Alberta Soils Research Articles

Effect of long-term cropping systems on soil hydrophobicity of a clay loam soil under dryland conditions in southern Alberta

The objective was to quantify the effect of crop rotations, crop type, life cycle, nitrogen fertilizer, manure application, and fallow on soil hydrophobicity (SH). The SH was measured for a long-term (16 yr) dryland field experiment on a Dark Brown clay loam soil in southern Alberta, Canada. Mean SH was significantly (P ≤ 0.05) greater in rotations with grass, perennial crops, manure application, and continuous cropping; whereas cereal–legume rotations and N fertilizer effects were undetectable. A strong, positive correlation occurred between SH and soil organic carbon concentration (r = 0.73). Soil water repellency should be measured on these plots using water-based methods.

Irrigated crop rotation and phosphorus fertilizer-manure addition impacts on soil water repellency of a clay loam soil in southern Alberta

Soil water repellency (SWR) was measured for a 28 yr field study under irrigation on a clay loam Dark Brown soil in southern Alberta. The objectives were to study the effect of legume–cereal crop rotations, feedlot manure, and phosphorus (P) fertilizer application on soil hydrophobicity (SH) and soil water repellency index (RI) under irrigation. Mean SH and RI were similar (P > 0.05) for a legume–cereal and cereal rotation and were unaffected by P fertilization. However, P fertilization shifted the RI classification from slight to subcritical. In contrast, SH was significantly greater for manured than nonmanured treatments, while RI was unaffected. Soil organic carbon (SOC) concentration was significantly (P ≤ 0.05) correlated with SH (r = 0.74), but not with RI (r = −0.17). This suggested a closer association between the quantity of SOC and quantity of hydrophobic compounds (SH method) compared with the hydrophobic coatings inhibiting infiltration of water (RI method). No significant correlation between SH and RI (r = −0.09) suggests that SH is not a good predictor of SWR using the RI method. Overall, manure application increased SH and P fertilization shifted the RI classification from slight to subcritical. In contrast, legume–cereal rotations had no influence on SH and SWR using RI method compared with continuous cereal.

Influence of crested wheatgrass on soil water repellency in comparison to native grass mix and annual spring wheat cropping

Crested wheatgrass (CWG) [Agropyron cristatum (L.) Gaertn.] is a commonly introduced grass in the Canadian prairies, but concerns remain about its possible long-term effects on soil quality, and its influence on soil water repellency (SWR) has not been determined. The long-term (24 yr) effects of CWG on SWR in comparison to seeded native grasses and annual cropping were determined for a clay loam soil in southern Alberta, Canada by measuring SOC concentration and SWR using soil hydrophobicity (SH) and soil water repellency index (RI) methods. The cropping treatments were CWG, seeded native grass mix (NGM), continuous wheat, and wheat–fallow rotation, each with fertilized (nitrogen) and non-fertilized subplots, replicated four times. Mean SOC concentration, SH, and RI in samples of surface soil were similar (P > 0.05) for CWG and seeded NGM, and they did not support our hypothesis (seeded NGM > CWG). Mean SOC was significantly greater for seeded perennial grasses than annual crops by 1.7–2 times and SH by 2.1–2.5 times, which supported our hypothesis, but RI was similar among treatments. As expected, nitrogen fertilization significantly increased SOC concentrations, but the effects on SH and RI were undetectable. A strong positive correlation occurred between SOC concentration and SH (r = 0.92) but not for RI (r = 0.10). Our findings suggested that SWR was similar for CWG and seeded NGM. The SWR as measured using SH was greater for seeded perennial grasses than annual cropping but was similar using RI.

