ALBERT

Beschreibung: While some studies indicate no denitrification activity in early spring, others have demonstrated that denitrifiers from temperate region soils can adapt to low temperatures. The aim of the present paper was to study how seasonal changes in temperature affect denitrifying enzyme activity (DEA) in a cropped humic gleysol located in a cold temperate climate (Quebec). Soil was sampled monthly during a 16-mo period and DEA was measured at nine temperatures from 2 to 35°C. A seasonal effect of temperature on DEA was significant at all incubation temperatures and was more important in November and in May–June. The effect of temperature on DEA was better fitted with the square root model of Ratkowsky than with the Arrhenius equation. The regression coefficient b (Ratkowsky parameter) varied seasonally with a trend similar to that of DEA. These results show that the Ratkowsky model should be used instead of Arrhenius equation to describe the effect of cold temperature on denitrification. Key words: Denitrification, temperature, cold, Arrhenius equation, Ratkowsky model

Beschreibung: Source materials and manure management may affect compost nutrient availability to plants. A laboratory experiment was conducted to determine the impact of these factors on the N and P release from 23 on-farm and 6 industrial composts. Composts were mixed with the Ap horizon of an Arago sandy loam (Humo-Ferric Podzol), at 200 mg N kg−1, and incubated for 13 wk in glass jars at 35 °C. The soil mineral N content at the end of incubation was the highest from poultry litter, sheep manure, horse manure and vegetable residue sources whereas the fresh solid, beef and young dairy manure composts resulted in high N immobilization. The release of N from the compost organic N fraction was in most cases negative. The soil Mehlich-3 P content at the end of the incubation period was higher from the poultry litter than from any other sources, whereas P was strongly immobilized from week 1 to week 13 in the fresh solid, beef and young dairy manure compost amended soils. Septic tank sludge compost was the least efficient N and P source among industrial products whereas the others showed N and/or P release comparable to most on-farm composts. In dairy manure compost, use of wood in bedding, turning compost windrow, increasing composting duration and sheltering material against precipitation all reduced P immobilization during incubation. Organic N mineralization in soil was only significantly increased by composting duration. This study indicated that the short-term N and P potential nutrient value of composts are dependent upon compost source materials and manure management, and should be based on their inorganic N and P content. Key words: Composting, farm manure management, N and P mineralization

Beschreibung: 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

Beschreibung: The study was conducted at the Lacombe Research Station, Alberta, on an Orthic Black Chernozem of loam to silt loam texture to investigate grazing impacts and cultivation on near-surface soil compaction. Four forages, smooth bromegrass (Bromus inermis Leyss 'Carlton'), meadow bromegrass (Bromus riparius Rhem 'Paddock'), a mixture of triticale (X Triticosecale Wittmack 'Pika') and barley (Hordeum vulgare L. AC Lacombe), and triticale were used for the study. Each forage species was subjected to heavy, medium and light intensity grazing. Measurements of bulk density and volumetric moisture content for the 0- to 10-cm depth interval were conducted using a surface moisture-density probe between spring 1994 and fall 1996. Relative compaction was calculated as the actual bulk density expressed as a percentage of the Proctor maximum density. Relative compaction values for all treatments and that for the benchmark were less than 90%, which is considered critical for limiting plant growth. Cultivation reduced bulk density under annual forages by only 3% and lowered it under heavy grazed annual treatments most. Regression analysis conducted on the dependence of bulk density to cumulative cow-days indicated a curvilinear relationship. Bulk density increased more rapidly with increasing cumulative cow-days for annuals compared to perennials. From a management perspective, adopting intensive rotational grazing systems for perennial and annual forages may not cause any serious surface compaction problems for soils in this area. Key words: Annuals, bulk density, cow-days, grazing intensity, perennials, volumetric moisture content

Beschreibung: Many agricultural fields contain excessive labile soil P in regard to crop needs. Its environmental fate must be assessed. The concept of P saturation degree is meaningful as it describes the portion of the soil binding sites already covered with P, and indicates the potential desorbability of soil P. The first objective of this study was to review different indices that have been proposed to estimate the degree of soil P saturation and the relationships between soil P saturation degree and P solubility. The second objective is to discuss their suitability as environmental indicators for P management in the province of Québec, Canada. In the Netherlands, the P saturation index is defined as the ratio of P to Al + Fe contents extracted by ammonium oxalate [Pox/( Alox + Feox ) or ( Pox/0.5( Alox + Feox )]. This approach has been mainly used with non-calcareous soils. In Québec, the ratio of Mehlich-III extractable P to Al (M3P/AlM3) is proposed as an alternative, which relies on routine laboratory test. However, the suitability of the M3P/AlM3 ratio has yet to be determined for some specific soil groups (e.g. gleyed soils, soils with Alox content 〉6 g kg−1) and for subsoil horizons. Regardless of the chosen index, it is suggested that the best way to manage the risk of water contamination by P in Québec (namely, defining critical levels of soil P saturation) may be to form homogeneous soil groups to account for their distinctive behaviour and characteristics. Key words: Phosphorus, saturation, management

Beschreibung: The influence of tillage and cropping system on soil organic matter, structure and infiltration was studied in a rolling, glaciolacustrine landscape in Saskatchewan with slopes ranging from 6 to 30%. A field that had been continuously cropped using zero tillage (ZTCC) for 11 yr was compared with conventional tillage in a crop–summerfallow rotation (CTCF) on an adjacent field. Soils in each field were sampled according to their position in the landscape. Soil organic C, aggregrate size and aggregate stability were significantly greater on the ZTCC plot than the CTCF. Infiltration rates averaged 74 and 52 mm h−1 on the ZTCC and CTCF plots, respectively. Differences between treatments were most pronounced at the shoulder positions. Increased soil strength was measured on the CTCF plot at depths corresponding to the action of tillage implements (0.05 m and 0.15 m). On the CTCF plot, infiltration rates correlated with initial moisture, aggregate stability and bulk density but on the ZTCC plot consistent correlations were only found between infiltration and bulk density. When measured infiltration rates were compared with expected storm intensities, the differences in infiltration rates between treatments and their distribution in the landscape resulted in substantially more runoff from the CTCF plot than the ZTCC. Key words: Zero tillage, cropping frequency, infiltration rate, aggregation, organic carbon, landscape

Beschreibung: Organic carbon depletion as a result of intensive potato production is a serious concern in northwestern New Brunswick, Canada. Underseeding of rotational grain crops with selected grasses and legumes is being used by farmers to increase crop residues in order to maintain soil organic carbon levels. The objectives of this study were to quantify changes in selected soil propertiesm, effects on grain yield, and increases in total biomass production resulting from different underseeding treatments on a Caribou fine-loamy Brunisolic Gray Luvisol. Clovers, ryegrasses and a mixture of timothy, Alsike and red clover were underseeded in Chapais barley plots. Underseeding did little to improve soil bulk density, macroporosity and saturated hydraulic conductivity of the upper plow layer (4–12 cm depth) over one growing season. Averaged over a 3-yr period, underseeding did not significantly affect barley grain yields; however, annual reductions of up to 17% were experienced with some of the more aggressive companion crops, such as Lemtal Italian ryegrass. Underseeding significantly increased total biomass contributions (residues) to the upper 20 cm of the soil by 40 to 90%, making the year in grain production a potential net organic carbon supplier rather than an organic carbon depletor. Key words: Companion crop, roots, soil organic carbon, soil bulk density, soil permeability, crop residue

Beschreibung: Surface area (SA) is an important property of soils, but different methods can give widely different estimates of SA, and of the contribution of organic matter to SA. This study was undertaken to compare two common methods of measuring SA (EGME [ethylene glycol monoethyl ether] and N2 sorption) with SA estimates using H2O sorption on selected Saskatchewan soils; some soils from Kenya were included to show the impact of clay mineralogy. For the Saskatchewan soils, the three estimates of SA were highly correlated to each other and to clay content, but SA EGME was 2 to 3 times SA H2O and 7 to 52 times SA N2. Organic matter did not appear to contribute to SA EGME, increased SA H2O and decreased SA N2. Clearly the three methods differ in their access to internal and external surface area and this should affect their utility as indices of the sorptive capacity of field soils. Key words: Surface area, EGME, N2 sorption, water sorption

Beschreibung: An estimate of the gypsum requirement (GR) of soils affected by Na salts has practical value. The estimated GR can indicate both the quantity of any Ca amendment needed and the progress of site remediation. Four published methods to estimate GR use analytical results that do not directly include any Na in excess of the soil's cation exchange capacity (CEC). GR values thus obtained, for a 15-cm soil layer, are at most 20 to 50 t ha−1. We used these four methods to calculate the GR for various soils with known, differing salt contents. The values obtained were often inconsistent with the sodium adsorption ratio (SAR) and electrical conductivity (EC), parameters that indicate the severity of site-contamination. We also used an unpublished method to estimate GR from the amount of Ca required to bring each soil's SAR down to a threshold value of 7, on the basis of concentrations of soluble ions in a saturated paste filtrate. Estimates of GR made in this way often exceeded 50 t ha−1, but were consistent with SAR and EC levels at the various sites. This method may be more appropriate for estimating GR after brine spills on soils where Na is not readily leached and the quantity of Na exceeds the CEC. This situation often applies on the Canadian prairies. Estimating GR from the quantity of Ca required to replace exchangeable Na may be appropriate for sodic, free-draining soils in areas with high rainfall, or on irrigated land. Key words: Gypsum requirement, salt contamination, sodium adsorbtion ratio, electrical conductivity, formation water

