bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential performance of pinto bean under varying levels of soil moisture
Authors: Nleya T. M. , Slinkard A. E. , Vandenberg A.
Published: April 2011

Common bean (Phaseolus vulgaris L.) is a relatively new crop in western Canada. Considerable effort is currently underway in Saskatchewan to expand bean production under both irrigated and rainfed conditions. The objectives of this study were to evaluate the performance of pinto bean genotypes under irrigation in the field and to determine the presence of phenological plasticity among specific pinto bean genotypes when subjected to intermittent drought stress. Six bean genotypes, three determinate and three indeterminate, were grown under irrigated conditions in the field in Saskatoon, SK, in 1994 and 1995. The same genotypes were grown under well-watered and drought stress conditions in the growth room. In the field, indeterminate genotypes were superior in seed yield. The indeterminate genotypes were also superior in seed yield in the growth room under well-watered conditions. Two indeterminate genotypes and one late-maturing determinate genotype performed well when drought stress was intermittent, but yielded the same or less than the early-maturing determinate types when drought stress was severe. The indeterminate genotypes and one late-maturing determinate genotype showed stronger recuperative growth than early-maturing determinate genotypes when released from drought stress. Recuperative growth resulted in delayed maturity relative to growth under optimum soil moisture levels, but it had little effect on other characteristics. Key words: Phaseolus vulgaris, common bean, pinto bean, genotype, drought stress
Phytotoxicity of canola residues: Release of water-soluble phytotoxins
Authors: Wanniarachchi S. D. , Voroney R. P.
Published: April 2011

Phytotoxicity of root, stem and leaf residues of canola (Brassica napus L.) was studied in a laboratory incubation for 8 wk. Bioassays were conducted with corn (Zea mays L.), barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) seeds to determine the relative toxicity of residue extracts. The release of volatile fatty acids (VFAs) and phenolic compounds (PCs) during incubation was studied to assess the role of these compounds in phytotoxicity. Canola residue extracts significantly inhibited (P ≤ 0.01) seedling growth (coleoptile and radicle lengths) of all crop species tested, with leaf and root residues causing the greatest and least toxicity, respectively. Incubation temperature had no impact on the toxicity of extracts. All residue extracts had VFAs prior to and during the incubation, with leaf residues producing relatively high levels of VFAs. The release of VFAs declined drastically during the incubation period. The release of PCs, measured as total phenolic compounds in extracts, was highest in leaf residues and remained higher than those of root or stem residues. Toxicity of residue extracts was not related to the amounts of VFAs and PCs found. However, toxicity appeared to be most related to the presence of total phenolic compounds in residue extracts. Key words: Phytotoxicity, canola residues, volatile fatty acids, phenolic compounds, residue decomposition
Rhizosphere chemistry in an ammonium sulfate and water manipulated Norway spruce [Picea abies(L.) Karst.] forest
Authors: Clegg S. , Gobran G. R. , Guan X.
Published: April 2011

The purpose of this study was to examine how the treatments ammonium sulfate, drought and irrigation changed chemical characteristics of three soil fractions (bulk soil, rhizosphere and soil root interface (SRI)) from E, Bh and Bs horizons of Podzol in a Norway spruce stand in southwestern Sweden. Regardless of the treatment, the properties of the rhizosphere and SRI nearly always differed from the bulk soil due to the high quantity of organic and root material. Irrigation and ammonium sulfate raised water soluble cations and base saturation in the bulk soil. This was possibly due to leaching from the humus and exchange reactions. In the rhizosphere and SRI, irrigation and ammonium sulfate lowered soluble base cations (BC) and base saturation when compared with control; this is attributed to a combination of leaching and high nutrient demand by trees creating a zone of relative depletion. Drought accumulated more organic matter (OM), acidity and cations in the soil fractions suggesting that the lack of water limited transport and uptake of nutrients. Generally, the magnitude of accumulation/depletion of nutrients in the soil fractions reflected the degree of stress which was in turn linked to root uptake of nutrients or to tree growth. Due to the apparent linkage between tree growth, uptake of nutrients and rhizosphere chemistry, we emphasise that soils must be studied at the rhizospheric rather than the bulk soil scale to further understand the effects of environmental stresses. Key words: Ecosystem manipulation, conceptual model, irrigation, organic matter, relative depletion, soil root interface
Effect of straw amendment and plant growth on selenium transfer in a laboratory soil-plant system
Authors: Arbestain M. Camps
Published: April 2011

Knowledge of the transfers of selenium (Se) in the soil-plant-atmosphere environmental compartments is fundamental in assessing Se cycling through the environment. The purpose of this study was to determine the effects of straw amendments and barley (Hordeum vulgare L.) on Se cycling in soils from Kesterson Reservoir, Merced County, CA (0.68 mg soluble Se kg−1, 6.15 mg total Se kg−1), and to evaluate the feasibility of these agricultural practices as bioremediation strategies. Four treatments were evaluated: soil only, soil + straw, soil + plant, and soil + straw + plant. Straw amendments greatly reduced Se from soil solution (92–97% of initial soluble Se). Selenate [Se(VI)] was the predominant species in soil solution. Phosphate-extractable Se did not account for the decline in soluble Se. Selenium volatilized by microbes represented only 4–5% of the soluble Se removed. Highest Se removal from soil solution and highest Se volatilization rates occurred when both microbial activity and growth were maximal. Selenate microbial reduction to more insoluble Se forms is indicated as being responsible for this removal. Plants did not account for as much Se removal from soil solution as did straw amendments. Total shoot Se corresponded to 1–9% of soluble Se removal. At the end of the experiment, Se in plants represented 0.1–0.7% of total Se in the system, and the Se volatilized accounted for 0.2 to 0.5% of total Se inventory. The results obtained in this study suggest the use of straw amendments as a remediation technique for managing Se contamination at Kesterson Reservoir. Key words: Barley, selenium, soil solution, straw, volatilization
Denitrification during the growing season following dairy cattle slurry and fertilizer application for silage corn
Authors: Paul J. W. , Zebarth B. J.
Published: April 2011

