ALBERT

Description: 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

Description: The objectives of this study were to evaluate if zero tillage had significantly altered the distribution of certain soil properties formally developed under the shallow cultivation (conventional tillage) soil management systems used on the Canadian prairies. To this end, concentration gradients of available plant nutrients, microbial biomass and mineralizable C and N, were determined in the Ap soil horizon from four locations representing zero and conventional (shallow) tillage systems of 2-, 4-, 12- and 16-yr duration. No significant change coud be detected in total soil organic C and N between tillages systems. Concentrations of plant-available P and K were slightly increased in the surface 0- to 2-cm depth after 16 yr of zero tillage. Except for the 2-yr tillage site, concentration gradients of potential microbial biomass C and N, and potential net mineralizable C and N were significantly greater in the surface soil under zero tillage in comparison to conventional tillage. The reverse situation was observed at the lower depth. The percentage of soil organic C and N that was in the microbial biomass also reflected the above trends. Accumulation of mineral N and calculated N mineralization potentials were closely correlated to both the initial microbial biomass N and the decrease in size of the latter during mineralization. The possible relationships of tillage induced change and redistribution in potential biological activity to N availability were discussed.

Description: Successful reduced tillage systems depend on suitable soil types and the maintenance of optimum soil structure. Studies were conducted to assess the tillage requirement of some well-drained Podzolic and Luvisolic soils in Prince Edward Island and their suitability for direct drilling. Relatively high amounts of silt and fine sand indicated that the soils were structurally unstable with a propensity for compaction. Compactability was inversely related (r2 = 0.90) to concentrations of soil organic carbon over a range of 0.2–2.0%. In the Ap horizons, where organic carbon exceeded 1.6%, the level of macroporosity (equivalent pore diam. 〉 50 μm) was generally greater than 10%. The B horizon and lower level of the Ap horizon, generally, had low porosity and organic matter, although pore continuity was adequate. Macroporosity was closely related to soil bulk density (r2 = 0.81). Penetrometer resistance down the soil profile indicated a relatively shallow rooting depth potential of 25–40 cm. A 3-yr direct drilling study with spring cereals illustrated that some degree of soil loosening is required to maintain optimum soil structure. Soil limitations for direct drilling were mainly low resistance to compaction combined with low potential for regeneration of soil structure. The possible implications of the soil physical properties are discussed in relation to the use of direct drilling within the short-term rotational mixed farming systems of Prince Edward Island. Key words: Soil structure, macropores, Podzolic soils, Luvisolic soils

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

Description: Growth chamber and field studies were conducted to assess the relative utilization of placed and broadcast 15N-urea by spring wheat. The field studies were conducted on zero and conventional (shallow) tillage systems, of 4-yr duration, located on Chernozemic soils at two locations in Saskatchewan. Placement below the seeding depth in comparison to broadcast application, generally reduced fertilizer N immobilization and increased fertilizer N uptake, recovery, and efficiency. Under moisture stress, placed applications were effective in enhancing dry matter yield and total N uptake. It is concluded that fertilizer N placement for these two contrasting tillage systems should be identical, thus some soil disturbance under zero tillage may be necessary to achieve optimum crop use of applied fertilizer N. The dominant N transformation processes and possible tillage induced differences, in regard to methods of N application, are discussed. Key words: Placed and broadcast N application, N efficiency, N utilization, 15N-urea, zero tillage, soil moisture

Description: The mineral N flush, a measure of microbial biomass N, and the N mineralization potential (No) were determined in eight representative agricultural soils (Humo-Ferric Podzols and Gray Luvisols) of Prince Edward Island. The acidic (pH 5.0–5.8) soils, varying in texture from loam to loamy sand had an organic C range of 0.75–2.74%. Both mineral N flush (4–38 μg N g−1 soil) and the percentage soil organic N in the mineral N flush (0.4–2.0%) were relatively low compared to other studies. This observation was related to the generally low pH range of these soils. Potentially mineralizable soil N (No) ranged from 44 to 247 μg N g−1 and accounted for 4.5–13.3% of the total soil organic N. The No was closely related to the mineral N flush (r2 = 0.94) but poorly related to percent organic matter (r2 = 0.26) or organic N (r2 = 0.38). The results indicate that for these soils of similar properties, with low levels of residual mineral N, the mineral N flush could be utilized as an indirect measure of the soil N mineralization potential. Key words: Biomass C, mineral N flush, N mineralization potential, Podzolic soil, Luvisolic soil

