bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrous oxide production in soils cropped to corn with varying N fertilization
Authors: Chantigny Martin H. , Prévost Danielle , Angers Denis A. , Simard Régis R. , Chalifour François-P.
Published: April 2011

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 <50 to 55% in the sandy loam, and <40 to 45% in the sandy clay. For most sampling dates, N2O 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
Anthropogenic vegetation transformation and the potential for deep convection on the Canadian prairies
Authors: Raddatz R. L.
Published: April 2011

Widespread agricultural cultivation has converted nearly 60% of the Canadian Prairie grasslands eco-climatic zone from native mixed perennial grasses to annual field crops, predominantly spring wheat. This study examined the effect this anthropogenic landscape transformation has had on the partitioning of latent and sensible heat. For each type of vegetation, a representative growing-season Bowen ratio curve, based on modelled evapotranspiration values, was determined for sample sites — Winnipeg, MB, in the transitional grassland, and Swift Current, SK, in the arid grassland. A relationship between the Bowen ratio, the noon global radiation and the change in the Lifted Index between morning and afternoon was used to asses how modifying the apportionment of surface heat flux may have changed the seasonal frequency and severity of thunderstorms. Prior to the emergence of annual crops, and again during their senescence and in the post-harvest period, Bowen ratios are generally higher (i.e., evapotranspiration rates are lower) than they would be if the Prairie grassland eco-climatic zone had remained a sea of perennial grasses. Thus, the available buoyant energy or the potential for deep convection has been reduced in these periods. Given similar atmospheric dynamic forcing and advection patterns, this change has likely reduced the frequency of thunderstorms during the early and the late portions of the growing season. In contrast, during rapid foliage expansion and seed production for spring wheat, and for similar annual field crops, Bowen ratios are generally lower (i.e., evapotranspiration rates are higher) than they would be without agriculture. Thus, the potential for deep convection has been enhanced in these periods. With similar dynamic and advection patterns, it is probable that thunderstorms are now more frequent in the middle of the growing season and increased available buoyant energy may have made them, on average, more severe. Key words: Agrometeorology, land-use change, thunderstorms
An exponential root-water-uptake model
Authors: Li K. Y. , Boisvert J. B. , Jong R. De
Published: April 2011

Macroscopic root-water-extraction models often do not adequately account for the non-uniform distribution of roots in the soil profile. We developed an exponential root-water-uptake model, which was derived from a measured root density distribution function. The model, incorporated in the Soil-Water-Atmosphere-Plant (SWAP) simulation model, was tested on a clay loam soil cropped to soybeans and on a sandy loam soil cropped to corn, near Ottawa. Comparisons of measured and simulated soil water contents with the exponential model, a linear depth-dependent model and a constant-extraction-rate model were also made. The exponential model performed satisfactorily (average relative errors <20%) when used to simulate measured field soil water contents at various depths. The constant-extraction-rate model overestimated the soil water contents in the upper part of the soil profile (maximum error 0.24 cm3 cm−3) and underestimated them (maximum error −0.09 cm3 cm−3) in the lower part. The exponential model and the linear model performed fairly similarly at the lower depths, but the exponential model gave better results in the near-surface horizons. The exponential model was sensitive to the root distribution coefficient and to the rooting depth, when the latter was approximately less than 40 cm. The results of this study suggest that the exponential root-water-uptake model as incorporated in SWAP is an improvement over those models, which do not account for the root distribution in the soil. Key words: SWAP, soil water simulation, root distribution, corn, soybeans, sensitivity analysis
Carbon storage and light fraction C in a grassland Dark Gray Chernozem soil as influenced by N and S fertilization
Authors: Nyborg M. , Malhi S. S. , Solberg E. D. , Izaurralde R. C.
Published: April 2011

A field experiment was conducted at Canwood, Saskatchewan to determine if annual applications of nitrogen (112 kg N ha−1) and sulphur (11 kg S ha−1) fertilizers to grass over 13 yr (1980 to 1992) could increase storage of total C (TC) and light fraction C (LFC) in a Dark Gray Chernozem soil. Hay was removed from the plots every year. The increase in mass of TC in the 0- to 30-cm soil depth from NS fertilizer was 3.88 Mg C ha−1. However, the increase in mass of LFC from NS was 9.50 Mg C ha−1, and most of the increase was found in the 0- to 5-cm soil depth. Key words: Soil carbon storage, light fraction carbon, N and S fertilizers
Particulate and mineral-associated organic matter in water-stable aggregates as affected by mineral fertilizer and manure applications
Authors: Aoyama M. , Angers D. A. , N'Dayegamiye A.
Published: April 2011