Beschreibung: There is no information on the effect, in northeastern Saskatchewan, of N and P fertilizers on forage seed production as influenced by these nutrients in the soil. Therefore, experiments were conducted at eight sites from 1988 to 1991 to determine the effect of N and P fertilizers and soil nutrients on seed yields of alfalfa (Medicago media Pers.), smooth bromegrass (Bromus inermis Leyss.), crested wheatgrass (Agropyron cristatum L.), intermediate wheatgrass (Agropyron intermedium [Host.] Beauv.) and timothy (Phleum pratense L.). Nitrogen fertilizer (urea) was applied on grasses annually at 0, 50, 100 and 150 kg N ha−1 in factorial combination with 0, 9 and 18 kg P ha−1 (monoammonium phosphate and triple superphosphate) and on alfalfa at 0 and 50 kg N ha−1 in combination with 0, 9, 18, 26 and 53 kg P ha−1. Nitrogen significantly increased forage seed yields of all species except alfalfa. Phosphorus increased yields of forage seed for all crops except intermediate wheatgrass. The site, N, P and year and their interactions influenced seed yields. Seed yields ranged from a low of 0.29 t ha−1 for smooth bromegrass in 1990, a dry year, to a high of 1.24 t ha−1 in 1989 a cool, moist year. The yield response to N and P fertilizers was affected by available soil N and P. Relative to control, the percentage increase in grass seed yield from applied N and P fertilizers was highly related to the available soil N and P (R2 = 0.93). The estimated smooth bromegrass seed yield response to 50N–9P kg ha−1 was 0.54 t ha−1 when the soil had intermediate amounts of available N and P (2 mg N ha−1 and 8 mg P ha−1, 0- to 60-cm and 0- to 15-cm depths, respectively). On a soil that tested high in available N and P, there was no response to fertilizer. Regression equations were developed that can be used to estimate forage seed yield response of different species in relation to available soil nutrients. These results are useful for estimating the most economical return on fertilizer investment for forage seed production in Saskatchewan. Key words: Forage, seed, N, P, fertilizer, soil tests, correlation

Beschreibung: The in situ use of anion exchange membranes (AEMs) as a soil-testing procedure may provide a more precise evaluation of N availability to forages than standard methods. The main objective of this study was to evaluate the potential of AEMs to predict soil NO3–N availability for forage production in the western part of the province of Quebec, Canada. In 1995 and 1996, AEMs were buried (0–15 cm) in soils at four sites. The fertilizer treatments consisted of five NH4NO3 rates (0, 60, 120, 180, and 240 kg N ha–1). At all sites, NO3−sorbed on the AEMs (NO3AEMs) increased with increasing N fertilizer rates. The NO3AEMs fluxes were significantly related to water soluble NO3–N (NO3w) concentration in soil (R2 varied from 0.35 to 0.98) in the two growing seasons. Forage N uptake was better related with NO3AEMs fluxes (R2 = 0.88 and 0.92 in spring 1996 and 1995, respectively) than with NO3w concentration (R2 = 0.39 and 0.97 in spring 1996 and 1995, respectively). Based on their simplicity, rapidity, and low cost, AEMs have many practical advantages over water NO3–N extraction for assessing grass forage soil N availability in cool continental climates. Key words: Resin, nitrogen, N uptake, grass forage, N mineralization

Beschreibung: The response of soil quality attributes to management practices across a diverse range of farming systems is key to identifying a robust minimum data set (MDS). The objectives of this study were to compare the response and consistency of different soil organic matter (SOM) attributes to changes in soil management practices in eastern Canadian agroecosystems. Soil samples (0–10 cm) were obtained at sites of several replicated experiments throughout eastern Canada, and 16 paired comparisons were selected to determine the effect of conservation (no-tillage, rotations, organic amendments) versus conventional (fall moldboard plowing, continuous cropping, no organic amendments) management practices. A sensitivity index was calculated for each of the attributes by dividing the values for conservation treatments with their conventionally managed counterparts (i.e., Conservation/Conventional). The index showed that light fraction (LF) N (1.58) and macro-organic matter-N (MOM-N) (1.54) were the most sensitive SOM attributes to conservation management practices. Light fraction-C (LF-C), macro-organic matter-C (MOM-C) and microbial biomass-C (MB-C) also showed high sensitivity to conservation management (1.48, 1.34 and 1.44, respectively). The sensitivity index for carbohydrates, whole soil C and total N were 1.23, 1.16 and 1.17, respectively. However, the Friedman two-way analysis of variance test indicated that the sensitivity of the different attributes to conservation management was site specific. For example, although LF-N was highly ranked, it did not respond as frequently as most of the other attributes. A non-parametric sign test showed that whole soil C and N provided the most consistent response to conservation management. The average sensitivity index was highest for the amendment (1.82) followed by the tillage (1.26) and rotational (1.14) conservation management practices, suggesting that organic amendments had the greatest impact on most of the attributes. These results suggest that for eastern Canadian soils, use of MOM-C and MOM-N, MB-C and whole soil C would provide a useful, easy to measure and robust MDS. Key words: Soil quality indicators, response, conservation management

Beschreibung: Aeration is a critical factor of substrate performance for container grown plants. In a 14-mo nursery study, although air-filled porosity dropped below optimum values, the gas relative diffusivity was unaffected, as a result of an increase in pore effectiveness. This indicates that, contrary to the general belief, aeration properties of potting substrates may not deteriorate with time. Key words: Potting soils, container substrates, air-filled porosity, gas diffusivity

Beschreibung: not available

Beschreibung: Field experiments were conducted on sandy loam soils in Prince Edward Island (PEI) with two cultivars of soybeans at two locations to determine the relationship between Se concentration in the seed sown and the Se concentration found in the harvested soybean crop. Seeds containing a range of Se from 0.78 to 38.5 mg kg−1 were used. These variable concentrations of seed Se were obtained in field experiments by varying the rates of seed and foliar applied Se. Grain Se concentration increased with increased Se concentration in the planted seed. A high proportion of the variation in Se concentration in the harvested soybean crop was explained by variation in the Se content of the planted seed (R2 = 0.98). The regression was calculated using averages of cultivars for both locations. From the regression equation it could be predicted that planting seed containing 24 mg Se kg−1 would produce a soybean crop containing 0.5 mg Se kg−1. When used at 200 kg soybean per tonne ration this would provide a Se concentration of 0.1 mg kg−1 assuming negligible contributions from other ingredients. Selenium concentration of 0.1 mg kg−1 in animal ration is considered adequate to protect livestock from Se deficiency diseases. Key words: Podzol soils, seed-applied Se, grain Se

Beschreibung: Conservation tillage practices such as no-till (NT) and conventional tillage (CT) with a heavy-duty cultivator can influence the physical properties of soils. This study was conducted to determine the effect of 24 yr of NT versus CT on the physical properties of a clay loam soil in southern Alberta. Physical properties quantified were bulk density (BD), mean weight diameter (MWD), plant-available water-holding capacity (PAWHC), saturated hydraulic conductivity (Ksat), soil water characteristic [θ(ψ)] and unsaturated hydraulic conductivity [K(ψ)] relationships, and pore-size distribution (PSD). Bulk soil samples and small soil cores (5-cm depth increments to 20 cm) were taken from CT and NT fields in 1992, and tension infiltrometer measurements were made in 1994. The results from this study are reported as general trends for the tillage fields. Statistical probability levels are not reported because of the unreplicated nature of the experiment, the limited number of sampling locations within each tillage field, and to a lesser extent, the different sampling times for CT and NT in 1992. Plant-available water-holding capacity was higher for the CT field (14.3%) than the NT field (10.8%), and a greater amount of water was held at a given water potential (−1500 to −1.5 kPa) for the former, indicating a higher potential for soil water conservation under conventional tillage. Geometric mean Ksat values (small soil cores) were higher for the NT field (18.20 × 10−6 m s−1) than the CT field (1.74 × 10−6 m s−1). The K(ψ) values (small soil cores) between −10 and −2 kPa were higher for the CT field than the NT field at the 0- to 5-cm, 10- to 15-cm and 15- to 20-cm depths, but values were higher for the NT field at the 5- to 10-cm depth. Near-saturated K(ψ) values (−1.5 to −0.3 kPa) of the surface soil, as derived from tension infiltration measurements in 1994, were higher for the CT field (2.43 × 10−7 m s−1) than for the NT field (6.09 × 10−8 m s−1). There was a greater percentage volume of larger pores (30–40, 40–67, 67–200, 〉200 µm) for the NT field than for the CT field, and there was a lower percentage volume of smaller pores (0.2–0.6, 0.6–4 µm) for the CT field than for the NT field. Differences in certain soil physical properties between CT and NT fields may be related to the lag time between the most recent tillage event and sampling for the CT field. Key words: Conservation tillage, heavy-duty cultivator, physical attributes, soil water, hydraulic conductivity, porosity

