Yang, L.-x., Li, S.-c., Sun, H.-l., Ye, F.-f., Liu, W. and Luo, S. 2011. Polyacrylamide molecular formulation effects on erosion control of disturbed soil on steep rocky slopes. Can. J. Soil Sci. 91: 917-924. Soil erosion caused by increasing runoff and soil disturbances is a severe problem on steep rocky slopes. One possible soil erosion control measure is the application of polyacrylamide (PAM). Little is known about PAM application in the ecological recovery field, especially for steep rocky slopes. Our objective was to examine the ability of a range of anionic PAMs to control soil erosion on steep rocky slopes. Nine types of anionic PAMs were studied, which consisted of three molecular weights (MW) and three charge densities (CD) in a factorial design. The study was conducted using laboratory soil trays exposed to simulated rainfall. Three soils of different textures were treated with PAM using hydro-seeding technology with soil trays at a 60° slope. This work demonstrates that PAMs are effective at improving infiltration, thereby decreasing soil erosion. The PAMs that performed best for erosion control were the 14 Mg mol^-1 MW and 30% CD for the loamy sand, the 10 Mg mol^-1 MW and 20% CD for the silty loam, and the 6 Mg mol^-1 MW and 30% CD for the silty clay. These results could assist ecologists in developing PAM application strategies to promote slope recovery.

Liu, T., Nan, Z. and Hou, F. 2011. Culturable autotrophic ammonia-oxidizing bacteria population and nitrification potential in a sheep grazing intensity gradient in a grassland on the Loess Plateau of Northwest China. Can. J. Soil Sci. 91: 925-934. Grazing is known to enhance the activity of soil microbial communities in many types of grasslands; however, the potential impacts of rotational grazing activity on soil microbial functional groups remain poorly understood. We investigated the effects of 9 yr of rotational grazing by livestock on culturable autotrophic ammonia-oxidizing bacteria (AOB) population size, nitrification potential and soil properties in a semi-arid grassland of the Loess Plateau in Northwest China. Three stocking rate treatments of 2.7, 5.3 and 8.7 wether lambs ha^-1 were evaluated in geographically separated paddocks. Grazing increased nitrification potential and culturable AOB populations compared with ungrazed treatments. Ammonia-oxidizing bacteria populations increased from 155 bacteria g^-1 dry soil with 0 sheep ha^-1 to 16 218 bacteria g^-1 dry soil with 8.7 sheep ha^-1. Grazing led to an increase in population of AOB at 0-10 cm soil depth, but had no effect on AOB at 10-20 cm soil depth. Nitrification potential increased from 1.21 mg NO₃-N kg^-1 soil d^-1 in ungrazed treatments to 2.86 mg NO₃-N kg^-1 soil d^-1 at the highest stocking rate. Soil ammonium and nitrate concentrations increased; however, total soil nitrogen and soil moisture content decreased with increased stocking rate for both sampling depths (0-10 cm and 10-20 cm). Soil organic matter was not affected by grazing treatments. Soil nitrification potential and the size of culturable AOB populations were dependent on grazing intensity, soil depth and season. This information is potentially important for the optimal selection of stocking rate for grazed ecosystems.

Miesel, J. R., Boerner, R. E. J. and Skinner, C. N. 2011. Soil nitrogen mineralization and enzymatic activities in fire and fire surrogate treatments in California. Can. J. Soil Sci. 91: 935-946. Forest thinning and prescribed fire are management strategies used to reduce hazardous fuel loads and catastrophic wildfires in western mixed-conifer forests. We evaluated effects of thinning (Thin) and prescribed fire (Burn), alone and in combination (Thin Burn), on N transformations and microbial enzyme activities relative to an untreated control (Control) at 1 and 3 yr following treatment in northern California. N mineralization and net nitrification were reduced by Thin and by Burn in year 1, and N mineralization was increased by Thin Burn in year 3, relative to the Control. In general, all experimental treatments reduced soil enzyme activity. To identify overall treatment effects on the below-ground ecosystem, we combined these data with soil physicochemical data from this site to perform non-metric multidimensional scaling (NMS) ordination. NMS ordination showed that Burn and Thin Burn produced the greatest overall effects on soil, and that overall differences in soil characteristics among treatments diminish over time. These results provide an important benchmark for monitoring ecosystem effects of large-scale wildfire hazard reduction strategies over the long term.