Application of cattle manure generally improves soil structure and organic matter (OM) content. However, changes in forms and location of OM within the aggregate structure are less well known. The effects of long-term (18-yr) applications of cattle manure (20 Mg ha–1 yr−1) and NPK fertilizer on the distribution of particulate and mineral-associated organic matter in water-stable aggregates were investigated in a Le Bras loam (Humic Gleysol). Soil samples from the 0- to 10-cm depth were taken from the untreated control, NPK, manure and NPK + manure treatments. They were separated into four aggregate-size fractions (>1000 µm, 250–1000 µm, 53–250 µm, and <53 µm) by slaking air-dried soil, followed by wet sieving. Particulate (>53 µm) and mineral-associated OM (<53 µm) were separated from water-stable aggregates >53 µm by sieving after mechanical dispersion. After 18 yr, manure increased the OM level of the whole soil and favored formation of slaking-resistant macroaggregates (250–1000 µm). This effect was primarily a result of the OM added by the manure. In contrast, NPK fertilizer did not affect soil OM level or macroaggregation. The increase in OM induced by manure application was observed primarily in macroaggregates, and both as mineral-associated and particulate OM. However, manure did not change OM located in the fraction <53 µm confirming that recently deposited OM preferentially accumulates within the aggregate structure and not in the finely or non-aggregated material. Since previous studies have shown that most of the C in cattle manure is composed of coarse particles, we hypothesize that manure-derived OM first enters the soil primarily as particulate material, then, during decomposition, is transformed within the aggregate structure into mineral-associated material thereby contributing to aggregate stabilization. Key words: Cattle manure, mineral fertilization, particulate organic matter, soil structure
Weathering characteristics of some soils formed in White River Tephra, Yukon Territory, Canada
Authors: Smith C. A. S. , Ping C. L. , Fox C. A. , Kodama H.
Published: April 2011

Soil formation under a cold, dry climate on two Late Holocene (approximately 1800 yr BP and 1150 yr BP) volcanic tephra deposits was examined to evaluate trends and rates of soil weathering. Presently under mature boreal forest, these soils are underlain by permafrost within 1 m of the soil surface. The soils are composed of buried forest floor materials and layers of coarse ashy-pumiceous rhyodacite tephra up to 60 cm thick. The bulk density in all tephra-derived horizons is less than 0.90 Mg m−3, water retention values for these horizons at 1500 kPa suction are less than 10% by weight. The mineralogy of the tephra-derived horizons is dominated by volcanic glass with lesser amounts of plagioclase, microcline and amphibole. Micromorphological investigation showed minor pitting of glass and feldspar grains and some oxyhydroxide coatings and Fe and Al-humus complexes. Several soil horizons meet glass composition, P retention and oxalate-extractable Fe and Al criteria established for andic soil material. However none of the profiles meet the thickness requirement to be classified as Andisol as specified in Soil Taxonomy. It is estimated that it would take >4000 yr under present climatic conditions to achieve such a degree of weathering. Key words: Tephra, Cryosol, andic, Yukon, Gelisol, glass
Mineralogy and genesis of selected soils and their implications for forest management in central and northeastern British Columbia
Authors: Arocena J. M. , Sanborn P.
Published: April 2011

Soil properties in central and northeastern British Columbia are strongly influenced by parent materials because of geologically young till, glaciolacustrine, and glaciofluvial deposits. We examined pedogenesis on various parent materials to support studies of long-term forest productivity. We sampled nine pedons developed on till (Bobtail, Lucille Mountain, Skulow Lake, Log Lake, Topley, and Kiskatinaw), glaciofluvial (Bowron), and glaciolacustrine (Aleza Lake 1, 2) deposits. The Skulow Lake pedon is distinctive in the occurrence of talc, while the Lucille Mountain pedon has the only clay fraction in which kaolinite is absent. Other pedons on till contain mica, kaolinite, chlorite, smectite, and vermiculite. The Bowron pedon has mica, kaolinite, and chlorite, while the Aleza Lake pedons have mica, kaolinite, chlorite, and 2:1 expanding minerals. In pedons with low amount of 2:1 expanding clays in the C horizon, mica and chlorite appear to degrade into 2:1 expanding clays, while in pedons with C horizons containing 2:1 expanding clays, mica and chlorite seem stable and the formation of hydroxy-interlayered clays is the predominant process. Podzolization and lessivage are major pedogenic processes, while redoximorphic processes are observed in some pedons with illuvial Bt horizons. Significant soil compaction hazards are presented by the medium and fine soil surface textures. Although clay-rich Bt horizons may benefit soil nutrient regimes, conservation of nutrient-rich forest floors is important, given the low S contents in mineral soils. High contents of feldspars in these soils provide a large reserve of nutrients such as Ca and K. Key words: Clay minerals, parent material, podzolization, lessivage
Effects of forest soil compaction and organic matter removal on leaf litter decomposition in central British Columbia
Authors: Kranabetter J. M. , Chapman B. K.
Published: April 2011