Beschreibung: Measurements of seasonal changes in soil biochemical attributes can provide valuable information on how crop management and weather variables influence soil quality. We sampled soil from the 0- to 7.5-cm depth of two long-term crop rotations [continuous wheat (Cont W) and both phases of fallow-wheat (F–W)] at Swift Current, Saskatchewan, from early May to mid-October, 11 times in 1995 and 9 times in 1996. The soil is a silt loam, Orthic Brown Chernozem with pH 6.0, in dilute CaCl2. We monitored changes in organic C (OC) and total N (TN), microbial biomass C (MBC), light fraction C and N (LFC and LFN), mineralizable C (Cmin) and N (Nmin), and water-soluble organic C (WSOC). All biochemical attributes, except MBC, showed higher values for Cont W than for F–W, reflecting the historically higher crop residue inputs, less frequent tillage, and drier conditions of Cont W. Based on the seasonal mean values for 1996, we concluded that, after 29 yr, F–W has degraded soil organic C and total N by about 15% compared to Cont W. In the same period it has degraded the labile attributes, except MBC, much more. For example, WSOC is degraded by 22%, Cmin and Nmin by 45% and LFC and LFN by 60–75%. Organic C and TN were constant during the season because one year's C and N inputs are small compared to the total soil C or N. All the labile attributes varied markedly throughout the seasons. We explained most of the seasonal variability in soil biochemical attributes in terms of C and N inputs from crop residues and rhizodeposition, and the influences of soil moisture, precipitation and temperature. Using multiple regression, we related the biochemical attributes to soil moisture and the weather variables, accounting for 20% of the variability in MBC, 27% of that of Nmin, 29% for LFC, 52% for Cmin, and 66% for WSOC. In all cases the biochemical attributes were negatively related to precipitation, soil moisture, temperature and their interactions. We interpreted this to mean that conditions favouring decomposition of organic matter in situ result in decreases in these attributes when they are measured subsequently under laboratory conditions. We concluded that when assessing changes in OC or TN over years, measurements can be made at any time during a year. However, if assessing changes in the labile soil attributes, several measurements should be made during a season or, measurements be made near the same time each year. Key words: Microbial biomass, carbon, nitrogen, mineralization, water-soluble-C, light fraction, weather variables

Beschreibung: The effects of glyphosate application and time of tillage of red clover on soil NO3-N profiles, the response of the subsequent potato crop to varying rates of N fertilizer application, and root and soil nematodes, were evaluated. The study was conducted over three cropping seasons on a Charlottetown fine sandy loam on Prince Edward Island. Red clover was moldboard ploughed in mid-September (early fall), or moldboard or chisel ploughed in mid-October (late fall), or moldboard ploughed in the spring. Glyphosate was applied in early fall and the dead clover was moldboard or chisel ploughed in mid-October or left undisturbed until spring. A barley control, where barley was harvested and straw incorporated with a tandem disc harrow in early September, was included. Potato were planted with 6 rates of N (0 to 250 kg ha–1 in 50-kg increments) band applied at planting. The barley control treatment produced lower potato yield without fertilizer N in all 3 yr of the study compared to red clover treatments, but potato yields were similar at high rates of applied N. Potato tuber yields after spring moldboard ploughing of red clover were higher at low N rates and lower at high N rates than yields after late fall treatment in one year of the study. Concentrations of nitrate-N in the soil in mid-November were highest following the early fall moldboard ploughing and lowest in the undisturbed clover plots. Fall soil nitrate-N levels were intermediate following the glyphosate application and late fall tillages. Early spring soil nitrate-N levels in the surface 30 cm were generally highest with the spring and late fall tillage and lowest with the early fall tillage. Levels of nitrate-N in potato petioles increased with increased rates of N application and generally increased as tillage of the red clover was delayed from early fall to late fall to spring. In general, cultivation and the application of glyphosate did not affect soil and root nematode populations. In two instances, the moldboard plough tillage treatments were associated with higher levels of the clover-cyst nematode, Heterodera trifolii. One of the tillage treatments was combined with glyphosate, but this was the only case where the herbicide had an impact on nematodes. To maximize the benefits to the subsequent potato crop and to minimize leaching of nitrate, incorporation of legume residue should be delayed until the rate of mineralization and nitrification of the legume N is minimized. It is suggested that incorporation of red clover be delayed until after mid-October for clover–potato systems on PEI. Key words: Glyphosate, nematodes, nitrate leaching, petiole nitrate-N, potato, soil nitrate-N, tillage time

Beschreibung: We examined the influence of dissolved organic carbon (DOC) source on the sorption of DOC by two clayey and two sandy soils using seven extracts from plant tissues and organic soil horizons. Sorption characteristics, such as null-point DOC concentration, partition coefficient and intercept, were determined over the initial solution concentration range of 0–50 mg DOC L−1. The clayey soils had larger partition coefficients and higher null points than the sandy soils. There was an average threefold variation in null-point DOC concentration and partition coefficient amongst the seven DOC extracts. Fractionation of the DOC samples into humic acid and hydrophobic and hydrophilic acids, bases and neutrals revealed weak relationships between the sorption characteristics and DOC chemistry. Key words: Dissolved organic carbon, sorption, fractionation, humic acid, fulvic acid

Beschreibung: In a long-term study with four rates each of fertilizer N, P, and K in factorial combination on timothy (Phleum pratense L.), soil C concentration in the 0- to 15-cm layer of an Orthic Dystric Brunisol in New Brunswick ranged from 25 to 37 g C kg−1 after 26 yr, and from 26 to 44 g C kg−1 after 35 yr. Soil C concentration was not related to the wide range of aboveground net productivity resulting from contrasted long-term fertilization treatments. Soil C concentration, however, was negatively correlated to soil pH. Key words:Phleum pratense L., timothy, carbon, fertilization

Beschreibung: Fertilizers are frequently used in agriculture to enhance crop yield and quality. Increasingly, microbial and enzyme inhibitors are being used to enhance the efficiency of fertilizer nitrogen use. The assumption being made is that the impact of these compounds is short-term or localized and thus does not adversely impact soil quality. This study investigates the implications of urea fertilizer with and without urease inhibitor [N-(n-butyl) thiophosphoric triamide, NBPT], conventional and zero tillage systems, and soil types on the soil biological characteristics including N mineralization. Microplot studies were conducted in clay loam and fine sandy loam soils in Manitoba. Soil type had a significant effect on the soil organic C but tillage did not have any significant effect. Soil microbial biomass C content ranged widely (131–1215 µg g−1 soil). The clay loam soil generally tended to contain higher biomass C than the sandy loam soil. The potential soil mineral N production (N0) was higher in clay loam soil (92.6 µg g−1 soil) than sandy loam soil (40.2 µg g−1 soil). Tillage systems, urea and urease inhibitor application had no significant impact on the soil biomass C, N0, arylsulfatase or acid and alkaline phosphatase content. At these sites considerable fluctuations occurred in the microbial and biochemical properties due to the variation of soil type. In general, these fluctuations were mainly related to soil organic matter and soil moisture content. Tillage system, urea with and without NBPT application did not contribute any notable impact on the soil biological properties reported in this study. Key words: Soil biological quality, soil type, urease inhibitor, conventional tillage, zero tillage

Beschreibung: Producers and scientists are seeking more accurate methods for estimating the N-supplying power of soil at the field level. This has become more urgent as new management technologies, such as precision farming, gain popularity on the Canadian Prairies. We characterized the N status of the soil on an 18-ha site on which a new long-term alternative farming experiment was being initiated at Scott, Saskatchewan, by taking 160 cores in a systematic manner in June 1994. In these cores we determined: i) total soil N; and ii) the N-supplying power of the soil by determining mineralizable N by aerobic incubation at optimum temperature and moisture, and by extracting NH4–N with 2 M KCl at 100°C. Because the field had been fertilized shortly before sampling, residual fertilizer N severely affected the quality of determinations of N supplying power at the 0- to 7.5-cm depth. Consequently, we limited our investigation to the 7.5- to 15-cm depth. We also determined pH, bulk density, and particle size distribution. Using geostatistics, simple correlations, and multiple regression analyses, we demonstrated a close association between the biological and chemical measures of N-supplying power of the soil. Semivariograms revealed that the spatial structure of the variance of both variables was similar, with about 70% of the variance resulting from unidentified processes, and the rest explained by spatial structure. Field maps prepared with block-kriged estimates, revealed that these two measures of N-supplying power were similarly distributed throughout the landscape, and followed closely the spatial distribution of total soil N throughout most of the field. However, we identified two areas of the field where the two estimators of N-supplying power had a weak association with total soil N. Multiple regression and cluster analysis indicated that this disparity was a function of differences in soil pH, bulk density, and geometric mean diameter of soil particles, suggesting that soil erosion-transport processes may have altered the nature of organic N in areas of the field. The relationship between N mineralized during a 24-wk incubation and NH4–N extracted with hot KCl was not affected by these differences, suggesting that the biological and chemical procedures tested were accessing similar pools of soil N. We concluded that hot KCl NH4–N should prove useful for quantifying the N supplying power of soils. Key words: Geostatistics, estimation, kriging, spatial variability, mineralizable N

