Soils Of Eastern Canada Research Articles

Graphical analysis of nitrogen and sulfur supply on yield and related traits of canola in eastern Canada

Profitable canola production depends upon an adequate supply of nitrogen (N) and sulfur (S) fertilizer. However, agricultural soils in eastern Canada seldom receive S fertilizer and rely on inherent S supply from biogeochemical and anthropogenic sources, which could be a yield-limiting factor for canola. The objective of this study was to document N × S fertilizer interactions to develop site-specific best management practices for canola production in eastern Canada. Factorial field experiments were conducted for four consecutive cropping seasons at five locations across eastern Canada. The N × S and N × S × environment interactions on seed yields and yield-related traits were visualized with the graphical analytical genotype and genotype-by-environment biplot tool. The highest seed yield was achieved with 150 kg N ha−1 together with 20–40 kg S ha−1 in 15 of the 19 test site-years. Seed yield was closely related to harvest index and number of seeds pod−1. Fertilizing canola with 20 kg S ha−1 enhanced the nitrogen use efficiency (NUE) of canola receiving 75 kg N ha−1, but the benefit of S fertilizer on NUE was negligible when N fertilizer rates increased to 150 kg N ha−1. Since canola yield response to fertilizer inputs varied from one site to another, due to the variation in environmental and soil conditions, we conclude that N × S fertilizer recommendations for canola production need to be developed on a site-specific basis in eastern Canada.

Impact of Climate Change on Soil Hydro-Climatic Conditions and Base Cations Weathering Rates in Forested Watersheds in Eastern Canada

Increases in mean annual air temperature (MAAT) and mean annual precipitation (MAP) are projected for north eastern North America, which will alter soil hydro-climatic conditions and hence the rate of many soil processes. Among them, chemical weathering of soil minerals is an essential source of base cations (BC) which control the acid-base status of surface waters and are crucial for forest nutrition. In this modeling study, MAAT and MAP projections from a regional and a global climate models were first used to project changes in soil temperature (MAST) and soil water content (SWC) with the ForStem and ForHym models for 21 eastern Canadian forested catchments. The models predicted an increase in MAST by 2.03-2.05°C and 2.87-3.42°C for the 2041-2070 and 2071-2100 periods, respectively, and small decreases (<5%) in SWC. In a second step, these projected changes in MAST and SWC were used to estimate changes in BC weathering rates (WR) and soil pH with the geochemical model PROFILE. The simulations indicated that BC WR would increase by 13-15% and 20-22% for the 2041-2070 and 2071-2100 periods, respectively. The increase in BC WR was accompanied by an increase not only in base cation concentrations, but also in soil pH at most sites, suggesting that future temperature increase has the potential to ameliorate the acid-base status and the fertility of soils in eastern Canada through its impact on WR.

A31P-NMR spectroscopic study of phosphorus forms in two phosphorus-fertilized grassland soils in eastern Canada

Phosphorus (P) fertilization can increase grassland production, but will also alter P forms, changing their cycling and potential for loss in runoff. We assessed the effects of mineral P fertilization on soil P forms in timothy swards at two sites in Quebec, Canada. Soil samples (10 cm depth) were collected in autumn 2013 from replicate plots at Lévis on a Kamouraska clay and at Normandin on a Labarre clay loam, each having received three rates of triple superphosphate (0, 20, and 40 kg P ha−1) for 4 yr. These were analyzed for pH, total carbon (TC), total nitrogen (TN), and total phosphorus (TP); Mehlich-3-extractable aluminium (AlM3), iron (FeM3), calcium (CaM3), and P (PM3); and31P nuclear magnetic resonance spectroscopy (31P-NMR) following sodium hydroxide–ethylenediaminetetraacetic acid (NaOH–EDTA) extraction. Phosphorus fertilization had no significant effects on soil TC, TN, AlM3, FeM3, CaM3, and pH, but significantly increased TP, NaOH–EDTA-extractable total P and total inorganic P, PM3, orthophosphate, and glucose 6-phosphate at both sites. In contrast, NaOH–EDTA-extractable total organic P, total orthophosphate diesters, and scyllo-inositol hexaphosphate decreased with P fertilization. Phosphorus fertilization over 4 yr increased soluble inorganic P and decreased organic P at both grassland sites.

