Georgallas, A., Dessureault-Rompré, J., Zebarth, B. J., Burton, D. L., Drury, C. F. and Grant, C. A. 2012. Modification of the biophysical water function to predict the change in soil mineral nitrogen concentration resulting from concurrent mineralization and denitrification. Can. J. Soil Sci. 92: 695-710. Uncertainty in soil N supply is an important limitation in making crop fertilizer N recommendations. This study modified a biophysical water function developed to predict net soil N mineralization, making it possible to consider how both N mineralization and denitrification processes affect the rate of soil mineral N accumulation. Data were from a published experiment measuring changes in soil mineral N concentration in five soils of varying texture (loamy sand to clay loam) incubated for 3 mo with or without addition of red clover residue and at two levels of compaction. The biophysical water function was effective in fitting the relationship between scaled change in the rate of soil mineral N accumulation (ΔSMN) and scaled water-filled pore space (WFPS_S) across soils and treatments provided that WFPS_S=1 was set to the water content at which the transition from mineralization to denitrification occurs. The water content at WFPS_S=1 varied with soil type, but not residue addition or compaction treatments, and was closely related to clay content. The k_D parameter, which controls the denitrification term of the function, was influenced by soil type, whereas legume residue application had no significant effect on the k_D parameter despite a twofold increase in net N mineralization. The modified biophysical water function holds promise for improving estimates of soil N supply because it can predict changes in ΔSMN in response to N mineralization and denitrification processes across a wide range of soil water contents.

Gagnon, B., Demers, I., Ziadi, N., Chantigny, M. H., Parent, L.-É., Forge, T. A., Larney, F. J. and Buckley, K. E. 2012. Forms of phosphorus in composts and in compost-amended soils following incubation. Can. J. Soil Sci. 92: 711-721. Information on the forms and bioavailability of P from composts applied to horticultural crops under organic production are required to promote soil quality and plant growth while protecting the environment. Seven composts were selected and characterized for their chemical composition. The composts were mostly mature and the total P contained 73 to 96% as inorganic P (Pi), although the total P concentration and P fractions varied amongst the materials selected for this study. These composts along with an inorganic P (KH₂PO₄) alone were added to three soils with contrasting chemical properties at a rate equivalent to 65 kg P ha^-1 and incubated in the dark at 25°C. An unfertilized control was included to estimate soil P contribution. The amount and relative solubility of P from these compost-soil mixtures were evaluated by a modified Hedley fractionation after 2 and 16 wk of incubation. Results indicated that P added with composts was preferentially found in the Pi portion of soil labile pools after 2 and 16 wk. Except for the dairy cattle manure compost, all composts resulted in the same amounts of labile P (51-58%) and total Pi (61-98%) in soils, which were significantly lower than the labile P (82%) and close to the total Pi (108%) from inorganic KH₂PO₄ alone. Unlike the other composts, the potato residue compost produced a significant increase in the organic P fraction (Po) extractable with NaHCO₃. This study indicated that Pi was the most important form of P in these composts and in the compost-amended soils. Nevertheless, it remains difficult to predict the availability of compost P following its application to soil.

Rezanezhad, F., Price, J. S. and Craig, J. R. 2012. The effects of dual porosity on transport and retardation in peat: A laboratory experiment. Can. J. Soil Sci. 92: 723-732. Peatlands cover up to half of the local landscape in the Athabasca oil sands region, and peat materials are commonly used in reclamation. The toxicity of oil sands process-affected water (OSPW) derived from the Athabasca oil sands is related to the elevated concentration of naphthenic acids (NAs) and sodium (Na). However, the transport and retardation of solutes through peat is significantly delayed by sorption and by diffusion into immobile water contained in the peat matrix. Approximately 94% of the 43.5 mg L^-1 of OSPW was sorbed by 1 kg of peat. For Na ~84% sorption occurred with 382 mg L^-1 kg^-1 of peat. The sorption and desorption of NAs and Na on peat fitted linear isotherms with distribution coefficients of 6.53 and 5.74 L kg^-1, respectively. Solute breakthrough tests were performed for NaCl and the retardation due to sorption (R) of 1.73 was estimated for Na using a two-region (mobile and immobile) non-equilibrium transport model. However, the estimated mass transfer coefficient describing solute exchange between the mobile and immobile liquid regions indicated that part of retardation is attributed to solute exchange between the mobile and immobile phases. This was evident because Cl, a conservative solute (R=1, no sorption), also exhibited characteristics of dual-porosity transport. Thus, the passage of the solute front was retarded by diffusion of solute into the immobile region and by solute exchange between the mobile and immobile phases, which occurs at a rate depending on the proportion of mobile/immobile pore spaces. In this study, we showed that the complex dual-porosity structure of the peat is the important factor in attenuating solute transport where the presence of immobile phase (dead-end pores) in the system contributes to the transport and sorption mechanism of solute into this porous medium.

