Humic Gleysol Research Articles

Soil organic carbon and nitrogen pools as affected by compost applicationsto a sandy-loam soil in Québec

Compost contributes plant-available nutrients for crop production and adds partially decomposed carbon (C) to the soil organic carbon (SOC) pool. The effect of compost applications and other agricultural practices on SOC and total nitrogen (N) pools was determined in a sandy-loam Humic Gleysol at the Research Farm of McGill University, Ste-Anne-de-Bellevue, Quebec. Experimental plots with continuous silage corn (Zea mays L.) and silage corn-soybean (Glycine max L. Merr.) production were under conventional tillage (CT) or no-tillage (NT) management. Composted cattle manure was applied each spring at rates of 0, 5, 10 and 15 Mg (dry weight) ha-1 and supplemental NPK fertilizers were added to meet crop requirements. The C input from crop residues was affected by tillage, crop rotations and compost application, but differences in the SOC and total N pools were due to compost applications. After 5 yr, compost-amended plots gained 1.35 to 2.02 Mg C ha-1 yr-1 in the SOC pool and 0.18 to 0.24 Mg N ha-1 yr-1 in the total N pool, as compared with initial pool sizes when the experiment was initiated. These gains in SOC and total N were achieved with agronomic rates of compost and supplemental NPK fertilizers, selected to match the phosphorus requirements of silage corn. Such judicious use of compost has the potential to increase the SOC and total N pools in agroecosystems under annual crop production. Key words: Composted cattle manure, corn silage, mineral fertilizer, plant-available nitrogen, soil organic carbon

Modelling nitrous oxide emission from water-logged soils of a spruce forest ecosystem using the biogeochemical model Wetland-DNDC

During the last decades, decision makers and policy have increasingly demanded for regional and national inventories of greenhouse gas emission, such as nitrous oxide (N2O), to develop appropriate strategies and mitigation options. A potential way to derive large-scale estimates of N2O emission is the use of process-based models, such as PnET-N-DNDC or Wetland-DNDC. While PnET-N-DNDC has been effectively applied for various upland forest ecosystems, the Wetland-DNDC model has not yet been validated with regard to N2O emission. We calibrated and validated the Wetland-DNDC model on the basis of a 4-year field data set of two water-logged soils (Humic Gleysol and Histic Gleysol) of a spruce forest ecosystem. Model calibration by means of the Levenberg–Marquardt algorithm considerably improved the model performance for the period of calibration (2001–2002). The error variance was reduced by up to a factor of two and the modelling efficiency was increased from −1.24 to −0.15 (Humic Gleysol) and from −0.42 to 0.1 (Histic Gleysol). However, the model performance for the period of validation (2003–2004) and particularly for the extreme dry period in summer 2003 was not fully satisfying, notably with regard to the temporal pattern of the N2O emission.

Assessment of the lateral and vertical variability of soil organic carbon

Accurate predictions of changes in soil organic matter are difficult, at least in part, because of the lack of precision in measurements of soil organic carbon (SOC). This lack of precision is mostly due to the spatial variability in SOC that occurs with depth through the profile and laterally across the soil surface. The objective of this study was to assess the lateral and vertical variability of SOC in several pedologically distinct agricultural soils across Canada. Our goal was to determine the effect of different sampling methods on the precision of SOC measurements, namely: the effect of sampling either by fixed depth or by genetic soil horizon, the influence of compositing samples from different depth increments, and the number of cores required for a minimum detectable difference. Soils were sampled in increments down to 60 cm using a 4 × 3 m grid at six sites: two each from Ontario (Gleysol and Melanic Brunisol), Quebec (Humic Gleysol and Humo Ferric Podzol) and Saskatchewan (Dark Brown Chernozem). At four of the six sites, sampling by genetic soil horizon appeared to increase the precision of SOC measurements, but only when the surface 30 cm of the soil profile was considered. At the other two sites (soil types: Gleysol and Melanic Brunisol) sampling by fixed depth increments was more effective for increasing the precision of SOC measurements than sampling by genetic horizon. The effect of compositing samples from different depth increments had little influence on the precision of SOC measurements for all six soil types. These results suggest that sampling more than two depth increments per soil core has limited advantages for increasing statistical power to detect change in SOC. The high background SOC levels in the Gleysol soil would require a large number of soil cores in order to detect a small change in SOC such as that which would occur in a typical monitoring project. The Chernozem soils had lower spatial variability in SOC than the soil types in eastern Canada. Determining a statistically significant change in SOC of 5 Mg ha-1 would be difficult with the sampling design used in this study. Key words: Soil organic carbon, statistical power, sampling design, coefficient of variation, spatial variability, Canada