Denitrification losses during the growing season may reduce the availability of manure and fertilizer N for crop production. Denitrification losses were measured during the growing seasons of 1992 and 1993 following spring manure or fertilizer application on a sandy soil with a high water table (Sumas) and a well-drained silt loam soil (Agassiz), both cropped to silage corn (Zeamays L.). Dairy cattle slurry (600 kg total N ha−1) was surface applied and incorporated in April. Ammonium nitrate (200 kg N ha−1) was surface applied at planting in early May. Denitrification rates were measured using the acetylene blockage technique on intact soil cores taken from 0- to 13-cm, 15- to 28-cm and 30- to 43-cm depths biweekly following manure application until mid-June, then monthly until after harvest in September. Denitrification rates were measured weekly in the control and manured treatment in 1993. In 1993, average denitrification rates were significantly higher following manure application (485 g N ha−1 d−1) than following fertilizer application (214 g N ha−1 d−1), and were higher at 15- to 30-cm depth (213 g N ha−1 d−1) than at 0- to 15-cm depth (22 g N ha−1 d−1) and the 30- to 45-cm depth (44 g N ha−1 d−1). Denitrification losses during the growing season in 1993 were 75 and 39 kg N ha−1 in the manured and fertilized soil at Sumas, compared with 68 and 34 kg N ha−1 in the same treatments at Agassiz. Denitrification losses during 1992 were 156 and 107 kg N ha−1 in the manured and fertilized soil at Sumas, compared with 95 and 27 kg N ha−1 in the same treatments at Agassiz. This research demonstrates that denitrification losses can be substantial during the growing season, and can be underestimated if denitrification rates are measured only to 15 or 20 cm depth.

Key words: Acetylene blockage, soil cores, nitrogen, manure, maize
Increased denitrification below the root zone in the fall following a spring manure application
Authors: Paul J. W. , Etches V. , Zebarth B. J.
Published: April 2011

Indirect measurements of denitrification to 120 cm depth in a coarse textured soil in October showed higher denitrification rates following a single spring application of dairy cattle slurry than following a spring application of fertilizer. The highest denitrification rates occurred immediately above and below the water table (90 cm depth) and resulted primarily from C applied in the manure moving down through the soil profile.

Key words: Dairy cattle slurry, carbon, nitrate, shallow water table
Tillage effects on soil microbial and biochemical characteristics in a fallow-wheat rotation in a Dark Brown soil
Authors: Biederbeck V. O. , Campbell C. A. , Hunter J. H.
Published: April 2011

As the adoption of reduced tillage increases on the prairies, so too does the use of herbicides and society's concern regarding their possible negative impact on the environment. Two experiments were conducted on Regina heavy clay, an Orthic, Dark Brown Chernozem, at Regina, Saskatchewan, for up to 21 yr, to determine the influence of tillage on yields of hard red spring wheat (Triticum aestivum L.) in a fallow–wheat (F–W) rotation. The treatments used to control weeds in the fallow phase were conventional mechanical tillage (CT) vs. zero tillage (i.e., herbicides only or ZT). In one experiment, glyphosate was the herbicide used; in the other, paraquat (plus Buctril M) was used. In 1991 (the 21st yr), soil sampled from the 0- to 5-cm depth of each rotation phase was used to determine the possible long-term effect of these treatments on selected soil microbial populations and soil biochemical characteristics. The samples were taken in early June (prior to herbicide application), in mid July (3 wk after the 21st herbicide application), and in early September (11 wk after the 21st herbicide application). Generally, the herbicides had no long-term or short-term (in the 21st yr) deleterious effects on soil microbial populations (bacteria, actimonycetes, fungi, nitrifiers, denitrifiers), nor on microbial biomass or potential C or N mineralization. Compared with ZT, CT had a negative impact on most soil characteristics. Microbial activity was primarily a function of crop residue inputs and growing season weather conditions near the time of sampling.

