ALBERT

Beschreibung: The main objective of this study was to compare the recovery of 15N-labelled fertilizer by different methods of N application and N rates. Field experiments were carried out for 3 yr at Saint-Hyacinthe (Saint-Damase, Du Contour, Sainte-Rosalie soils) and at Saint-Lambert, Lévis (Le Bras soil). Grain corn (cv. Pride K228, 2700 CHU) and silage corn (cv. Hyland 3251, 2300 CHU) were grown at Saint-Hyacinthe and Saint-Lambert, respectively. In 1988 and 1989, field trials were arranged in a randomized complete bloc design consisting of five treatments in three replications: control 0 N and four split application methods of N fertilizer. Labelled 15NH4 15NO3 fertilizer was applied either banded at planting as starter (D), broadcast and incorporated before planting (Vs) or sidedressing between rows at V6 to V8 stages of corn (Bp). In 1990 field trials, treatments consisted of four N rates (0, 60, 120 and 180 kg N ha−1) labelled with 15NH4 15NO3. The effect of N rates on yield and N uptake by corn was significant in all years. However, the effect of application methods was significant only on the soil Du Contour in 1989 where corn grain yield was highest when N fertilizer was split as starter and sidedress band. The CUR of N fertilizer applied broadcast before planting (42 to 48%) was generally lower than sidedressing band application (43 to 54%). N fertilizer recovery in the starter showed also high CUR values (45 to 60%). Consequently, it is recommended to split N fertilizers and apply in band to increase efficiency for grain corn. The CUR values decreased with N rates only in Le Bras soil in 1990. Residual N fertilizer increased from 27 to 103 kg N ha−1 for 60 and 180 kg N ha−1 rates, respectively. Consequently, the environmental impact of N fertilization may increased with high N rate. Key words: Grain corn, silage corn, 15N recovery, fertilizer N split application

Beschreibung: Snow management (tall vs. conventional height stubble) and one-time deep tillage were investigated for increasing water conservation and annual crop production on a rolling soil landscape developed on glacial till in the semiarid Brown soil zone of the Canadian prairies. Tillage depths were 0, 13, 25, and 45 cm. Gleysolic soils had more soil water at time of seeding and greater 3-yr mean durum wheat (Triticum turgidum L.) grain yields than the Chernozemic soils. On the Chernozemic soils, tall (25 cm) stubble increased over-winter soil water at seeding by 15 mm compared with conventional short (14 cm) stubble. Mean 3-yr durum grain yields were 165 kg ha−1 higher with tall than short stubble although yield increases were only significant (P 

Beschreibung: Pedotransfer functions (PTFs) were used to assess the sensitivity of the structural characteristics of coarse- and medium-textured calcareous illitic soils at different levels of relative compaction (RC) to changes in the organic carbon (OC) content. The analyses predicted that an increase in the OC content of 0.01 kg kg−1 would:• increase the available water content from 0.02 to 0.04 m3 m−3 with the largest increases occurring in coarser-textured soils and not being strongly influenced by RC;• decrease the air-filled porosity at field capacity from 0.01 to 0.04 m3 m−3 with the largest decreases occurring in the finer-textured soils and not being strongly influenced by RC;• decrease the soil resistance to penetration with the decreases most pronounced at lower water potentials and higher RC; at the permanent wilting point and a RC of 0.95 the decrease would range from 1.2 to 3.8 MPa;• increase the least limiting water range from 0.01 to 0.05 m3 m−3 with the increase varying with clay content.A comparison with predictions based on PTFs derived from data sets from other parts of the world indicated caution should be exercised in applying PTFs to soil and climatic conditions that are different from those from which the PTFs were derived until the impacts of these conditions are better understood. Key words: Bulk density, field capacity, permanent wilting point, available water; aeration, soil resistance, least limiting water range

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

Beschreibung: Erosion control practices were evaluated for their ability to reduce soil loss and runoff and for their effects on strawberry (Fragaria × ananassa Duch.) yield on a silt loam soil in the uplands area of the Lower Fraser Valley. Three treatments (underdrainage, winter cover cropping of barley [Hordeum vulgare L.] and cross slope planting) were compared to a control. Soil and runoff losses from natural rainfall were measured on replicated experimental plots (0.01375 ha) from 1991 to 1994. Soil and runoff losses were significantly lower with the winter cover crop and cross-slope planting treatments than the control. Results for the underdrainage treatment were not significantly different from the control and non-representative of proper underdrainage due to too deep an installation under wet conditions. Soil protection by the barley cover crop reduced mean annual soil loss and runoff by 78 and 43%, respectively. Cross slope planting reduced soil and runoff losses by 97 and 84%, respectively, compared with the control. Annual runoff coefficients of up to 21% were observed for the control, while coefficients of 40% were not uncommon for single storm events. Except for the cross slope treatment, strawberry yields were not compromised by the erosion control practices. Winter cover cropping is the preferred erosion control practice for strawberries grown on upland soils, since cross slope planting may cause depressed yields from root rot disease resulting from stagnant water between the rows. Key words: Soil loss, runoff, runoff coefficient, cover crop, across slope, erosion control

Beschreibung: Liming of forest soils, currently practiced in Europe, may be necessary in the future in North America to counteract calcium (Ca) depletion due to whole tree harvesting. With current concerns over increasing carbon dioxide (CO2) levels in the atmosphere, the effects of forest practices such as liming on carbon (C) cycling in forest ecosystems has been receiving increasing attention. This laboratory study investigated the effect of an increase in pH on dissolved organic matter (DOM) in water extracts of organic horizons. Organic horizons were collected from nine forested sites, some predominantly hardwood and some predominantly softwood stand types. The soils were chemically characterized. Water extracts of limed and unlimed treatments of nine organic horizons were analyzed for pH, Al, Fe, Ca, C, and DOM negative charge density. Total luminescence fluorescence spectra were also obtained for each extract. The addition of lime (CaCO3) to organic horizons caused an average of 55% more C to be released than in unamended samples. Liming caused no significant changes in negative charge density of the DOM. Liming decreased organically-complexed aluminum (Al) and increased organically-complexed Ca. There was a negative correlation between Al concentration of extracts and fluorescence intensity. Chemical changes in the DOM released by liming were suggested by decreased fluorescence emission and excitation wavelengths due to liming. Hardwood samples did not respond differently than softwood samples with respect to DOM concentration, functional group concentration, or spectroscopic characteristics. However, there was a suggestion that particular tree species, such as cedar, may have unique effects on C concentrations and DOM chemistry. Key words: Lime, forest soil, dissolved organic matter, fluorescence

Beschreibung: Despite its importance to the degradation of the land resource, few estimates of soil loss or soil erodibility for water erosion from cropland have been made for the semiarid Brown soil zone of western Canada. To estimate these, we calibrated the event-based Modified Universal Soil Loss Equation with measured sediment yield for three 5-ha fields near Swift Current, Saskatchewan. The calibration used predetermined C, LS, P, and warm-season K factors with all erositivities and the K factors for other seasons optimized. Using this calibrated equation with 31 yr of measured runoff data, mean annual sediment yield for a conventional-tillage spring wheat-fallow cropping system on an undulating landscape (0 to 5% slopes) was estimated to be 0.8 Mg ha−1 yr−1. Estimated erosion from fallow land from 16 March to 15 April constituted 86% of the mean annual sediment yield. Erosion occurring during rainfall-runoff were relatively unimportant, accounting for about 4% of the estimated total sediment yield. An exceptionally severe rainstorm was predicted to have caused erosion of many Mg ha−1but the frequency of such events on a given field is too low to greatly affect mean annual erosion. Apparent field-scale soil erodibility was least in the winter (November to 15 March) when the soil would typically be frozen to the surface and was greatest in April when the soil would typically be partially frozen. Apparent erodibility in the summer and in late March was intermediate between those values. Key words: Erosion, runoff, snow, Universal Soil Loss Equation