Beschreibung: Freeze-drying has been implicated as a factor causing soil aggregate breakdown on the Canadian Prairies and northern Great Plains. Aggregates of a Dark Brown Chernozemic clay loam soil sampled in October 1993 and January and April 1994 were subjected to repeated cycles of wetting (to 0.1, 0.2 and 0.3 kg kg−1 water contents) freezing, and freeze-drying under laboratory conditions. The October 1993 samples showed less disruption when initially exposed to freeze-drying cycles compared to samples taken in January and April 1994. Using regression analysis, we predicted that 31 freeze-dry cycles were required for the 0.1 kg kg−1 water content aggregates to reach 60% erodible fraction (EF, % aggregates

Beschreibung: Microbial biomass, as part of the active pool of soil organic matter, is critical in decomposition of organic materials, nutrient cycling, and formation of soil structure. We evaluated chloroform fumigation-incubation with subtraction of a control (CFI/F–C) and without subtraction of a control (CFI/F) as methods to assess biological soil quality. Relationships between CFI/F and potential C mineralization, particulate organic C, and soil organic C were stronger (r2 = 0.86 ± 0.07, n = 232) than those between CFI/F–C and the same soil C pools (r2 = 0.25 ± 0.09) in soils from Georgia. From published data, relationships of CFI/F with potential C mineralization and soil organic C were stronger than those of chloroform fumigation-extraction and substrate-induced respiration with these soil C pools. Effects of land management on biological soil quality using CFI/F were consistent with those determined using other soil C pools as response variables. However, land management effects on biological soil quality using CFI/F–C were either contrary to those using other soil C pools or not detectable because of greater inherent variability in CFI/F–C. Chloroform fumigation-incubation without subtraction of a control is a robust and reliable method to assess biological soil quality under a wide range of soil conditions. Key words: Active soil carbon, chloroform fumigation-extraction, microbial biomass, soil organic matter, soil quality, substrate-induced respiration

Beschreibung: not available

Beschreibung: Municipal solid waste (MSW) compost contains large amounts of organic matter that can be beneficial to soil. The objectives of this study were to measure N mineralization and acid hydrolyzable N in soil amended with MSW compost and correlate corn (Zea mays L.) grain yield with acid hydrolyzable N. The soil, an Orthic Black Chernozem (Entic Hapludoll) cropped to corn, was amended with composts at either 90 dry Mg ha−1 yr−1 from 1993 to 1995, or at 270 dry Mg ha−1 in one application in 1993. Soil samples were collected in the fall of 1994 and 1995 to measure C and N mineralization and acid hydrolyzable N. Potentially mineralizable N was estimated with the NCSOIL model after using C and N mineralization observed in the laboratory to calibrate the model. Net N immobilization occurred in compost-amended soils collected in 1994 with less than 0.2% of the total soil N mineralized in the compost treatments. In 1995, there was net mineralization in compost treatments but less than 5% of total soil N mineralized in 120 d. The addition of compost increased the acid hydrolyzable N of soil with 43–63% of the total soil N being acid hydrolyzable. Acid hydrolyzable soil N did not correlate to No but weakly correlated with corn grain yield. The MSW compost source was more important than the timing of application in inducing differences in soil biochemical properties. Keys words: Municipal solid waste compost, organic matter, potentially mineralizable nitrogen, acid hydrolysis

Beschreibung: The clay mineralogy of the soil is important in that it can affect potassium (K) availability, particularly if vermiculite is present. Large areas of Glacial Lake Agassiz in Manitoba contain fine-grained lacustrine sediments that support boreal forest vegetation. The purpose of this investigation was to identify the clay mineralogy of several commonly occurring soils and document its influence on soil fertility, particularly K availability. The soils were classified as either Eluviated Eutric Brunisols or Orthic Eutric Brunisols. X-ray diffraction analysis verified that vermiculite, hydrous mica and kaolinite were the principal clay minerals in these soils. Vermiculite was demonstrated to have hydroxy Al-interlayers and the amount of vermiculite decreased in the deeper soil horizons. Smectite was present in the Btj horizons of the Eluviated Eutric Brunisols, while trace amounts of chlorite were present in every inorganic horizon. Quantity/intensity curves for K and an experimental estimate of the K-fixation potential indicated that the Ae horizons of several Eluviated Eutric Brunisols supported higher K activities in the soil solution and that K-fixation was greater in subsurface horizons. Potassium fixation and the quantity/intensity curves for selected horizons of the Orthic Eutric Brunisols were nearly identical and each showed a reduced intensity to maintain the aqueous activity of K. Key words: Potassium fixation, vermiculite, quantity/intensity

Beschreibung: Peat is a hetorogenous material containing humic substances (HS) that increase its fertilizer value, and acid functional groups that react with ammonia. However, polyvalent cations may block some ammonia-sorbing sites. Sixty-seven peat samples were collected in Quebec (i) to relate the colorimetric Kaila pyrophosphate test for extracting HS to the von Post field test and (ii) to correlate ammonia sorption capacity (ASC) to selected peat properties as follows: von Post test, Kaila pyrophosphate test, pH(H2O), pH(CaCl2), pH(KCl), exchangeable acidity as well as ash, Ca, Al and Fe contents. Exchangeable acidity was the most highly correlated with ASC (P 

Beschreibung: In Canada and the United States approximately 82% of the annual total dose of radiation to any person comes from terrestrial and cosmogenic sources. The soil is also the main source of radon exposure to humans. Therefore it is important to know the background levels of natural and anthropogenic radioactivity in soils. In this study the radionuclides 40K, 226Ra, 232Th and 137Cs were measured in the soils of southwestern Ontario in order to determine the background levels and to understand the soil profile distribution. Clay content is the most important variable affecting the background levels of 40K, 226Ra, and 232Th in the soil. The profile distribution of these radionuclides is further influenced by pedogenic processes, particularly carbonate leaching from the solum and clay illuviation from the Ae to the Bt horizons. The lateral and vertical distribution of bomb-fallout 137Cs is influenced by soil management such as tillage, biopedoturbation by soil animals such as earthworms and groundhogs, soil erosion and soil organic matter cycling. Multiple regression analysis showed that clay content, sand content, percent CaCO3, pH and organic carbon content had variable influences on each of the radionuclide contents in the soil. Key words: Radionuclides, 40K, 226Ra, 232Th, 137Cs, pedogenesis

Beschreibung: Cereal straw has many potential on-farm and off-farm uses. If straw is to be removed from land, the practice should not adversely impact long-term crop production and soil quality. A 10-yr experiment was conducted on a Dark Grey Solod near Beaverlodge, Alberta (55°13′N, 119°20′W) to determine the effects of fertilizer and straw management on the yield of, and nutrient (N and P) use by, continuous barley (Hordeum vulgare L.). Four straw management treatments: (i) straw removal; (ii) straw ploughed in; (iii) straw disked in; and (iv) straw disked in plus a red clover (Trifoleum pratense L.) green manure disked in every fifth year, were superimposed on four fertilizer treatments. The fertilizer treatments were application of N and P: (i) banded at soil-test recommended rates (ST,b); (ii) broadcast and incorporated at soil-test recommended rates (ST,bi); (iii) banded at soil-test rates of N+ 25 kg ha−1 and P+ 10 kg ha−1 (ST+,b); and (iv) as in (iii) but broadcast-applied and incorporated (ST+,bi). The straw ploughed-in treatment tended to produce lower annual barley yield and N uptake (by 9 and 13%, respectively) than the other three residue treatments. Barley yield and utilization of N and P were unaffected by straw removal as compared to disking-in straw. Barley yield and N uptake were higher (by 12 and 17%, respectively) with N and P application at the higher rate. At the recommended rate, broadcast-and-incorporated application of fertilizers resulted in lower yields and nutrient use than banded-in application. Treatment effects on P uptake tended to be small. The green-manured treatment used less fertilizer N, resulted in less total barley grain production, and did not increase the amount of crop residues incorporated. It is concluded that grain yield and nutrient (N and P) use of a continuous barley cropping system, fertilized at recommended rates of N and P, were unaffected by straw removal. Key words: Crop residue management, continuous barley production, fertilizer N and P

Beschreibung: Soil properties, mineral composition, available microelements for plant uptake and ultramicromorphological gravel characteristics in skeletal soils from amphibolite and serpentinite rocks with additions of silicon-rich colluvial materials were studied in the Mediterranean region (Sierra Nevada, southern Spain). The soils (Entic Cryumbrept, Typic Xerochrept, Pachic Cryoboroll and Typic Cryorthent) showed mineralogical discontinuities, exchangeable Ca:Mg ratios greater than 1 and a pH and base saturation profile that decreases in the central and lower parts of the solum. The different soil particle-size fractions had similar mineral compositions (X-ray diffraction [XRD] and infrared [IR] techniques) retaining unstable phases (amphibole, feldspar, serpentine). Inherited or slightly transformed phyllosilicates (serpentine, mica, chlorite, talc and interstratified phases) were shown to be dominant in the clay fraction. The scant pedogenic evolution contrasted with a high free iron content. The concentrations in fine earth of DTPA-Zn, -Cu, -Mn, -Co, -Cr, -Ni and -Fe were not toxic, showed interdependence and were related to the silt, clay and free forms content. The gravel fraction revealed significant amounts of free iron and available microelements (DTPA-extractable), which could be bound to deposits of precipitated secondary forms and to finer pedogenic material present in the fragments. Scanning electron microscope (SEM) observations confirmed these morphological characteristics in serpentinite and amphibolite pebbles. Key words: Mafic-ultramafic soils; mineralogy; DTPA-microelements; rock fragments