Lignin biomarkers signatures of common plants and soils of Eastern Canada

Lignin CuO oxidation byproducts have been successfully used as biomarkers to describe terrigenous organic matter (TOM) dynamics in the environment in particular to understand various pedological processes. The fact that the major lignin biomarkers data-set used in environmental studies in temperate zones across the globe is based on pure vegetal samples from the Northwestern U.S.A. constitutes a major drawback in this field of research. This study presents a new lignin biomarker data-set of common plant species and soil types from the forest domain of Eastern Canada. Our results show that lignin signatures in pure vegetal samples can be significantly different from those listed as references in the literature for the same plant type (angiosperm/gymnosperm) demonstrating that location is a crucial parameter to consider. We also present characteristic lignin signatures of boreal soils that have evolved from the taxon of tree that grow on such soils. Some watershed specificities such as the presence of Sphagnum can increase the difficulty to decipher lignin sources. Specifically determining lignin signatures for pure plants and corresponding soils in a region of study is recommended to effectively use lignin biomarkers to study TOM dynamics at the watershed scale of that region.

Declining Acidic Deposition Begins Reversal of Forest-Soil Acidification in the Northeastern U.S. and Eastern Canada.

Decreasing trends in acidic deposition levels over the past several decades have led to partial chemical recovery of surface waters. However, depletion of soil Ca from acidic deposition has slowed surface water recovery and led to the impairment of both aquatic and terrestrial ecosystems. Nevertheless, documentation of acidic deposition effects on soils has been limited, and little is known regarding soil responses to ongoing acidic deposition decreases. In this study, resampling of soils in eastern Canada and the northeastern U.S. was done at 27 sites exposed to reductions in wet SO4(2-) deposition of 5.7-76%, over intervals of 8-24 y. Decreases of exchangeable Al in the O horizon and increases in pH in the O and B horizons were seen at most sites. Among all sites, reductions in SO4(2-) deposition were positively correlated with ratios (final sampling/initial sampling) of base saturation (P < 0.01) and negatively correlated with exchangeable Al ratios (P < 0.05) in the O horizon. However, base saturation in the B horizon decreased at one-third of the sites, with no increases. These results are unique in showing that the effects of acidic deposition on North American soils have begun to reverse.

Sweet pearl millet and sweet sorghum have high nitrogen uptake efficiency under cool and wet climate

Nitrogen use efficiency is a key factor for the economic and environmental sustainability of farms. It comprises the ability for crops to recover applied fertilizer N in their aboveground biomass, called fertilizer N uptake efficiency (NupE). Sweet pearl millet (Pennisetum glaucum (L.) R.BR.) and sweet sorghum (Sorghum bicolor (L.) Moench) are C4 annual crops known for their capacity to produce high yield under N-limiting conditions, suggesting high NupE. A field study was conducted for 2 years on sandy loam soils in eastern Canada. The NupE was determined using a 15 N-tracing approach. Compar- isons were made for both species in regards to their response to (1) increasing mineral N rate (0-160 kg N ha -1 ), (2) mineral versus organic N (liquid swine and dairy cattle manures), and (3) single versus split N application. For mineral N treatments, NupE ranged from 54 to 82 %, which is greater than values generally reported for conventional crops such as corn. Moreover, NupE increased with N rates. These findings suggest than both species expressed N luxury consumption. The NupE was lower with organic than with mineral N, and a larger proportion of N remained in the soil, suggesting that N immo- bilization occurred. The presumed losses (unrecov- ered 15 N) were\24 kg N ha -1 in all mineral and most organic N treatments. Splitting N application had little effect on NupE. Our results confirm that sweet pearl millet and sweet sorghum are highly efficient at recovering fertilizer N and, with adequate residue management, may represent a low environmental risk.