Quenum, M., Nolin, M. C. et Bernier, M. 2012. Cartographie numérique de la capacité maximale de sorption du phosphore des sols à l'échelle de la parcelle agricole à l'aide de variables auxiliaires. Can. J. Soil Sci. 92: 733-750. La gestion modulée des engrais à base de P en fonction de la variabilité spatiale de la capacité maximale de sorption du phosphore (CMSP) des sols propose des solutions pour réduire la contamination des eaux de surface par le P à l'échelle de la parcelle agricole. Les objectifs de l'étude sont 1) caractériser et interpréter en termes de stratégie d'échantillonnage des sols l'intensité de la variation et la structure d'organisation spatiale de trois indicateurs de la CMSP, soit les teneurs en aluminium et fer extraits au Mehlich-3 ou à l'oxalate d'ammonium (Al_M3, Al_M3 Fe_M3 et Al_ox Fe_ox) et 2) évaluer l'utilité de variables auxiliaires (modèle numérique d'élévation, image IKONOS ou conductivité électrique apparente (CEA) des sols mesurée à l'aide du VERIS 3100 ou du Geonics EM-38) à la cartographie numérique de la CMSP des sols à l'échelle de la parcelle agricole. Le site étudié est constitué de trois parcelles contiguës (16 ha) du bassin versant du Bras d'Henri (Québec, Canada). Un échantillonnage intensif (grille de 30 m×30 m) de la couche de surface (0-20 cm) des sols y a été effectué. L'analyse variographique montre que tous les indicateurs de la CMSP étudiés présentent une structure spatiale à l'échelle de la parcelle et que Al_M3 est l'indicateur qui présente les structures spatiales les mieux définies. L'approche anisotrope a permis de réduire l'erreur standard moyenne (ESM) de krigeage. La CEA mesurée avec le Geonics EM-38 est la variable auxiliaire qui donne la plus faible ESM lors de l'interpolation de Al_M3 par cokrigeage. Cependant, ESM s'avère relativement élevée (ESM=171 mg Al_M3 kg^-1) compte tenu de la forte densité d'échantillonnage utilisée (11 échantillons par ha). La cartographie numérique de la CMSP à l'échelle de la parcelle est réalisable mais requiert le développement d'une stratégie d'échantillonnage mieux adaptée au contexte agropédologique de l'Est du Canada.

Whalen, J. K., Benslim, H. and Vanasse, A. 2012. Insecticides (dimethoate and lambda-cyhalothrin) for soybean aphid control - are they toxic to earthworms? Evidence from laboratory and field bioassays. Can. J. Soil Sci. 92: 751-758. Outbreaks of the exotic soybean aphid (Aphis glycines Matsumura) cause significant yield loss of soybean [Glycine max (L.) Merr.] grown in North America. This study assessed the toxicity of dimethoate and lambda cyhalothrin, recommended to control soybean aphid, to earthworms, a non-target organism present in soybean fields. Laboratory bioassays showed the lethal and sub-lethal concentrations of dimethoate and lambda cyhalothrin to adult Eisenia fetida (Savigny) and their offspring. The most sensitive toxicity endpoint was adult E. fetida growth rates, which had a half maximal effective concentration (EC₅₀) of 6.39 mg active ingredient (a.i.) kg^-1 soil for dimethoate and 5.41 mg a.i. kg^-1 soil for lambda cyhalothrin after 28 d exposure. The field bioassay was done on two commercial farms with naturally occurring earthworms (including Aporrectodea turgida,Allolobophora chlorotica, Aporrectodea rosea, Lumbricus terrestris and Eiseniella tetraedra). Soybean fields received insecticidal sprays during 2007 and 2008. Timely application of dimethoate (both farms) and lambda cyhalothrin (one farm) controlled the aphid outbreak in 2007 and increased soybean yield by 9 to 22% over the untreated control. These insecticide treatments had no effect on field earthworm populations, probably because application rates recommended to control soybean aphid were up to three orders of magnitude lower than the EC₅₀ determined in laboratory tests. In conclusion, recommended application levels of dimethoate and lambda cyhalothrin for soybean aphid control are not toxic to earthworms in soybean fields.

