J. M. Cisneros, J. J. Cantero, and A. Cantero

Universidade Nacional de Río Cuarto, Facultad de Agronomia y Veterinaria, Oficina Postal N13, 5800 Río Cuarto, Argentina

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

Key words: Saline and sodic soils, infiltration, runoff, grazing, exclosure, model

Soil organic matter quality and aggregate stability under eight potato cropping sequences in a fine sandy loam of Prince Edward Island

Denis A. Angers¹, Linnell M. Edwards², J. Brian Sanderson², and Nicole Bissonnette¹

¹Agriculture and Agri-Food Canada, Soil and Crops Research Centre, 2560 Hochelaga Blvd., Sainte-Foy, Québec, Canada G1V 2J3;²Agriculture and Agri-Food Canada, Crops and Livestock Research Centre, 440 University Ave. Charlottetown, PEI, Canada C1A 7M8

Soil degradation and soil organic matter (SOM) reduction have long been suspected to occur under intensive potato (Solanum tuberosum L.) production in Prince Edward Island. Thus, this study was conducted to evaluate the effect of eight potato cropping sequences involving barley (Hordeum vulgare L.), ryegrass (Lolium multiflorum L.), red clover (Trifolium pratense L.) and barley underseeded with red clover on aggregate stability and SOM properties of a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol). Total C and N, light-fraction (density < 1.7 g cm^–3) C (LF-C) and light-fraction N (LF-N), microbial biomass C (MBC), carbohydrate content, alkaline phosphatase activity (APA) and aggregate stability were determined in the 0- to 15-cm soil layer in the 6th and 10th years of the trial. Average C and N contents were 20 to 27% greater in sequences that included 3 or 4 yr of potatoes and a high frequency of red clover than in a 9-yr potato sequence; and were attributed to the less frequent tillage and higher organic matter inputs associated with the forage component. The response for MBC, LF-C, LF-N and APA was greater than those for total C and N suggesting that the former parameters may better reveal SOM changes caused by variations in potato management than the latter. Light-fraction N was particularly sensitive to the inclusion of perennial legumes in the cropping sequence. Wet-aggregate stability was 33% higher after 6 yr in the sequence with 50% frequency of red clover than in the continuous potato system, but no effect was noted after 10 yr. The results of this study indicate that sequences which are limited to 30 to 40% of potatoes and have a high frequency of perennial forage such as red clover, lead to greater SOM content and quality of a Charlottetown fine sandy loam compared to continuous potatoes. Trends in aggregate stability generally followed those of SOM fractions but the effects were relatively smaller and varied with time.

Key words: Potato, Solanum tuberosum L., soil aggregation, organic matter, carbon, nitrogen, light fraction, particulate, microbial biomass

Protected organic matter in water-stable aggregates as affected by mineral fertilizer and manure applications

M. Aoyama¹, D. A. Angers², A. N’Dayegamiye³, and N. Bissonnette²

¹Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Aomori, 036 Japan; ²Agriculture and Agri-Food Canada, Soil & Crops Research Centre, 2560 Hochelaga Blvd, Sainte-Foy, Québec, Canada G1V 2J3; ³Institut de Recherche et de Développement en Agro-environnement, 2700 rue Einstein, Sainte-Foy, Québec, Canada G1P 3W8

Effects of long-term (18-yr) applications of cattle manure (20 Mg ha^–1 yr^–1) and NPK fertilizer on the labile organic matter (OM) and its protection in water-stable aggregates were investigated in a Le Bras silt loam (Humic Gleysol). Soil from the 0- to 10-cm depth was sampled from the untreated control, NPK, manure and NPK + manure treatments and fractionated into four size classes of slaking-resistant aggregates (>1000 µm, 250–1000 µm, 53–250 µm, <53 µm). Intact and crushed macroaggregates (250–1000 and >1000 µm) and intact microaggregates (<250 µm) were incubated for 21 d at 25° C, and mineralized C and N were determined. The amount of mineralized C in intact aggregates increased with increasing aggregate size irrespective of the agronomic treatments, but there was no consistent trend for total N. Manure application led to an increase in mineralized C in most aggregate fractions. Crushing the macroaggregates enhanced mineralization of C by 14 to 35% and N by 17 to 103%. Additional C and N rendered mineralizable by crushing represents a fraction of the macroaggregate-protected OM. Manure application increased the protected pools of C (up to threefold) and N (up to fourfold) located in the small macroaggregates (250–1000 µm). In contrast, NPK fertilization increased the pool of macroaggregate-protected N by 2.5-fold but had no effect on the protected C. We conclude that manure application contributed to the accumulation of macroaggregate-protected C and N, whereas mineral fertilizers increased the protected-N pool only. Macroaggregates can provide a mechanism for the protection of labile soil OM in an annually tilled cropping system and this mechanism is enhanced with long-term manure application.