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

Beschreibung: Field studies conducted throughout the calendar year are needed to improve flux estimates for the greenhouse gas nitrous oxide (N2O). In this study, we report monthly N2O emissions measured using micrometeorological techniques and a Tunable Diode Laser Trace Gas Analyzer (TDLTGA). Nitrous oxide fluxes were measured at the Elora Research Station (20 km north of Guelph, Ontario) from July to November 1992, and from March 1993 to February 1995, giving a total of 2445 daily averages obtained during the full length of the experiment. The soil at the experimental site was a Conestogo silt loam (Gleyed melanic brunisol). Several fields were monitored including fallow, manured fallow, Kentucky bluegrass, alfalfa, barley, canola, soybeans and corn plots. Spring thaw emissions from fallow or ploughed plots measured from March to April ranged from 1.5 to 4.3 kg N ha−1, corresponding to approximately 65% of the total annual emission. Similar effects were not observed on the vegetated (alfalfa and grass) plots. The lowest total annual N2O emissions were measured for second year alfalfa (1 kg N ha−1 yr−1) and bluegrass (0 to 0.5 kg N ha−1 yr−1). Higher annual emissions (2.5 to 4.0 kg N ha−1 yr−1) were observed for corn, barley, canola, and fallow plots. Highest annual emissions were measured after addition of nitrogen in the form of animal manure on a fallowed plot (5.7 to 7.4 kg N ha−1 yr−1), and alfalfa residue by fall-ploughing (6.1 kg N ha−1 yr−1). Plot management during the previous year affected N2O emissions, particularly on the soybean plot (5.9 kg N ha−1 yr−1) that followed a manured fallow treatment. The micrometeorological technique used in this study was successful at quasi-continuous monitoring of N2O fluxes from several plots, and therefore, useful for detecting long-term effects of management on emissions. Key words: Nitrous oxide, N2O fluxes, trace gases, agriculture, greenhouse gases

Beschreibung: Losses of total sediment phosphorus, total sediment nitrogen and dissolved nitrite, nitrate and ammonium resulting from natural rainfall erosion were studied in southern Manitoba during the summers of 1988–1990. Soils used were a Gretna clay, Leary sandy loam, Ryerson sandy clay and a Carroll clay loam. "Standard" erosion plots, i.e 22.13 m slope length, 4.6 m wide on a 9% slope were used. Crop management systems were 1) alfalfa, 2) corn, 3) wheat – minimum tillage, 4) wheat – conventional tillage, and 5) fallow. Nutrient losses averaged over the study period were greatest from the corn and fallow treatments, as high as 160 kg ha−1 yr−1 for nitrogen and 70 kg ha−1 yr−1 for phosphorus. Losses from wheat were intermediate. Losses from alfalfa were negligible. Most of the nutrient losses occurred with the sediment fraction, a result consistent with previous studies. Thus, nutrient loss can be estimated from a knowledge of soil loss. The amount of nutrient loss per unit soil varied with soil, and was a function of the inherent nutrient status of the soil. Key words: Nitrogen, phosphorus, rainfall erosion, nutrients

Beschreibung: We present a calculation for soil microbial biomass N:C ratio determined from a 10-d incubation following chloroform fumigation. The calculation is based on a mathematical model of the N content of the pre- and post-fumigation soil microbial biomass and the growth yield of the biomass that develops after fumigation. Biomass N is calculated from the N:C ratio and biomass C. The mineralization of bacteria and fungi, with different N contents, added to fumigated soils was used to establish the model parameters. The model was tested against an independent set of measurements and considers two assumptions: 1) The ratio of N:C mineralized from killed biomass is equal to the ratio of N:C mineralized from soil non-biomass constituents. 2) More realistically, the N and C mineralization in the fumigated soil, from sources other than killed biomass, is a residual fraction of the N and C mineralization in the unfumigated soil. Biomass C:N ratios calculated without a control correction (assumption 1) were, on average, 20% wider than corrected values (assumption 2). Biomass N calculated as the product of N:C and biomass C was compared with published values for several data sets. The new calculation method was robust even when net immobilization of N followed fumigation. Key words: Soil microbial biomass, nitrogen, chloroform fumigation, C:N ratio

Beschreibung: A study was conducted on a 4-m-high ridge in southwestern Saskatchewan to determine the relationship of slope position with the soil water regime and spring wheat (Triticumaestivum L.) production and to determine if those relationships were altered by subsoiling. In all years, available soil water in the spring to 120 cm increased significantly with distance upslope. This pattern was attributed to residual subsoil water in the rooting zone that had not been used by previous crops in a long-term crop-fallow rotation. After 3 yr of annual spring wheat production, soil water to 1.2 m at all slope positions approximately equalled the water content wilting point (4.0 MPa) water content, showing this residual water had been largely consumed. Apparent use of soil water between seeding and harvest at the upper slope positions was equal to or greater than that at the lower slope positions. Over-winter soil water conservation, using tall (≥ 30-cm-high) wheat stubble for snow trapping, at the upper slope positions was equal to or greater than that at the lower slope positions. In the non-drought years of 1987 and 1989, wheat yields and crop water use efficiency increased significantly with distance downslope. Since these slope effects were not related to water use or availability, they were attributed to higher soil productivity, probably related to more historical net erosion with distance upslope. During the drought year of 1988, wheat yields and water use efficiency were greatest at the upslope positions, but these results were confounded by uneven crop emergence. Subsoiling to 35 cm or deeper increased the amount and depth of infiltration of water in years with near-average November–April precipitation. Subsoiling had little effect on wheat yields and no effect on crop water use. Key words: Landscape, wheat, productivity, soil moisture

Beschreibung: Non-irrigated corn (Zea mays L.) produced on coarse-textured soils during droughty years can result in excess NO3 available for leaching. To evaluate the effect of overseeding cereal rye (Secale cereale L.) into corn on yields, NO3 leaching and a pre-sidedress nitrate test (PSNT), we broadcast rye seed (Aug. 1993, 1994 and 1995) into conventional tillage (CT) and no-tillage (NT) corn receiving six fertilizer N rates. There was no corn yield penalty with the cover crop. Corn grain yields and the extent to which NO3 leaching was reduced by the rye cover depended on rainfall. With the rye (compared with no rye) subsoil solution NO3 concentrations were: unchanged (fall 1994) following above normal rainfall and corn yields; reduced by 8 mg NO3N L−1 (fall 1995) following intermediate rainfall and yields; and reduced by 28 mg NO3-N L−1 (fall 1993) and 11 mg NO3-N L−1 (spring 1994) following the driest growing season (average of CT and NT). Improved N availability with the rye was detected by a PSNT under CT, but not under NT. Therefore sidedress N rates can be adjusted for release of rye residue-N under CT, and potential NO3 contamination of groundwater can be reduced by overseeding winter rye into both CT and NT corn systems. Key words:Zea mays, Secale cereale, pre-sidedress nitrate test, tillage, nitrogen fertilization