Soil and vegetation as the determinants of lake nitrogen concentrations in forested watersheds in British Columbia, Canada

Abstract This study used soil type, drainage class, parent material, and vegetation type to quantify the concentrations of lake water nitrogen for nine coastal lakes in forested watersheds in British Columbia, Canada. The results showed that forest soil type, drainage class, parent material, and vegetation type can predict more than 80% of the variance of nitrogen concentrations in these coastal lakes. The lakes in the watersheds with Orthic Humic Gleysol soils, moraine soil parent material, poor drainage, and coastal western hemlock and Douglas-fir vegetation type had higher nitrogen concentrations than the lakes in the watersheds with the other soil and vegetation types and properties. The impact factor of forest soil and vegetation on lake nitrogen concentration was defined according to the ability of each watershed soil and vegetation to contribute lake nitrogen input. This paper also demonstrates how to construct a model of lake nitrogen concentrations in response to the change of forest vegetation types and soil properties. The developed models can be used as watershed management tools for establishing and maintaining high quality water through managing soil and vegetation in forested watersheds.

Iron‐bearing phases in a peat‐derived duricrust from Brazil

SummaryThe formation of aluminium‐substituted iron‐minerals is still subject to debate. We report a case study in a Humic Gleysol soil profile, developed on a sedimentary saprolite, from a basin floor on the Uberaba Plateau (Minas Gerais State, Brazil) where iron‐phases are crystallized by a ferruginization process. The mineralogical and chemical properties were investigated by X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry and Mössbauer spectroscopy. The specific surface area (BET method) and cation exchange capacity (CEC) were also determined. The soil profile is mainly composed of gibbsite, kaolinite and amorphous alumino‐silicate phases, the latter being more frequent in the H horizon where the organic carbon content is greater. The surface area and CEC values are also greater in the H horizon (58.6 m2g−1 and 4.65 molckg−1, respectively) which indicates an increase in porosity caused by the presence of 20.8% of organic matter and amorphous materials. Goethite occurs as a secondary mineral in the H horizon and as the main mineral in the duricrust in association with haematite. The omnipresence of aluminium in the environment (24.6–46.2% of Al2O3) resulted in Al‐substitution in all iron‐bearing phases but the goethite from the H horizon has the greatest Al‐for‐Fe substitution, with at least 20 mole per cent of aluminium. In spite of the greater microporosity and wetness of the H horizon, the immediate contact with the richest Al‐source (gibbsite) favours the precipitation of unusually greatly Al‐substituted goethite instead of haematite in this horizon.

Impact of flow path length and flow rate on phosphorus loss in simulated overland flow from a humic gleysol grassland soil

In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.

N2O emissions of a mature Norway spruce (Picea abies) stand in the Black Forest (southwest Germany) as differentiated by the soil pattern