Influence of feedlot manure on reactive phosphorus in rainfall runoff during the transition from continuous to legacy phases

Little research has compared land application of stockpiled (SM) or composted (CM) beef feedlot manure with straw (ST) or wood-chip (WD) bedding on loss of reactive phosphorus (RP) in runoff. We conducted a 6 yr (2013–2018) rainfall simulation-runoff study and utilized surface (0–5 cm) soil collected from a long-term (since 1998) field experiment on a clay loam soil in southern Alberta, Canada. The treatments consisted of SM or CM with ST or WD bedding applied at 13, 39, and 77 Mg·ha−1 (dry weight), as well as an unamended control and mineral fertilizer treatment. Surface soil was collected from all treatments after 15–17 (C15, C16, C17; 2013–2015) continual annual applications, and then 1–3 yr (L1–L3, 2016–2018) into the legacy phase after manure applications were first discontinued in 2015. The soil was packed into runoff trays, and flow-weighted mean concentrations (FWMCs) and mass loads of RP5 (<5 μm filter) in runoff water were determined during rainfall simulations. Our findings generally supported our null hypothesis of similar RP5 losses for manure type (CM = SM) and bedding (ST = WD) for most years. Successively higher application rates increased RP5 loss by 32%–121%. Termination of long-term applications dramatically reduced FWMCs by 58%–77% and mass loss by 56%–65% from the C17 to L3 years. This suggests an accumulation of soil P during continuous phase and depletion during legacy phase; therefore, lower application rates or termination of applications may reduce RP5 loss in runoff.

Short‐term legacy effects of feedlot manure application on soil mesofauna

Little research exists on short-term legacy effects of feedlot manure application on soil mesofauna. This long-term (since 1998) study was on an irrigated clay loam soil in southern Alberta cropped to barley (Hordeum vulgare L.). We sampled the soil 3-4 yr (2017-2018) into the legacy period following 17 annual manure applications (1998-2014). The selected treatments sampled were stockpiled feedlot manure containing straw bedding applied at 0, 13, 39, and 77 Mg ha-1 (dry wt.). Intact soil cores were taken at three depth intervals (0-3, 3-6, and 6-9cm) in the fall over 2 yr to determine the densities of Acari (mites) suborders and Collembola (springtails) families. Significant (P ≤ .05) application rate effects occurred on Oribatida and Astigmata after 3 yr (but not after 4yr) into the legacy phase, whereas Prostigmata were unaffected. Densities of Astigmata after 3 yr were 3.2- to 4.1-fold greater at the 77 Mg ha-1 rate compared with three lower rates. Significant application rate effects occurred on Entomobryidae, Isotomidae, and Onychiuridae after 4 yr (but not after 3yr), with no treatment effects on Neelidae. Densities of mesofauna were generally greater at higher than at lower rates, except for Entomobryidae in 2018, where the reverse trend occurred. Significant application rate effects were attributed to lower soil bulk density and greater volumetric soil water content and soil organic carbon. Therefore, legacy effects of feedlot manure application generally persisted on soil mesofauna 3-4 yr into the legacy phase but depended on mesofauna type, year, and depth.

Influence of feedlot manure amendments on dissolved organic carbon in runoff during transition from continuous to legacy applications

Little research has compared land application of stockpiled (SM) or composted (CM) beef feedlot manure with straw (ST) or wood-chip (WD) bedding on loss of dissolved organic carbon (DOC) in runoff. We conducted a 6 yr (2013–2018) rainfall simulation-runoff study and utilized surface (0–5 cm) soil collected from a long-term (since 1998) field experiment on a clay loam soil in southern Alberta, Canada. The treatments consisted of SM or CM with ST or WD bedding applied at 13, 39, and 77 Mg·ha−1 (dry weight), as well as an unamended control and mineral fertilizer treatment. Surface soil was collected from all treatments after 15–17 (C15, C16, and C17; 2013–2015) continual annual applications and then after one to three legacy years (L1–L3, 2016–2018) after manure applications were first discontinued in 2015. The soil was packed into runoff trays, and flow-weighted mean concentrations (FWMCs) and mass loads of DOC in runoff water were determined during rainfall simulations. Mean DOC losses were generally significantly (P ≤ 0.05) lower for CM with ST bedding compared with the other manure type – bedding treatments in certain years and were consistent with this amendment having the lowest total carbon (C) content. The total C content of the amendments explained 92% of the variation in DOC concentration. Termination of long-term manure applications reduced FWMCs by 85%–91% and mass loss by 76%–89% from the C17 to L3 year. Therefore, our findings suggested that composting manure with ST or discontinued long-term manure application may reduce DOC loss in runoff.