Key words: Aggregate-protected organic matter, manure application, mineralization, mineral fertilizer, water-stable aggregates

Carbon and nitrogen mineralization in soil treated with chloride and phosphate salts

D. Curtin¹, H. Steppuhn², C. A. Campbell³, and V. O. Biederbeck²

¹New Zealand Institute for Crop and Food Research, Private Bag 4704, Christchurch, New Zealand; ²Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada, P.O. Box 1030, Swift Current, Saskatchewan, Canada S9H 3X2; ³Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, Central Experimental Farm, Ottawa, Ontario, Canada K1A 0C6

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

Key words:  Mineralization, organic matter, salinity, chloride, sulfate

Mafic-ultramafic soils affected by silicic colluvium in the Sierra Nevada mountains (southern Spain)

M. Sánchez-Marañón¹, E. Gámiz², G. Delgado², and R. Delgado²

¹Departamento de Edafología y Química Agrícola, Escuela Politécnica Superior, Universidad de Almería, 04120 Almería, Spain (E-mail: masanche@filabres.ualm.es); ²Departamento de Edafología y Química Agrícola, Facultad de Farmacia, Universidad de Granada, 18071 Granada, Spain

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

Key words: Mafic-ultramafic soils; mineralogy; DTPA-microelements; rock fragments

Evidence for solum recarbonation following forest invasion of a grassland soil

L.G. Fuller¹, D. Wang², and D. W. Anderson²

¹AXYS Environmental Consulting Ltd., Calgary, Alberta, Canada T2P 3E7; ²Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5A8

Calcareous organic-matter-rich Black Chernozemic soils often persist under poplar forests in Saskatchewan, not acquiring the Ae horizons and related properties more characteristic of Gray Luvisol soils. These are Rego Black Chernozems, locally termed "Wooded Calcareous" because of the occurrence of a dark, calcareous horizon (AC) at depths of 10 to 30 cm. We hypothesize that dark, calcareous horizons are former Bm horizons that have been recarbonated because of intense biocycling of Ca by aspen (Populus tremuloides). The comparatively small amounts of carbonate occur mainly in the fine silt and clay fractions, and are dominantly calcite, indicating secondary origin, in comparison to the carbonate minerals of the Ck horizons where both calcite and dolomite occur, the latter more common in coarse fractions. The d¹³C values of the carbonate minerals indicate that virtually all the carbonate in fine fractions of the upper horizons of the Wooded Calcareous soil is pedogenic. The dominance of pedogenic carbonate in the Ahk and AC horizons of the Wooded Calcareous soil is consistent with a secondary enrichment, a probable result of increased biocycling of Ca where aspen grows on sites with large amounts of soluble Ca in the subsoil. High concentrations of soluble Ca²⁺ and SO₄^2– in the LFH of the Wooded Calcareous are consistent with increasing biocycling of these ions, from a gypsum-rich subsoil.