As part of the long-term soil productivity study in central British Columbia, we examined the effect of soil compaction and organic matter removal on trembling aspen (Populus tremuloides Michx.) litter decomposition. We compared three levels of organic matter removal (stem-only, whole-tree harvest, and scalped mineral soil) and two levels of compaction (no compaction and heavy compaction) in a factorial design replicated as blocks on three sites. Whole-tree harvesting significantly increased litter decomposition rates compared to stem-only (by 36%) and scalped (by 41%) treatments. Soil compaction had inconsistent effects on decomposition rates (k) for forest floor and scalped treatments and, overall, did not significantly affect litter decomposition rates. Litter on scalped plots had higher rates of nutrient translocation than litter on forest floors. We found the treatments altered soil heat sums, so changes in temperatures at the soil surface might be partly responsible for the changes in decomposition rates. We could not detect differences in soil mesofauna populations collected from the litter bags, so treatment effects on fauna probably had less influence than microclimate on decomposition rates. The effects of these early changes in litter decomposition on biological productivity will be part of the ongoing long-term soil productivity study. Key words: Litter decomposition, soil compaction, scalping, whole-tree harvest, nutrient translocation
Cautionary notes on the assumptions made in erosion studies using fallout 137Cs as a marker
Authors: VandenBygaart A. J. , King D. J. , Groenevelt P. H. , Protz R.
Published: April 2011

not available
Predicting yield of Norway spruce and Douglas-fir using a morphopedological approach in the granitic landscapes of French Massif Central
Authors: Curt Thomas
Published: April 2011

To investigate the productivity of two coniferous species in granitic uplands of the French Massif Central, relationships between soil–landscape units (= morphopedological units) and forest yield were examined. An alveola landscape model composed of seven main morphopedological units (MPU) characterizes these two granitic areas. In total, 460 forest stands were studied and joined to the MPU. Each type of MPU was correlated to the yield of Norway spruce and Douglas-fir, evaluated by the site index (dominant height of stand at a reference age). Results stress that MPU explain a large part of site index variations: 68.7% in Cevennes uplands and 50% in Limousin for Norway spruce, 42% in Limousin for Douglas-fir. The hierarchy of the productivity among MPU is comparable for both species and study areas. Highest site index values correspond to MPU with deep Brunisols in vales and bottom of alveolas, with a high soil water storage capacity but without waterlogging. Ridges and summits with coarse parent materials topped by shallow and nutrient-depleted soils experience the lowest site index values. The strong relationship between MPU and forest yield can be explained by a combination of ecological factors affecting forest yield: topoclimatic conditions, parent materials and soils. These results stress that inheritances from Tertiary, and from Quaternary periglacial environments still influence the present-day potentials of ecosystems. In conclusion, the advantages and drawbacks of morphopedological surveys for forest applications are discussed. Key words: Soil–landscape units, forest yield, Picea abies (L.) Karst., Pseudotsuga menziesii (Mirb) Franco
Legume green manure as partial fallow replacement in semiarid Saskatchewan: Effect on carbon fluxes
Authors: Curtin D. , Wang H. , Selles F. , Zentner R. P. , Biederbeck V. O. , Campbell C. A.
Published: April 2011

Increasing atmospheric CO2 concentrations, largely due to burning of fossil fuels, may accentuate the risk of global warming. Scientists are optimistic that with appropriate management soils can function as sinks for C and contribute to CO2 abatement strategies. The objective of this study was to determine if soil C can be increased using an annual legume green manure (GM) as partial fallow replacement in a fallow-wheat (Triticum aestivum L.)-wheat (F-W-W) rotation in the Brown soil zone of Saskatchewan. In 1995 and 1996 we measured soil C fluxes in all phases of F-W-W and GM-W-W rotations, which were two of the treatments in an experiment initiated in 1987 on a medium-textured Orthic Brown Chernozem. The GM, Indianhead black lentil (Lens culinaris Medikus) was estimated to add 1800 and 1400 kg C ha−1 in 1995 and 1996, respectively. Annual inputs of C in residues of the wheat crops were two to three times those of GM. Comparison of CO2 emissions from GM with those from the fallow phase of the F-W-W system suggested that GM largely decomposed in the interval between incorporation (mid-July) and freeze-up in fall. Fluxes of CO2 from the wheat phases of GM-W-W closely matched those from the corresponding phases of F-W-W, confirming that there was little carryover of undecomposed GM to the following growing season. Our results suggest that, in a 3-yr rotation, partial fallow replacement with legume GM may have only a minor impact on C sequestration because the increase in C inputs is relatively small (~ 25% in this study) and GM decomposes rapidly in the soil due to its narrow C:N ratio (12–13). Green manuring may, however, play a more significant role in enhancing soil C levels in a F-W system, where relatively large increases in C inputs could be achieved using currently-available legume species. Key words: Carbon sequestration, carbon dioxide emissions, crop residue decomposition, wheat, summerfallow, lentil
Soil aeration for dairy manure spreading on forage: Effects on ammonia volatilisation and yield
Authors: Gordon R. , Patterson G. , Harz T. , Rodd V. , MacLeod J.
Published: April 2011

Experiments were conducted to evaluate the effects of performing soil aeration either before or after spreading liquid manure in forage production systems. The experiments included eight trials performed in 1996 using a non-interfering diffusion method to determine ammonia (NH3) flux emissions from both aerated and control plots. For all eight trials, the manure application rate was 75 355 L ha−1. The average NH3 loss for the aerated treatment was 67.3 kg ha−1 while the loss for the control plots was 63.0 kg ha−1. Although differences in the NH3 loss between treatments were low, substantial variations were observed between individual trials depending on the prevailing meteorological conditions.To further evaluate the effects of soil aeration, 11 trials were carried out on Nova Scotia dairy farms in 1996 and 1997 to identify yield effects. Manure application rates ranged from 18 000 to 64 000 L ha−1. The average forage yield on aerated treatments was 9.4% below control treatments (i.e., manure without aeration). Of the 11 trials, 9 resulted in significantly (P < 0.05) reduced yield with soil aeration. Key words: Liquid manure, ammonia volatilisation, soil aeration
Response of canola, wheat and green beans to leonardite additions
Authors: Akinremi O. O. , Janzen H. H. , Lemke R. L. , Larney F. J.
Published: April 2011