Key words: Zero tillage, glyphosate, paraquat, microbial biomass, mineralization
Ammonia sources in agriculture and their measurement
Authors: McGinn S. M. , Janzen H. H.
Published: April 2011

There are several reasons why the measurement of ammonia emissions is important in agriculture. The emission of ammonia from stored and land-applied manure to the atmosphere can result in a significant loss of nitrogen for crop production. It is necessary to quantify this loss to evaluate manure handling practices for maintaining the nutritive value of the manure. Minimizing the emissions of ammonia from manure also reduces agriculture's impact on the environment. A high atmospheric concentration of ammonia can result in acidification of land and water surfaces, cause plant damage and reduce plant biodiversity in natural systems. Ammonia emissions from manure coincide with odors, which are a nuisance in areas of intensive livestock operations. Reducing ammonia emissions by altering manure management will also reduce odor problems. The purpose of this paper is to review agricultural sources of ammonia and describe techniques used in determining the loss of ammonia from manure-amended soils. Micrometeorological techniques are used to estimate field scale emissions whereas, for small plots where treatment (effects) is used, chambers and mass balance techniques are more suitable methods. A simple method is described, which, when combined with a denuder sampler mounted on a wind vane, permits flexibility in experimental design and requires fewer ammonia samples than the traditional mass balance approach. A chamber method making use of diffusion samplers that can measure the ammonia concentration in the air at the soil surface is also described. Key words: Ammonia, nitrogen loss, agriculture, manure, micrometeorology, chamber
Row-centred log ratios as nutrient indexes for saturated extracts of organic soils
Authors: Parent L. E. , Cissé E. S. , Tremblay N. , Bélair G.
Published: April 2011

Composition of soil solution was investigated in the top layer of a Typic Mesisol across seven crop sequences. Each sequence started and ended with carrots (C) and included onions (O), barley (B) and weeded fallow (F) as follows: CCCC, CCBC, CBCC, CCOC, COBC, CBOC and CFFC. The soil showed adequate pH and electrical conductivity values. Soil solution composition was assessed by the saturated soil extraction procedure. The changing levels of nutrients in the saturated soil extracts over seasons, years and crop sequences were analyzed using absolute values of nutrient concentrations, nutrient percentages relative to total soluble salts (the nutrient intensity and balance concept) and row-centred log ratios of nutrient concentrations or activities (compositional data analysis). The row-centred log ratio is the log-transformed ratio of a given element to the geometric mean of soluble elements. Nutrient percentages were highly correlated with row-centred log ratios. The three relative nutrient expressions reduced seasonal variations as compared with raw nutrient concentrations by incorporating component proportions. Concentration of total soluble salts was significantly correlated (P < 0.01) with concentrations of NO3-N (r = 0.37), P (r = 0.80), K (r = 0.80), Ca (r = 0.96) and Mg (r = 0.92) in saturated soil extracts. Between-years homoscedasticity as well as reduced skewness and kurtosis for all nutrients were obtained using row-centred log ratios of ion activities. Other advantages of using row-centred log ratios are discussed. Key words: Saturated soil extract, compositional nutrient diagnosis, seasonal variability
Temporal influence of fly ash on select soil physical properties
Authors: Salé L. Y. , Chanasyk D. S. , Naeth M. A.
Published: April 2011

Fly ash, as a source of calcium, has potential for soil structure amendment. This potential was tested by examining the influence of fly ash on select soil physical properties of an easily clodded clay loam soil. Fly ash:soil mixtures were varied from 0 to 100% (vol/vol). Pots of these mixtures were placed into the soil of a reclaimed surface mine and sampled four times during a 15.5-mo period: upon mixing, after one summer, after one summer and a winter and after the second summer. Bulk density, dry aggregate size distribution, penetration resistance (PR) and modulus of rupture (MOR) were assessed on soils within the pots.Adding fly ash up to 25 to 50% generally increased bulk density; adding more decreased it. Bulk density decreased over time for most of the treatments. Adding 12.5 or 25% fly ash produced the greatest percentage of aggregates within the ideal range (0.5 to 4.0 mm). Blunt-end PR was a more sensitive parameter than cone resistance. Adding 25% fly ash resulted in lower MOR while maintaining a desirable level of aggregation, thus reducing cloddiness. In general most properties varied over time, indicating the need to consider the dynamic nature of them in reclamation. Key words: Fly ash, soil reclamation, bulk density, penetration resistance, particle size distribution
Strategies for variable rate nitrogen fertilization in hummocky terrain
Authors: Beckie H. J. , Moulin A. P. , Pennock D. J.
Published: April 2011

A study was conducted from 1994 to 1996 in a hummocky landscape near Prince Albert, Saskatchewan in the moist Black soil climatic zone to determine the best criterion for defining fertilizer management zones within a field and how much fertilizer to apply in each zone. A uniform rate fertilization (CF) treatment was compared with three variable rate fertilization (VRF) treatments that used management zones based on soil residual nitrate-N (VRFrn), organic carbon (VRFom) and topography (VRFt). For VRFom and VRFt, fertilizer recommendations were based on soil residual N levels within zones and yield potentials that differed between zones. Flax (Linum usitatissimum) was grown in 1994, spring wheat (Triticum aestivum) in 1995, and canola (Brassica rapa) in 1996. Fertilizer use efficiency (FUE), defined as kilograms seed per kilogram fertilizer N, was markedly higher for VRFom and VRFt than CF or VRFrn. This enhanced FUE resulted in net returns, defined as crop revenue minus fertilizer cost, of about $10 ha−1 more than that of CF. Three successive years of VRF in this study suggests that this practice can enhance the efficient use of fertilizer N and has potential to increase profitability of fertilizer use, by more closely matching fertilizer N inputs with crop nutrient requirements. Key words:Brassica rapa, Linum usitatissimum, Triticum aestivum, nitrogen, variable rate fertilization, precision agriculture
CH4 fluxes from a soil amended with dairy cattle manure and ammonium nitrate
Authors: Lessard R. , Rochette P. , Gregorich E. G. , Desjardins R. L. , Pattey E.
Published: April 2011