Ige, D. V., Abioye, O. S., Akinremi, O. O., Nyachoti, C. M. and Flaten, D. N. 2011. Phosphorus solubility in Manitoba soils treated with pig manure from phytase supplemented diets. Can. J. Soil Sci. 91: 947-955. Phytase supplementation has been shown to reduce manure P content. However, this manipulation can influence manure P solubility upon land application. Therefore, the objectives of this study were to investigate the solubility of P in soils amended with manure from diets with reduced or no inorganic P supplement with and without phytase addition and to evaluate the influence of soil type on the solubility of manure P from phytase supplemented pig diets. Two calcareous and two non-calcareous Manitoba soils were amended with manure produced by pigs that were fed with diets containing different levels of supplemental inorganic P with and without phytase. Manure was applied at the rate of 75 kg P ha^-1 and the amended soils were incubated for 1, 4 and 16 wk. Soil P was extracted with water (H₂O-P), Olsen (Ols-P) and Mehlich-3 (M3-P) solutions. Manure application mostly increased H₂O-P above the control. Complete removal of supplemental inorganic P from the diet irrespective of phytase addition significantly increased M3-P (P<0.05) in the two calcareous soils during the 16-week incubation. Similarly, when no supplemental inorganic P was included in the diet, Ols-P was increased in the fine textured, calcareous soil at 16th week of incubation. Thus, the complete removal of inorganic P from pig diet has potential to increase P solubility in some soils. Addition of phytase to pig diet did not have consistent effects on the soil extractable P in these soils. Soil factor had the greatest influence (77 to 94%) on P solubility. Our results showed that while phytase supplementation with concurrent reduction in inorganic P will reduce manure P with no adverse effect on P solubility in soils, total elimination of dietary inorganic P through the use of greater rate of phytase may not be feasible as this has the potential to increase P solubility in some soils.

Halde, C., Hammermeister, A. M., McLean, N. L., Webb, K. T. and Martin, R. C. 2011. Soil compaction under varying rest periods and levels of mechanical disturbance in a rotational grazing system. Can. J. Soil Sci. 91: 957-964. In Atlantic Canada, data are limited regarding the effect of grazing systems on soil compaction. The objective of the study was to determine the effect of intensive and extensive rotational pasture management treatments on soil bulk density, soil penetration resistance, forage productivity and litter accumulation. The study was conducted on a fine sandy loam pasture in Truro, Nova Scotia. Each of the eight paddocks was divided into three rotational pasture management treatments: intensive, semi-intensive and extensive. Mowing and clipping were more frequent in the intensive than in the semi-intensive treatment. In the extensive treatment, by virtue of grazing in alternate rotations, the rest period was doubled than that of the intensive and semi-intensive treatments. Both soil bulk density (0-5 cm) and penetration resistance (0-25.5 cm) were significantly higher in the intensive treatment than in the extensive treatment, for all seasons. Over winter, bulk density decreased significantly by 6.8 and 3.8% at 0-5 and 5-10 cm, respectively. A decrease ranging between 40.5 and 4.0% was observed for soil penetration resistance over winter, at 0-1.5 cm and 24.0-25.5 cm, respectively. The intensive and semi-intensive treatments produced significantly more available forage for grazers annually than the extensive treatment. Forage yields in late May to early June were negatively correlated with spring bulk density.

Wilske, B. and Johnson, E. A. 2011. Measuring unsaturated hydraulic conductivity (K(ψ_m)) of the F and H soil organic layers at small matric potential (ψ_m). Can. J. Soil Sci. 91: 965-968. K(ψ_m) of the soil organic layers is a key parameter to assess water redistribution in cold-climate forests. This study tested the twin suction disc apparatus (TSD) as a new method to measure K(ψ_m) of the F and H layers directly. We compared the results to two studies. One represents a large data base, the other used similar sample locations; but both derived K(ψ_m) from combining two methods, i.e., pressure plate measurements combined with the instantaneous profile technique or the constant head approach. The TSD data are consistent with previous results considering the large variability in K(ψ_m) from the combined methods. This suggests that the TSD method represents an alternative to determine K(ψ_m) of the soil organic layer.