Biogeochemical controls on methane, nitrous oxide, and carbon dioxide fluxes from deciduous forest soils in eastern Canada

[1] The exchange of the important trace gases, methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2), between forested soils and the atmosphere can show great temporal and spatial variability. We measured the flux of these three gases over 2 years along catenas at two forested sites, to determine the important controls. Well-drained soils consumed atmospheric CH4, while poorly drained swamp soils embedded in depressions were a source. CH4 fluxes could be predicted primarily by temperature and moisture, and tree cover exerted an influence mainly through the creation of large soil porosity, leading to increased consumption rates. In contrast, there were very poor relationships between N2O fluxes and environmental variables, reflecting the complex interactions of microbial, edaphic, and N cycling processes, such as nitrification in well-drained soils and denitrification in poorly drained soils, which led to N2O production (or consumption) in soils and hence larger variability. At the broad temporal and spatial scale, soil C:N ratio was a good predictor of N2O emission rates, through its influence upon N cycling processes. Soil CO2 emission rates showed less spatial and temporal variability, and were controlled by temperature and moisture. The source strength, in global warming potential of CH4 and N2O fluxes in CO2 equivalents, was reduced markedly when trace gas fluxes from 5 to 15% poorly drained soils were included in the net global warming potential calculation of whole forested watersheds. Soils drainage class integrates many of the biogeochemical processes controlling the flux of these gases providing a framework for extrapolating results.

N2O emissions from an irrigated and non‐irrigated organic soil in eastern Canada as influenced by N fertilizer addition

Drainage and cultivation of organic soils often result in large nitrous oxide (N2O) emissions. The objective of this study was to assess the impacts of nitrogen (N) fertilizer on N2O emissions from a cultivated organic soil located south of Montréal, QC, Canada, drained in 1930 and used since then for vegetable production. Fluxes of N2O were measured weekly from May 2004 to November 2005 when snow cover was absent in irrigated and non‐irrigated plots receiving 0, 100 or 150 kg N ha−1 as NH4NO3. Soil mineral N content, gas concentrations, temperature, water table height and water content were also measured to help explain variations in N2O emissions. Annual emissions during the experiment were large, ranging from 3.6 to 40.2 kg N2O‐N ha−1 year−1. The N2O emissions were decreased by N fertilizer addition in the non‐irrigated site but not in the irrigated site. The absence of a positive influence of soil mineral N content on N2O emissions was probably in part because up to 571 kg N ha−1 were mineralized during the snow‐free season. Emissions of N2O were positively correlated to soil CO2 emissions and to variables associated with the extent of soil aeration such as soil oxygen concentration, precipitation and soil water table height, thereby indicating that soil moisture/aeration and carbon bioavailability were the main controls of N2O emission. The large N2O emissions observed in this study indicate that drained cultivated organic soils in eastern Canada have a potential for N2O‐N losses similar to, or greater than, organic soils located in northern Europe.

Using a sequential density and particle-size fractionation to evaluate carbon and nitrogen storage in the profile of tilled and no-till soils in eastern Canada

Tillage influences the retention and storage of organic matter (OM) in soil. We used a sequential density and particle-size fractionation to evaluate the total quantity and distribution of organic carbon (C) and nitrogen (N) in the profile of soils under mouldboard ploughing and no-till. Cores (0-60 cm) from four long-term tillage studies (in Prince Edward Island, Quebec, and two sites in Ontario) on soils of different textures, from sandy loam to clay were collected and divided into six depth increments. Four soil OM fractions were isolated on the basis of size and density from each sample. At two sites the standing stocks of C and N were larger in tilled than in no-till soil profiles at depths slightly greater than plough depth; tillage effects were also evident at a third site, where the mass of C in a layer close to the depth of ploughing was greater in tilled soils. Ploughing also had a substantial and consistent positive effect in all four soils on the quantity of C (and in some cases N) protected within aggregates, particularly at or near the bottom of the plough layer, and sometimes in surface soil layers. We attribute differences observed in whole soil C and N due to tillage mostly to differences in mineral-associated OM, particularly in soils with heavier textures, but the other size and density fractions could, together, account for as much as 25% of the difference. Because the C capacity level was not reached in heavy-textured soils, these soils show greater potential for further accumulation of C in the soil profile than coarse-textured soils, especially near the bottom of the plough layer.Key words: Light fraction, soil organic matter, soil tillage, physically-protected organic matter, no-till, soil texture