Nitrous oxide is a greenhouse gas contributing to stratospheric ozone depletion with major sources that derive from soils. Most measurements were performed at well‐aerated or anaerobic sites, excluding common hydromorphic soils (e.g., Gleysols). The main thesis of this study was that the intermediate aeration of such soils promotes N2O emissions. The investigated catena “Wildmooswald,” which is little more than 200 m long, includes common temperate forest soils (n = 7) of three aeration categories (Cambisols, Gleysols, and Histosol). The influence of fluctuating water tables of the Gleysols led to distinctively higher N2O release compared to the Cambisol within the same mature Norway spruce ecosystem. Even a stable “hot spot” of N2O emissions was detected at a Histosol, where artificial drainage created a redox environment comparable to the Gleysols. Ranking the soils according to emission rate results in fairly regular doubling steps; for example, mean annual flux rates in kg N ha−1 yr−1 for the 2.5 years of measurements were −0.1, 0.4, 1.0, 1.9/1.9, 3.2, and 6.4 for Fibric Histosol, Chromic Cambisol, Endoskeletic Cambisol, Histic Gleysol 1/2, Humic Gleysol, and Sapric Histosol, respectively. The annual emission rates (0.93 kg N ha−1 yr−1) of the predominant Cambisols (63.4% of the area) are comparable to other studies, but only 34.3% of intermediately aerated soils led to a redoubling of the average to 1.86 kg N ha−1 yr−1, which is clearly higher than previously presented from temperate forests. Therefore N2O releases of soils are underestimated if soils having intermediate aeration conditions are left unconsidered.

Soil Test Phosphorus and Phosphorus Fractions with Long‐Term Phosphorus Addition and Depletion

The fate of fertilizer P in soil during crop production has to be determined to evaluate the long‐term economic value and sustainability of fertilizer practices. We assessed changes in soil test P and soil P fractions with continuous P fertilization and soil P depletion under continuous corn (Zea maysL.) in a Ste. Rosalie clay soil (humic Gleysol; fine, mixed, frigid, Typic Humaquept). Soil samples were analyzed for Mehlich‐3 P (M‐3 P) and P fractions using a modified Hedley's procedure. Soil M‐3 P values remained constant in spite of crop removal in soil not receiving fertilizer for 10 yr. Continuous P fertilization at rates from 44 to 132 P ha−1yr−1increased linearly soil M‐3 P, with 6.3 kg P ha−1of net P addition required to increase M‐3 P by 1 mg P kg−1Residual fertilizer P in soil resulted from the continuous P addition were found predominately in labile inorganic P (LPi) (NaHCO3–Pi) and moderately labile Pi(MLPi) (NaOH‐Pi). Increased P rates favored soil P transformation from LPito MLPi, indicating enhanced soil P retention. With P depletion, soil M‐3 P declined in plots previously receiving 132 kg P ha−1yr−1, with 4.2 kg P ha−1crop P removal decreasing soil M‐3 P by 1 mg P kg−1Continuous crop removal of soil residual P (Res‐P) resulted in decreases in soil LPiand increases in MLPi, an indication of increased retention of Res‐P with time. However, moderately stable Pi(HCl‐Pi) remained constant, both with continuous P addition and P depletion. Conversion of residual fertilizer P to less available P forms in soil was a slow process and thus the fate of the Res‐P should be taken into consideration when developing soil nutrient management plans.

Influence of paper mill sludges on corn yields and N recovery

Mixed paper mill sludges are an important source of N for crop production. An estimate of direct and residual N recovery is necessary for their efficient management. A 3-yr field study (1997-1999) was conducted in central Quebec, Canada, to evaluate mixed paper mill sludges (PMS) effects on corn (Zea mays L.) yields and N nutrition, N recovery and N efficiency. The effects of PMS on soil NO3-N and total N levels were also determined. The study was situated on a silt loam Baudette soil (Humic Gleysol). The treatments included 3 PMS rates (30, 60 and 90 t ha-1 on wet basis) applied alone or in combination with N fertilizer (90 and 135 kg N ha-1, respectively, for 60 and 30 t ha-1). Treatments also included a control without PMS or N fertilizer, and a complete mineral N fertilizer (180 kg N ha-1) as recommended for corn. The previous plots were split beginning with the second year of the experiment, for annual and biennal PMS applications. Similar treatments as above were made on an adjacent site to evaluate N recovery under climatic conditions in 1999. In all years, PMS applied alone significantly increased corn yields by 1.5–5 t ha-1, compared to the unfertilized control. However, corn yields and N uptake were highest from the application of PMS in combination with N fertilizer. Biennial PMS applications at 60 to 90 ha-1 significantly increased corn yields and N uptake, which suggest high PMS residual effect; however, these increases were lower than those obtained with annual PMS applications. The N efficiency varied in 1997 from 13.0 to 15.4 kg grain kg N-1 for mineral N fertilizer and ranged from 3 to 13.7 kg grain kg N-1 for PMS, decreasing proportionally to increasing PMS rates. Apparent N recovery ranged from 1 3 to 19% in 1997 and from 10 to 14% in the residual year (1998), compared to 30 and 49%, respectively, for mineral N fertilizer. Depending on the PMS rate, N recovery varied from 13 to 21% in 1999. The results indicate high N supplying capacity and high r esidual N effects of PMS, which probably influenced corn yields and N nutrition. Annual PMS applications alone or combined with mineral N fertilizer had no significant effect on soil NO3-N and total N levels. This study demonstrates that application of low PMS rate (30 t ha-1) combined with mineral N fertilizer could achieve high agronomic, economic and environmental benefits on farms. Key words: Mixed paper mill sludges, corn yields, N uptake, N efficiency, residual effects, soil N