Miller, J. J., Beasley, B. W., Drury, C. F. and Zebarth, B. J. 2011. Accumulation and redistribution of residual chloride, nitrate, and soil test phosphorus in soil profiles amended with fresh and composted cattle manure containing straw or wood-chip bedding. Can. J. Soil Sci. 91: 969-984. Limited research has compared the effect of fresh versus composted beef (Bos taurus) cattle feedlot manure containing straw or wood chips on accumulation and redistribution of residual chloride (Cl), NO₃-N, and soil test P (STP) in soil profiles of the Great Plains region of North America. Barley (Hordeum vulgare L.) was grown (1999-2007) on an irrigated clay loam soil in southern Alberta where organic amendments and fertilizer were annually applied for 9 yr from 1998 to 2006. The field experiment was a factorial arrangement of two manure types (fresh versus composted feedlot manure), two bedding materials (straw versus wood-chips), and three application rates (13, 39, 77 Mg ha^-1 dry wt). There was also one inorganic (IN) fertilizer treatment and an unamended control. The soil profile (0-1.5 m) was sampled in the fall of 1999 to 2002, 2004, 2006, and 2007 and analyzed for residual soil NO₃-N, Cl, and STP. Manure type had a significant (P≤0.05) effect on the accumulation of these chemicals, but there was an interaction with application rate (NO₃-N), or with bedding and year (STP). The maximum accumulation of Cl after 9 yr was at the 0.6 to 0.9 m depth, but mean values at this depth were similar for the four organic amendments. The maximum accumulation of NO₃-N after 9 yr (2007) was at the 0.3 to 0.6 m depth, and mean values at this depth were significantly greater by four- to sixfold for FM and CM with straw than wood-chips, which suggested greater N immobilization in soils with wood. Redistribution of Cl and NO₃-N downward into the soil profile suggested a potential for leaching of these chemicals below the root zone. In contrast, soil test P did not accumulate below the 0.3 m depth, suggesting little potential for leaching. However, accumulation of soil test P at this depth was generally greater for the amendment treatments compared with inorganic fertilizer and was likely related to greater P applied in the amendments.

Beyaert, R. P. and Voroney, R. P. 2011. Estimation of decay constants for crops residues measured over 15 years in conventional and reduced tillage systems in a coarse-textured soil in southern Ontario. Can. J. Soil Sci. 91: 985-995. Crop residues are the primary means of sustaining soil organic matter levels in agricultural soils. This study was undertaken to determine the effects of tillage practices on the rate of decomposition of crop residues over a 15-yr period under field conditions in southern Ontario. Microplots were amended with ¹⁴C-labelled above-ground residues of five annual agricultural crops: corn (Zea mays L.), soybean (Glycine max L.), winter wheat (Triticum aestivum L.), winter rye (Secale cereale L.) and tobacco (Nicotiana tobaccum L.). The crop residues were added to the soil immediately following harvest during the 1990 growing season using a simulated conventional mouldboard plough-disc management (CT) or conservation tillage management (RT), and the amounts of crop residues remaining were measured periodically. The rate of decomposition of the labile C was positively correlated to the levels of hot-water soluble C and N content and negatively correlated to the C:N ratio and hemicellulose concentration of the residues. Decomposition of the residue C was greater under CT during the initial phase of decomposition, indicating that the incorporated residues were exposed to a more favourable environment for microbial activity compared with surface-applied residues. Kinetic analysis of residue decomposition showed that residues managed under CT had a larger labile component and faster rate of decomposition and a smaller resistant component with a slower decomposition rate than RT. Comparisons of models describing the decomposition of combined crops/tillage practices did not describe the decomposition process as well as models for individual crop/tillage combinations.