Dairy cows and heifers in Québec and Ontario produce 19 Mt of manure annually. Most of this manure is applied to soils and may influence the atmospheric loading of greenhouse gases such as CH4 In this study, soil surface CH4 fluxes were measured 36 times during the snow-free season of 1993, and 28 times in 1994, on plots fertilized with organic or inorganic-N. In 1993, stockpiled dairy cattle manure was applied at rates of 0, 56 and 112 Mg ha−1 In 1994, the treatments were: zero N, 100 Mg ha−1 of stockpiled dairy cattle manure, 100 Mg ha−1 of composted dairy cattle manure and 200 kg N ha−1 as ammonium nitrate. Methane fluxes (−0.012 to 0.004 mg m−2 h−1) were usually higher (less negative) on manured than on unmanured plots, but the differences were not statistically significant. No significant effect of mineral-N fertilization was observed as the ammonium nitrate treatment showed uptake rates similar to those of the control. In 1993, episodic above-ambient CH4 concentrations were measured at 0.15 m (8 ppmv) and 0.05 m (2.7 ppmv) using stationary air probes, but were not associated with significant CH4 emissions at the soil surface. This observation suggested that CH4 produced in the soil was oxidized by methane-consuming organisms as it diffused towards the surface. Methane concentrations in soil air were higher in manured than in unmanured plots during most of the 1994 snow-free season, but were similar late in the season when soluble organic C concentrations in the manured plots returned to levels measured in the control plots early in the season. The results of this study indicate that the application of quantities up to 100 Mg ha−1 of dairy cattle manure to a soil under maize is not likely to have a large impact on the net exchange of CH4 between the soil and the atmosphere in central Canada. Key words: Methane, greenhouse gases
Tillage and fallow frequency effects on selected soil quality attributes in a coarse-textured Brown Chernozem
Authors: Campbell C. A. , McConkey B. G. , Biederbeck V. O. , Zentner R. P. , Tessier S. , Hahn D. L.
Published: April 2011

An 11-yr study was conducted on a coarse-textured Brown Chernozemic soil in the semiarid prairie of southwestern Saskatchewan. Soil was sampled after 3, 7 and 11 yr, and the results were used to assess the influence of fallow frequency and tillage on selected soil quality attributes [e.g., total soil organic C and N, microbial biomass C (MB-C) and microbial biomass N (MB-N), C mineralization (Cmin) and N mineralization (Nmin), and specific respiratory activity (SRA)] in the 0- to 7.5-cm and 7.5- to 15-cm depths. Although it took 11 yr before we observed significant treatment effects on total organic C or N, effects on Cmin and Nmin were observed in 7 yr in the 0- to 7.5-cm depth and by 11 yr, MB and SRA also showed significant treatment effects in this depth. Generally, soil quality attributes were greater in no-tillage (NT) systems than in conventional mechanical tillage (CT) or minimum tillage (MT), and greater in continuous wheat (Triticum aestivum L.) (Cont W) than in fallow-wheat (F-W) systems. With time, the labile constituents tended to increase under the Cont W cropping, but to decrease when F-W was coupled with MT. After 11 yr there was a strong, direct association between the labile attributes (viz., Cmin, Nmin and MB-C) in the 0- to 7.5-cm depth and the mean annual straw produced (kg ha−1yr−1) in the four cropping systems tested. Of the soil quality attributes tested, Cmin and Nmin were the most sensitive indices to tillage and fallow frequency effects. Key words: Mineralizable C, mineralizable N, microbial biomass, specific respiratory activity, crop residues
Estimating wetness duration on maize ears from meteorological observations
Authors: Rao P. S. , Gillespie T. J. , Schaafsma A. W.
Published: April 2011

The onset and cessation of surface wetness on maize ears were simulated with six models, using hourly meteorological data, to examine the linkage between wetness duration and possible forecasting of fungal infections that produce mycotoxins. Two threshold models (using relative humidity and dew point temperature), one regression model (using humidity and wind speed), and three physical models based on the energy balance approach, were compared. Also, spatial and temporal variability in wetness duration was measured and simulated at three sites located at distances up to 29 km from a central weather station. The estimated wetness values were compared with observations from cylindrical wetness sensors placed near ear level in maize canopies. The results relate to potential mycotoxin warning systems and indicate that threshold models can provide reasonable estimates of ear wetness duration in this region, that a comprehensive physical model can give superior estimates, and that wetness estimates made from a central weather station data can be extended to nearby crop fields with a moderate degree of confidence. Key words: epidemiology, mycotoxins, surface wetness models
Cation exchange and buffer potential of Saskatchewan soils estimated from texture, organic matter and pH
Authors: Curtin D. , Rostad H. P. W.
Published: April 2011