Estimation of N2O emissions from agricultural soils in Canada. I. Development of a country-specific methodology

International initiatives such as the United Nations Framework Convention on Climate Change and the Kyoto Protocol require that countries calculate national inventories of their greenhouse gas emissions. The objective of the present study was to develop a country-specific (Tier II) methodology to calculate the inventory of N2O emissions from agricultural soils in Canada. Regional fertilizer-induced emission factors (EFreg) were first determined using available field experimental data. Values for EFreg were 0.0016 kg N2O-N kg-1 N in the semi-arid Brown and 0.008 kg N2O-N kg N-1 in the sub-humid Black soil zones of the Prairie region, and 0.017 kg N2O-N kg-1 N in the humid provinces of Quebec and Ontario. A function relating EFreg to the "precipitation to potential evapotranspiration" ratio was determined to estimate annual emission factors (EFeco) at the ecodistrict scale (≈ 150 000 ha) in all agricultural regions of Canada. Country-specific coefficients were also developed to account for the effect of several additional factors on soil N2O emissions. Emissions from fine-textured soils were estimated as being 50% greater than from coarse- and medium-textured soils in eastern Canada; emissions during winter and spring thaw corresponded to 40% of emissions during the snow-free season in eastern Canada; increased emissions from lower (wetter) sections of the landscape and irrigated areas were accounted for; emissions from no-till soils were 10% greater in eastern, but 20% lower in western Canada than from those under conventional tillage practices; emissions under summerfallow were estimated as being equal to those from soils under annual cropping. This country-specific methodology therefore accounts for regional climatic and land use impacts on N2O emission factors, and includes several sources/offsets that are not included in the Intergovernmental Panel on Climate Change (IPCC) default approach. Key words: Nitrous oxide, soils, greenhouse gases, inventory

Pulp Fiber Residue and Supplemental Irrigation on Yield and Nutrient Uptake of Potato

ABSTRACT Organic matter levels combined with drought periods during the growing season have adverse impacts on rain-fed potato production in coarse textured soils of eastern Canada. Using pulp fiber residues (PFR) may build up soil organic matter, improve crops yield and nutrient uptake, and reduce the need for supplemental irrigation in this region. A box experiment with 3 rates of PFR [0, 45, and 90 Mg ha− 1 dry mater carbon (C) basis] with or without supplementary drip irrigation was established in a sandy loam soil in New Brunswick, Canada. Red clover, barley, and potato were cultivated as three crops of the rotation in 1999, 2000, and 2001, respectively. The PFR only applied before red clover in fall 1998. Selected soil chemical and physical properties were measured before planting and after harvest. Crops yield and nitrogen (N), phosphorus (P), and potassium (K) accumulation were determined at harvest. Soil organic-C content, bulk density and water holding capacity were improved by PFR application. Red clover and barley biomass production were significantly increased by PFR application. This effect was promoted by supplemental irrigation. Potato tuber yield was not affected by PFR and it was higher in rain-fed compared to supplementary irrigated system. Although, there was some initial evidence of N immobilization but generally PFR application increased N, P, and K bioavailability. This research has demonstrated that PFR can successfully be used as soil amendment in coarse textured soils without any adverse effect.

Potential fluxes of N 2O and CH 4 from soils of three forest types in Eastern Canada

We conducted laboratory incubation experiments to elucidate the influence of forest type and topographic position on emission and/or consumption potentials of nitrous oxide (N 2O) and methane (CH 4) from soils of three forest types in Eastern Canada. Soil samples collected from deciduous, black spruce and white pine forests were incubated under a control, an NH 4NO 3 amendment and an elevated headspace CH 4 concentration at 70% water-filled pore space (WFPS), except the poorly drained wetland soils which were incubated at 100% WFPS. Deciduous and boreal forest soils exhibited greater potential of N 2O and CH 4 fluxes than did white pine forest soils. Mineral N addition resulted in significant increases in N 2O emissions from wetland forest soils compared to the unamended soils, whereas well-drained soils exhibited no significant increase in N 2O emissions in-response to mineral N additions. Soils in deciduous, boreal and white pine forests consumed CH 4 when incubated under an elevated headspace CH 4 concentration, except the poorly drained soils in the deciduous forest, which emitted CH 4. CH 4 consumption rates in deciduous and boreal forest soils were twice the amount consumed by the white pine forest soils. The results suggest that an episodic increase in reactive N input in these forests is not likely to increase N 2O emissions, except from the poorly drained wetland soils; however, long-term in situ N fertilization studies are required to validate the observed results. Moreover, wetland soils in the deciduous forest are net sources of CH 4 unlike the well-drained soils, which are net sinks of atmospheric CH 4. Because wetland soils can produce a substantial amount of CH 4 and N 2O, the contribution of these wetlands to the total trace gas fluxes need to be accounted for when modeling fluxes from forest soils in Eastern Canada.