Leonardite, an oxidized form of lignite obtained from coal mines, is readily available and high in humic acids (HA). It has potential as a soil amendment and may have positive effects on crop growth and yield. This greenhouse experiment evaluated the agronomic effect of leonardite on three crops: canola (Brassica napus), wheat (Triticum aestivum) and green beans (Phaseolus vulgare). The factorial design combined five rates of leonardite with five fertility treatments. The fertility treatments had a significant effect on the dry matter yield (DMY) of canola, wheat and green beans. There were also significant effects of fertility on the concentration and uptake of N, P and K by the three crops and S by canola. The application of leonardite had no significant effect on the DMY of wheat and green beans but that of canola was significantly increased. Application of 10 g of leonardite to 3 kg of soil caused a 27% increase in the DMY of canola when S was excluded from added nutrients, while 1 g of leonardite resulted in a 15% increase in yield when all nutrients were applied. In addition, uptake of S, N, P and K by canola were significantly affected by the application of leonardite. The yield response of canola was apparently due to the supply of S by leonardite with an increasing rate of leonardite supplying increasing amounts of S. This result was confirmed in a second experiment where high quantities of leonardite were applied. We concluded that leonardite increased the yield of canola by supplying S directly and by possibly facilitating the uptake of other nutrients. The lack of response of wheat and green beans to leonardite was attributed to their lack of response to S. The experiment showed beneficial effects of leonardite on canola, though high rates may be needed to exploit this benefit in field situations. Key words: Leonardite, humic acid, green house, canola, fertility
Rhizobial inoculant formulations and soil pH influence field pea nodulation and nitrogen fixation
Authors: Rice W. A. , Clayton G. W. , Olsen P. E. , Lupwayi N. Z.
Published: April 2011

Crop production systems that include field pea (Pisum sativum L.) in rotation are important for sustainable agriculture on acid soils in northwestern Canada. Greenhouse experiments were conducted to compare the ability of liquid inoculant applied to the seed, powdered peat inoculant applied to the seed, and granular inoculant applied in a band with the seed to establish effective nodulation on field pea grown at soil pH(H2O) 4.4, 5.4 and 6.6. Plants were grown to the flat pod stage, and then total plant biomass dry weight, dry weight of nodules, number of nodules, plant nitrogen content, and proportion of plant nitrogen derived from the atmosphere (%Ndfa) were measured. Granular and powdered peat inoculants produced greater nodule numbers and weight, plant nitrogen content, %Ndfa and total biomass than liquid inoculant in at least two of the three experiments. Only granular inoculant was effective in establishing nodules at soil pH 4.4, but granular and powdered peat inoculants were effective at pH 5.4, and all three formulations were effective at pH 6.6. The results showed that granular inoculant has potential for effective nodulation of field pea grown on acid soil. Key words: Rhizobium, inoculant formulations, field pea, nodulation, acid soil
Underseeded clover as a nitrogen source for spring wheat on a Gleysol
Authors: Garand M J , Simard R R , MacKenzie A F , Hamel C.
Published: April 2011

Although there is a potential to substantially reduce N fertiliser inputs by cropping spring cereals with an interseeded legume, the agronomic value and the nitrate catch-crop effect associated with this practice are not documented under the conditions of eastern Canada. This 3-yr study estimated N credits and non-N nutritional effects for interseeded clover (Trifolium pratense L. 'Arlington') in spring wheat production (Triticum aestivum L. 'Algot') and assessed fall and spring nitrate (NO3−) in soil. The soil is a St. Urbain clay (Orthic Gleysol) located in the St. Lawrence lowlands. Ammonium nitrate (NH4NO3) was applied at 0, 40, 80, 120 and 160 kg N ha-1 with or without red clover as a companion crop. Clover was incorporated as a green manure crop in mid-November. Clover significantly (P = 0.05) influenced wheat yield response to N fertilisation for 2 of the 3 yr. Clover did not reduce wheat grain yield through competition between the two plant species. Higher wheat yields with clover were attributed to N supplied by clover through mineralisation of residues incorporated in the soil the previous fall. Nitrogen fertiliser replacement value of clover was approximately 80 kg N ha-1 for 1994 and 1995. Clover occasionally increased NO3−-N measured in the soil profile in late fall and in spring. Interseeded red clover may provide most of the N needs of a companion spring wheat crop in fine-textured gleysolic soils, but is an inefficient N catch-crop. Key words: N credits, non-N nutritional effect, N catch-crop
Climate change in the semiarid prairie of southwestern Saskatchewan: Temperature, precipitation, wind, and incoming solar energy
Authors: Cutforth H. W.
Published: April 2011