Beschreibung: Water-use of three field-grown potato cultivars (Atlantic, Monona and Norchip) was examined using a commercially available sap flow monitoring system over three consecutive growing seasons. The objectives of the investigation were to utilize the sap flow system to assess the water use of three field-grown potato cultivars. This included an assessment of the relationship between environmental conditions, water status and measured sap flow including the plant-to-plant variation in sap flow and an evaluation of relative transpiration in relation to the soil water status.Each cultivar maintained daily sap flow close to the atmospheric potential transpiration until approximately 70% of the available water was depleted. Under conditions where the soil was drier (〉70% depleted), Monona potato plants exhibited a more rapid decline in transpiration than Norchip and Atlantic.Hourly sap flow rates were closely related to solar irradiance, especially under well-watered conditions, with no apparent light saturation point. Vapour pressure deficit effects on sap flow were less pronounced, although maximum vapour pressure deficits encountered were only 2 kPa. Key words: Water use, sap flow, transpiration, potato

Beschreibung: The potential impacts of limed sludge on nutrient and heavy metal bioavailability must be studied for their safe use on acidic soils. The objective of this study was to assess the impact of limed sludges on six acidic soils from eastern Canada. CaCO3 and raw sewage sludges (RSS) stabilized with either CaO (CaO + S) or cement kiln dust (CKD + S) were added to soils in amount necessary to reach pH 6.5 and the mixtures were then incubated for 64 d. CaO + S treatments were the most efficient to neutralize soil acidity. After 10 d of incubation, the Sr-citrate extractable P was significantly increased by the CaO + S treatment in low P sorption soils. The extractable K, Zn and Cu contents were also slightly increased by CaO + S compared to CaCO3 whereas CKD + S resulted in an excessive soil exchangeable K content. After 64 d, labile Al content was decreased by all liming amendments. RSS and CaO + S tended to increase labile Cu and Mn contents. The RSS increased NaOH-extractable Cu but the treatments had no significant effects on the labile and stable forms of heavy metals. A combination of CaO + CKD to stabilize sewage sludge would be more suitable to provide appropriate levels of P and K without resulting in large increases in extractable heavy metal contents. Key words: pH, extractable P and K, cement kiln dust, Al and Mn toxicity, Cu fractions, water-soluble metals

Beschreibung: 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

Beschreibung: Soil solution analysis may provide useful information on nutrition status and Al toxicity in soil. Nevertheless, obtaining soil solutions in low-moisture soils causes a problem. Saturated extracts may act as an alternative for getting information on soil solution. Their effectiveness in assessing representative base cations and aluminum distribution in soil solution was demonstrated in this study. Saturated extracts, which were obtained from air drying and fresh soil, were compared with the "true" soil solution for base distribution and base/Al ratio. Molar fraction and equilibrium ratio in the "true" soil solution depended on soil moisture before extraction. Nevertheless, they were less affected by this approach than intrinsic concentrations. The results showed that molar fraction and equilibrium ratio in soil solution can be predicted from the molar fraction or equilibrium ratio in saturated extracts and soil moisture information, however, saturated extracts obtained from fresh soil were better models. Base/Al ratios in saturated extracts were closely dependent on pH extracts but they were not well linked with the same ratio in soil solution. Key words: Soil solution, molar fraction, equilibrium ratio, soil acidity, sugar maple, Acer saccharum

Beschreibung: The study was done to quantify the effect of uncovered field storage of solid poultry manure in south coastal British Columbia on a site where solid Turkey manure was stored uncovered each fall and winter for approximately 6 yr. The soil was sampled to 370 cm depth in a transect with six sampling locations: two in the manure storage area, and two on either side of the manure storage area. The soil was analyzed for the concentrations of total organic C, total Kjeldahl N, ammonium, nitrate, K, P, Mg, and Na in addition to soil pH and electrical conductivity. The mass of nutrients to 370 cm depth was 39 700 and 330 kg NH4+–N ha−1, 500 and 480 kg NO3−–N ha−1, 36 400 and 1440 kg K ha−1, 12 100 and 2190 kg P ha−1, 3150 and 1140 kg Mg ha−1 and 9850 and 975 kg Na ha−1 for the manure storage and non-storage sampling locations, respectively. The depth weighted average soil pH was 8.4 and 4.7 and average soil electrical conductivity was 3.3 and 0.3 dS m−1 for the manure storage and non-storage sampling locations, respectively. The lack of an increase in soil nitrate concentration in the manure storage area was attributed to concentrations of free ammonia in soil solution toxic to nitrifying bacteria. The results highlight the high potential for nutrient loss from uncovered fall and winter field storage of poultry manure in south coastal British Columbia. Key words: Turkey manure, soluble C, soil ammonium, free ammonia, electrical conductivity

Beschreibung: Vesicular-arbuscular mycorrhizae (VAM) generally enhances uptake and translocation of P and encourages plant growth and development in nutrient-deficient soils. Contradictory reports about the role of VAM in S uptake and translocation may result from insufficient consideration of soil S status. In this study, using soils of low S status, VAM inoculation increased the content of radioactively labelled S (35S) in shoots of maize plants. Key words: Maize plant, S-uptake, Vesicular-arbuscular mycorrhizae fungi

Beschreibung: 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

Beschreibung: Organic matter (OM) generally plays an important role in soil aggregate stability. The objective of this work was to characterize the hot water-extractable OM and its role in the aggregate stability of clayey ferrallitic soils under different land use management. The macroaggregate (〉200 µm) stability of these soils was determined before (AS) and after hot-water extraction (ASe). The contents in total organic carbon and in carbon present as carbohydrates, as well as the sugar composition, were determined on the bulk soils and their hot-water extracts.The carbon and macroaggregate contents decreased upon land-clearing and cultivation, but to a lesser extent when some cultural practices were used. Whatever the situation considered, the hot-water extract always presented a higher carbohydrate content than the bulk soil. The high values of ratios r = (galactose + mannose)/(arabinose + xylose) suggested that a large proportion of carbohydrates was of microbial origin. There were significant correlations between AS and the carbon content of bulk soils or hot-water extracts, and between AS and the soil carbohydrate content. On the opposite, whatever the soil sample studied, no significant difference could be found between AS and ASe, showing that hot-water extractable OM had thus no clear aggregating role in these soils. Key words: Organic matter, macroaggregate stability, hot-water extraction, carbohydrates, ferrallitic soils

Beschreibung: 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

Beschreibung: To maintain a sustainable agricultural system, management practices such as grazing must ensure adequate soil water for plant growth, yet minimize the risk of soil erosion. The objective of this study was to characterize the soil water regime of perennial and annual forages under three grazing intensities (heavy, medium and light). The study was conducted at the Lacombe Research Station, Alberta, on an Orthic Black Chernozem of loam to silt loam texture. The forages used were smooth bromegrass (Bromus inermis L. 'Carlton'), meadow bromegrass (Bromus riparius L. 'Paddock'), a mixture of triticale (X Triticosecale Wittmack 'Pika') and barley (Hordeum vulgare L. 'AC Lacombe') and triticale. Soil water measurements were conducted between April and October of 1994 and 1995 using a neutron scattering hydroprobe to a depth of 90 cm. Surface (0–7.5 cm) soil water was more responsive to grazing intensity than soil water accumulated to various depths. For all grazing treatments and forages, both surface soil water and accumulated soil water generally fluctuated between field capacity and wilting point during the growing season. Although plant water status was not determined, no visual permanent wilting of forages was observed during the study. Differences in evapotranspiration (ET), as determined by differences in soil water were evident among forage species but not grazing intensities, with perennials having high ET in spring and annuals having high ET in summer. Estimated values of water-use efficiency (WUE) were greater for perennials than for annuals and grazing effects on WUE were minimal. From a management perspective, grazing of annuals and perennials altered soil water dynamics but still maintained adequate soil water for plant growth. Key words: Evapotranspiration, forages, grazing intensity, water-use efficiency

Beschreibung: This study was undertaken to characterize the response of organic matter mineralization to soluble electrolyte concentration. We added salts (either KCl or KH2PO4) to a non-saline Black Chernozem at rates of 0 to 64 mmol kg−1 and measured the amounts of C and N mineralized in a 40 d incubation (21 °C and field capacity). Precipitation of calcium phosphate in KH2PO4-treated soil resulted in electrical conductivity (EC), measured in a 1:2 soil:water extract, being lower than in KCl-treated soil. Dissolved organic C (DOC) was increased (up to twofold) by KH2PO4 addition but KCl had little effect. The relationship between C mineralization and EC appeared to be independent of salt type. Mineralization decreased sharply (by 50%) when EC increased from 0.5 dS m−1 (check value) to 1.3 dS m−1. Inhibition of nitrification was not detected until EC increased to about 2 dS m–1. Key words: Mineralization, organic matter, salinity, chloride, sulfate