Beschreibung: Previous field research in Alberta has suggested that denitrification occurs mostly when soil thaws in the spring, with associated soil water saturation. Our objective was to determine if denitrification and N2O emission in fact take place in cold, thawing soil in the field. Denitrification and N2O flux were measured in two springs and the intervening summer. Cylinders were placed in soil in November, 1988, and 57 kg N ha−1 of 15Nlabeled KNO3 was added. Soil 15N mass balance technique showed 23 kg N ha−1 of added-N was lost by 15 May 1989. Gas trappings were made (28 March to 29 April) and nearly all of the N2O emission (3.5 kg N2O-N ha−1) occurred during an 11-d period of thaw. The accumulated N2O flux from 20 June to 31 August was small (0.5 kg N2O-N ha−1, or less); during that time there were no rainfall events intense enough to produce water saturated soil. In 1990, 15N-labeled KNO3 (100 kg N ha−1) was applied on 26 March (outset of the thaw) and mass balance showed 32.7 kg N ha−1of added-N was lost by 7 May. A flux of 16.3 kg N2O-N ha−1 occurred largely in a 10-d period during and immediately after soil thaw. The N2O emitted from soil left a considerable fraction of the lost N unaccounted for. This unaccounted N was most likely lost as gaseous N other than N2O (e.g., N2). We conclude that large amounts of soil nitrate may be denitrified, with smaller amounts emitted as N2O, as the soil thaws and soon thereafter. Key words: Denitrification, frozen soil, thawing soil, nitrogen, nitrous oxide

Beschreibung: The development of sound management approaches to reduce soil organic carbon (SOC) losses presupposes that we thoroughly understand the sources of these losses. We used a landscape-scale research design to estimate human-induced SOC losses by comparing SOC storage in undisturbed landscapes with comparable landscapes disturbed by clear-cutting of forests in the Mixedwood/Gray Luvisolic zone of central Saskatchewan and by agricultural activity in the Black soil zone. A 14.0% decrease in soil organic carbon storage in the upper 45 cm of the soil (from 57.1 Mg ha−1 in mature Mixedwood sites to 49.1 Mg ha−1 in clear-cut landscapes) occurred due to clear cutting at the research sites in the Mixedwood forest. The dominant soil type at these sites, Gray Luvisolic soils developed in glacial till, experienced a 11% loss in SOC storage; higher losses (36% loss) occurred from sandy Brunisolic inclusions in the sites. Changes in SOC storage at the research sites in the Black soil zone landscapes varied with texture and parent material: sandy glacio-fluvial landscapes experienced slight gains of SOC (from 54.1 to 60.1 Mg ha−1); silt and clay glacio-lacustrine landscapes experienced a 15.3% decrease in SOC (from 145.2 to 122.9 Mg ha−1); and loamy glacial till landscapes underwent a major decrease in SOC storage (from 116.2 to 75.2 Mg ha−1) Our results indicate that attempts to increase SOC storage in Saskatchewan soils should concentrate on agricultural landscapes, especially those dominated by glacial till. Key words: Landscape, soil organic carbon, Chernozemic, Mollisol

Beschreibung: Nitrous oxide (N2O) produced from agricultural activities represents a threat to the ozone layer and economic losses. Rates and magnitudes of N2O emissions of cropping systems must be determined to establish corrective management procedures. In 1994, N2O emissions were determined with corn (ZeaMays L.) and corn-legume rotations. Continuous corn was studied on four soils, two from a long-term experiment, a Ste. Rosalie heavy clay (Humic Gleysol) and a Chicot sandy loam (Grey-Brown Podzol), at 0, 170, 285 or 400 kg N ha−1, and two from a corn rotation study, a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Treatments included no-till (NT) and conventional tillage (CT), monoculture corn (CCCC), monoculture soybean; corn-soybean; and soybean-corn-alfalfa phased rotations. Nitrogen rates of 0, 90, or 180 kg N ha−1 for corn and 0, 20, or 40 kg N ha−1 for continuous soybean were used, and soybean/alfalfa following corn no fertilizer N. Rates of N2O emission were measured from closed chambers through the growing season. About 0.99 to 2.1% of N added was lost as N2O. Nitrous oxide emission increased with increased soil water content, NO3 concentration and fertilizer N rates. Emission of N2O was higher with NT than with CT, and with corn than with soybean or alfalfa. A corn system using CT, legumes in rotation and moderate fertilizer N would reduce N2O emission. Key words: Greenhouse gases, soil nitrate, tillage methods, water-filled pore space, denitrification, rotations

Beschreibung: An Acadia silty clay and a Pugwash sandy loam were each fertilized with three rates of either composted chicken manure, fresh chicken manure, or synthetic fertilizer. The effects of these amendments on soil microbial activity (dehydrogenase enzyme activity, DHA), organic C and pH were monitored. The sandy loam soil, which was relatively high in organic C, did not experience increases in DHA due to organic amendments while compost produced higher DHA than manure or fertilizer treatments to the silty clay soil. There was no treatment effect on soil organic C in the sandy loam, while organic treatments increased organic C in the silty clay soil. Soil pH was affected by treatments to both soils with compost amendments producing the greatest increases in this parameter. The results emphasize the importance of considering initial soil organic C and soil texture when planning studies of the effect of organic amendments on soil microbial activity. Key words: Dehydrogenase, compost, chicken manure, pH, soil organic carbon

Beschreibung: A kinetic expression for oxygen, nitrate, nitrite and nitrous oxide reduction in soil was developed. The formulation was based on competitive Michaelis-Menten kinetics for a steady microbial population whose respiratory activity was assumed to be constant so that the number of electrons produced per unit of time was constant. Competition among the electron acceptors was characterized by their affinity toward the electron and by their concentration. Several different values for the affinity coefficients were used to simulate the concentration of O2, NO3−, NO2−, N2O and N2 at various times. When relative magnitudes of affinity coefficients were chosen to be 100 000, 1, 100 and 0.1, for O2, NO3−, NO2− and N2O, respectively, the temporal plot of concentration showed that the disappearance of O2 and NO3− was zero order. The accumulation of NO2− was very small and it was rapidly reduced to N2O. The production rate of N2O was nearly zero order but the magnitude of the rate was rather small as opposed to the rate of disappearance of NO3−. The reduction of N2O to N2 took place only after NO3− had almost disappeared. With these competition parameters NO3− was stable in the presence of O2. The reduction of N2O was also very much retarded in the presence of NO3−. NO2− was relatively unstable, even in the presence of O2, and it was further reduced to N2O. With the relative magnitude of the chosen affinity coefficients, the kinetic formulation effectively simulated the "inhibitory" effect of O2 upon the denitrification process, and the "inhibitory" effect of NO3− and NO2− upon the reduction of N2O to N2. Key words: Oxygen consumption, denitrification, kinetics, competition

