soil cores were radioassayed and the pattern of radioactivity was used as an indication of root distribution. Root distribution and distribution of P-32 were significantly correlated.Root distribution of irrigated tomatoes was measured 35, 66 and 97 days after transplanting. At all times, 75% or more of the roots were present directly under the plant in a core 25 cm in diameter and 45 cm deep. In the wet plots, the quantity of roots decreased more gradually with depth than in the dry plots. This was attributed to the fact that rainfall interfered with the scheduling of the irrigation of some plots.

The relations among soil structure, soil mechanical impedance, and moisture retention and movement were investigated on undisturbed soil cores from soil horizons exhibiting six distinct kinds of soil structure (prismatic, columnar, blocky, granular, platy, massive) over a broad range of soil texture. Mechanical impedance was characterized by measurements of bulk density and soil strength. Moisture retention and movement were characterized by measurements of [Formula: see text]-atm moisture content and saturated hydraulic conductivity. The columnar structures from Solonetzic soils were singled out as having a higher mechanical impedance and lower hydraulic conductivity than the other structures, most of which were sampled from Chernozemic soils. Total porosity (P) and bulk density (Db) were highly correlated; however, the regression coefficient for P vs. Db for columnar structures was significantly higher than that found for the other five structural types. Regression equations predicted that the hydraulic conductivity of platy structures could be zero for samples having as much as 15% air-filled pore space at [Formula: see text]-atm suction as compared with 6–8% for the other structures.

The pH, electrical conductivity, sodium-adsorption ratio, saturation percent, hydraulic conductivity, NO3 content, and NaHCO3-extractable phosphorus were determined on an irrigated Solonetzic soil complex. The soils were sampled to the 142-cm depth at 20 locations on a small, levelled field. Yields of barley were obtained in the field and in the greenhouse on soil cores. Stepwise multiple regression analyses indicated that hydraulic conductivity and available phosphorus in the 0- to 15-cm depth were the most important factors explaining yield variation in the field. In the greenhouse, available phosphorus was more important and hydraulic conductivity was of secondary and minor importance.

The two best and two lowest yielding of nine bromegrass (Bromus inermis Leyss.) strains were as readily identified from two-year as from three-year hay yield data. Root production was not satisfactorily evaluated from four soil cores per plot. Grass stand was very variable, for both strains and management systems. Spring vigor in the first year of production tended to be associated with plant number established in the seedling year. Strains were satisfactorily characterized for spring vigor in the second year of production and third-year data were not necessary. Strain differences in fall growth and rhizome extension were more pronounced, and coefficients of variation were reduced, as the stands aged.Alfalfa seeded with bromegrass masked the grass and made it difficult to evaluate most grass characters. Bromegrass strains evaluated in pure grass swards either with or without fertilizer gave comparable results. An advantage from fertilizer application was that the coefficient of variation for hay yield was reduced.

A miscible displacement technique was used to study the movement of EDTA and Zn EDTA in soils. EDTA moved quite readily through the soil. The EDTA from a Zn EDTA complex also moved readily through the soil cores; however, the Zn was replaced to a large extent. If the Zn EDTA complex remained intact, then it moved through the soil with the liquid phase. These data have implications on the use of chelated metals for plant nutrition. If the desired element remains in the chelate complex, it could move with water and thus can be leached out of a soil. If the complex breaks down in the soil, the metal can react with the soil. In either case, the desirable element may not remain available to plants.

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