Beschreibung: Land use and grazing regime can influence the dynamic of soil water and salt in humid areas. In Central Argentina, more than 2 ×106 ha are subjected to either permanent or cyclical processes of land salinization, alkalinization, flooding and sedimentation. In this region, the natural vegetation is the principal resource on which most systems of animal production are based. The objective of this study was to evaluate the effects of plant cover and grazing over some hydrophysical properties of three saline-sodic soils (two Gleic Solonetz in duripan phase and one Mollic Solonetz in fragipan phase), within a catena sequence. The effects on bulk density, saturated hydraulic conductivity, infiltration runoff, superficial salt accumulation and soil salinity distribution were determined in both bare and covered soil conditions, inside and outside of grazing exclosures. The results showed increased bulk density of topsoil for bare conditions, while saturated hydraulic conductivity did not show significant differences. In soils without any cover, the infiltration decreased significantly. Consequently, the runoff coefficient and salinity were greater, as indicated by significant salt accumulation in the topsoil. The soil profile salinity was reduced as a function of exclosure time, showing a trend toward desalinization resulting from a combined effect of soil cover and changes in intensity of land use. A conceptual model of salt and water dynamics in the soil profile for the landscape scale is postulated. The role of vegetation in regulating water and salt movement in poorly drained areas is emphasised as a basis for the development of management strategies. Key words: Saline and sodic soils, infiltration, runoff, grazing, exclosure, model

Beschreibung: In sandy soils water shortage may result in the loss of crops. During prolonged droughts an increase in time to wilting by a few days may diminish yield losses. Soil incorporation of highly water-swelling polymers (hydrogels) to increase time to wilting and to increase biomass production was investigated. The soil conditioner used was a post cross-linked sulphonated polystyrene. The soil used was a sand with sunflowers (Helianthus annuus) grown for 10 wk. The plant parameters examined were emergence time, growth, wilting time and aboveground biomass. Soil parameters included field capacity, wilting point and available water. These parameters were correlated with the polymer content in the soil and the degree of water equilibrium swelling of the polymers. The tests were performed in pots under water deficiency conditions. Second-order factorial designs were applied and the resultant mathematical models proved adequate and reasonable. The presence of soil conditioner resulted in improvements of all parameters investigated. Key words: Arid soils, water economy, soil conditioners, experimental design

Beschreibung: Manure management and composting methods may greatly affect compost characteristics. An experiment was conducted to characterize 23 on-farm and 6 industrial composts in Québec (Canada). Cluster analysis identified two major groups characterized by their chemical composition, source materials, management intensity and degree of decomposition. Electrical conductivity, total N and K, water-soluble NH4+, PO4, K, Al and organic C, and a cress test were the best chemical and biological parameters for grouping composts. These groups were strongly associated with bedding rate, turning frequency, composting duration, profile windrow appearance, material aggregation and odor. When restricted to dairy manure composts, no clear relationship could be established by cluster analysis between material grouping and their farm management. Statistical analysis on single chemical parameters of dairy manure composts, however, identified five farm management factors: type and amount of bedding, system of manure handling and storage, compost windrow turning, composting length and milk production intensity. These factors affected one or several major parameters: pH, dry matter, electrical conductivity, total and water-soluble C, N, P and K, and humic components characteristics. This study demonstrated the importance of leaching losses in the on-farm composting operations in humid cold regions and the need for more environmentally sustainable composting methods. Key words: Farm manure management, composting, chemical composition

Beschreibung: 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

Beschreibung: The role of soil organic matter (OM) on SO4 retention was investigated by comparing OM content, SO4 retention, and the distribution of Fe, Al and Si compounds in OM-poor (Grands-Jardins, PGJ) and OM-rich (Hermine, HER) Podzols from Québec, Canada. At both sites, four pedons were sampled by horizon; soil pH in H2O, organic C, phosphate-extractable SO4 and, sodium pyrophosphate, acid ammonium oxalate and dithionite-citrate-bicarbonate (DCB) extractable Fe, Al and Si were measured for each mineral horizon. The mineralogy of the clay (

Beschreibung: Low organic matter content and weak soil structure, combined with high annual precipitation, make the soils of the Maritime Provinces extremely susceptible to compaction. Although many pasture studies have been conducted in the Maritime Provinces, none has investigated the impact of pasturing cattle on soil physical properties. Soil properties such as resistance to penetration, bulk density and hydraulic conductivity were monitored on pasture swards receiving various rotational-grazing intensities. These parameters were measured concomitantly on traffic-free areas that had been harvested as conserved forage. Resistance to penetration measurements indicate that a significant amount of compaction by cattle occurred during the 1990, 1991 and 1992 grazing seasons. Penetration resistance was generally greatest in the top 6 cm of soil, but was alleviated by frost action during the subsequent winter and spring. The other soil parameters measured were either more variable (surface and subsurface saturated hydraulic conductivity) or less sensitive (bulk density) to compaction. Although more variable, surface hydraulic conductivity was significantly higher in the traffic-free conserved forage areas than in the pasture paddocks. Rest intervals between grazings had no significant effect on saturated hydraulic conductivity. Seasonal change in resistance to penetration generally increased as rest interval decreased. The timothy/alfalfa swards (little alfalfa was left in the pastures by 1992) had the least seasonal change in resistance to penetration. Key words: Cattle, compaction, resistance to penetration, bulk density, hydraulic conductivity

Beschreibung: Soil microbial biomass (SMB) measurements are often used in soil biological analysis; however, their interpretation can be problematic. In this review, both the limitations and benefits of indirect (both CHCl3 fumigation incubation and fumigation extraction, and substrate-induced respiration) SMB measurements are outlined, along with their value and interpretation as attributes or indicators to assess some soil quality (SQ) functions (e.g., enhance plant growth, maintain aggregation, regulate energy) for mainly humid, temperate soils, with specific emphasis on research conducted in eastern Canada and New Zealand. Indirect SMB methods are subject to limitations analogous to "soil test" procedures (e.g., soil sampling and handling, water content, storage prior to treatment), and also the difficulties with establishing an acceptable "control" and fraction (i.e., k value) of SMB mineralized or extracted. In many cases, such limitations present a need for some degree of standardization (e.g., pre-conditions of 7- to 10-d incubation at 25°C and −0.001 MPa water potential) prior to SMB measurement. However, for SQ assessment, where "comparative" rather than "absolute" values of SMB are often of interest, use of commonly derived k values seem appropriate for surface soils.Soil ecological factors govern SMB and often underlie much of the spatial and temporal variation in SMB. Plant species composition, mainly through net primary productivity and litter quality, can affect SMB measurements along with trophic cascades in soil, where interactions among soil organisms can influence microbial activity. Benefits of SMB measurements relate mainly to the assessment of both soil C turnover and management induced changes in organic matter. The combination of SMB and δ13C to elucidate the transformations and fate of organic C in cropping and soil management systems has also shown that both temporal and spatial redistribution of C inputs, and soil type (i.e., particle size distribution) are dominant factors in turnover and nutrient flow through the SMB.For SQ assessment, SMB is not a useful indicator for the function of soil as a "medium for plant growth" in regard to plant productivity for intensively farmed temperate soils. For the function of soil to "maintain aggregation", where SMB is one agent only of a multi-faceted process, the relationship between SMB and soil aggregation is not always present and tends to be site-specific. In regard to the "regulate energy" soil function, SMB is related to some degree with decomposition and mineralization processes. The main role of SMB for SQ assessment is to serve within a minimum data set of other indicators (e.g., macroorganic C) to monitor soil organic C storage and change. Key words: Soil microbial biomass, humid climate, soil quality

Beschreibung: 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

Beschreibung: Uptake of Cu, Zn, Mn, Pb, and Cd by Taraxacum officinale Weber (dandelion) growing on abandoned industrial sites, community gardens and parks in urban Montreal was measured to evaluate trace metal bioavailability. Total soil trace metal concentrations exceeded the Canadian remediation levels only in the industrial sites, but tissue concentrations at all land use types were normal. Multiple regression analysis suggests that available PO4 may reduce uptake of Cu and Zn. It is evident that sites classified as contaminated on the basis of total soil metal may have low levels of bioavailability. Key words: Trace metals, urban contaminated soils, dandelion

Beschreibung: Differences in the properties of bulk forest and rhizosphere soils are often attributed to ectomycorrhizal association, or the symbiosis characterized by a fungal sheath surrounding the root (mantle) and intercellular root colonization (Hartig net). We compared the soil pH, total C, N, cation exchange capacity, and the contents of mica, chlorite, kaolinite, 2:1 expandable clays, feldspars and amorphous materials between two ectomycorrhizosphere soils (or soil environment in the vicinity of ectomycorrhizae (ECM)) and non-ectomycorrhizosphere soils to study the influence of ectomycorrhizae on chemical and mineralogical properties of soils. The two ectomycorrhizosphere soils were characterized by ectomycorrhizal colonization dominated by (1) Piloderma spp., and (2) Mycelium radicis atrovirensand cottony yellow-brown (MRA-CYB) types or where Piloderma spp. colonization was