Beschreibung: This study examines three methods of evaluating N2O flux and accumulation in soil profile over a growing season under three soil management regimes (fallow, fallow with manure addition and cropped to alfalfa). Estimates of N2O flux were made based on measured soil atmosphere concentration gradients in the top 15 cm and compared to flux estimates based on ex situ cores and micro-meteorological measurements made in parallel studies. All methods indicated strong seasonal trends relating to precipitation events. The amounts of N2O accumulating the profile decreased in the order alfalfa 〈 fallow 〈 fallow/manure. The amounts of N2O accumulating in the profile ranged from ambient (0.35 µL L−1) to 490 µL L−1. Diffusion of N2O to the lower profile was shown to provide temporary storage of N2O and thereby provide the opportunity for further reduction to N2 prior to efflux from the surface. In comparing the estimates of surface flux, all three methods were of the same order of magnitude for the fallow site but profile-based estimates were much lower and much higher for fallow/manure and alfalfa sites, respectively. Differences were attributed to the location and timing of carbon addition in each system. Key words: Nitrous oxide, N2O, flux, measurement, soil, management

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

Beschreibung: Soybean (Glycine max L. Merill) can produce high-N residues that may benefit subsequent corn (Zea mays L.) production, but the degree of benefit is often unpredictable and may be related to tillage methods. This study investigated the effects of conventional-tillage (CT) and no-tillage (NT) on fertilizer replacement values for corn in a corn-soybean rotation. Field experiments were conducted for two growing seasons on two soils, a Ste. Rosalie clay (Humic Gleysol), and an Ormstown silty clay (Humic Gleysol). Continuous corn, corn following soybean, soybean following corn, continuous soybean, and three levels of fertilizer N (0, 90, 180 and 0, 20, and 40 kg N ha−1 for corn and soybean, respectively) were compared. Tillage did not effect yield or N uptake consistently. Corn grain yields and N uptake were greater following soybean than following corn. Soybean provided N fertilizer credits ranging from 40 to 150 kg N ha−1, which was greater than the residual NO3 in the soil prior to planting. Credits were greater in the year with higher corn yields and lower previous winter precipitation resulting in greater NO3 carryover. Tillage effects on N credits from soybean differed between the sites. Consequently, N contributions of soybean to corn could not be related to tillage method or soil type. Key words:Zea mays L., Glycine max L. Merill, rotations, grain yield, N uptake, tillage, fertilizer N

Beschreibung: Long-term mineral fertilizer applications could reduce organic matter (OM) levels in soil if coupled with crop rotations with low organic residues inputs. The main objective of this study was to evaluate the C and N contents in whole soil, in densimetric OM fractions and in different aggregate size fractions of a Le Bras silt loam (Humic Gleysol). The treatments were arranged in a split-plot design, with dairy cattle manure applied at 0 and 20 Mgha−1 as the main factor. The subplots consisted of six fertilizer treatments (NK, PK, NP, NPK, NPKMg and the unfertilized check). The four year rotation included silage corn, (Zea mays L.) silage corn, wheat (Triticum Aestivum L.) and barley (Hordeum vulgaris L.). Contrary to mineral fertilizer, long-term manure applications significantly increased the C content in whole soil and also in the light and heavy fractions of OM (Fl and Fd). Mineral fertilizer significantly increased the C and N contents only in Fl. Moreover, manure application also increased the weight of the 5–8 mm aggregate size fraction and the C and N content in the 5–8 mm, 2–5 mm, 1–2 mm and 0,25–1 mm aggregate size fractions, compared to mineral fertilizer alone. In manured plots, soil C biomass, microbial respiration (CO2) and N mineralization (NO3) levels increased by 30% compared with mineral fertilizer treatments. Results of this study demonstrate the important effect of manure applications on C and N enrichment in soil and also on soil macroaggregation and biological activity. To maintain optimal C and N levels in soil and to favour soil macroaggregation, long-term mineral fertilizer application should be combined with crops in rotations which ensure high organic residues returns to soils. Key words: Macroaggregation, microbial biomass, N mineralization, long-term, light fraction, heavy fraction

Beschreibung: Soil nitrogen (N) and phosphorus (P) supply is one of the growth limiting factors in many forest ecosystems. Seasonal patterns in soil N and P supply rate were examined during a 2-yr period (1994–1995) for forest floor (L, F and H) and upper mineral (Ae) horizons in an 80-yr-old aspen forest in Saskatchewan, Canada. Accumulation of plant nutrient ions on ion exchange resins incubated in the field can provide an estimate of nutrient supply rate in soils because ion exchange resins have the potential ability to simulate nutrient flux to plant roots. Nutrient supply rates and the effect of plant uptake on nutrient supply rate was assessed using ion exchange membranes buried inside and outside polyvinyl chloride (PVC) cylinders. The difference between ion flux to the membranes inside (root uptake excluded) versus outside the cylinders was used as an index of plant nutrient uptake. From May to October, nutrient uptake (µg 10 cm−2 2 wk−2) by plants ranged from 1.6 to 31.7 (NO3−-N), from 2.7 to 13.7 (NH4+-N) and from 2.6 to 12.7 (P), with maximum N and P uptake in summer. Nutrient uptake by plants also varied among horizons. In general, plant uptake of NO3−-N, NH4+-N and P was highest in the H horizon, followed by the F and Ae horizons, with lowest uptake apparent in the L horizon. The results are consistent with the distribution of plant fine roots: most were found in the H horizon (68%), followed by the Ae and F horizons (15%), and the L (2%) horizon. Autumn litterfall represented a nutrient return of 28–40 kg N ha–1 and 4–7 kg P ha–1 to the forest floor which coincided with an increase in ion supply rates in the forest floor. During the growing season, atmospheric inputs via bulk deposition and throughfall contributed small amounts of N (1.8 kg NH4+-N ha–1 and 0.23 kg NO3–-N ha–1) and P (1.38 kg ha−1 inorganic P) to the forest floor. Recycling of nutrients by litterfall and subsequent mineralization and re-assimilation by plant roots in the forest floor is a dynamic and important component of nutrient cycling in boreal aspen forest ecosystems. Key words: Forest floor, ion exchange membranes, nutrient supply

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

Beschreibung: We need an easy-to-use chemical index for estimating the amount of N that becomes available during the growing season, to improve N use efficiency. This paper discusses how producers may, in future, use crop growth models that incorporate indices of soil N availability, to make more accurate, risk-sensitive estimates of fertilizer N requirements. In a previous study, we developed an equation, using 42 diverse Saskatchewan soils, that related potentially mineralizable N (N0) to NH4N extracted with hot 2 M KCl (X), (i.e., N0 = 37.7 + 7.7X, r2 = 0.78). We also established that the first order rate constant (k) for N mineralization at 35°C is indeed a constant for arable prairie soils (k = 0.067 wk−1). We modified the N submodel of CERES-wheat to include k and N0 (values of N0 were derived from the hot KCl test). With long-term weather data (precipitation and temperature) as input, this model was used to estimate probable N mineralization during a growing season and yield of wheat (grown on fallow or stubble), in response to fertilizer N rates at Swift Current. The model output indicated that the amount of N mineralized in a growing season for wheat on fallow was similar to that for wheat on stubble, as we hypothesized. Further the model indicated that rate of fertilizer N had only minimal effect on N mineralized. We concluded that, despite the importance of knowing the Nmin capability of a soil, it is available water, initial levels of available N and rate of fertilizer N that are the main determinants of yield in this semiarid environment. The theoretical approach we have proposed must be validated under field conditions before it can be adopted for use. Key words: N mineralization, Hot KCl-NH4-N, potentially mineralizable N, CERES-wheat model