Description: Conservation tillage (CT) for potato crop land has been increasing in Atlantic Canada, but producers are concerned that fields managed in this way may be wet, slow to warm in spring, have increased debris at harvest, exhibit higher soil compaction and result in reduced yield. The objective of this study was to compare the effects of four tillage practices on potato yield, soil properties and weed growth over a 3-yr period. The four tillage practices were: (1 ) conventional autumn mouldboard plowing followed by spring secondary tillage; (2) spring mouldboard plowing followed by secondary tillage; (3) autumn chisel plowing followed by spring secondary tillage; and (4) spring CT. Tillage practices significantly affected soil water content (at both the 0- to 15-cm and 15- to 30-cm soil depths) with CT generally showing a greater soil water content prior to spring tillage in comparison to the other treatments. Soil temperature (at the 2- to 5-cm soil depth) prior to spring tillage was not influenced by tillage differences. Conservation tillage increased soil compaction at the 10- to 30-cm soil depth, but not to a level considered detrimental to root growth. Tillage treatments had no effect on amount of soil clods and plant debris passing over the harvester. Potato yield (range of 43 to 51 Mg ha-1) and quality were not adversely influenced by tillage practices. There were few treatment effects on individual weed species or groupings of annual, perennial and total weeds. Overall, CT can be a viable management alternative to conventional tillage because this practice does not negatively affect field management, potato yield, or soil quality. Key words: Conservation tillage, residue management, potato, soil temperature, soil moisture, tillage methods

Description: The spatial variability of soil strength, porosity, and microbial biomass was determined under 4-yr continuous direct-planted silage corn (Zea mays L.) on Prince Edward Island. All soil properties changed relative to the row position. Microbial biomass C and N were lower in the in-row compared to the between-row position. Positional and depth differences for soil bulk density and volume of macropores (EPD 〉 50 μm) were only evident at the soil surface (0–8 cm). Temporal and spatial variations in soil strength indicated the extent of the rooting potential within the soil profile, the depth to compacted soil layers, and the degree of soil structure regeneration during the winter period. Key words: Spatial variability, soil strength, soil porosity, microbial biomass, direct-planted corn, Zea mays L.

Description: Conservation practices in potato (Solanum tuberosum L.) cropping systems can reduce excess tillage, provide crop residue cover, and maintain crop productivity; however, little is known about their long-term influence on soil biota and biological properties. Conservation tillage was evaluated in two potato rotations: a 2-yr barley-potato rotation and 3-yr clover-based (barley-red clover-potato) rotation initiated in 1994 on a fine sandy loam (Orthic Podzol) in Prince Edward Island, eastern Canada. Soil samples were obtained in 2003 from the 0- to 10-cm soil depth of the potato phase of both rotations to evaluate the influence of conservation, compared with conventional tillage, on changes in soil fertility, soil structural properties, soil C and N fractions, soil-borne pathogens, nematode communities, and micro-arthropod (Collembola and Acari) communities. The 3-yr conservation tillage practice improved soil structural stability, increased soil extractable P and K, increased soil organic C and total N and their particulate fractions, compared with the other treatments. Comparisons with earlier studies indicated that soil organic C had reached an equilibrium level at the 0- to 10-cm soil depth. Reduction of potato disease caused by Rhizoctonia solani was evident in the 3-yr rotation, compared with the 2-yr rotation, but was not influenced by tillage practice. Plant parasitic nematodes were not greatly influenced by rotation and tillage treatments; however, densities of the beneficial bacterial-feeding nematodes were increased under the 3-yr conservation tillage treatment. The abundance of micro-arthropods was increased by conservation tillage, while their diversity was mainly influenced by the rotation cycle rather than tillage practice. Overall, the 3-yr conservation tillage treatment provided a more beneficial soil biological condition than the other treatments, especially when compared with the 2-yr conventional tillage practice. Key words: Conservation systems, potato rotation, fine sandy loam, soil fertility, soil organic C and N fractions, soil structure, soil-borne pathogens, nematode, Collembola; Acari

Description: 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