Beschreibung: Soils knowledge through the ages accumulated from direct experience through contact with the soil, whether preparation of a seed bed, building roads, or founding buildings. Soil uses were tied with religious observances. Gatherers proceeding to become settled agriculturalists would have used soils knowledge to choose farming sites. The knowledge accumulated by practitioners was written down and extended to others in print during the past two millennia. This changed about 150 years ago, when research studies using the scientific method became the dominant source of soils information. By 1900 this pattern of analytical thought was set. This was fostered by, or at least coincided with, increasing application of technology to use of soils during the second third of the 20th century, and became the dominant source of soil knowledge. We are now seeing a return to the importance of the "other" soil scientists in increasing soil knowledge. There is increasing appreciation of the importance of indigenous soil knowledge; on-farm research where soil users perform their own controlled experiments is becoming an important source of information on soil management. Parallelling this change have been changes in attitude toward soil as a resource, toward conservation, and toward the appreciation of soil performing unique ecological and spiritual functions of concern to mankind. Holistic approaches to soil are again becoming mainstream. As we grapple with global problems such as soil degradation, we will see all soil scientists making contributions to soil knowledge. Key words: Soil knowledge, soil users, ecological functions

Beschreibung: Routine determination of soil microbial biomass C has shifted during the past decade from chloroform fumigation-incubation to chloroform fumigation-extraction using 0.5 M K2SO4 as extractant. We compared extractable C with water and 0.5 M K2SO4 in eight soils ranging in pH from 5.4 to 8.3. In unfumigated soils with low pH, extractable C was 0.8- to 1.2-fold greater with water than with 0.5 M K2SO4. However, in unfumigated soils with pH 〉 7.7, extractable C, although not statistically significant, was 11 to 19% less with water than with 0.5 M K2SO4. In fumigated soils, no difference in extractable C between water and 0.5 M K2SO4 was detected among soils with pH  7.7. Our results suggest that 0.5 M K2SO4 (1) may flocculate soil and cause adsorption of solubilized C onto colloids at pH  7.7, thereby differentially affecting the fate of solubilized C depending upon soil pH. Our results put into question the widespread adaptability of using chloroform fumigation-extraction to estimate microbial biomass C. Key words: Extractable carbon, chloroform fumigation-extraction, microbial biomass

Beschreibung: The physical quality of peat mixes is in part related to the capacity of the substrate to store and supply air and water to plant roots. During manufacturing, the mixing of various substrate components modifies the substrate characteristics. The objective of this study was to assess the changes in air storage and supply properties caused by varying the particle size of the substrate components. The substrate was composed of 40% wood bark (WB), 50% peat, and 10% coarse gravel (volume basis). Wood bark particle size was varied in a first (0–2, 2–4, 4–8 and 8–25 mm) and a second (1–2, 2–4, 4–8 and 8–16 mm) experiment. When increasing bark particle sizes to 8–25 mm or 8–16 mm, air supply characteristics, as assessed with gas diffusivity measurements, decreased to 0.78 or 0.45 its value for the 2–4 or 1–2 mm average bark particle size. This occurred despite no significant changes in air storage, as assessed from air-filled porosity measurements. Key words: Gas diffusivity, pore tortuosity, air-filled porosity, peat lite mixes, peat substrates

Beschreibung: Some soils develop severe water repellency several years or decades following oil contamination. We previously reported on the characteristics of three such soils. Here we report on the characteristics of putative water-repellent substances in them. We examined the effectiveness of various polar, nonpolar and amphiphilic solvents for removal of water-repellent substances in three nonwettable soils. Only the amphiphilic solvent mixture isopropanol/14.8 M ammonia (7:3, vol/vol) (IPA/NH4OH) completely eliminated soil water repellency in all three soils. We thus define putative water-repellent substances as those substances whose removal from soil by IPA/NH4OH removes water repellency. High-resolution CPMAS 13C-NMR spectroscopy and thermal desorption followed by conventional gas chromatography/mass spectroscopy with electron impact ionization (GC/EI/MS) and GC/MS with chemical ionization (GC/CI/MS) were used to characterize extracted putative water-repellent substances. We conclude that: (i) the identified representatives of these substances consist mostly of homologous series of long-chain and polycyclic aliphatic organic compounds; namely, n-fatty acids, n-alkanes, and cycloalkanes, and that (ii) they are of petroleum origin rather than plant or microbial origin. Key words: Soil hydrophobicity, petroleum hydrocarbons, soil water repellency, amphiphilic solvents, crude oil, nonwettable soil

Beschreibung: 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

Beschreibung: Effects of long-term (18-yr) applications of cattle manure (20 Mg ha−1 yr−1) and NPK fertilizer on the labile organic matter (OM) and its protection in water-stable aggregates were investigated in a Le Bras silt loam (Humic Gleysol). Soil from the 0- to 10-cm depth was sampled from the untreated control, NPK, manure and NPK + manure treatments and fractionated into four size classes of slaking-resistant aggregates (〉1000 µm, 250–1000 µm, 53–250 µm, 1000 µm) and intact microaggregates (

Beschreibung: Soil organic matter is important both from an agronomic and an environmental perspective because it affects the capacity of the soil to sustain crop growth, and it is a source and sink of atmospheric CO2-C. Soil microbial biomass comprises a small proportion of total soil organic matter, but it is more dynamic than total soil organic matter. Therefore, measurements of soil microbial biomass may show the effects of soil management on potential changes in soil organic matter before such effects can be detected by measuring total soil organic matter. The effects of tillage and crop rotation on soil microbial biomass and activity were studied in 1995–1997 in the wheat phase of different cropping rotations that had been established in 1992 under zero tillage or conventional tillage in northern Alberta. Soil microbial biomass was often significantly (P 

Beschreibung: 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

Beschreibung: A procedure involving equilibration of soil with 0.40 M acetic acid (normally used to estimate lime) was used instead to monitor changes in acid-buffering capacity of topsoil, in an area exposed to acid emissions. Samples taken from 15 sites in 1997 were analyzed together with matching samples taken in 1992. The procedure detected a smaller acid-buffering capacity in 1997 than in 1992 at two sites. Key words: Acid buffering capacity, acid emissions, lime

Beschreibung: Although approximately 1.3 million ha of mixed Solonetzic – Chernozemic landscapes are cultivated in Saskatchewan, little information is available on the effects that agriculture has had on the quality of these soils. At our research site in southwestern Saskatchewan a clear landscape-scale pattern of soil distribution occurred. Regosolic and thin Chernozemic soils were associated with the long, gentle (2–5%) slopes and Solonetzic-influenced soils were associated with higher catchment area footslope and depressional positions. High rates of soil loss occurred throughout the landscape – overall a net soil loss of 31 Mg ha yr−1 was calculated using 137Cs redistribution techniques. No net depositional sites were observed in the 45 sampling points in the landscape, suggesting that the site was dominated by wind erosion. The high rates of loss were consistent with very low levels of soil organic carbon storage (37 to 46 Mg ha−1 to 45 cm) at all slope positions in the landscape and with the occurrence of sub-soil features in the plough layer. The Solonetzic-influenced soils occupy 38% of the site and have high sodium adsorption ratios (from 18 to 38 in the B horizon) and high soil resistance values as determined with a penetrometer. For the Solonetz and Solodized Solonetz soils these growth-limiting properties occur immediately below the 10-cm plough layer and may constitute a largely irreversible decrease in their productive capacity. Key words: Cesium-137, soil erosion, soil quality, landscape-scale, organic carbon

Beschreibung: 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

Beschreibung: 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

Beschreibung: Calcareous organic-matter-rich Black Chernozemic soils often persist under poplar forests in Saskatchewan, not acquiring the Ae horizons and related properties more characteristic of Gray Luvisol soils. These are Rego Black Chernozems, locally termed "Wooded Calcareous" because of the occurrence of a dark, calcareous horizon (AC) at depths of 10 to 30 cm. We hypothesize that dark, calcareous horizons are former Bm horizons that have been recarbonated because of intense biocycling of Ca by aspen (Populus tremuloides). The comparatively small amounts of carbonate occur mainly in the fine silt and clay fractions, and are dominantly calcite, indicating secondary origin, in comparison to the carbonate minerals of the Ck horizons where both calcite and dolomite occur, the latter more common in coarse fractions. The δ13C values of the carbonate minerals indicate that virtually all the carbonate in fine fractions of the upper horizons of the Wooded Calcareous soil is pedogenic. The dominance of pedogenic carbonate in the Ahk and AC horizons of the Wooded Calcareous soil is consistent with a secondary enrichment, a probable result of increased biocycling of Ca where aspen grows on sites with large amounts of soluble Ca in the subsoil. High concentrations of soluble Ca2+ and SO42− in the LFH of the Wooded Calcareous are consistent with increasing biocycling of these ions, from a gypsum-rich subsoil. Key words: Pedogenic carbonate, prairie-forest transition, stable carbon isotopes, biocycling, δ13C values