Cation exchange capacity (CEC) data provide information on important chemical attributes of soil (e.g., ability of soil to retain cations against leaching and to buffer pH). Measurements of CEC are expensive to perform. Further, since CEC is dependent on measurement pH, CEC data are difficult to interpret, especially in the case of soils whose field pH is far removed from measurement pH. We analyzed a large data set (n = 1622), collected in support of soil survey activities in Saskatchewan, to develop a method of estimating CEC as a function of pH and to establish relationships between soil buffer capacity and properties such as texture and organic matter content. A regression equation with organic C and clay as independent variables explained 86% of the variability in CEC measured using BaCl2 buffered at pH 8.2. The CECs (at pH 8.2) of organic matter and clay were estimated at 2130 and 510 mmol (+) kg−1, respectively. About 15% of exchange sites were not accounted for by organic matter and clay and were assumed to reside in the fine silt fraction. The CEC at field pH, i.e., effective CEC (ECEC), was described (R2 = 0.86***) by a function based on the assumption that the ECECs of organic matter and clay increase linearly as pH increases to 8.2, where their values are 2130 and 510 mmol (+) kg−1, respectively. This relationship is especially useful because it enables soil CEC to be estimated at any pH based solely on organic matter and texture. Soil buffer capacity values were obtained by estimating the change in soil ECEC (or titratable acidity) needed to produce a unit change in pH. Buffer strength of clay was low [∼30–50 mmol (±) kg−1 (pH unit)−1]. Our estimates of organic matter buffer capacity [∼400 mmol (±) kg−1 (pH unit)−1] were consistent with published values. The results suggest that prairie soils that are low in organic matter may be susceptible to acidification even if clay content is relatively high. Key words: Buffered CEC, effective CEC, pH dependence of CEC, buffer capacity, titratable acidity
Effect of crop management on C and N in long-term crop rotations after adopting no-tillage management: Comparison of soil sampling strategies
Authors: Campbell C. A. , Selles F. , Lafond G. P. , McConkey B. G. , Hahn D.
Published: April 2011

Society is interested in increasing C storage in soil to reduce CO2 concentration in the atmosphere, because the latter may contribute to global warming. Further, there is considerable interest in the use of straw for industrial purposes. Using soil samples taken from the 0- to 7.5-cm and 7.5- to 15-cm depths in May 1987 and September 1996, we determined organic C and total N in five crop rotations (nine treatments) using automated Carlo Erba combustion analyzer. The experiment was managed using conventional mechanical tillage from 1957 to 1989; it was changed to no-tillage management in 1990. Our objective was to determine: (a) if change to no-tillage management had changed soil C and N storage, and (b) if method of calculating organic C and N change would influence interpretation of the results. All three methods of calculation confirmed the efficacy of employing best management practices (e.g., fertilization based on soil tests, reducing summerfallow, including legumes in rotations) for increasing or maintaining soil organic matter, and showed that the latter was directly associated with the amount of crop residues returned to the soil. Where bulk density was significantly different between sampling times, the often used mass per fixed depth (MFD) (i.e., volume basis) calculation can lead to erroneous conclusions. When the recently recommended mass per equal depth (MED) method of calculation was used, it showed that 6 yr of no-tillage did not increase soil organic C or total N. However, in unfertilized systems, where crop yields are gradually decreasing since the change, there is an accompanying decrease in organic matter, while fertilized, or high-fertility systems that include legume hay crops, in which wheat yields have been maintained have tended to maintain the organic matter level over time. When the MFD calculation was used, there was no change in C over time when straw was harvested in the F–W–W system; however, the MED calculation and concentrations tend to show a decrease in soil C and N. This suggests that in time, industrial use of straw may have negative consequences for soil conservation. We concluded that concentrations may be as effective as MED for assessing changes in organic matter, provided "amounts" are not required. Key words: Straw removal, fertilizers, legumes, cropping frequency, C mass calculation
Soil compaction under grazing of annual and perennial forages
Authors: Mapfumo E. , Chanasyk D. S. , Naeth M. A. , Baron V. S.
Published: April 2011

This study investigated the impact of heavy, medium and light grazing of meadow bromegrass an triticale on soil bulk density, relative compaction and penetration resistance. The study was conducted at Lacombe, Alberta, on a Orthic Black Chernozem of loam to silt loam texture. Sampling was conducted in fall 1995, spring 1996, fall 1996 and spring 1997. Core samples to a 15-cm depth were collected for measurement of bulk density and moisture content. Penetration resistance to 15 cm was measured with a hand-pushed cone penetrometer. The standard Proctor test was used to determine maximum bulk density. Relative compaction was the ratio of actual bulk density to the Proctor maximum bulk density expressed as a percentage. Surface (0–2.5 cm) bulk density and penetration resistance were significantly greater under heavily grazed than under medium and lightly grazed meadow bromegrass only for fall 1995. Differences in bulk density, relative compaction and penetration resistance for different grazing intensities in spring and fall 1996 and spring 1997 were either small or not significant. Generally, bulk density decreased over winter in the top 2.5 cm, was not consistent in the 5- to 10-cm depth interval and did not change in the 10- to 15-cm interval. Except in fall 1995, the relative compaction values for all grazing intensities and forage species were less than 90%, a value considered critical for plant growth. Generally, within each grazing level, there were minimal differences in bulk density, relative compaction and penetration resistance under triticale compared to those under meadow bromegrass. Key words: Bulk density, relative compaction, penetration resistance
Tillage and crop residue effects on soil nitrate under three years of corn (Zeamays L.) on land previously in corn and forage crops
Authors: Burgess M. S. , Mehuys G. R. , Madramootoo C. A.
Published: April 2011