Key words: Pedogenic carbonate, prairie-forest transition, stable carbon isotopes, biocycling, d¹³C values

A comparison of methods for gypsum requirement of brine-contaminated soils

John Ashworth, Doug Keyes, and Jean-Michel Crépin

Norwest Soil Research Ltd., 9938 67 Ave., Edmonton, Alberta, Canada T6E 0P5

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

Key words: Gypsum requirements, salt contamination, sodium adsorption ratio, electrical conductivity, formation water

Influence of tillage and cropping system on soil organic matter, structure and infiltration in a rolling landscape

J. A. Elliott and A. A. Efetha

¹Environment Canada, National Water Research Institute, National Hydrology Research Centre, 11 Innovation Boulevard, Saskatoon, Saskatchewan, Canada S7N 3H5; ²Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5A8

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

Key words: Zero tillage, cropping frequency, infiltration rate, aggregation, organic carbon, landscape

Impacts of forage grazing and cultivation on near-surface relative compaction

D. A. Twerdoff¹, D. S. Chanasyk¹, E. Mapfumo¹, M. A. Naeth¹, and V. S Baron²

¹Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2H1; ²Agriculture and Agri-Food Canada, Lacombe, Alberta, Canada T4L 1W1. Received 19 October 1998, accepted 1999.

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

Key words: Annuals, bulk density, cow-days, grazing intensity, perennials, volumetric moisture content

Tillage effects on the dynamics of total and corn residue-derived soil organic matter in two southern Ontario soils

S. D. Wanniarachchi¹, R. P. Voroney¹, T. J. Vyn², R. P. Beyaert³, and A. F. MacKenzie⁴

¹Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1; ²Department of Agronomy, Purdue University, 1150 Lilly Hall, West Lafayette, IN, 47907, USA; ³Agriculture and Agri-Food Canada, Research Centre, Delhi, Ontario, Canada N4B 2W9; ⁴Department of Natural Resource Sciences, Macdonald Campus of McGill University, Ste-Anne-de-Bellevue, Quebec, Canada H9X 3V9

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

Key words: Soil organic matter, ¹³C natural abundance, tillage practices

Nitrogen and phosphorus release from on-farm and industrial composts

Bernard Gagnon and Régis R. Simard¹

Centre de Recherches et de Developpement sur les Sols et les Grandes Cultures, Agriculture et Agroalimentaire Canada, 2560 Blvd. Hochelaga, Sainte-Foy, QC, Canada G1V 2J3

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

Key words: Composting, farm manure management, N and P mineralization

Predicting yield of Norway spruce and Douglas-fir using a morphopedological approach in the granitic landscapes of French Massif Central

Thomas Curt

Cemagref – Forest and Agroforestry Research Team 24 av. des Landais - BP 50085 -F- 63172 Aubière, France.

To investigate the productivity of two coniferous species in granitic uplands of the French Massif Central, relationships between soil–landscape units (= morphopedological units) and forest yield were examined. An alveola landscape model composed of seven main morphopedological units (MPU) characterizes these two granitic areas. In total, 460 forest stands were studied and joined to the MPU. Each type of MPU was correlated to the yield of Norway spruce and Douglas-fir, evaluated by the site index (dominant height of stand at a reference age). Results stress that MPU explain a large part of site index variations: 68.7% in Cevennes uplands and 50% in Limousin for Norway spruce, 42% in Limousin for Douglas-fir. The hierarchy of the productivity among MPU is comparable for both species and study areas. Highest site index values correspond to MPU with deep Brunisols in vales and bottom of alveolas, with a high soil water storage capacity but without waterlogging. Ridges and summits with coarse parent materials topped by shallow and nutrient-depleted soils experience the lowest site index values. The strong relationship between MPU and forest yield can be explained by a combination of ecological factors affecting forest yield: topoclimatic conditions, parent materials and soils. These results stress that inheritances from Tertiary, and from Quaternary periglacial environments still influence the present-day potentials of ecosystems. In conclusion, the advantages and drawbacks of morphopedological surveys for forest applications are discussed.

Key words: Soil–landscape units, forest yield, Picea abies (L.) Karst., Pseudotsuga menziesii (Mirb) Franco

Influence of organic waste amendments on selected soil physical and chemical properties

B. J. Zebarth¹, G. H. Neilsen², E. J. Hogue², and D. Neilsen²

¹Potato Research Centre, Agriculture and Agri-Food Canada, PO Box 20280, Fredericton, New Brunswick, Canada E3B 4Z7; ²Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, Summerland, British Columbia, Canada V0H 1Z0

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

Key words: Cation exchange capacity, water retention, soil pH, soil organic matter, soil bulk density