Phosphorus status of a Humic Gleysol after 10 year of cultivation under contrasting cropping practices

Cropping practices interactively affect soil P status. Previous studies mostly focused on cropping practices individually and limited assessments within the plow layer. This study assessed the P status of a Labarre silty clay (Humic Gleysol) profile after 10 yr cultivation under contrasting practices. Soils of 0–15, 15–30, 30–60, and 60–90 cm layers were sampled from a split-plot experiment comprising barley (Hordeum vulgare L.) monoculture and a 3-yr barley-red clover-timothy rotation both tilled with either chisel or moldboard plow as main plots, and receiving fertilizer P or liquid dairy manure as subplots. A modified Hedley sequential fractionation was used to characterize soil P status. Labile P pools were more affected than stable ones by cropping practices. The P fractions depended more on nutrient sources than cropping systems in the 0- to 30-cm soil layer, whereas the impacts were predominated by cropping systems in the subsoil. Compared to the manure, fertilizer P resulted in higher contents of Mehlich III extractable P, resin-P, NaHCO3-Pi and NaOH-Pi, and lower contents of NaHCO3-Po, NaOH-Po and H2SO4-P in the 0- to 30-cm layers. The rotation produced larger labile P fractions than the monoculture in the 30- to 60-cm layer. The impacts of the investigated cropping practices on labile P fractions extended deeper in the soil profile than the depth disturbed by primary tillage. Crop sequence, primary tillage and nutrient source had large effects on P status in the soil profile, of this clayey and poorly drained soil. Key words: rotation; primary tillage; liquid dairy manure; P forms, Mehlich III extractable P (M3P)

Crop rotation and soil N amendment effects on maize production in eastern Canada

Relying less on fertilizer N and more on crop residual and biological N2 fixation by legume crops has been suggested as an effective way to meet the challenge of maximizing economic return while minimizing environmental pollution. A field study was conducted on a Brandon loam soil (Orthic Humic Gleysol) to determine the effects of crop rotation and N amendments on grain yield, crop growth, N uptake and use efficiency (NUE) of maize ( Zea mays L.) and fertilizer replacement values of legume. The rotations included maize in annual rotation with soybean [Glycine max (L.) Merrill], alfalfa ( Medicago sativa L.) or continuous maize. The soil N amendments included no amendment, NH4NO3 at 100 kg N ha-1, stockpiled or rotted dairy manure at 50 Mg ha-1 (wet weight). Averaged across 4 yr, increases in maize grain yield, total plant N uptake, and NUE ranged from 13 to 35% in the maize-soybean and maize-alfalfa rotations compared to continuous maize monoculture. During the study, total dry matter production was 15 to 35% higher and crop growth rate was 13 to 23% higher for maize following alfalfa than for continuous maize monoculture. The effect of legumes on the subsequent growth of maize (i.e., total dry matter production a n d crop growth rate) was most apparent during the grain filling period. Total maize dry matter production was similar up to silking stage for all three rotation systems; however, the difference in total dry matter between maize monoculture and maize in rotation with legume continued to increase after this stage so that the greatest differences were observed at physiological maturity. Grain yield was 19% higher in the 100 kg N ha-1 treatment and 23% higher in the repeated manure amendment than in the unfertilized treatment. Fertilizer N replacement values were on average, 68 kg ha-1 for soybean and 133 kg ha-1 for alfalfa. Our results indicate that maize in annual rotation with legume crops could increase the maize yields by as much as 20% and reduce the amount of chemical fertilizer N by as much as 180 kg N ha-1. The effect of legume preceding crop on maize dry matter production and N uptake is expressed mostly in the later stages of crop growth in this mid- to short-growing- season region. Key words: Rotation, Zea mays, dry matter accumulation, crop growth rate, manure, nitrogen use efficiency