Zebarth, B. J., Snowdon, E., Burton, D. L., Goyer, C. and Dowbenko, R. 2012. Controlled release fertilizer product effects on potato crop response and nitrous oxide emissions under rain-fed production on a medium-textured soil. Can. J. Soil Sci. 92: 759-769. Controlled release fertilizers and split fertilizer N applications are expected to provide plant-available nitrogen (N) in synchrony with crop requirements, which should mitigate nitrous oxide (N₂O) emissions from agricultural soils. This study compared a polymer coated urea (PCU) controlled release N fertilizer (Environmentally Smart Nitrogen), split fertilizer N application and conventional fertilizer N management on the crop response and growing season N₂O emissions from rain-fed potato (Solanum tuberosum L.) production on a medium-textured soil in Atlantic Canada from 2008 to 2010. Fertilizer were applied at the recommended rate (193 kg N ha^-1) and treatments included the PCU product banded at planting, conventional fertilizer in a split application (60% as diammonium phosphate plus ammonium nitrate at planting plus 40% as ammonium nitrate at final hilling), conventional fertilizer (diammonium phosphate plus ammonium nitrate) banded at planting, and an unfertilized control. Within each year, cumulative growing season N₂O emissions were closely related to soil nitrate availability as measured by nitrate exposure (sum of daily nitrate concentration in the surface soil). Split N application had no effect on crop response, and significantly reduced nitrate exposure, but did not reduce N₂O emissions. With the PCU, there was evidence of increased plant N availability and greater N₂O emissions. In situations where the risk of nitrate leaching is limited, substitution of a PCU product for conventional fertilizer at the same N application rate will not necessarily reduce growing season N₂O emissions and may in some cases increase the risk of N₂O emissions. Further research is required to determine if lowering N rates with PCU products will be effective agronomically and environmentally.

Srinivasarao, Ch., Venkateswarlu, B., Lal, R., Singh, A. K., Kundu, S., Vittal, K. P. R., Sharma, S. K., Sharma, R. A., Jain, M. P. and Chary, G. R. 2012. Sustaining agronomic productivity and quality of a Vertisolic Soil (Vertisol) under soybean-safflower cropping system in semi-arid central India. Can. J. Soil Sci. 92: 771-785. Enrichment of soil organic carbon (SOC) stocks through sequestration of atmospheric CO₂ in agricultural soils is important because of its impacts on improving soil quality and agronomic production, and also for adaptation to and mitigation of climate change. Thus, a 15-yr soil fertility management experiment was conducted in the semi-arid tropical region of central India to evaluate the impact of crop residue C input on soybean (Glycine max L.)-safflower (Carthamus tinctorius L.) cropping sequence and SOC sequestration in soils of Vertisolic order (Vertisols). Retention of crop residues of soybean/safflower, and application of farmyard manure (FYM) at 6 Mg (t) ha^-1 alone or in combination with 20 kg N and 13 kg P ha^-1 supplied through chemical fertilizers or comparatively higher dose of chemical fertilizer (60 kg N and 35 kg P ha^-1) either maintained or increased the SOC stock. However, the combination of FYM and chemical fertilizer increased the profile SOC stock (69.9 Mg ha^-1), overall SOC build up (37.1%) and also sequestered high amount of SOC (11.9 Mg C ha^-1 or 0.79 Mg C ha^-1 yr^-1) compared with control and chemical fertilizer alone. Higher grain yield (2.10 and 1.49 Mg ha^-1 of soybean and safflower, respectively) was obtained through the application of FYM at 6 Mg ha^-1 N₂₀P₁₃. For every Mg C ha^-1 increase in the root zone, there was 0.145 and 0.059 Mg ha^-1 increase in grain yield of soybean and safflower, respectively. Stabilization of the SOC stock requires a minimum input of 3.47 Mg C ha^-1 yr^-1. Application of 40 kg N 26 kg P ha^-1 through chemical fertilizer also maintained the SOC stock at the antecedent level based on the SOC stocks in 1992. Therefore, the combined use of organic manure (crop residues and FYM) along with chemical fertilizer is essential to enhancing the SOC sequestration in a soybean-safflower sequence under rainfed conditions on Vertisols in central India.