A 3-yr field study in Quebec assessed effects of tillage (no-till, reduced, or conventional) × crop residues (removed or retained) on soil nitrate under corn production. Fall nitrate levels were greatest in plots without residues 1 yr after treatments began, but not thereafter. No-till and conventional tillage had similar values, but sometimes differed from reduced tillage. Key words: Nitrate, corn, no-till, reduced tillage, conventional tillage, crop residues
Assessment of the contribution of denitrification to N losses from compacted grassland soil by NO3− disappearance and N2O production during anaerobic incubation
Authors: Abbasi M. K. , Adams W. A.
Published: April 2011

Decreases in herbage production and of N uptake and utilization have been observed on Denbigh series soils in mid-Wales after several years in permanent pasture. Laboratory experiments were conducted to examine the contribution of denitrification to N loss from these wet grassland soils. Denitrification capacity was measured in seived soil following the addition of KNO3 and maintained at 20°C under anoxic conditions. Emission of N2O was measured from intact field cores equilibrated under conditions of simulated "field capacity" using glucose as C substrate. The rate of loss of NO3−–N decreased with depth and in the 0–2.5 cm layer all added NO3−–N was lost in 10 d incubation. Net mineralization of NH4+–N occurred at about one-sixth of the rate of NO3−–N disappearance. The presence of NO3− reduced the rate of decrease in redox potential (Eh) and the Eh did not fall below about +200 mV until all NO3−–N had been lost. Emission of N2O was greatest between 6 and 48 h and denitrification rate decreased with depth. Addition of glucose increased N2O emission in the 2.5–5.7 cm layers indicating that C limitation to denitrification may occur at shallow depths in the soil profile of compacted grassland. On average, the total denitrification ranged between 15 and 20 kg N ha−1, equivalent to 20–30% of applied N. The potential rates of denitrification change markedly over quite shallow depths in these compacted grassland soils. Furthermore, since denitrification occurred at substantial rates under simulated field capacity, conditions conducive to denitrification are likely to persist for quite long periods in the moist climatic conditions. Key words: Compacted soil, denitrification, glucose, grassland, nitrous oxide
Changes in pore structure in a no-till chronosequence of silt loam soils, southern Ontario
Authors: VandenBygaart A. J. , Protz R. , Tomlin A. D.
Published: April 2011

Many research studies have dealt with the influences of minimum or no-till soil management practices on the major physical, chemical, biological and morphological properties in the soil profile. However little work has been done on the assessment of the rates of changes in pore properties as management practices are converted from conventional to no-till (NT) methods. Short-term changes in soil micromorphology attributed to conversion to no-till from conventionally tilled management are evaluated in this paper. As the number of years in no-till increased there was a decrease in the number pores of 30- to 100-µm diameter in the no-till soils. However, pores from 100- to 500-µm diameter increased in number only after 4 yr of NT. The pores of this size are important for water storage, transmission and root development. The decline in the number of these pores after no-till initiation followed by the increase after 4 yr may explain why crop yields tend to be lower only after the first few years after implementing no-till. The 100- to 500-µm diameter pores may be crucial for the proper development of roots in wheat and corn. The no-till soils had greater numbers of horizontally oriented elongated macropores in the top 5 to 15 cm of the soil profile due to the lack of tillage and annual freeze-thaw processes. These pores may inhibit proper drainage and root penetration. Rounded macropores increased with the number of years the soil was in no-till as these pores were maintained each year due to the lack of tillage and greater faunal activity in the no-till soils. Key words: Micromorphology, image analysis, earthworms, no-till, soil structure
Effect of nitrogen application on concentration of cadmium and nutrient ions in soil solution and in durum wheat
Authors: Mitchell L. G. , Grant C. A. , Racz G. J.
Published: April 2011

A growth chamber experiment was conducted to study the effect of nitrogen fertilizer on the chemical composition of the soil solution over time, and to determine Cd uptake as a function of rates of nitrogen fertilizer application and transpiration. Sceptre durum wheat was grown in a fine sandy loam soil, in pots with treatments of 0, 50, 100, 200, 400, and 800 µg N g−1 as urea. The soil solution was removed by water displacement and analyzed for Cd and other nutrient ions at time of seeding, 10, 20, 30, and 40 d after seeding, and at the time of crop maturity. Soil samples were analyzed at each sampling time, and aboveground plant material was also harvested at these times and analyzed for Cd and other nutrient ions. Behaviour of Cd was compared to that of the nutrient ions to gain a better understanding of patterns of ion behaviour. Conductivity measurements were taken as estimators of ionic strength. Both solution Cd concentration and DTPA-extractable soil Cd increased significantly with increasing nitrogen rate. The increases in Cd concentration with N fertilization were greatest immediately after fertilization and appeared to be related to an increase in soil and solution conductivity, with pH also having an influence on DTPA-extractable Cd. The soil solution concentration of all nutrients, with the exception of phosphate, increased with N rate. The effects of N fertilization on the amounts of extractable nutrients in the soil were more variable. Plant Cd concentrations increased with increasing N application rate to 800 µg g−1, but dry matter yield and transpiration only increased with N rate to 200 µg g−1. Cadmium was the element most affected by increasing the N rate, and there were minor changes in uptake of other elements such as N, P, K, Ca, Mg, Mn, Zn, and Cu with N application rate and time. This study clearly illustrated the effect of nitrogen fertilization on the concentration of Cd in the soil solution and its uptake by durum wheat. Key words: Cadmium, nitrogen, urea, soil solution, ionic strength, durum, uptake
Assessing corn seedbed conditions for emergence
Authors: Dwyer L. M. , Ma B. L. , Jong R. de , Tollenaar M.
Published: April 2011