Temporal trends in soil properties at a soil quality benchmark site in the Lower Fraser Valley, British Columbia

A national soil quality monitoring program was established in 1990 to address concerns that the quality of Canada's agricultural soils was in decline. The British Columbia benchmark site (01-BC) was established in 1991 and is located on the Pelly soil series (Orthic Humic Gleysol) supporting a corn-forage-pasture rotation in the Lower Mainland ecoregion. The objectives of this study were to report on the differences in: (1) the measured soil properties for the 5-yr period between baseline data collection in 1991 and resampling in 1996 and (2) the properties measured annually as indicators of soil compaction. A 25-m (25-m grid was used at the site to locate sampling points for bulk density and collecting soil samples of the Ap, BCg, and Cg horizons, as well as the measurement locations for saturated hydraulic conductivity and penetration resistance. A 5-yr interval sampling regime was used to sample the Ap, BCg, and Cg horizons and bulk density. Saturated hydraulic conductivity and penetration resistance were sampled annually from 1992 to 1998. Between 1991 and 1996 in the A horizons, pH, available P, C:N ratio and bulk density increased by 4.6, 7.8, 2.5, and 8%, respectively, and available K, total C and total N decreased by 21, 16.5, and 18.3%, respectively. In the BCg horizon, pH, available P and C:N ratio increased by 5, 126, and 8%, respectively, and the available K and total N both decreased by 21%. Bulk density remained unchanged. The assumption that the soil chemical properties in the Cg horizon would remain stable during the study period did not hold. The trends detected for the Cg horizon were similar to those measured for the upper two horizons. However, only the reductions in available K and total N and increases in C:N were significant. The changes in the soil physical properties measured at this site indicate that some soil compaction has occurred. Both bulk density at 20 cm and penetration resistance increased at all depths between 1994 and 1998, which coincided with the time period that grazing was included in the crop rotation. Field saturated hydraulic conductivity at 25 cm (Ap2 horizon), although highly variable from year to year also tended to be lower during the pasture rotation. The penetration resistance measurements, which detected changes at all depths, appeared to be a more sensitive indicator of soil compaction than either bulk density or field saturated hydraulic conductivity. Key words: Soil quality, soil monitoring, soil properties, soil compaction, temporal change

Magnetic susceptibility of Gleysolic and Chernozemic soils in Saskatchewan

In Saskatchewan, Gleysolic and Chernozemic soils often are found close to each other in hummocky terrain. Magnetic susceptibility (χ) is known to be reduced in poorly drained soils compared to well-drained soils, and this study investigated the use of χ as an accessory criterion for identifying Gleysols. Archived soil samples from an area near Saskatoon were analyzed for χ and sand content, and where necessary for organic and inorganic C and oxalate (Feo) and dithionite (Fed) extractable iron. The lowest χ values were found in Humic Luvic Gleysols and the highest in Dark Brown Chernozems; Rego and Orthic Gleysols and Rego Humic Gleysols had χ values that overlapped those of the Dark Brown Chernozems. Within the upper 50 cm of the profile, all Gleysols except the Rego Humic Gleysol had at least one horizon with %chi; less than 150 × 10-9m3kg-1. The χ of the A and B horizons was negatively correlated to their Feo/Fed ratios, and not correlated to their sand content. The χ of the deep tills was positively correlated to sand content, and not correlated to Feo/Fed ratio. It appears that χ may be as useful as the Feo/Fed ratio for assisting in classifying Gleysols. Key words: Magnetic susceptibility, Gleysols, Chernozems, Feo, Fed, CaCo3