Invading earthworms pose climate threat

Invasive earthworms are spreading into the northern forests of Canada and the US, disturbing the soil and transforming ecosystems, researchers reported at the American Geophysical Union Fall Meeting in San Francisco in December. This “global worming” could contribute to climate change by potentially unleashing the large stocks of carbon stored in northern soils. The boreal forests—large expanses of wild lands in the planet’s northern latitudes—are Earth’s largest terrestrial carbon sink. Their soils hold an estimated 200 billion metric tons (t) of carbon, 60 billion t of it in Canada alone. Until about 20 years ago, scientists didn’t think it was possible for earthworms to survive in the relatively cold, acidic soils of the Canadian boreal forests. But these days researchers find the worms just about everywhere they look, says Justine Lejoly, a researcher in the lab of University of Alberta soil biogeochemist Sylvie Quideau. People spread the critters when they

Drought differentially affects autotrophic and heterotrophic soil respiration rates and their temperature sensitivity

Climate change predictions indicate that extreme drought is likely to become more frequent in the future. In this study, the impact of drought on soil respiration (Rs) and its autotrophic (Ra) and heterotrophic components (Rh) were studied in a cultivated Black Chernozemic soil in central Alberta, Canada. The mean Rs was 24.4% lower in the drought relative to the plots with ambient precipitation (P < 0.001), with a larger decrease in Ra (26.8%) relative to Rh (21.0%), and a higher (P < 0.05) contribution of Rh to Rs under drought (52.8%) than under the ambient condition (47.7%). Both Rs and its Ra and Rh components had an exponential relationship with soil temperature and a quadratic relationship with soil water content. Drought caused a greater decrease in the tipping point of soil water content for Rh (a 39.6% reduction) than for Ra (a 15.1% reduction) relative to the ambient precipitation treatment. In addition, drought resulted in a greater increase in the temperature sensitivity (Q10 values) of Ra (a 45.0% increase) than that of Rh (a 14.1% increase) relative to the ambient precipitation treatment. The results suggest that drought amplified the water limitation effect on CO2 emission, especially that from microbial respiration, and resulted in a tighter relationship between temperature and root or autotrophic respiration, based on this 1-year study. We conclude that it is important to assess the impact of drought on soil respiration components rather than the total soil respiration, and such differential effects of drought on soil respiration components should be incorporated into global carbon circulation models.

An assessment of long-term soil acidification trends in Alberta, Canada

Long-term soil acidification monitoring was initiated in 1981 to track potential effects of acidic atmospheric deposition on soils in Alberta, Canada. Six of eight long-term sampling sites were located in forest ecosystems on sandy soils in northern and central Alberta, and two were situated in grasslands on sandy and fine-loamy soils in southern Alberta. Sampling was undertaken every four or five years, with 12 replicate samples taken from seven depth increments from 0–60 cm at each site. The statistical analysis of pH, exchangeable base saturation (BS) percentage, and solution base cation (BC) to aluminum (Al) ratio was conducted in the topmost soil layers (0–2, 2–5 and 5–10 cm). Analysis of variance (ANOVA) and linear regression indicated decreasing trends in pH and BS percentage in some of the sites. Comparison of the initial and most recent monitoring data indicated decreases of up to 0.5 pH units in these layers at five of the forested sites. At two forested sites located in the vicinity of oil sands and heavy oil processing plants, decreasing BS was observed early in the monitoring period, but the trend showed more variability since 2000, even though pH has continued to decline since 1981. BC to Al ratio showed statistically significant variations within some sites over time, but except for a downward trend at one central Alberta site, there were no overall patterns evident at the other sites over time. Both grassland sites had much higher BC to Al ratio and exchangeable BS percentages than the forested sites, and acidification trends were not detected at either of these sites. ANOVA and linear modelling approaches showed significant differences even in instances where pH differed by 0.1–0.2 units, or where other parameters showed very small differences. It is therefore necessary to distinguish between statistically important and biologically important differences in this monitoring program, which is intended to continue for several more years.