Long-term weather data were analyzed to study annual as well as seasonal climate change within an approximately 15 000-km2 area in the semiarid prairie near Swift Current, SK. The climate of the study region has changed over the past 50 yr. Annually, average maximum (Tmx) and minimum (Tmn) air temperatures have increased – rainfall amounts and the number of rainfall events (≥0.5 mm) have increased since the late 1960s-early 1970s; incoming solar energy has decreased, and wind speed has decreased since the early 1970s. Seasonally, for January through April (JFMA), both Tmx and Tmn have increased, the number of rainfall events has increased since the early 1970s, snowfall amounts and the number of snowfall events (≥0.5 cm) have decreased; the number of precipitation events (≥0.5 mm) has decreased, incoming solar energy has decreased, and wind speed has decreased since the early 1970s. For May through August (MJJA), Tmn has increased, incoming solar energy has decreased, and wind speed has decreased since the mid-1970s. For September through December (SOND), the number of rainfall events has increased since the early 1970s and wind speed has decreased. Since 1950, JFMA has become drier and, relative to JFMA, SOND has become wetter. Generally, JFMA has experienced the largest change in climate, whereas SOND has experienced the least climate change. Precipitation amounts and events were negatively correlated with increasing Tmx, suggesting a future decrease in precipitation amounts for southwestern Saskatchewan if global warming continues. Key words: Climate change, semiarid prairie, temperature, precipitation, wind, solar energy
Carbon and nitrogen mineralization in soil amended with non-tabletized and tabletized poultry manure
Authors: Paré T. , Dinel H. , Schnitzer M.
Published: April 2011

The recycling of poultry (Gallus gallus domesticus) manure (PM) needs to be done in a manner that will not only improve soil physical, chemical and biological properties but also minimize environmental risks. Untreated PM is more difficult to handle and more expensive to apply than granular fertilizers; the application of PM in the form of tablets may be a suitable alternative. It is necessary to determine whether C and N mineralization in tabletized PM (T-PM) differs from non-tabletized PM (NT-PM). Net C and N mineralization from a Brandon loam soil (Typic Endoaquoll) amended with NT-PM and T-PM, were measured in an incubation study at 25 °C. After 60 d of incubation, about 62 and 77% of total PM carbon was mineralized in NT-PM and T-PM amended soils, respectively. Carbon mineralization was not stimulated by the addition of PM tablets containing NPK to soil, while in soils mixed with NT-PM + NPK, soil respiration was reduced. Net N mineralization was similar in soils amended with T-PM and NT-PM, although changes in ammonium (NH4+–N) concentrations during incubation differed. Generally more NH4+–N accumulated in soil amended with T-PM and T-PM + NPK than with NT-PM and NT-PM + NPK The concentrations of nitrate (NO3−–N) did not differ in soils amended with T-PM and NT-PM, indicating a reduction in nitrification and NH4+–N accumulation in soils amended with PM tablets. Key words: Poultry manure, tablets, carbon mineralization, nitrogen mineralization, organic fertilizer
Spatial and temporal trends in soil properties at a soil quality benchmark site in central Nova Scotia
Authors: Webb K. T. , Wang C. , Astatkie T. , Langille D. R.
Published: April 2011

In response to concerns over the widespread soil degradation occurring on Canada's agricultural lands, Agriculture and Agri-Food Canada established a network of benchmark sites to assess soil quality change by monitoring agronomically important soil properties. The Nova Scotia site was established in 1989 on Queens (Gleyed Brunisolic Gray Luvisols) and Debert (Gleyed Dystric Brunisols) soil series under a corn–forage rotation within the Annapolis–Minas Lowlands ecoregion. The objectives of the project were to quantify temporal changes in agronomically important soil properties and determine how the property values vary with the landscape and components of the soil map unit. A 20 × 25 m grid was used in 1990 and again in 1995 to sample soil from the Ap horizon and to locate saturated hydraulic conductivity and penetration resistance measurements. The samples were analyzed for pH, organic C, total N, and available P and K. The results indicate that over 5 yr, organic C, C:N ratio, available P, and saturated hydraulic conductivity declined by 7.9, 4.7, 12.5, and 53%, respectively. Significant differences in pH, organic C, total N, available K, penetration resistance and saturated hydraulic conductivity were associated with selected components of the soil map unit. Slope position had a minimal effect on soil properties except for available K where the highest levels were located on middle slope positions. Interactions between particle size and slope position were found, with soils with coarse-loamy sola on upper slope positions having the lowest pH. The results of this study also demonstrated the utility of the method for monitoring soil quality change and the importance of the soil map unit in interpreting the spatial and temporal differences in soil properties. Key words: Soil variability, soil monitoring, soil properties, soil map unit, spatial correlation
A novel laboratory apparatus for simulating isotropic oceanic turbulence at low Reynolds number
Authors: Webster Donald R. , Brathwaite Aisha , Yen Jeannette
Published: April 2011