Models for potassium release kinetics of four Humic Gleysols high in clay by electro-ultrafiltration

The rate of K release from the soil solid phase to its solution, especially from its rapidly and slowly exchangeable forms, can affect plant K uptake. The electro-ultrafiltration (EUF) technique was used to kinetically characterize the K release from four soils (Humic Gleysols) from Abitibi-Temiscaming, Quebec, Canada. Potassium was desorbed from soils that received over 166 kg K ha-1 yr-1 from 1994 to 1996. The desorption was carried out for 58 min (4, 4, and every 5 min thereafter for a total of 12 desorptions) at 400 V and 80°C. The amount of K desorbed was between 199 and 342 mg kg-1. Cumulative K desorption was described by the following six equations: power function, simplified Elovich, extended Elovich, parabolic diffusion, zero-order, and first-order. An incremental first-order equation was also tested. The studied soils have large K supplying capacities as suggested by forage K-uptake and total soil K desorption by EUF. In general, all tested equations adequately described the K release by EUF from the four soils. The incremental first-order equation, used for the first time, described well the soil K release data. The k rate constant from this model was significantly related to forage K uptake (R2 = 0.58). Results from this study indicate that the investigated soils have large K reserves and that the incremental first-order equation and most of the cumulative ones are suitable for describing the kinetics of the large K release from these fine-textured Gleysols. Key Words: Potassium, desorption, cumulative model, incremental model

Interactive effects of management practices on water-stable aggregation and organic matter of a Humic Gleysol

In many soils, the content and quality of organic matter (OM) control water-stable aggregation, which in turn preserves soil surface integrity. The effects of management practices on soil OM and aggregation remain to be determined for certain soils and climatic conditions. We assessed the effects of eight management systems involving two crop sequences: [barley ( Hordeum vulgare L.) monoculture (M) and barley in rotation (R) with a forage mix of red clover ( Trifolium pratense L.) and timothy ( Phleum pratense L. ‘Champ’)], two fall tillage [moldboard plowing (MP) and chisel plowing (CP)] and two nutrient sources [liquid dairy manure (LDM) and mineral fertilizers (MIN)] on soil aggregation and OM fractions of a silty clay Humic Gleysol. Soil samples from the 0–7.5 cm layer were taken periodically during 7 yr, and the total C and N, microbial biomass C (MBC) and carbohydrate (AHC) contents, alkaline phosphatase activity (APA), and water-stable aggregation were determined. By the 7th yr, initial total C and N contents of the surface soil had increased by 35 and 45%, respectively, in R-CP-LDM. They were slightly increased in R-CP-MIN an d R-MP-LDM, whereas they decreased by an average of 19% in R-MP-MIN and all monoculture plots. Increases in C contents were attributed to higher annual C inputs from forage residues and LDM, less frequent tillage in the rotation, and shallower tillage with CP. The MBC, APA, AHC and aggregation generally responded faster and to a greater degree to conservation management practices than total C and N. Overall, conservation tillage and manure applications resulted in greater improvement in surface soil conditions when used in a rotation system rather than in a monoculture. The rapid rate of changes in soil properties suggests that the surface quality of this cold silty clay soil can be improved relatively quickly with selected management combinations. Key Words: Cropping systems, total soil C, microbial biomass, carbohydrate, alkaline phosphatase, soil aggregation, liquid dairy manure, reducted tillage, rotations