Spatial patterns and competition in trees in early successional reclaimed and natural boreal forests

Spatial distribution of plants in early successional stands provides an indication of future plant community structure and population dynamics. Determining the factors driving plant interactions and their demographic relationships at stand initiation is critical to gain a better understanding of plants’ responses to competition and limited resource conditions. Reclaimed ecosystems are ideal for studying such community mechanisms because they are completely reconstructed ecosystems with known community filters such as soil type, propagule composition, and the presence of both planted and naturally establishing trees. The current study explored the spatial patterns and competition-facilitation mechanisms in deciduous and evergreen trees in two oil sands reclaimed sites with different reclamation age (2-year old and 5-year old) and cover soils (wetland peat origin – PMM; and forest floor origin – FFMM) in Alberta, Canada, and compared this with a naturally-disturbed site at 5 years since fire. Spatial point pattern analysis was performed using pair correlation function g(r), mark correlation function kmm(r), and bivariate g-function. Intraspecific competition in deciduous seedlings was stronger in the 5-year old reclaimed site than in the 2-year old site. Spatial patterns in deciduous seedlings on PMM were aggregated at 1–3 m scale similar to the natural site, whereas seedlings on FFMM sites had aggregated patterns at greater than 5 m scale. Planted conifers had regular pattern at 1–2 m scale in the 2-year old sites which reflects the plantation spacing, but showed a random pattern in the 5-year old sites indicating the effect of random mortality. Bivariate spatial analysis indicated a significant repulsion between deciduous and coniferous seedling at 1 m in the 2-year old PMM site and a significant attraction in the 5-year old FFMM site suggesting that the mechanism of competition-facilitation between trees is different in different cover soils. Density dependent thinning was only observed in the 2-year old PMM and natural sites; however, a gradual increase in nearest neighbour distances with increasing seedling size in all the reclaimed sites suggests that density dependent thinning has started.

Use of Modelled Soil Data Ranges to Explore Post-Reclamation Soil Suitability Ratings for 30 Alberta Soil Series

Return to equivalent capability is the principle governing land reclamation in Alberta. However, land capability rating systems are seldom used to determine post-reclamation equivalency in agricultural lands. This study used the Land Suitability Rating System for Agricultural Crops (LSRS) to estimate reclaimed soil profile ratings. Baseline soil data for 30 soil series obtained from the Alberta Soil Layer file were changed to yield synthetic data. Admixture was simulated by mixing 10 equal increments of B horizon (subsoil) into the A horizon (topsoil) to a maximum of 50% of initial A horizon thickness. Subsoil density was changed in 2.5% increments above baseline to a maximum increase of 25%. Admixture effects on texture, organic carbon, and thickness of topsoil and density change in subsoil were quantified across these 10 treatment levels and deductions were calculated with the LSRS. At level 10 in which topsoil consisted of 33% subsoil admixture by volume and subsoil density had increased by 25%, capability declined from one to five classes below baseline. Future work will employ quantitative field data to explore the accuracy of these findings and to test the hypothesis that current assessment methods may be unreliable for confirming a return to equivalent capability.

Surface Soil Salinity and Soluble Salts after 15 Applications of Composted or Stockpiled Manure with Straw or Wood-Chips

ABSTRACTThe influence of 15 annual applications of composted (CM) or stockpiled (SM) beef feedlot manure with straw (ST) or wood-chip (WD) bedding on electrical conductivity (EC), soluble cations and anions (Na, K, Ca, Mg, SO4-S, Cl), sodium adsorption ratio (SAR), potassium adsorption ratio (PAR), and pH of a clay loam soil (0–15 cm) in southern Alberta was examined in an irrigated barley silage cropping system. Manure type (CM versus SM) had a significant effect on certain soil salinity parameters. Calcium, Mg, Na, K, and SO4-S were significantly (p ≤ 0.05) greater for SM- than CM-amended soils for certain bedding materials and rates. Electrical conductivity, concentration of soluble cations and anions (Na, K, SO4-S, Cl), SAR, PAR, and pH in the surface soil were greater for ST than WD bedding. Two exceptions were Ca and Mg, where soil concentrations were generally greater for WD than ST. Salinity parameters were greater with increased application rate, and greater for amended than unamended soils. Overall, bedding had considerably more significant effects on soil salinity parameters compared to manure type. Wood-chip bedding may be a management tool for feedlots to lower EC, soluble cations and anions, and pH of surface soils.