A new experimental apparatus to simulate oceanic turbulence at low Reynolds number in the laboratory is described. Actuators located at each corner of a cubic Plexiglas box generated synthetic jets that interacted to create turbulent flow at the center of the saltwater apparatus. Four turbulent intensity levels were established, and velocity measurements were performed using digital particle image velocimetry. The flow characteristics in the center of the apparatus were confirmed to be nearly isotropic and homogeneous. The range of the dissipation rate (10−3 to 1 cm2s−3) and the Kolmogorov microscale (0.03 to 0.2 cm) agreed well with natural oceanic environments in the coastal zone, and the length scales and magnitude of the velocity and strain rate fluctuations were appropriate for zooplankton studies. The flow characteristics compared favorably with previous approaches for generating turbulence in the laboratory, in particular, oscillating‐grid apparatus. The current design also possessed increased simplicity, controllability, and transportability. Future objectives include studying the behavioral response of zooplankton to turbulent fluid motions.
Estimating prokaryotic diversity: When are 16S rDNA libraries large enough?
Authors: Kemp Paul F. , Aller Josephine Y.
Published: April 2011

As a necessary step in the study of prokaryotic diversity using 16S rDNA libraries, authors should evaluate how well their libraries represent diversity in the source environment. Phylotype‐richness estimates can be used to judge whether a library represents diversity sufficiently for its intended purpose. We have argued that richness estimates are most useful if libraries are first shown to be large enough to yield stable estimates. In this article, we (1) evaluate two potentially suitable, non‐parametric richness estimators (SACE and SChao1), tested against model libraries and libraries drawn from natural prokaryotic communities; (2) evaluate whether stable richness estimates are also unbiased; and (3) examine characteristics of prokaryotic libraries that influence the usefulness of richness estimators. Richness estimates consistently reached a stable asymptotic value for libraries that sampled diversity exhaustively. Stable estimates appear to be unbiased or minimally biased estimates of phylotype richness. The SACE estimator was often undefined, sometimes overestimated phylotype richness at intermediate sampling efforts, and sometimes stabilized at a larger library size than the SChao1 estimator. The SChao1 estimator appears well suited for estimating phylotype richness from prokaryotic 16S rDNA libraries. Libraries judged too small to yield a stable richness estimate typically had a highly uneven frequency distribution of phylotypes, with a preponderance of phylotypes that occurred only once in the library. Libraries considered large enough typically had a more even frequency distribution of phylotypes. A software tool is provided to aid others in assessing whether their libraries are large enough to yield stable phylotype‐richness estimates.
A physicochemically constrained seawater culturing system for production of benthic foraminifera
Authors: Hintz Christopher J. , Chandler G. Thomas , Bernhard Joan M. , McCorkle Daniel C. , Havach Suzanne M. , Blanks Jessica K. , Shaw Timothy J.
Published: April 2011

We present an apparatus and procedure for culturing deep‐sea (i.e., bathyal) benthic foraminifera under physicochemically constrained conditions. A 1600‐L recirculating culture system was constructed to contribute negligible trace metal contamination; the system was housed in an environmental room maintained near in situ temperatures but at atmospheric pressure. Peristaltic pumps continuously circulated 3 mL seawater min−1 from the reservoir to 9 to 12 culture chambers. A 2‐mm‐thick layer of high‐purity clay‐sized silica substrate was used to minimize the impact of sedimentary microhabitats. Physicochemical parameters (salinity, alkalinity, pH, temperature) varied <2% throughout two culture experiments. Trace metal concentrations were initially set near open‐ocean values and remained constant (i.e., within our analytical precision) during the experiments. Culture seawater was equilibrated with atmospheric CO2, thus dissolved inorganic carbon δ13C varied ~1‰ over the course of each experiment, reflecting the seasonal atmospheric CO2 isotopic variation. Culture seawater δ18O varied ~0.2‰. Each culture chamber was inoculated with as many as 100 foraminifers of single or multiple species. Pre‐existing foraminiferal calcite was identified by fluorescent labeling prior to specimen introduction into culture. The cultures remained viable for >200 d in each experiment and produced up to 2,800 individuals per culture. The growth and reproduction of benthic foraminifera in a physicochemically constrained culture provide a new method for the experimentation and validation of geochemical proxies.
Evaluation of biophysical and optical determinations of light absorption by photosystem II in phytoplankton
Authors: Suggett David J. , MacIntyre Hugh L. , Geider Richard J.
Published: April 2011