Effects of green manures on soil organic matter and wheat yields and N nutrition

A field study was conducted for 5 yr (1993-1997) to evaluate the effects of green manure residues applied to the soil in 1993 and 1995, on wheat (Triticum aestivum L.) yields and N nutrition as subsequent crop in 1994, 1996 and 1997. The effect of green manure application was also evaluated on soil microbial activity (CO2), on C and N contents of whole soil and on labile (LF) and heavy fractions (HF) of organic matter (OM). The experiment was initiated on a Le Bras silt loam (Humic Gleysol). The green manures, as a main factor, were clover (Trifolium pratense L.), buckwheat (Fagapyrum esculentum L.), millet (Echinicloa crus galli L.), mustard (Brassica hirta Moench), and colza (Brassica campestris L.), and there was a control without green manure. The sub-factors consisted of four N fertilizer rates for wheat in the subsequent years at 0, 30, 60 and 90 kg N ha–1. Broadcast application of 15N- labelled NH4NO3 was made in 90 kg N ha–1 fertilizer treatments. Two green manure applications did not influence the C and N contents of densimetric fractions of OM (LF and HF), but significantly increased those of whole soil, and microbial respiration (CO2). Green manures significantly increased wheat yields and N uptake in 1994 and 1996. Levels of N derived from fertilizer (Ndff) were lower in all green manure treatments as compared to the control, which indicates that the proportion of N derived from soil and green manures (% Ndfs) was higher in these treatments. The contribution of N from green manure varied in the following order: buckwheat &lt; clover &lt; mustard &lt; millet &lt; colza. With the exception of the clover treatment (&lt; 100%), the N recoveries from the other green manure N (NRGM) ranged from 23 to 34% and from 19 to 36% for 1994 and 1996, respectively. Green manure application provided 15 to 24 kg N ha–1 in 1994 and from 16 to 36 kg N ha–1 in 1996 and this contribution accounted for 25 to 31% of the total wheat N uptake. Significant green manure effects on wheat yield and N nutrition were primarily due to the improvement of soil properties and to high N recoveries from the green manure. In the cold temperate climate of Québec, green manure incorporation into soil in late summer or early fall of the preceding year allowed N synchronization with wheat N needs in subsequent cropping seasons. Nitrogen fertilizer rates could be reduced after the incorporation of green manures having high yields and N contents in the previous season. Key words: Green manure, wheat yields and N uptake, N recoveries, microbial respiration, labile and heavy fractions of OM, C and N contents

Changes in phosphorus fractions of a Humic Gleysol as influenced by cropping systems and nutrient sources

Information about the dynamics of soil P fractions is useful to predict their bioavailability and risk of P transfer from soils to surface waters. The objective of this study was to assess the effects of cropping systems and nutrient sources on P fractions in a Labarre silty clay (Humic Gleysol). Soil samples (0-15 cm) were collected in 1989, 1994 and 1997 from a field with four cropping systems, combining two crop rotations, barley (Hordeum vulgare L.) monoculture and 3-yr barley-forage rotation, with two tillage operations (chisel and moldboard plowing) as main plots, and two nutrient sources (mineral fertilizer and liquid dairy manure) as subplots. A modified Hedley sequential fractionation scheme was used. The inorganic P (Pi) fractions (resin-P, NaHCO3-Pi, and NaOH-Pi) increase with time in all cropping system and nutrient source combinations. Organic (Po) fraction (NaHCO3-Po and NaOH-Po) changes were related to C inputs and total soil C contents. The barley monoculture combined with mineral fertilizer slightly reduced NaHCO3-Po and NaOH-Po. The barley-forage rotation increased labile Po fractions. Rotation, chisel plowing and liquid dairy manure addition result in a buildup of labile P. A larger labile P increment per unit of P added, in surplus to plant exports, was observed with dairy manure than for mineral fertilizer, suggesting a higher risk of surface water contamination by P. Cropping systems and nutrient sources have a large influence on the changes in P fractions in this fine-textured Gleysolic soil. Key words: P fractions, crop rotations, liquid dairy manure, chisel plowing, moldboard plowing

Single‐ and dual‐porosity modelling of multiple tracer transport through soil columns: effects of initial moisture and mode of application