Determination and Mapping Critical Loads of Acidity and Exceedances for Upland Forest Soils in Eastern Canada

Critical loads of acidity were estimated for upland forests in Eastern Canada using the steady-state Simple Mass Balance (SMB) Model. A consistent methodology was applied to the entire region, although critical loads were estimated separately for the Atlantic provinces (New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland), Quebec and Ontario using different data sources. In this project, critical load estimates and steady-state exceedance values did not include the effect of forest fire and forest harvesting, which could have a considerable impact on critical loads in Eastern Canada. The observed soil pH – base saturation relationship for forest soils indicated that the constants used into the calculation of alkalinity leaching should be set to 10 (M/M) for the molar Bc/Al ratio in soil leachate and 109 (mol L−1)2 for the gibbsite dissolution constant. The area-weighted median critical load for each province varied between 519 (Quebec) and 2063 eq ha−1 y−1 (Prince Edward Island), with a median critical load value for Eastern Canada of 559 eq ha−1 y−1. It is estimated that approximately 52% of the mapped area is exceeded in terms of acidity according to the 1994–1998 average total (wet + dry) atmospheric deposition. Greatest exceedances occurred in Ontario and Quebec and in the south of Nova Scotia, due to low critical loads and high loads of acid deposition.

Emissions of Nitrous Oxide and Carbon Dioxide

Innovative management practices are required to increase the efficiency of N fertilizer usage and to reduce nitrous oxide (N2O) and carbon dioxide (CO2) emissions from agricultural soils. The objectives of this study were to evaluate the feasibility of using conservation tillage and N fertilizer placement depth to reduce N2O and CO2 emissions associated with corn (Zea mays L.) production on clay loam soils in Eastern Canada. A 3‐yr field study was established on a wheat (Triticum aestivum L.)‐corn–soybean [Glycine max (L.) Merr.] rotation with each phase of the rotation present every year. Investigations were focused on the corn phase of the rotation. The tillage treatments following winter wheat included fall moldboard plow tillage (15 cm depth), fall zone‐tillage (21 cm width, 15 cm depth), and no‐tillage. The N placement treatments were “shallow” placement of sidedress N (2‐cm depth) and “deep” placement of sidedress N (10‐cm depth). Nitrous oxide emissions were measured 53 times and CO2 emissions were measured 43 times over three growing seasons using field‐based sampling chambers. There was a significant tillage and N placement interaction on N2O emissions. Averaged over all three tillage systems and site‐years, N2O emissions from shallow N placement (2.83 kg N ha−1 yr−1) were 26% lower than deep N placement (3.83 kg N ha−1 yr−1). The N2O emissions were similar among the tillage treatments when N was placed in the soil at a shallow depth. However, when N was placed deeper in the soil (10 cm), the 3‐yr average N2O emissions from zone‐tillage (2.98 kg N ha−1 yr−1) were 20% lower than from no‐tillage (3.71 kg N ha−1 yr−1) and 38% lower than those from moldboard plow tillage (4.81 kg N ha−1 yr−1). Tillage type and N placement depth did not affect CO2 emissions (overall average = 5.80 Mg C ha−1 yr−1). Hence, zone‐tillage and shallow N placement depth reduced N2O emissions without affecting CO2 emissions.