Whitman, T., Yanni, S.F. and Whalen, J.K. 2011.Life cycle assessment of corn stover production for cellulosic ethanol in Quebec. Can. J. Soil Sci.91: 997-1012. The province of Quebec has a target of 5% ethanol (EtOH) content in fuel by 2012, which means the province will require about 400 million L of ethanol per year based on current consumption. Current research is focused on “second generation biofuels” such as cellulosic EtOH, which can be produced from agricultural by-products like corn stover. A life cycle assessment (LCA) evaluates the “cradle to gate” impact of corn stover feedstock production for cellulosic EtOH production in three corn-producing regions in Quebec for two impact categories: energy and greenhouse gas (GHG) impacts. The modelled system boundaries include in-field processes: corn stover production, collection, transport, soil organic carbon (SOC) loss, and N₂O emissions, as well as background processes: herbicide, fertilizer, seed, and fuel production and transport. Sensitivity analyses vary the percentage of corn stover collected, contrast a multiple-pass with a one-pass stover-grain collection system, and compare mass, economic and system expansion allocation methods. Total energy impact is 931-1442 MJ t^-1 dry stover collected under 15% stover collection, with stover harvest, transport, and field operationscontributing most strongly to the total impact. Total GHG emissions from corn stover production and transport of stover to the ethanol facility are320-488kg CO₂e t^-1 dry stover under 15% stover collection, with SOC loss, N₂O emissions, and stover harvest contributing the most to the total impact. Sensitivity analysis reveals that the energy and GHG impacts of stover production are strongly influenced by the mass of stover collected, the use of a one-pass system, and the choice of allocation methods. Scaling-up results from the modelled system suggest that 100% of Quebec's EtOH targets could technically be supplied using corn stover feedstock, but this may come at the expense of GHG emissions and soil health.

Neilsen, G. H. and Neilsen, D. 2011. Consequences of potassium, magnesium sulphate fertilization of high density Fuji apple orchardsConsequences of potassium, magnesium sulphate fertilization of high density Fuji apple orchards. Can. J. Soil Sci. 91: 1013–1027. Three annual broadcast fertilizer treatments of 0, 100 or 200 kg K ha^-1 as K, Mg sulphate (KMag) were applied in a randomized complete block design with six replicate multi-tree plots. The study was undertaken for three successive growing seasons in eight commercial apple orchards of fruiting ‘Fuji’/M.9 (Malus × domestica Borkh.) located on coarse-textured soils typical of the Okanagan valley fruit production region of southern British Columbia. After 3 yr, KMag fertilization increased the amount and proportion of exchangeable K and Mg at the 0-10 and 10-20 cm depth. Soil exchangeable Ca was generally decreased in the surface 0-10 cm layer although the Ca/∑[Ca Mg K] ratio decreased over the surface 20 cm. During the study, application of KMag fertilizer often increased leaf and fruit K concentrations, minimally affected leaf Mg and sometimes decreased fruit Ca concentration by years 2 and 3 and had little effect on fruit K/Ca or Mg/Ca ratio. KMag fertilization was effective in an orchard of marginal K nutritional status, increasing cumulative yield, fruit size and red colouration, implying an economic response to the K contained in the fertilizer. KMag fertilization was effective for maintaining leaf Mg concentration, but could not be relied upon to increase deficient leaf Mg. There were no widespread declines in fruit Ca concentration, nor increases in Ca-related harvest disorders after 3 yr of KMag fertilization, despite declines in exchangeable Ca and Ca/∑[Ca Mg K] in surface soil layers.

Larney, F.J., Janzen, H.H. and Olson, A.F. 2011. Residual effectsof one-time manure, crop residue and fertilizer amendments on a desurfaced soil. Can. J. Soil Sci. 91: 1029-1043. Organic amendments are often used to mitigate the effects of soil degradation caused by erosion. In spring 1992, a desurfaced soil (~15 cm depth mechanically removed to simulate erosion) received one-time applications of amendments (20 Mg ha^-1 dry wt), and was subsequently seeded annually to spring wheat (Triticum aestivum L.). By 2009, six treatments (fresh and old cattle manure, hog and poultry manure, alfalfa (Medicago sativa L.) hay and straw 200 kg P ha^-1) had cumulative yields which were not significantly different (-6.5 to -19.5%) from the topsoil check treatment (no topsoil removed, no amendment). Most (8 of 13) amendment treatments showed significant power function relationships between cumulative grain yield (expressed as a percent of topsoil check) and time while two (hog and poultry manure) were quadratic. Soil organic carbon (SOC) accrued on all treatments over time, increasing significantly from an average of 12.2 g kg^-1 in 1992 to 13.2 g kg^-1 (0-15 cm depth) in 2003. Residual amendment effects on total nitrogen (N) and phosphorus (P) were apparent 11.5 yr after application. Results demonstrated that while drastically disturbed soils may recover productivity in the absence of organic amendments (e.g., eroded check treatment), organic amendments play a residual role in their ongoing maintenance.