Seedbed temperature and moisture conditions affect crop emergence rate and stand establishment. A 4 × 4 factorial experiment arranged in a split plot design with four replications was conducted for 3 yr at four sites to measure corn emergence rate and stand establishment while monitoring seedbed temperature and soil water content in situ. Four planting dates, beginning as early as the soil could be worked and every 10 d thereafter, were the main plots and four corn (Zea mays L.) hybrids the subplots. Volumetric soil water content in the top 0.10 m was measured a minimum of two times per week using time domain reflectometry (TDR) and estimated daily using a budget model. Measured and estimated soil water contents were similar (R2 = 0.73) and daily estimated values were used in the analysis. Stand establishment for most planting date-site-years ranged from 80 to 99%. Less than 15% of planting date-site-years had stands below 80%, and they were characterized by soil temperatures at or below 12.5°C combined with high soil water contents (>90% available water). Rate of emergence was not associated with stand establishment (P > 0.10) and could not be predicted from soil temperatures below 12.5°C. Results suggest that reduction in stand establishment under conditions of low (12.5°C) soil temperature and high (>field capacity) soil water content may be a factor in corn yield reductions associated with reduced or no tillage. Key words: Time domain reflectometry, soil water content, soil temperature, maize
Soil water storage dynamics in peatlands with shallow water tables
Authors: Lapen David R. , Price Jonathan S. , Gilbert Robert
Published: April 2011

Time domain reflectometry (TDR) was used to estimate soil water storage dynamics in several uncultivated blanket bogs and poor fens in southeastern Newfoundland during the summer growing season. The purpose of the research was to evaluate links between surface moisture conditions, evapotranspiration, and recharge processes in order to elucidate factors that govern blanket peat formation in the region. Water storage changes in the peat/Sphagnum above the water table (ΔSWS) were found to be important storage terms in daily water balance estimates. Daily mean ΔSWS values for bog and fen approximated −0.3 and −0.45 mm, respectively. It was also found that, i) fairly high peat water-holding capacities, ii) frequent atmospheric recharge, iii) atmospheric controls on evapotranspiration, and, iv) the transport of water into the unsaturated zone from the shallow water table via capillary and external wicking processes helped to preclude significant de-watering over the bulk of the peatland surfaces. Recharge via groundwater appears to be an important factor governing moisture conditions requisite for peat accrual and the growth of Sphagnum spp., especially in the fens. Key words: Time domain reflectometry, blanket peats, soil water, evapotranspiration, water table depth
Residual effects of nitrogen fertiliser on the yield and N composition of succeeding cereal crops and on soil chemical properties of an Ethiopian highland Vertisol
Authors: Kidanu Selamyihun , Tanner D. G. , Mamo Tekalign
Published: April 2011

A trial was conducted on an Ethiopian Vertisol from 1990 to 1995 to determine the residual effects of fertiliser N applied to tef [Eragrostistef (Zucc.) Trotter] on the grain and straw yield, N content, and total N uptake of succeeding crops of durum wheat (Triticum turgidum var. durum) and tef. The mean agronomic efficiency of 60 kg fertiliser N ha−1 was 13.1 kg grain kg−1 fertiliser N applied in the current year and 5.4 kg grain kg−1 fertiliser N applied in the previous year. Thus, the residual fertiliser N benefit was equivalent to 41.2% of the response to current season N application for the two cereal crops. The mean rates of apparent recovery of fertiliser N were 65.8% for current season N application and 31.0% for previous season N application. Soil organic matter and nitrate levels increased linearly in response to both previous and current season N application rates. The current study demonstrates that the residual effect of fertiliser N enhanced the yields and N contents of the grain and straw of both wheat and tef, resulting in a significant increase in total N uptake. Any analysis of the profitability of fertiliser N response should reflect the multi-year benefit period. Key words: N recovery, N residue, N uptake, tef, wheat
A modified diffusion‐based methane sensor and its application in freshwater sediment
Authors: Bussmann Ingeborg , Schink Bernhard
Published: April 2011

Methane is the main end product of anaerobic degradation in freshwater sediments. The flux of methane from the sediment into the water column, and possible methane oxidation at the sediment surface, can be estimated on the basis of its distribution in the sediment and the overlying water. Nonetheless, the quantification of methane in sediments at high spatial resolution is difficult, owing to its chemical inertia. In this study, we describe the improvement of a diffusion‐based methane sensor and its application in freshwater sediment cores. The sensor consists of a steel cannula with small openings, which are covered by thin silicone tubing. Methane diffuses into the cannula and is flushed directly to a flame ionization detector for quantification. With this sensor, methane profiles in freshwater sediment can be measured at high spatial (1.5 mm) and temporal (3 minutes per measurement) resolution. The detection limit was 2 µmol L−1. The relative accuracy of the sensor was ± 15% with a precision of ± 7.5%. Analysis of fine‐scale methane profiles in littoral and profundal sediments of Lake Constance indicate that owing to structural inhomogeneities and temporal changes a high‐resolution analysis is required to allow exact calculations of diffusive fluxes and turnover rates of methane.
Quantification of denitrification in permeable sediments: Insights from a two‐dimensional simulation analysis and experimental data
Authors: Cook Perran L. M. , Wenzhöfer Frank , Rysgaard Søren , Galaktionov Oleksiy S. , Meysman Filip J. R. , Eyre Bradley D. , Cornwell Jeffrey , Huettel Markus , Glud Ronnie N.
Published: April 2011