Influence of long-term application of composted or stockpiled feedlot manure with straw or wood chips on soil cation exchange capacity

ABSTRACTThe influence of annual applications of composted (CM) or stockpiled (SM) beef feedlot manure with straw (ST) or wood-chip (WD) bedding on cation exchange capacity (CEC) of a clay loam soil in southern Alberta was examined after 1, 8, and 15 years. The hypotheses in our study were that soil CEC should be greater for amended than unamended soils; manure type and bedding should have no effect on soil CEC; and soil CEC should increase with greater manure application rate. After fifteen applications, the CEC was significantly greater for amended than unamended soils. Manure type had no significant (P > 0.05) effect on soil CEC after fifteen applications, and the mean soil CEC was 5% greater for WD than ST. Mean CEC was significantly greater by 7 to 12% for the 77 than the 13 and the 39 Mg ha−1 rates after fifteen applications. The soil CEC was increased by 0.061 cmolc kg−1 for a unit increase in application rate (Mg dry wt. ha−1 yr−1), and 96% of the variation in CEC for amended soils could be explained by application rate. Overall, bedding, rate, or adjusting both bedding type and manure rate (but not manure type), may be possible practices for feedlot producers to manage soil CEC.

Stand Age and Productivity Control Soil Carbon Dioxide Efflux and Organic Carbon Dynamics in Poplar Plantations

Establishment of hybrid poplar (HP) plantations has been advocated as an effective method for sequestering CO2 from the atmosphere. However, how carbon (C) cycling in HP plantations changes during stand development under different soil fertility and climatic conditions is poorly understood. We studied the dynamics of soil respiration (Rs) and its heterotrophic (Rh) and autotrophic (Ra) components and soil organic C (SOC) content in HP plantations of different stand ages established on soils with different productivity (Class 1 vs. Class 3 soils) in Alberta (AB) and Ontario (ON), Canada. The Rs was the highest for AB-Class 1 (high-productivity) soils, followed by AB-Class 3 and ON-Class 3 (low-productivity) soils. Annual Rs, Rh, and Rh/Rs decreased in the first 3 yr in AB-Class 1 and 6 yr in AB-Class 3 soils after plantation establishment and increased thereafter, but they increased with stand age after plantation establishment in ON-Class 3 soils. The SOC content in the AB-Class 1, AB-Class 3, and ON-Class 3 sites decreased in the first 3, 5, and 1.5 yr, respectively, after plantation establishment and then increased, reaching the pre-establishment level after 6, 10, and 3 yr, respectively. From this first attempt to understand C cycling across multiple sites with different soil fertility levels, we conclude that stand age and soil productivity play a significant role in affecting C cycling, and such effects should be considered in regional and global C cycling models, especially when assessing the C sequestration potential of HP plantations.

Crop rotation effects on Pratylenchus neglectus populations in the root zone of irrigated potatoes in southern Alberta