SummaryWe investigated the effect of initial moisture contents and mode of application on the displacement of multiple conservative tracers through undisturbed columns of a Humic Gleysol. Bromide was applied at the soil surface and chloride was injected at 5 cm depth. The columns were irrigated with deuterium‐enriched water. A dual‐porosity model and two single‐porosity models were calibrated separately to Br– and Cl– elution curves in the two columns.Elution curves were almost identical for Br– and Cl– under initially wet conditions, whereas the displacement of Br– was faster than that of Cl– in the initially dry column, indicating rapid transport with preferential flow. Only the dual‐porosity model described the long‐tailing breakthrough of Cl– in the initially dry column adequately. The parameter values giving acceptable fits for ‘Br dry’ were not compatible with the description of the three other elution curves, which could be adequately modelled with a single set of parameter values.The estimated set of common parameters was validated by comparing with the elution curves of deuterium water, nitrate and sulphate, as well as with resident tracer concentrations at four depths. The results showed that solutes can be displaced much faster when applied at the surface of initially dry soil than when applied to wet soil or when resident in the soil matrix. The simulation results suggest that solute transport under initially dry conditions was governed by preferential flow of infiltration water through macropores by‐passing the matrix due to shrinkage cracks and water repellence of matrix surfaces.

Mixed papermill residues affect yield, nutritive value and nutrient use of a grass-alfalfa sward

Mixed papermill residues (MPR) can improve soil quality, but their impact on forage yield and quality is not well documented. Three MPRwere applied to mixed grass-alfalfa (Medicago sativa L.) sward in 1997 and 1998 at near 100, 200 and 400 kg N ha-1 and were compared to calcic ammonium nitrate (CAN) at 0, 50, 100 and 200 kg N ha-1 on a Bedford clay loam (Humic Gleysol). The MPR and CAN induced a significant linear increase in forage DM yield and relative yield (RY). The sward response to MPR addition in 1997 was related to the MPR C:NH4+ ratio. MPR and CAN increased the forage NDF concentration in 1998, but there was no effect in 1997. Nitrogen concentration in forage tissues was increased by MPR and CANinputs in 1997, but was decreased in 1998. In all treatments, NO3− tended to accumulate in forage tissues when the N nutrition index (INN) exceeded the optimum level. Forage nutritive value from the MPR was comparable to CAN.The results of this study suggest that MPR can be an efficient N source for grass-alfalfa swards on fine-textured soils. Key words: Acid detergent fiber, forage, grass, Medicago sativa L., mineral fertilizer, neutral detergent fiber, papermill residues

Combined primary/secondary papermill sludge as a nitrogen source in a cabbage-sweet corn cropping sequence

Combined primary/secondary papermill sludge (PS) is rich in N and may potentially be used as a N source for horticultural crops. A 3-yr experiment was conducted to determine the effects of PS application on crop yields, N uptake and N recovery. The PS was applied in 1996 on a Bedford silty clay (Humic Gleysol) cropped to winter cabbage (Brassica oleracea var capitata L. 'Bartolo') at 0, 8, 16, 32, and 64 Mg ha-1 (dry basis). In 1997, PS was applied at 44% of the 1996 rates to the same plots and cropped to sweet corn (Zea mays L. 'Delectable'). No PS was applied in 1998 to evaluate residual effects on corn. Treatments with ammonium nitrate (AN) at 50, 100 and 200% of N fertiliser recommendations were included each year as a reference for crop response. The PS had a C:N ratio of 42:1 in 1996 and of 28:1 in 1997. About 29% of the total N in PS was inorganic. Cabbage and corn marketable yields and N uptake increased with increasing amounts of PS applied. AN supplemented with PS further increased cabbage yields. Based on the N fertiliser replacement value, the N efficiency coefficient of PS was 44% in the first year. A N residual effect of the PS applied in 1996 was observed on the corn yield in 1997. The two PS applications also had a very significant residual effect on corn yield in the third year, although supplemental AN at 150 kg N ha-1 tended to further increase yields. The apparent total N recovery by the three crops was similar for PS and AN (i.e., 34 vs. 38%). The apparent recovery of organic N from PS decreased with increasing rates of application from 46 to 25%. These results suggest that PS is an effective source of N for crops and that significant residual N effects should be considered when estimating the N needs of subsequent crops. Key words: Cabbage, nitrogen, mineralization coefficient, paper mill residues, sweet corn