Using a two‐dimensional simulation analysis, we investigated the effects of sediment flushing on denitrification and the implications for two methods commonly used to measure denitrification in intact sediment cores: the N2:Ar‐ratio method and isotope pairing technique (IPT). Our simulations of experimental chamber incubations showed that advective flushing of the sediment can significantly increase sediment denitrification driven by NO3− from the water column (up to a factor of 5), but that nitrification and coupled nitrification‐denitrification is reduced under conditions of sediment flushing (up to a factor of 6). N2 fluxes across SWI may differ significantly from actual rates of denitrification for periods lasting from 1 up to more than 5 d after changes in parameters such as sediment flushing rate and water column NO3− concentrations. Simulations of the isotope pairing technique, showed that the rate of labeled N2 production, after the addition of 15NO3− may take up to ~24 h to reach steady state, depending on NO3− concentrations in the water column and sediment flushing rate. Measurements of denitrification in sand using IPT confirmed that short term incubations (11 h) underestimated the actual denitrification. Furthermore, model simulations were able to give a good estimate of measured N2 fluxes across SWI at different flushing rates under non‐steady state conditions, confirming the ability of the model to realistically simulate experimental situations.
A novel flume for simulating the effects of wave‐ and tide‐driven water motion on the biogeochemistry of benthic reef communities
Authors: Falter, James L. , Atkinson Marlin J. , Fleming James H. , Bos Melissa M. , Lowe Ryan J. , Koseff Jeffrey R. , Monismith Stephen G.
Published: April 2011

We present a new flume for simulating the effects of both steady and oscillatory flow on the biogeochemical fluxes to coral reef communities based on a modified U‐tube design. The flume is designed to recreate the in situ characteristics of a wide range of flows generated by wind, waves, and tides through two configurations. In the first configuration, a propeller driven by a 12‐V DC motor generates steady, unidirectional flow speeds of 5 to 70 cm s−1. In the second configuration, a piston driven by a 1500‐W AC motor is used to generate oscillatory flows that are 5‐12 s in period and have root‐mean‐square flow speeds of up to 50 cm s−1, thus simulating the kinematics of real surface gravity waves in coral reef environments. Experimental coral reef communities are housed in a 3‐m long test section covered with acrylic windows and lit with either 400‐ or 1000‐W metal halide lamps generating photosynthetically active radiation (PAR) irradiances of up to 1000 µEin m−2 s−1. The ratio of the volume of water in the flume to the projected area occupied by the experimental communities ranges from 1.1 to 1.7 m, making possible the expedient measurement of chemical fluxes to and from experimental reef communities. The total cost of the flume is just under $20,000 US for materials and approximately 700 person‐hours of labor.
Correcting acoustic Doppler current profiler discharge measurement bias from moving‐bed conditions without global positioning during the 2004 Glen Canyon Dam controlled flood on the Colorado River
Authors: Gartner Jeffrey W. , Ganju Neil K.
Published: April 2011

Discharge measurements were made by acoustic Doppler current profiler at two locations on the Colorado River during the 2004 controlled flood from Glen Canyon Dam, Arizona. Measurement hardware and software have constantly improved from the 1980s such that discharge measurements by acoustic profiling instruments are now routinely made over a wide range of hydrologic conditions. However, measurements made with instruments deployed from moving boats require reliable boat velocity data for accurate measurements of discharge. This is normally accomplished by using special acoustic bottom track pings that sense instrument motion over bottom. While this method is suitable for most conditions, high current flows that produce downstream bed sediment movement create a condition known as moving bed that will bias velocities and discharge to lower than actual values. When this situation exists, one solution is to determine boat velocity with satellite positioning information. Another solution is to use a lower frequency instrument. Discharge measurements made during the 2004 Glen Canyon controlled flood were subject to moving‐bed conditions and frequent loss of bottom track. Due to site conditions and equipment availability, the measurements were conducted without benefit of external positioning information or lower frequency instruments. This paper documents and evaluates several techniques used to correct the resulting underestimated discharge measurements. One technique produces discharge values in good agreement with estimates from numerical model and measured hydrographs during the flood.
A low‐blank photochemical extraction system for concentration and isotopic analyses of marine dissolved organic carbon
Authors: Beaupré Steven R. , Druffel Ellen R. M. , Griffin Sheila
Published: April 2011

We report the development of a modified, low blank, ultraviolet oxidation and vacuum line system to convert marine dissolved organic carbon into carbon dioxide for concentration, Δ14C, and δ13C analyses. The system performs quantitatively and precisely with preservation of isotopic signatures (± 3‰) based on additions of pure International Atomic Energy Agency standards. Analytical blank reduction from < 1.5 µM to 0.2 µM enabled a decreased detection limit from a sample size of ~650 mL to 30 mL using a simple dilution technique. Combined with advances in analyses of ultra‐small (2 µgC) samples using accelerator mass spectrometry, the technique provides a means for measuring Δ14C values in samples that were previously not analyzable.