Root-lesion nematodes (Pratylenchus spp.) are important pests of potato (Solanum tuberosum L.), particularly in sandy soils and in the presence of Verticillium dahliae. We assessed the effects of crop rotation and soil management practices (reduced tillage, cover crops and composted manure applications) on population densities of P. neglectus on potato in a sandy loam soil in southern Alberta. Crops in rotation included potato (P), dry bean (DB, Phaseolus vulgaris L.), wheat (W, Triticum aestivum L.), sugar beet (SB, Beta vulgaris L.), oats (O, Avena sativa L.) and timothy (T, Phleum pratense L.). The rotations included ‘conventional’ and ‘conservation’ versions of 3-year (DB-W-P) and 4-year (W-SB-DB-P) rotations, as well as 5-year (W-SB-W-DB-P) and 6-year (O/T-T-T-SB-DB-P) rotations. Conservation practices included autumn cover crops and incorporation of compost as a substitute for inorganic fertilizer. Population densities of P. neglectus in the potato phase of each rotation were assessed in autumn of 2006 and 2007, and at the beginning, middle and end of 2008, 2009 and 2010 growing seasons. Pratylenchus neglectus populations were affected by rotation length but not soil management practices; population densities in the 3-year rotations were larger than in most other rotations at most sample dates. Potato yields in the 3-year conventional rotation were consistently lower than in longer rotations. In the 3-year rotation, potato was preceded by wheat, which is known to be a good host for P. neglectus. We speculate that greater population build-up on wheat in the year before potato, rather than rotation length or crop diversity per se, was the cause of the larger population densities in the 3-year rotations than in longer rotations.

Organic capping type affected nitrogen availability and associated enzyme activities in reconstructed oil sands soils in Alberta, Canada

Organic materials applied in land reclamation play a key role in the development of ecosystem properties and functions. Peat mineral soil mix (PMM) and LFH (identifiable litter (L), fragmented litter (F) and humus (H)) mineral soil mix (LFH) are commonly used organic amendments for oil sands reclamation in northern Alberta. These materials have contrasting soil properties, with organic matter in LFH more decomposed and having a lower carbon-to-nitrogen (C:N) ratio than that in PMM. We quantified the effects of LFH and PMM capping material on N availability and enzyme activities during early ecosystem development in the oil sands region. Monthly samples were taken from 0 to10 and 10 to 20cm layers from June through October in 2011 and 2012. The N availability and activities of soil enzymes including β-1,4-N-acetyl glucosaminidase (NAGase), urease, arylamidase and protease were measured. In-situ N availability was measured using plant root simulator (PRS™) probes. Repeated measures ANOVA indicated that N availability and NAGase, arylamidase and protease activities were greater in LFH than in PMM and were affected by time of sampling. These differences were attributed to the lower C:N ratio in LFH than in PMM. We found greater N availability and enzyme activities in the fall than in the summer in both years. These differences were likely caused by fresh labile C inputs through root exudates and litter fall during fall that induced greater enzyme activities and led to greater N mineralization despite the potential limitation by the lower fall temperature. Overall, the greater N availabilities and enzyme activities in LFH suggest that LFH would be a better soil capping material than PMM for early ecosystem development in oil sands reclamation.

Soil nitrogen mineralization in a soil with long-term history of fresh and composted manure containing straw or wood-chip bedding

Long-term effects of fresh (FM) versus composted (CM) beef manure application to barley (Hordeum vulgare L.) on potentially mineralizable nitrogen (N 0 ), and mineralizable nitrogen (N) pools, were evaluated in a clay loam soil in southern Alberta, Canada. A suite of laboratory-based indices were evaluated for prediction of soil N supply. The treatments were three rates (13, 39, 77 Mg ha−1 dry wt.) of FM or CM containing either straw or wood-chip bedding, 100 kg N ha−1 as inorganic fertilizer, and an unfertilized control. Treatments were fall-applied annually for 8 years (1998–2005). Soil samples (top 15 cm) were collected in spring 2006. The medium and high rates of organic amendment resulted in increases in N 0 , and readily (Pool I) and intermediate (Pool II) mineralizable N pools in ranges of 140–355 % compared with the average of the fertilizer and control treatments. Fertilizer application had no significant effect on mineralizable N pools, but increased the mineralization rate constant (k) compared with the control. Application of FM and use of straw bedding resulted in a greater quantity of readily available and intermediate mineralizable N, and also increased the rate of N turn-over as indicated by greater values of k, compared with CM and wood-chip bedding. Among laboratory-based measures of soil N supply, CaCl2–NO3 (r2 = 0.84) and NaHCO3-205 (r 2 = 0.79) were strong predictors of plant N uptake (PNU). Increased soil mineralizable N did not translate into greater barley dry-matter yield or PNU. Composted beef manure and use of wood-chip bedding can be recommended as alternatives to FM and use of straw bedding for barley production is Southern Alberta.