Beschreibung: Spring soil nitrate and ammonium dynamics in south coastal British Columbia soils were examined with respect to the potential to develop a soil nitrate test for silage corn (Zea mays, L.). Soil nitrate and ammonium contents were measured to 90 cm depth in two soils from April to July of two growing seasons. Treatments included a control, spring application of either 300 or 600 kg total N ha−1 as liquid dairy manure, or 200 kg N ha−1 as inorganic fertilizer. Significant amounts of ammonium were present until late May following manure and until mid-June following fertilizer application, requiring simultaneous determination of both nitrate and ammonium concentrations to assess soil inorganic N contents during this period. Most of the changes in soil nitrate over time occurred in the top 30 cm, suggesting that sampling to 30 cm depth would be sufficient in most cases for a soil nitrate test in this region. Most of the increase in soil inorganic N associated with the spring application of manure occurred by 1 June. A soil nitrate test in early to mid-June when the corn is at the six leaf stage appeared to be most suitable for use in south coastal British Columbia to determine if additional fertilizer N is required. A sample taken at this time will measure soil nitrate contents just before the period of rapid corn N uptake, after most of the additional inorganic N associated with spring manure application is already present in the soil as nitrate, and after nitrification of the manure ammonium has occurred. Key words: N recovery, preplant nitrate test, pre-sidedress soil nitrate test

Beschreibung: An insight into sulphate (SO42−) retention by podzolic and brunisolic soils was obtained by examining SO42− sorption by B horizons from forest soils in northeastern Ontario. The amount of water soluble and adsorbed SO42− present in the soils and the ability to adsorb additional SO42− was evaluated. Relationships between soil pH, organic carbon and different iron (Fe) and aluminum (Al) fractions with water soluble and adsorbed SO42− were examined. Using a surface complexation approach, modelling was carried out to predict the soil SO42− sorption capacity at any given pH. The potential SO42– adsorption capacity was also measured by applying adsorption equations. Both the Freundlich and Langmuir sorption isotherms gave comparative fits to the SO42− adsorption data. The soils contained small amounts of water extractable SO42− (0.1 to 0.8 mmole kg–1). There was a significant positive correlation between water extractable SO42− and organic carbon in the podzolic soils but not for the brunisolic soils. Approximately 90% of the sulphate extracted was contained in the insoluble SO42− fraction. Sulphate sorption by both soil types was most closely related to amorphous inorganic Al. In brunisolic soils, total adsorbed SO42– also had a strong positive correlation with the oxalate extractable silica fraction and a negative correlation with pH. Sulphate adsorption simulations were close to the measured values. Key words: Soluble SO42−, adsorbed SO42−, Podzol, Brunisol, amorphous Al oxide, SO42− adsorption model

Beschreibung: In order to predict the potential of soils to store carbon in response to land use or climate changes, we measured the fluxes and distribution of residence times of C in French cultivated soils. We used the natural abundances in 13C and 14C to measure this distribution in long-term experiments of maize cultivation in France. 75% of the topsoil carbon had a mean residence time of 40 yr. Coarse particle-size fractions contained most of the younger carbon. A compartment of stable C was estimated using radiocarbon dating. Belowground plant material inputs stored as much as C as aboveground inputs. The effect of temperature on soil carbon mineralization affected only rate constants, with a Q10 = 3.1 constant in the range 1–25 °C. The data were summerized in a simple simulation model, which predicted a nil or low effect of climatic change on soil carbon storage in the next 50 yr. In France, land use changes will have more influence than atmospheric changes on C storage. Key words: France, greenhouse gases, mineralization, model, soil carbon, storage, temperature

Beschreibung: Thermal conductivity was measured with thermal probes in undisturbed mor samples subjected to water desorption and sorption. The volumetric water content was determined simultaneously with time domain reflectometry. The thermal conductivity increased from 0.06 to 0.24 W m−1 K−1, when the water content increased from 0.10 to 0.40 m3 m−3. There was little spatial variation in the mor layer. The results were similar to those found in the literature for peat and humus materials. The thermal conductivity of the mor layer could be predicted with the de Vries model with good accuracy if the humus and air particles were assumed to be of lamellae shape and latent heat transport in air-filled pores was neglected. Key words: humus, thermal probe, thermal properties, time domain reflectometry

Beschreibung: Water erosion due to snowmelt is a major form of erosion in boreal regions of the Canadian Prairie. Evaluation of erosion models is an essential step before recommending their use in local or regional assessments of erosion rates and control methods. Using inputs from a runoff study conducted at La Glace, Alberta (55°25'N, 119°10'W) from 1984 to 1986, we evaluated the Erosion-Productivity Impact Calculator (EPIC) for its ability to simulate runoff and sediment yield from snowmelt events. The model was initialized with soil profile data acquired at the study site and complemented with data from standard soil databases (Albright series; loam, Dark Gray Chernozem). Daily weather data were acquired from the nearest climatological station (annual precipitation = 475 mm). Management data were as reported and included combinations of conventional and reduced tillage, annual and perennial, and fallow cropping. Mean runoff volume measured in 1985 was 57 mm while in 1986 it was 76 mm. EPIC over-predicted runoff volume by 25% in 1985 but under-predicted it by 7% in 1986. The period in which snowmelt occurred (mid-March – beginning of April) was predicted correctly. Under the conditions of this study, with many cropping inputs obtained from different sources, the model was unable to reproduce the reported management effects on runoff and sediment yield. EPIC simulated springmelt soil temperature trends at 9-cm depth, although the predicted temperatures in 1985 were generally underestimated. Our results suggest that the EPIC model calculates adequate values of runoff volumes and sediment yields during snowmelt. Key words: Runoff, sediment yield, soil erosion, crop rotations

Beschreibung: The real contribution of composts to N availability depends on their characteristics and maturity. A laboratory incubation experiment (140 d) was conducted parallel to a greenhouse study (330 d) in a split-split-plot design, with, respectively, two peat rates (0, 20 gkg−1 soil), five manure composts and four compost rates (0, 250, 500 and 750 gkg−1 soil). Compost N mineralization, orchardgrass (Dactylis Glomerata L.) yield and N uptake were measured. Total amount of mineralized N and yields and N uptake for six cuts of orchardgrass varied significantly with the type of composts and rate. Peat addition temporarily decreased compost N mineralization rate but significantly increased orchardgrass yields and N uptake as compared to peatless treatments. Mineralized N represented