Fast repetition rate (FRR) fluorescence can provide highly resolved estimates of light absorption by photosystem II (PSII), a variable that is critical to bio‐optical determinations of phytoplankton productivity. We compared estimates of chlorophyll a‐specific light absorption by PSII, achlPSII, using both biophysical (FRR) and optical (chlorophyll a‐specific light absorption coefficient, achl) techniques on cultures of phytoplankton from diverse taxa. Biophysical determinations of achlPSII were obtained from the product of the effective light absorption cross‐section of PSII (σPSII), measured by FRR fluorescence, and the ratio of PSII reaction centers to chlorophyll a (nPSII), measured by oxygen flash yields. Both parameters were highly variable between individual taxa. In mixtures of algae, the estimates of σPSII were largely determined by the taxon that dominated fluorescence intensity. Independent optical estimates of achlPSII were obtained by weighting the light absorption spectra of photosynthetic pigments by the fluorescence excitation spectra. The biophysical and optical estimates of achlPSII were highly correlated (r2 = 0.94) with a slope that was not significantly different from 1 and an intercept of 0. Estimates of productivity using biophysical or optical absorption measurements should therefore be comparable when the latter are adjusted to account for the proportion of light provided for photochemistry into both photosystem I and II. Finally, we show how simultaneous measurements of σPSII and achlPSII can be used to derive nPSII where flash‐yield measurements are impractical, as is almost universally the case in field measurements.
Automated analyses of 18O/16O ratios in dissolved oxygen from 12‐mL water samples
Authors: Barth Johannes A.C. , Tait Andrew , Bolshaw Mike
Published: April 2011

We introduce a new technique to routinely determine the 18O/16O ratio of O2(aq) from 12‐mL Exetainer® vials. Results were expressed in a δ‐notation versus air and the Vienna Standard Mean Ocean Water (VSMOW). Samples were prepared by creating a He‐headspace and stripping O2(aq) from solution by shaking for 30 min on a wrist shaker. Subsequent isotope analysis of the extracted O2(g) was achieved by converting the entire headspace into a large sampling loop using a double‐hole needle. This enabled admission of sufficient O2(g) into a packed A5‐Å‐molecular sieve column, where it was separated from N2 before admission to the isotope ratio mass spectrometer. The latter was tuned to an m/z ratio of 32, thus enabling direct determination of molecular O2(g) without conversion to CO2. External standards consisted of dry air samples in helium‐flushed vials and had between 1.5 and 16.8 parts per thousand O2(g) in a He matrix and a known isotopic composition of 0‰ air (+23.8‰ VSMOW). The method allows automated analyses of up to ~180 samples in one single batch and will provide new quantitative information about oxygen turnover in aqueous systems, including rates of gas transfer, redox processes, respiration, and photosynthesis. Repeat δ18OO2(aq) measurements on samples with concentrations between 15.6 µmol L−1 and saturation revealed standard deviations of 0.3‰. This is a typical precision encountered in continuous flow applications, and the method is available for studies using either 18O‐labeled water to evaluate O2 gross production by incubation experiments or for natural abundance studies when isotope shifts are larger than 0.8‰. It may also become useful in microbiological and medical applications and can serve to quantify plant‐gas exchange and soil gas processes.
Optimization of DNA extraction for quantitative marine bacterioplankton community analysis
Authors: Boström Kjärstin H. , Simu Karin , Hagström Åke , Riemann Lasse
Published: April 2011

The coupling between the presence of predominant bacterial species and particular biogeochemical processes is of primary interest in current microbial ecology. Molecular methods such as microarrays and real‐time polymerase chain reaction (PCR) may be used to estimate presence or expression of different genes (e.g., 16S rDNA and nifH) in environmental samples; however, to be quantitative, these methods require a reproducible and efficient DNA extraction protocol. Using picogreen DNA quantification, real‐time PCR, and an internal DNA standard, we step‐wise examined and optimized a protocol for DNA extraction from centrifuged or filtered seawater samples (vol. 2 to 300 mL). Sample volume had a pronounced effect on DNA extraction efficiency showing that comparison of samples with different volumes is problematic. The duration of enzyme treatment (lysozyme and proteinase K) significantly influenced the DNA extraction efficiency. Dissolved DNA contributed significantly to total DNA when extracted from small filtering volumes (<10 mL). Addition of a coprecipitant (yeast tRNA) improved the precipitation of low‐concentration DNA from 13% to 89%. When tested on various seawater samples, as well as on isolates, the optimized extraction protocol was found to be highly reproducible with an average extraction efficiency for seawater samples of 92% and for isolates of 96%. The quantitative outcome and the high extraction efficiency of the presented extraction protocol will be of value to future studies based on DNA extracted from seawater samples.
An inexpensive, automatic, submersible water sampler
Authors: Martin Jonathan B. , Thomas Ray G. , Hartl Kevin M.
Published: April 2011

Currently available water samplers are manually actuated, can only be deployed onshore, limiting their use to small or developed water bodies, or are designed for deployment in the deep sea, making them large and expensive. The automatic submersible water sampler described here is small, lightweight, actuated by a microprocessor, and inexpensively and easily constructed. The sampler consists of a pressure case, sample containers constructed of 10 spring‐loaded 60 mL syringes connected to solenoid valves, and electronics to control opening and closing of the solenoid valves. Vacuum in the syringes keeps the springs compressed while the solenoid valves are closed. When a valve opens, the spring expands and draws water past a screen and/or filter into the syringe. Once the syringe is filled, the solenoid valve closes, storing the sample. More than one syringe can be opened simultaneously if more than 60 mL are required. Preservatives can be added to the syringe prior to deployment. Some environments where it could be used include karst aquifers, lakes, large rivers, and estuaries.
Evaluation of the collection efficiency of upper ocean sub‐photic‐layer sediment traps: a 24‐month in situ calibration in the open Baltic Sea using 234Th
Authors: Gustafsson Örjan , Andersson Per , Roos Per , Kukulska Zofia , Broman Dag , Larsson Ulf , Hajdu Susanna , Ingri Johan
Published: April 2011