Relative Nitrogen Fertilizer Requirements of Forage Versus Grain for Barley and Oat

Field experiments were conducted at 15 site-years with barley and 10 site-years with oat over five years to determine the relative nitrogen (N) fertilizer requirements of forage versus grain for barley and oat on Black Chernozem (Typic Agricryoll – 6 site-years on barley and 3 site-years on oat) and Gray Luvisol (Typic Haplocryalf – 9 site-years on barley and 7 site-years on oat) soils in central and north-central Alberta, Canada. Barley harvested for forage responded to higher level of applied N than when it was harvested for grain at most site-years. On average for barley, the amount of N fertilizer required to achieve maximum yield of forage was 58 kg N ha−1 greater than that of grain, and also was somewhat greater on Black Chernozem soils than on Gray Luvisol soils. The results for oat were inconclusive, with almost equal numbers of site-years showed higher N requirements for grain as for forage.

Genetic Diversity and Aggressiveness of Fusarium spp. Isolated from Canola in Alberta, Canada.

Canola (Brassica napus) is one of the most economically important oilseed crops in Canada. Fusarium seedling blight is a root disease with the potential to cause severe yield reductions in canola. Fusarium spp. are commonly isolated root pathogens from fields in Alberta. Fusarium infection can also cause root rot in adult plants. In this study, 128 isolates identified as Fusarium spp. were recovered from field soils in central Alberta and from the roots of diseased canola plants with typical Fusarium seedling blight symptoms. Six species of Fusarium were identified, with Fusarium acuminatum as the predominant species (57 of 128 isolates, 44.5%). Phylogenetic analyses based on the translation elongation factor 1-α and the internal transcribed spacer sequence data were used for evaluation of genetic variations, and also used for Fusarium spp. identification in combination with morphological characteristics and polymerase chain reaction-based analyses. Based on disease ratings in pathogenicity tests, six isolates of F. avenaceum showed high aggressiveness on canola. Also, the aggressiveness varied within all Fusarium spp. No correlation was observed between aggressiveness and the geographic origin of the isolates.

Effects of soil pH and salt on N2O production in adjacent forest and grassland soils in central Alberta, Canada

Purpose The effects of soil pH manipulation and KCl addition on N2O production in adjacent forest and grassland soils in central Alberta were studied in a 16-day laboratory incubation experiment. Materials and methods The soils were subjected to four pH and two salt treatments: CK (control)—no addition of acid or alkali solution (pH 4.50 and 4.48 for the forest and grassland soils, respectively; same below); HCl—addition of HCl solution to lower soil pH (3.95 and 3.75); L-KOH and H-KOH—addition of 6 mL of 0.2 (5.36 and 5.57) and 0.4 (6.41 and 6.72)molL �1 KOH solution, respectively, to increase soil pH to two different levels. In order to differentiate between the effect of a change in pH and of changed salt concentrations on N2O production, 6 mL of 0.2 (L-KCl) (4.56 and 4.41) or 0.4 molL �1 (H-KCl) (4.59 and 4.42) KCl solutions were also applied as treatments to create two levels of salt application rates. Results and discussion Increasing pH promoted gross nitrification and cumulative N2O production in both soils, particularly in the forest soil. However, cumulative N2O production decreased in the forest soil but increased in the grassland soil when pH decreased. Cumulative N2O production in the grassland soil was 36 times higher in the L-KCl treatment (1,442 μgNkg �1 ) than in the CK (40 μgNkg �1 ), whereas the H-KCl treatment reduced cumulative N2O production. In contrast, in the forest soil, both KCl treatments reduced cumulative N2O production. Conclusions (1) The most important factor to increase N2O production in this study was increasing soil pH, suggesting that careful soil pH management could be used as a tool to control soil N2O production; (2) salt effect was also involved in affecting N2O production.