Beschreibung: Complete loss of topsoil resulting from erosion or other causes generally results in reduced crop yield. To determine, under dryland conditions, the effect of loss of various amounts of soil and of various amendment practices suitable for use under a cereal production program on soil properties and crop yields, a field was artificially eroded during cut and fill of land-levelling in 1957. Continuous cropping to barley for 7 yr was followed by a wheat-fallow rotation for 22 yr. A continuous wheat experiment was conducted from 1987 to 1991 to determine the effects of five fertility amendments on restoring the productivity to soil from which 10–20 cm and 46+ cm of soil had been removed. In 1990, a below-average precipitation year, after 33 yr and 23 crops, yields from the unfertilized 46+ cm eroded field were only 44% of the yields from the uneroded field. However, with the increased precipitation in 1991 this value was 66%. A one-time topsoil amendment was beneficial in the earlier stages of the experiment, but lost its effect as cultivation mixed it into the "subsoil" over time. Plot treatments with annual applications of manure and high rates of fertilizer generally out-yielded the yields of the check plots of the uneroded treatment. Amendment with straw + fertilizer was not very effective. Soil, once lost, is non-renewable without amendments within the working lifetime of the producer. Key words: Soil erosion, manure, commercial fertilizer, topsoil soil, productivity

Beschreibung: Current interest in carbon (C) exchange processes between terrestrial ecosystems and the atmosphere have identified a need to assess soil C stocks or inventories for specific soil types and climates. In this study, the mean store of C and nitrogen (N) was determined in the soil profile of several Gleysolic, Podzolic, Luvisolic, and Brunisolic soils under different agricultural management systems, in the cool, humid region of eastern Canada. Based on a total of 69 management treatments from 16 agroecosystem sites, mean soil C and N densities (to a soil depth of 60 cm) ranged from 3.1 to 13.1 kg C m−2 and from 0.36 to 1.05 kg N m−2 The C:N ratio ranged from 8.3 to 17.1. Distribution of C and N down the soil profile showed a relatively regular pattern of C and N decrease with depth. Estimated C stocks or storage for the 1-m soil depth ranged from 8.3 to 13.3 kg C m−2 for the Gleysolic soils, and 5.4 to 10.5 kg C m−2 for the Podzolic soils, with an overall range and mean for all soils of 3 to 16 kg C m−2 and 9.8 kg C m−2 ± 2.8 This indicates that some agricultural soils in eastern Canada possess a relatively high potential for organic matter storage. Key words: Organic carbon and nitrogen storage, agroecosystem, Gleysol, Podzol, Luvisol, Brunisol, cool-humid climate

Beschreibung: In a greenhouse study, deinking sludge was evaluated as a soil amendment supplemented with four nitrogen (N) fertilization levels for the growth of the grasses Agropyron elongatum (Host.) Beauv. (tall wheatgrass), Alopecurus pratensis L. (meadow foxtail), Festuca ovina var. duriuscula (L). Koch (hard fescue), and four levels of phosphorus (P) for the growth of the legumes Galega orientalis Lam. (galega), Medicago lupulina L. (black medic), Melilotus officinalis (L.) Lam (yellow sweet clover). Fertilizers were applied on the basis of sludge level to maintain uniform carbon (C)/N or C/P ratios across sludge treatments. In one experiment, sand was mixed with 0, 10, 20 or 30% sludge while, in a second experiment, mineral soil was mixed with 0, 27, 53 or 80% sludge (vol/vol). In sand mixtures of 30 and 20% sludge, grasses had similar or greater growth than in unamended mineral soil when N was added at about 6.5 and 8.4 g kg−1 deinking sludge, respectively. For all legumes but Medicago lupulina, P at about 0.8 g kg−1 sludge was required for these sand mixtures. In soil mixtures of 53 and 27% sludge, grasses grew well when supplemental N was about 5.3 and 6.9 g kg−1 sludge, respectively. Legumes required P at 0.5 and 1.2 g kg−1 sludge, respectively. In general, growth was closely related to total amount of added N or P in spite of the wide range of C/N or C/P ratios. When growing in media amended with sludge, grasses needed higher tissue N concentration for an equivalent growth than in control soil; legumes had similar tissue P concentration. The grasses Agropyron elongatum and Alopecurus pratensis as well as the legumes Melilotus officinalis and Galega orientalis are promising species for field testing, based on dry matter production. Deinking sludge can be used as soil amendment when adequate N and P supplements are provided. Key words: Soil amendment, papermill sludge, Agropyron elongatum, Alopecurus pratensis, Festuca ovina, Medicago lupulina, Galega orientalis, Melilotus officinalis

Beschreibung: Cation exchange capacity (CEC) data provide information on important chemical attributes of soil (e.g., ability of soil to retain cations against leaching and to buffer pH). Measurements of CEC are expensive to perform. Further, since CEC is dependent on measurement pH, CEC data are difficult to interpret, especially in the case of soils whose field pH is far removed from measurement pH. We analyzed a large data set (n = 1622), collected in support of soil survey activities in Saskatchewan, to develop a method of estimating CEC as a function of pH and to establish relationships between soil buffer capacity and properties such as texture and organic matter content. A regression equation with organic C and clay as independent variables explained 86% of the variability in CEC measured using BaCl2 buffered at pH 8.2. The CECs (at pH 8.2) of organic matter and clay were estimated at 2130 and 510 mmol (+) kg−1, respectively. About 15% of exchange sites were not accounted for by organic matter and clay and were assumed to reside in the fine silt fraction. The CEC at field pH, i.e., effective CEC (ECEC), was described (R2 = 0.86***) by a function based on the assumption that the ECECs of organic matter and clay increase linearly as pH increases to 8.2, where their values are 2130 and 510 mmol (+) kg−1, respectively. This relationship is especially useful because it enables soil CEC to be estimated at any pH based solely on organic matter and texture. Soil buffer capacity values were obtained by estimating the change in soil ECEC (or titratable acidity) needed to produce a unit change in pH. Buffer strength of clay was low [∼30–50 mmol (±) kg−1 (pH unit)−1]. Our estimates of organic matter buffer capacity [∼400 mmol (±) kg−1 (pH unit)−1] were consistent with published values. The results suggest that prairie soils that are low in organic matter may be susceptible to acidification even if clay content is relatively high. Key words: Buffered CEC, effective CEC, pH dependence of CEC, buffer capacity, titratable acidity

Beschreibung: The distribution of Cd with depth, its particulate-bound speciation and availability index were studied in nine typical soil profiles of Saskatchewan, Canada. In the Ap horizons, Cd was predominantly in the metal-organic complex-bound form, accounting for about 38.8%, on average, of the total Cd present in the soils. The carbonate-bound Cd and the metal-organic complex-bound Cd accounted for 33.5 and 12.9%, respectively, on average, of the total Cd present in the B horizons. In the Ck horizons, Cd was predominantly in the carbonate-bound form, accounting for about 70.9%, on average, of the total Cd present in the soils. The M NH4Cl-extractable Cd of the soils, which is a measure of availability index of soil Cd, generally decreased with depth. Statistical treatment of the M NH4Cl-extractable Cd with different particulate-bound Cd species of various horizons in the soil profiles showed its highest correlation (P = 2.0 × 10−9, n = 42) with the amount of the metal-organic complex-bound Cd species, indicating the importance of the metal-organic complex-bound Cd species in Cd availability to the plants. Key words: Cadmium, soil profile, speciation, availability index, metal-organic complexes