Kasongo, R. K., Kanyankogote, P., Verdoodt, A., Baert. G., Dumon, M. et Van Ranst, E. 2012. Effet in vitro de la roche verte de Gangila sur les propriétés physico-chimiques des sols sableux de l'hinterland de Kinshasa (RD Congo). Can. J. Soil Sci. 92: 787-797. Les roches vertes de Gangila (Bas-Congo), sont constituées principalement d'amphibolites et de schistes verts et ont un grand potentiel en nutriments. Une étude in vitro a été conduite pour étudier les effets d'application de ces roches comme fertilisants sur diverses propriétés physico-chimiques des sols sableux de l'hinterland de Kinshasa, RD Congo. Ces sols, classifiés comme Orthic Régosols selon le système Canadien de classification des sols (Arénosols en WRB), sont caractérisés par une faible fertilité chimique, une capacité de rétention en eau très limitée, et une réaction acide susceptible d'induire une toxicité aluminique, voire manganique, pour les cultures. Quatre doses correspondant à 0,0; 12,5; 25,0 et 50,0 Mg ha^-1 de roche finement broyée ont été mélangées avec des sols de surface (0-25 cm), puis incubées et lessivées pendant 3, 6, 9, 12, 15 et 18 mois. L'apport de la roche verte de Gangila au sol accroît significativement le pH (>5,5), la disponibilité en P, la somme des cations basiques (SCB), la CEC, et augmente d'environ 3 % (volume) la capacité de rétention d'eau dans les sols. Des augmentations allant jusqu'à 50 % P extractible, 2,2 cmol_c kg^-1 SCB et 75 % CEC ont été enregistrées dans les sols amendés de 50,0 Mg ha^-1 après 6 mois d'incubation. Par ailleurs, l'accroissement du pH et la réduction du pH₀ (point de charge zéro) due à l'adsorption des ions silicates ont produit une augmentation significative des charges négatives CEC_B (capacité d'échange cationique basique) et CEC_T (capacité d'échange cationique totale) avec une neutralisation complète de la phytotoxicité aluminique (pH-H₂O>5,5). L'étude du percolat a révélé que l'application de roches vertes de Gangila finement broyées influence sensiblement la dynamique des cations et immobilise certains microéléments (Fe, Cu, Mn, Zn). La perte relative des cations monovalents (K , Na ) a été plus importante que celle des ions bivalents (Ca , Mg ). Les roches vertes de Gangila peuvent servir d'amendements naturels pour augmenter la fertilité des sols sableux tropicaux.

Veverica, T. J., Kane, E. S. and Kasischke, E. S. 2012. Tamarack and black spruce adventitious root patterns are similar in their ability to estimate organic layer depths in northern temperate forests. Can. J. Soil Sci. 92: 799-802. Organic layer consumption during forest fires is hard to quantify. These data suggest that the adventitious root methods developed for reconstructing organic layer depths following wildfires in boreal black spruce forests can also be applied to mixed tamarack forests growing in temperate regions with glacially transported soils.

Cutforth, H. and Judiesch, D. 2012. Temperature trends in the semiarid prairie of southwestern Saskatchewan revisited. Can. J. Soil Sci. 92: 803-806. Average annual and seasonal temperatures for 1950-2007 were compared with 1950-1997 for warming trends in the semiarid Canadian prairie south of Swift Current, SK. The additional 10 yr did not alter the direction or magnitude of the warming trends. Briefly, late winter-early spring (January through April) continued to experience the largest warming trend, whereas there continued to be no warming trend for the fall-early winter (September through December) period.