The collection efficiency of cylindrical sediment traps of common design was assessed in situ for more than 2 y in an offshore shelf regime using the 234Th proxy and simultaneously collected hydrological and biogeochemical parameters. The traps were found to systematically record an undertrapping bias of 234Th by, on average, a factor of three (range 0.8 to 10). Seasonal variations in trapping efficiency were related to the seasonally varying ballasting properties of the settling particle pool. Sediment trap 234Th fluxes agreed within a factor of two of the estimated 234Th export from the overlying surface waters in the winter‐spring periods in both 1999 and 2000 and appeared related to a particle pool that included, presumably rapidly sinking, mineral particles and diatom tests acting as ballast. In contrast, discrimination against slowly settling organic‐rich aggregates of apparent exudate origin resulted in undertrapping of 234Th by factors of three to ten throughout the summerfall seasons. These data are consistent with hydrodynamic predictions that the collection efficiency of sinking particles is inversely related to their intrinsic settling velocities. Recognition of changing particle composition along a settling velocity spectrum combine with carbon mass balance restrictions to suggest that these 234Th‐based collection efficiencies, ranging from 0.1 to 1, may not be directly applicable to “correct” sediment trap fluxes of other components, such as organic carbon. However, the 234Th‐derived insights of settling‐velocity‐related undertrapping may beneficially be taken into account when interpreting trap records both in studies of biogeochemical element fluxes and in phytoplankton ecology.
A nonradioactive assay of bacterial productivity optimized for oligotrophic pelagic environments
Authors: Nelson Craig E. , Carlson Craig A.
Published: April 2011

The measurement of bacterial production is a cornerstone of research in aquatic biogeochemistry and microbial ecology, yet the standard radioisotope‐based techniques are threatened by increasing logistical obstacles. The two primary goals of this study were (1) the development of a reliable nonradioactive assay of bacterial productivity interpretable in the context of previous 3H‐thymidine (3H‐TdR)—based metrics, and (2) maximizing the sensitivity of the assay to allow routine measurement of bacterial productivity in open‐ocean and low‐productivity environments. We optimize existing methods for immunochemical detection of the incorporation of the thymidine analog 5‐bromo‐2′‐deoxyuridine (BrdU) to present a functional assay of community bacterial productivity comparable to radioisotope‐based assays in economy and field implementation and capable of consistently detecting bacterial production rates within the range of 0.1 to 10 pmol BrdU L−1 h−1. A standardization procedure provides complete separation of radioisotopes from the working methodology and gives statistically consistent results between calibrations with no degradation of the labeled DNA standards. Immunoassayed BrdU incorporation rates were highly correlated with parallel measurements of 3H‐TdR incorporation rates spanning a range of 0.1 to 10 pmol L−1 h−1 (r = 0.96, n = 20, P < 0.001). Model II linear regression (BrdU = 0.65[3H‐TdR] + 0.12) yielded a conversion factor not significantly different from that reported previously comparing incorporation rates measured using radioisotope protocols (3H‐BrdU = 0.69[3H‐TdR] − 0.81). The assay is interpretable in the context of 3H‐TdR—based measures of production, providing continuity as a nonradioactive measure of bacterial production in low‐productivity aquatic ecosystems.
The dissolved organic iodine species of the isotopic ratio of 129I/127I: A novel tool for tracing terrestrial organic carbon in the estuarine surface waters of Galveston Bay, Texas
Authors: Schwehr Kathleen A. , Santschi Peter H. , Elmore David
Published: April 2011

Variations in 129I/127I ratios were used to trace terrestrial organic carbon (tDOC) across an estuary because (1) iodine is biophilic, up to 75% of total iodine in fresh and coastal marine waters partitions into organic iodine; (2) 129I/127I ratios in tDOC are greatly elevated over those from marine systems because atmospheric emissions of 129I from European nuclear fuel reprocessing facilities were mixed more quickly in the surface ocean, up to 500 m in a decade, than the terrestrial system, which mixed approximately 10 cm in 10 to 50 y; and (3) the oceanic contribution of 127I (50 to 65 ppb) to the ratio has a greater dilution effect than 127I from freshwater (0.5 to 40 ppb). Analytical techniques were developed for 129I/127I ratio determination in dissolved organic iodine (DOI) and the other iodine species, using dehydrohalogenation, anion chromatography, high‐performance liquid chromatography, and accelerator mass spectrometry, to be applied to samples from Galveston Bay, Texas. Results indicate that 129I/127I ratios in DOI from terrestrial sources are elevated in the upper estuary up to salinity of about 20, similar to a behavior previously described for this estuary for stable isotopic signals for dissolved organic matter. 129I/127I ratios in the other iodine species, e.g., iodide and iodate, did not show this feature, indicating fast isotopic and chemical equilibration between the two isotopes among the different inorganic species in the estuary. These results thus provide proof of concept that 129I/127I‐DOI can serve as a tracer for tDOC in the coastal zone.