Characterizing organic matter retention for surface soils in eastern Canada using density and particle size fractions

Interest in the storage of organic matter in terrestrial ecosystems has identified a need to better understand the accumulation and retention of organic C and N in soil. The proportions of C and N associated with clay and silt particles (i.e., “capacity level”), water-stable macro-aggregates (WSA) (&gt;250 µm), particulate (POM) (&gt;53 µm), and light fraction (LF) organic matter, for the 0- to 10-cm soil depth, were assessed at 14 agricultural experimental sites established on Gleysolic, Podzolic, Luvisolic , and Brunisolic soils in the cool, humid region of eastern Canada. Organic C and N in the clay plus silt particles was at or near the capacity level for soils with clay plus silt content &lt; 40%. For soils with &gt;60% clay plus silt, the degree of saturation was 65–70% indicating a potential for further organic C and N retention. The mean proportion of C and N found in the POM was 22 and 27%, whil e the LF organic matter contained 7 and 5% C and N, respectively. Mean soil WSA content, determined by wet-sieving analysis, was 42% for air-dry soil and 54% for wetted soil, and was significantly (P &lt; 0.05) related to both soil clay plus silt (r = 0.65) and organic C (r = 0.54). Water-stable macro-aggregate C content was proportional to soil organic C (r = 0.96, P &lt; 0.01). At four of the sites, where soil C and N were influenced by management, an increasing level of soil organic C and N was associated with both the clay plus silt particles and the POM fraction until the former was saturated. Once the capacity level was saturated, further organic C and N accumulation was associated with the POM fraction. Although stabilized organic C and N in soil exists as a continuum, both soil particle and particulate fractions provided a practical approach to monitor, quantify and differentiate the storage and retention of C and N in soils of eastern Canada. Key words: Soil organic matter, clay plus silt associated organic C and N, size fractions, particulate organic matter, light fraction organic matter, water-stable macro-aggregates, organic amendments, Canada

Elucidation of the source and turnover of water soluble and microbial biomass carbon in agricultural soils

Understanding the dynamics of soil C is key to managing soil organic matter to enhance soil quality and ecosystem functioning, and reduce trace gas emissions from soils. Our objective was to determine the source and turnover of C pools in some agricultural soils in eastern Canada. Soils from five field experiments under continuous maize cropping for 4–37 yr were sampled, and the organic C content and stable C isotope ( 13C) composition of whole soil and water soluble and microbial biomass fractions determined. The 13C results showed a clear distinction between the water soluble organic C and microbial biomass C, with the water soluble organic C more like the whole soil and the microbial biomass more like the maize residues. A simple linear model was used to explore the relationship among the soil organic constituents and evaluate the turnover of these carbon pools. Even though the water soluble organic C had a higher turnover rate than the microbial biomass C, the proportion of C 4-derived C in the biomass was about 2.5 times greater than that in water soluble organic C. Apparently the large amount of native soil C, the small amount of water soluble organic C, and its equilibrium with the native soil C, cause humus to dominate the isotopic composition of water soluble organic C even though the water soluble C is very active. Our results suggest that the quantity, as well as the turnover rate, of soil organic matter constituents that are in equilibrium influence the isotopic composition of such constituents.

Effects of cement kiln dust on soil and potato crop quality

Cement kiln dust is a potential source of K and Ca for crops on acidic soils in Eastern Canada. The objective of this study was to assess the effect of cement kiln dust on soil chemical properties and potato (Solanum tuberosum L. cv. Superior) yield and quality on two Spodosols. Four rates of cement kiln dust, commercial K fertilizers, and lime were yearly applied and arranged in a randomized complete block design with four replicates. Soil extractable K and Ca increased rapidly after cement kiln dust applications and were comparable to commercial fertilizers or lime treatments. Heavy metal soil contents and plant uptake were not influenced by treatments. Soil metal contents decreased from to initial soil levels and were lower than recommended maximal norms. Tuber yields increased with rates of cement kiln dust and commercial fertilizers but decreased with lime rates. Yields were positively correlated to soil extractable K and partially with extractable Mg. The K and Mg plant uptake increased with cement kiln dust and commercial fertilizers rates but was significantly reduced by liming. Tuber specific gravity decreased with the highest commercial fertilizers and cement kiln dust rates. These results showed that cement kiln dust is an effective source of K and Ca for potato production without short term loss in tuber quality or soil contamination by metals.