Beschreibung: Leaching of water soluble soil carbon plays an important role in downward transport of soil nutrients and pollutants and may be influenced by soil and management factors. We examined the leaching of water soluble carbon from two sandy soils under nitrogen fertilization by adapting an intermittent leaching-incubation technique using packed soil columns (94 × 10 cm). After 30 d, cumulative amounts of water-soluble organic carbon (SOC) leached from the Candler and Wabasso sand for various treatments in mg C column−1 were: 77 and 302 (NH4NO3), 64 and 265 (control), and 45 and 239 (isobutylidene diurea, IBDU), respectively. The IBDU and NH4NO3 treatments increased the leaching of water-soluble inorganic carbon (SIC), which ranged from 2 to 38 mg C column−1 over 30 d. At the end of eight cycles of leaching/incubation, the total carbon content increased at depth (control and NH4NO3 treatment) in the Candler sand, but decreased in the Wabasso sand. In the first leaching event, the average rate of SOC leaching from the Wabasso sand was 26 mg C column−1 d−1 which dropped rapidly to about 5 mg C column−1 d−1 towards the end of the experiment. The rate of SOC leaching from the Candler sand was much lower (

Beschreibung: Zero tillage systems are receiving attention as possible strategies for sequestering atmospheric carbon. This benefit may be offset by increased N2O emissions, which have been reported for soils under zero tillage (ZT) compared to those under more intensive tillage (IT). Comparisons of N2O emissions from the two systems have been restricted to the growing season, but substantial losses of N2O have been reported during spring thaw events in many regions. Inorganic and organic additions of nitrogen and fallowing have also been shown to increase levels of soil-emitted N2O. The objectives for this study were: (i) to confirm that losses of N2O are higher under ZT than under IT in Alberta Parkland agroecosystems; (ii) to compare the relative influence of urea fertilizer (56 or 100 kg N ha−1), field pea residue (dry matter at 5 Mg ha−1), sheep manure (dry matter at 40 Mg ha−1) additions, and fallow on total N2O losses; and (iii) to investigate possible interactions between fertility and tillage treatments. Gas samples were collected using vented soil covers at three sites near Edmonton, Alberta during 1993, 1994, and 1995. Gas samples were analyzed using a gas chromatograph equipped with a 63Ni electron capture detector. Estimated annual N2O loss ranged from 0.1 to 4.0 kg N ha−1. Emissions during summer were slightly higher, similar, or lower on ZT compared to those under IT, but were consistently lower on ZT plots during spring thaw. Combined estimates (spring plus summer) of N2O loss under ZT were equal to or lower than those under IT. Highest overall losses were observed on fallow plots, followed by fertilizer, pea residue, and then either manure or control plots. We conclude that ZT management systems have potential for reducing agricultural greenhouse gas emissions in the Alberta Parkland region. Key words: Nitrous oxide, thawing soil, tillage, nitrogen fertilizer, manure, fallow

Beschreibung: Agricultural systems are sources and sinks for carbon and to quantify the net effect of these systems on atmospheric CO2 concentration, the amounts of carbon fixed in primary production and that respired by the soil must be known. The objectives of our study were (1) to quantify the amount of soil respiration from fallow and barley plots during the growing season; and (2) to determine the relationship between these fluxes and soil temperature and moisture. This study was conducted on field plots measuring 200 by 200 m with one plot planted to barley (Hordeum vulgare L.) while the other plot was in fallow. Two automated chambers were permanently installed in the fallow plot and three in the barley plot at the start of the growing season. When CO2 fluxes were integrated over a 24-h period, the daily soil respiration under fallow ranged from a low of 1.6 g CO2 m−2 d−1 on a dry day to a high of 8.3 g CO2 m−2 d−1 on a wet day. The corresponding values for barley were 3.3 and 18.5 g CO2 m−2 d−1 in 1994. Similar values were obtained in 1996 and, on average, daily soil respiration under barley was twice of that under fallow. The integrated daily CO2 flux under fallow was strongly related to daily soil moisture and mean soil temperature with moisture alone accounting for 76 to 80% of the variation in CO2 flux. While good relationships were obtained between soil moisture and CO2 flux under fallow, the relationship under barley was not as good. The CO2 fluxes, measured eight times per day, displayed a diurnal pattern similar to that of soil temperature; however, there was no consistent quantitative relationship between these 3-hourly fluxes and temperature. A poor relationship was obtained when the fluxes during several days were related to soil temperature as soil moisture confounded flux-temperature relationship. Under the semi-arid conditions of southern Alberta, moisture is the main parameter controlling soil respiration during the growing season. Key words: Soil respiration, soil moisture, soil temperature, CO2 flux, chamber measurements, diurnal CO2 flux

Beschreibung: Agricultural management practices affect the dynamics of soil organic matter (SOM) by influencing the amount of plant residues returned to the soil and rate of residue and SOM decomposition. Total organic C and δ13C of soil were measured in two field experiments involving corn cropping to determine the effect of tillage practices on SOM dynamics. Minimum tillage (MT) and no tillage (NT) had no significant impact on the soil C compared with conventional tillage (CT) in the 0- to 50-cm soil depth sampled at both sites. Continuous corn under MT and CT for 29 yr in a silt loam soil sequestered 61–65 g m−2 yr−1 of corn-derived C (C4-C), and it accounted for 25–26% of the total C in the 0- to 50-cm depth. In a sandy loam soil cropped to corn for 6 yr, SOM contained 10 and 8.4% C4-C under CT and NT, respectively. Reduced tillage practices altered the distribution of C4-C in soil, causing the surface (0–5 cm) soil of reduced tillage (MT and NT) plots to have higher amounts of C4-C compared to CT. Tillage practices did not affect the turnover of C3-C in soil. Key words: Soil organic matter, 13C natural abundance, tillage practices

Beschreibung: Knowledge of the response of soil biochemical attributes to crop management and growing season weather is important for assessing soil quality and fertility. Long-term (38–39 yr) crop rotations on a Black Chernozem at Indian Head, Saskatchewan, were sampled (0- to 7.5-cm depth) between early May and mid-October, 11 times in 1995 and 9 times in 1996. We assessed the effect of cropping frequency [fallow–wheat (Triticum aestivum L.) (F–W) vs. F–W–W, vs. Continuous (Cont) W], fertilizers (unfertilized vs. N + P applied), straw harvesting, legume green-manure (GM) in GM–W–W (unfertilized), and legume-grass hay (H) in F–W–W–H–H–H (unfertilized) systems. Changes in organic C and total N (OC, TN), microbial biomass C (MBC), light fraction C and N (LFC and LFN), mineralizable C and N (Cmin and Nmin), and water-soluble organic C (WSOC) were monitored. Organic C and TN were constant and unaffected by rotation phase during the season, but most of the other more labile soil biochemical attributes varied during the season. Much of this temporal variability was associated with changes in soil moisture, temperature and precipitation, and with rhizodeposition in some cases. Whenever conditions favoured rapid decomposition in situ (e.g., high moisture, temperature and/or precipitation) we obtained lower values for the more labile attributes in subsequent laboratory measurements. Seasonal trends in the more labile attriutes were more pronounced in 1995 (a much wetter year) than in 1996, and the proportion of the variability attributable to weather conditions was greater in 1995 than in 1996 (viz., R2 ranged from 20 to 44% in 1996 and from 37 to 60% in 1995). Seasonal variability was greater in the more fertile treatments [e.g., Cont W (Fert) and F–W–W–H–H–H) than in F–W or Cont W (Unfert). Seasonal variability in LF was unaffected by cropping. Light fraction was lower in 1995 than 1996 because of faster decomposition in 1995 (335 mm of growing season precipitation compared to 157 mm in 1996). Microbial biomass was not influenced by cropping in 1996, but in 1995 it was higher in cropped than in fallow phases of the rotations, suggesting a positive effect of rhizodeposition. Water-soluble organic C was greatest in the more fertile treatments and in cropped than in fallow phases. Mineralizable C and N were greater in cropped than in fallow rotation phases in 1995, but unaffected by cropping in 1996. Further, Cmin and Nmin were higher in 1996 than in 1995, likely due to more rapid decomposition in the wetter 1995. Over the last 10 yr of this experiment LFC and Cmin have increased markedly in the more fertile treatments [e.g., Cont W (Fert), F–W–W–H–H–H], but have hardly changed in the less fertile treatments such as F–W or Cont W (Unfert). In this period the less labile attributes (e.g., OC) have hardly changed in any treatment. Key words: Microbial biomass, carbon, nitrogen, mineralization, water-soluble C, light fraction, weather variables

Beschreibung: 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) and mineral-associated OM (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

Beschreibung: Sandy, infertile soils can benefit from the addition of organic waste amendments. Annual applications of organic wastes for as long as 4 yr increased soil organic matter content, decreased soil bulk density, and increased soil water retention of a coarse-textured soil. However, soil water-holding capacity was not necessarily increased, and there was a limited effect on soil cation exchange capacity. Key words: Cation exchange capacity, water retention, soil pH, soil organic matter, soil bulk density

Beschreibung: Soil degradation and soil organic matter (SOM) reduction have long been suspected to occur under intensive potato (Solanum tuberosum L.) production in Prince Edward Island. Thus, this study was conducted to evaluate the effect of eight potato cropping sequences involving barley (Hordeum vulgare L.), ryegrass (Lolium multiflorum L.), red clover (Trifolium pratense L.) and barley under-seeded with red clover on aggregate stability and SOM properties of a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol). Total C and N, light-fraction (density