Beschreibung: Hydraulic conductivity in the mor layer of a Scots pine (Pinus sylvestris L.) stand was measured in undisturbed samples using the constant-head permeameter and instantaneous-profile method. Saturated hydraulic conductivity (Ks) averaged 2.9 × 102 m d−1. With a decrease in matric potential (ψ) from −4 kPa to −70 kPa the unsaturated hydraulic conductivity (K(ψ)) decreased from 3.1 × 10−3 to 1.1 × 10−8 m d−1. Ks and K(ψ) were similar to those reported in the literature for low-humified peat. The variation in hydraulic conductivity within a stand of Scots pine at a given matric potential was large, ranging from one to two orders of magnitude. Key words: F horizon, humus, hydraulic properties of soil

Beschreibung: Soil respiration is an important component of the net carbon dioxide exchange between agricultural ecosystems and the atmosphere, and reliable estimates of soil respiration are required in carbon balance studies. Most of the field measurements of soil respiration reported in the literature have been made using alkali traps. The use of portable CO2 analysers in dynamic closed chamber systems is recent. The introduction of this new technique requires its evaluation against existing methods in order to compare new information with older data. Nine intercomparisons between dynamic systems and alkali traps were made. Measurements of Fc,s obtained by both chambers showed a good agreement in all but two comparisons in which alkali trap measurements were lower than the dynamic chamber by about 22%. This first report of agreement between both techniques suggests that many measurements made in the past using alkali traps may be comparable to the measurements made more recently using the dynamic chambers. Analysis of the soil temperature and CO2 concentration inside the alkali traps failed to explain why the alkali traps occasionally underestimated the fluxes. Soil respiration measured with a dynamic closed chamber were also compared to eddy-correlation measurements. The results did not reveal any consistent bias between techniques but the scattering was large. This dispersion is likely the result of the difference between the areas measured by the two techniques. Key words: Carbon dioxide, greenhouse gases, CO2 flux, soil carbon

Beschreibung: The recurrence of agricultural drought on the prairies has increased the demand for soil moisture information by farmers, regional planners and supporting sectors of agriculture. In response, estimation of regional soil moisture by soil survey is conducted despite its being resource intensive and having limited resolution in time and space. Models that estimate soil moisture on a regional scale would contribute to the evaluation of regional water deficits and overcome problems related to conducting field surveys. This study uses a modified version of the versatile soil moisture budget to estimate available soil moisture within the root zone on a regional scale. The spatial pattern of modelled soil moisture in the fall was similar to that mapped by soil survey. Of the 145 grid points compared, agreement between modelled and field survey was 60% or higher in 5 out of 8 yr. However, too few years of data were available for a reliable assessment of model performance in the spring. The simulated soil moisture was sensitive, and directly related to the value used for available water capacity (AWC). Accurate values of AWC are necessary for accurate simulation of regional soil moisture. Key words: Soil moisture, modelling, water capacity, regional estimates, Canadian prairies

Beschreibung: This study shows how the stress manipulations, ammonium sulfate, drought and irrigation changed the P and K status of three soil fractions (bulk soil, rhizosphere and soil-root interface) from E, Bh and Bs horizons of a Norway spruce stand in southwestern Sweden. The results indicate that dynamic linkages exist between the three soil fractions and tree growth. Accumulation rather than depletion of P and K were observed in the vicinity of the roots which we attribute primarily to accumulated organic matter and high rates of mineralization. Relative depletion of P and K around roots resulted from treatments that stimulated tree growth and P and K uptake. The ratio of organic P, the largest extractable P fraction, to inorganic P indicated that organic P is an important P resource when inorganic P is heavily utilized in treatments where growth has increased. There are indications that K supply was reduced by stimulating growth with ammonium sulfate and irrigation, suggesting that K rather than P can become the second limiting factor to growth at this site after N. Key words: Organic matter, available P and K, relative depletion, Norway spruce, ecosystem manipulation, conceptual model, environmental stress

Beschreibung: A vermicompost (VC) from biological sludges was incorporated into two soils, or applied on their surfaces as mulch with the addition of worms (Eisenia foetida) or grass seeds (Lepidium sativum) in the experiments of "living mulch". The purpose of this research was to study the influences of different methods of organic matter application on soil chemico-physical and biochemical properties. Two texturally different soils from a Mediterranean climate, a clayey and a sandy soil, were tested in laboratory-scale experiments. Water-soluble C (WSC), NO3-N/NH4-N ratio (nitrification index), and enzyme activities (BAA-protease, dehydrogenase, and β-glucosidase) were taken as indices of soil biochemical fertility as they are related to soil physical properties and microbial activities. Surface cracking area in both soils increased, with the formation of small–medium (

Beschreibung: Aggregate distribution and stability of surface soil were determined for different cropping systems of a Luvisolic soil in the Peace River region of Alberta. Gray Luvisolic soils have inherent problems that include weak platy structured surface horizons which are underlain by compact sub-soils. The cropping systems consisted of (i) continuous barley (CB) (Hordeum vulgare L.); (ii) barley/forage (BF), 3 yr of barley followed by 3 yr of forage (mixture of bromegrass [Bromus inermis Leyss] and red clover [Trifolium pratense L.]); (iii) continuous grass (CG) (bromegrass); and (iv) continuous legume (CL) (red clover). The barley/forage rotation consisted of two phases, the barley phase (BF) and forage phase (BF). Each phase was present every year. Aggregate separation by dry-sieving with a rotary sieve indicated that the CL cropping system had fewer large aggregates and more small aggregates than the other cropping systems. The CG, BF and CB cropping systems had more larger aggregates and were similar to each other. Wet-sieving, by contrast, resulted in the CG cropping system having greater amounts of large aggregates while the CL, BF phases, and CB cropping systems were similar with more smaller aggregates. Wet-sieving of the different aggregate size fractions from the rotary dry-sieve indicated that the cropping system aggregate stability was in the order of: CG 〉 CL 〉 BF ≥ BF ≥ CB. The stability of the BF cropping system was greater than that of the BF as it had recently come out of the BF phase (3 yr of forage production). Aggregate stability for the cropping system soils was consistent among the evaluation method of wet-sieving and the McCalla water-drop method. Inclusion of forage crops are important in maintaining or improving soil structure of Luvisolic surface horizons. Key words: Luvisolic soil, cropping systems, aggregation, aggregate stability, Peace River region

Beschreibung: Transport equations for O2, NO3−, NO2−, N2O and N2 were formulated to investigate NO3− stability, denitrification and formation of gaseous nitrogen compounds in a soil profile under different moisture and temperature conditions. The source-sink terms of the transport equations, including those for O2, were based upon competitive Michaelis-Menten type kinetics of denitrification. The equations were solved under various soil and seasonal temperature conditions typical of the Prairie Region of Canada in order to explore the effects of these parameters upon predicted NO3− stability, denitrification product distribution in a soil profile and gaseous N fluxes from the soil surface. The depth to the aerobic-anaerobic interface from the soil surface was controlled by temperature, moisture and microbial activity distributions in the soil. The kinetic expressions predicted that NO3− was generally stable under aerobic conditions since the affinity coefficient of O2 for electrons is much greater than that of NO3−. However, nitrate in the anaerobic zone was subject to denitrification to produce N2O and N2. The N2O produced in the anaerobic zone diffused into the aerobic zone where it was stable and eventually emitted to the atmosphere. As the NO3− concentration decreased, a greater proportion of N was emitted to the atmosphere as N2. Thus, the ratio of N2O to N2 emitted from the soil decreased with decreased NO3−. We found that the potential for denitrification to take place in a soil profile was actually greater in late summer than in mid-summer since subsoil temperatures were higher later on in the season. The ratio of fluxes of N2O to N2 was a function of time, moisture content distribution, the depth at which the maximum reduction of NO3− took place, and NO3− concentration. Key words: Transport, denitrification, gas flux, nitrous oxidenot available