Organic C and N storage, and organic C fractions, in adjacent cultivated and forested soils of eastern Canada

As a major attribute of soil quality, organic matter is responsive to agricultural land use practices including tillage. A study was initiated in eastern Canada to characterize changes in the masses of organic C and total N, and organic matter fractions in forested and adjacent cultivated or forage sites. Generally, the cultivated and forage sites had denser soil profiles than the forest sites. Based on an equivalent soil mass, to accommodate differences in soil bulk density, the paired forest and cultivated sites showed that cultivation decreased the mass of organic C (35%) and total N (10%) in the soil profile of the Podzolic soils, but increased organic C (25%) and total N (37%) in the Brunisolic (Cambisol) and Gleysolic soils. For the Podzolic soils, use of forages increased soil stored organic C and N by 55% and 35%, respectively. Organic C fractions were mainly of significance in the A horizon. Soil microbial biomass C was greater in the forested, compared to the cultivated soil, but the proportion of soil organic C as microbial biomass C (1.3% to 1.6%) was similar. The proportion, however, was greater (2.1%) for the forage soil, compared to the corresponding cultivated (1.3%) soil, suggesting that organic C was continuing to increase under the former. The relatively large proportion (19%) of organic C found in the light fraction of forest soils in the A horizon was decreased (up to 70%) by cultivation. In contrast, the proportion of macro-organic C present in the soil sand fraction was not greatly influenced by cultivation. Overall, soils in eastern Canada have a relatively large potential to store organic matter. The study illustrates the importance of soil type and cultivation interactions for maintenance of soil organic matter storage, and the positive influence of forages in this regard in agroecosystems.

Organic carbon and nitrogen stocks and storage profiles in cool, humid soils of eastern Canada

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

Cation exchange capacities of upland soils in eastern Canada

Relationships between cation exchange capacity (CEC), clay and organic carbon contents and soil pH were analyzed by way of multiple regressions for upland soils in eastern Canada (mostly Ontario, with additional data for New Brunswick). This was done by vegetation type in an attempt to explain some of the otherwise unexplained CEC variations. Data were taken from about 2000 soil horizons (organic L, F, and H horizons as well as A, B, and C mineral soil horizons) under broadleaves (mostly maples, beech, birch or aspen as dominant species), conifers (mostly fir, spruces and/or pines), and grass vegetation. For the organic forest floor horizons (or L, F, and H horizons), both organic carbon content (%) and pH were highly significant for predicting CEC, i.e.,CEC (L, F, and H of broadleaves) = −38 + 0.71 × org. C (%) + 10.3 × pH (R2 = 0.69), andCEC (L, F and H of conifers) = −31 + 0.34 × org. C (%) + 12.1 × pH (R2 = 0.58).For the mineral soil, clay and organic carbon contents (%) and pH were highly significant for predicting CEC. Soils with forest vegetation were found to have lower contributions of organic matter to CEC than grassland soils, i.e.,CEC (forest soils) = −7.0 + 0.29 × clay (%) + 0.82 × org. C (%) + 1.4 × pH (R2 = 0.72),CEC (wooded grasslands) = −6.0 + 0.31 × clay (%) + 1.31 × org. C (%) + 1.0 pH (R2 = 0.74), andCEC (grasslands) = −8.3 + 0.24 × clay (%) + 2.14 × org. C (%) + 1.3 × pH (R2 = 0.79).Relationships that were developed from Ontario data for specific vegetational types (maple sites, strongly podzolized conifer sites, grasslands/croplands) were tested by comparing CEC predictions with reported values for similar sites in New Brunswick and Quebec. The predictions were consistent with the general trends for maple sites and grasslands/croplands, but CEC values were strongly overpredicted for Podzolic subsoils on conifer sites.Literature information of the CEC dependency on in situ pH is sparse. Existing information that is based on buffering grassland/cropland soil samples from pH 2.5 to 8 appears to mimic this dependency quite well. Key words: Cation exchange capacity, clay, organic carbon, soil pH, forests, grasslands