Beschreibung: Representative profiles of the Owena, Egbeda, Alagba, and Balogun series were studied. The Owena soil is formed in amphibolite whereas Egbeda and Balogun soils are formed in biotite gneiss derived parent materials. The Alagba soil is formed in sandstone parent rock. The main objectives were to characterize the soils and their clay fraction, and to classify and interpret soil properties for agricultural land use. Most soils exhibit 2.5 YR hues in subsurface horizons. A pedon formed in biotite gneiss has the highest dithionite Fe content and Fed/clay ratio. The relationships between clay content and Fed values vary according to parent material origin and, therefore, would have to be interpreted differently for soil weathering processes. Clay coatings were noticeable in some soil horizons of all pedons studied. Soils are generally medium to slightly acid with sandstone-derived soils being the most acid. The clay mineral suite in all soils is dominated by kaolinite with traces of 2:1 and 2:2 clay minerals, goethite, hematite, anatase, maghemite, and rutile. In addition, some soils contain trace amounts of gibbsite. Kandic horizons have been identified in all soils. The low charge properties of the soils reflect the intensely weathered clay mineral suite. The base status is probably influenced by the cropping system and therefore may tend to unnecessarily differentiate highly weathered soils at the order level. The Egbeda and Balogun series were classified as Rhodic Kandiudults, clayey-skeletal, oxidic and Rhodic Kandiudalfs, clayey-skeletal, oxidic, respectively. Others, Owena, and Alagba series, were classified as Typic Kanhaplohumults, clayey, oxidic and Rhodic Kanhaplustults, fine loamy or clayey, oxidic, respectively. In the FAO-Unesco legend, all soils become Rhodic Ferralsols. In addition, the Owena (with its nitic properties) is further classified as niti-rhodic Ferralsol. The two classification systems are at variance for highly weathered (variable charge property) soils and this difference will definitely influence management decisions depending on which system is used at any particular time. Soil attributes favorable for agricultural use include thick sola and favorable structures. Chemical properties suggest minimal fixation of phosphorus. Key words: Dithionite Fe, kandic, oxidic, variable charge, ferralic, exchangeable Al

Beschreibung: Topsoil depth is an indirect indicator of soil quality and crop productivity. A 2-yr field study was conducted in north-central Alberta with the following objectives: (1) to determine aboveground barley dry matter yield, N uptake, and fertilizer-use efficiency (FUE) in two artificially eroded soils of contrasting properties, and (2) to assess the effectiveness of KNO3 and urea in compensating for lost productivity. Field experiments were conducted on an Orthic Gray Luvisol (Site 1) and on an Eluviated Black Chernozem (Site 2) in 1991 and 1992. The treatments consisted of three depths of topsoil removal (0, 10 and 20 cm) and three N fertilizers (KNO3 and urea at 150 kg N ha−1, and the control). The plots were sown to barley (Hordeum vulgare L.). Yields and N uptake of aboveground barley dry matter decreased with each increment of topsoil removal and were lowest in the 20-cm topsoil removal. Fertilizer N improved yields and N uptake at each depth of erosion. In most of the erosion treatments barley yields and N uptake tended to be greater with KNO3 than with urea. The effectiveness of each N source, however, varied with site. At the 20-cm depth of erosion, KNO3 was more effective than urea. The trend in fertilizer-use efficiency increased with depth of erosion at Site 1 but decreased at Site 2. Key words: Artificial erosion, barley, fertilizer-use efficiency, potassium nitrate, urea

Beschreibung: Interpreting soil loss from rainfall simulators is complicated by the uncertain relationship between simulated and natural rainstorms. Our objective was to develop and test a method for estimating soil loss from natural rainfall using a portable rainfall simulator (1 m2 plot size). Soil loss from 12 rainstorms was measured on 144-m2 plots with barley residue in conventional tillage (CT), reduced tillage (RT) and zero tillage (ZT) conditions. A corresponding "simulated" soil loss was calculated by matching the simulator erosivity to each storm's erosivity. High (140 mm h−1) and low (60 mm h−1) simulation intensities were examined. The best agreement between simulated and natural soil loss occurred using the low intensity, after making three adjustments. The first was to compensate for the 38% lower kinetic energy of the simulator compared with natural rain. The second was for the smaller slope length of the simulator plot. The third was to begin calculating simulator erosivity only after runoff began. After these adjustments, the simulated soil loss over all storms was 99% of the natural soil loss for CT, 112% for RT and 95% for ZT. Our results show that rainfall simulators can successfully estimate soil loss from natural rainfall events. Key words: Natural rainfall events, simulated rainfall, erosivity, tillage

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

Beschreibung: Mor is a typical humus form in the boreal coniferous forests, but little is known about its air permeability and pore geometry. Thirty undisturbed core samples were collected from a mor layer under a mature Scots pine (Pinus sylvestris L.) stand. Air permeability (Ka) was measured in each sample at six different air-filled porosities (εA) using a constant-pressure air permeameter. The air permeability and the air-filled porosity were used to determine different indices of pore geometry and continuity. The average Ka increased logarithmically from 7.4 × 10−1 to 1.3 × 103 µm2 when εA increased from 0.1 to 0.8. Both the air permeability and pore continuity were high when compared with most other mineral soils and well-decomposed peats. The variations in air permeability and pore continuity with εA were very large. The studied properties had a very large spatial variation in the mor layer which could be caused by the variation in the quality of the debris and the environmental factors affecting the decomposition process during the development history of the mor layer. Key words: Aeration, humus, pore continuity

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

Beschreibung: The spatial and temporal variations in soil water play a key role when considering issues such as irrigation and drainage requirements, crop growth and yield potential and contamination of groundwater by agricultural chemicals. In this study a previously validated deterministic model was used to estimate water (evapotranspiration) deficits and surpluses during the growing season of a perennial forage crop at 14 locations in Ontario. Three different hydraulic soil profile characteristics, representing a clay, clay loam and sandy loam soil, and three different lower boundary conditions (free drainage, fixed and fluctuating water table) were considered. Seasonal deficits ranged from less than 15 mm in abnormally wet years (90% probability of exceedence) in the north, to more than 300 mm in exceptionally dry years (5% probability of exceedence) in the extreme southwest region of the province. With a water table fluctuating between 25 cm depth during the middle of April and 140 cm in early October, 28 to 49% of the evapotranspiration deficit was caused by excess water in all three soils. The flux of water at 100 cm depth, accumulated during the growing season, was used as a measure of the net amount of surplus water moving through the root zone or being extracted from the water table. This flux ranged from significant upward values in dry years in a sandy loam with a fixed water table at 120 cm depth, to downward fluxes of more than 300 mm in abnormally wet years when a fluctuating water table was present. Our simulations show important spatial and temporal interactions among soil and climatic factors and suggest that each one, including the lower boundary condition, should be properly characterized in soil water investigations. Key words: Soil water, modelling, spatial and temporal variability, forage crop

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