Search

Improving technologies and the challenge of producing more bio-products while reducing the environmental footprint of humans are shifting paradigms in agricultural research. Harnessing the microbial resources of arable soils is a new avenue to improve the efficiency of nutrient use in agriculture. The objective of this study was to define how crop management influences the contribution of resident AM fungi to nutrient efficiency and crop productivity. The AM fungal communities of 72 organically and 78 conventionally managed wheat fields of the Canadian prairie were described by 454 pyrosequencing and related to crop productivity and N and P use efficiency. Conventional management reduces soil pH and increases the fluxes of all soil nutrients except S, B, and K. Organic management increased the abundance of Claroideoglomus reads. The efficiency of N and P uptake from soil by organic wheat was 2.3 and 1.8 times higher than that of conventional systems. This high N and P uptake efficiency in organic wheat crops was mainly attributable to the low soil fertility of organic fields, as wheat biomass production was 1.44 times greater in conventional than organic systems. Overall, the amounts of N and P taken up by conventional and organic wheat crops were similar. Plant nutrient balance and the abundance of Paraglomus drove conventional wheat production, whereas organic production depended mainly on soil moisture, plant nutrient balance, and abundance of Glomus , which was associated with reduced and nutrient-inefficient wheat production. The high nutrient concentrations at maturity and the low productivity of organic wheat fit a model of limiting CO 2 -assimilation. The trade-off between nutrient use efficiency and productivity in low input wheat production could be relieved by reducing the abundance of Glomus species, increasing soil moisture and early N availability, or by improving the inherent CO 2 assimilation capacity of wheat.

Pageni, B. B., Lupwayi, N. Z., Larney, F. J., Kawchuk, L. M. and Gan, Y. 2013. Populations, diversity and identities of bacterial endophytes in potato ( Solanum tuberosum L.) cropping systems. Can. J. Plant Sci. 93: 1125–1142. Most plants host endophytic bacteria, but their identities and functions are usually unknown. Bacterial endophytes associated with potato grown after dry bean (Phaseolus vulgaris L.) or wheat (Triticum aestivum L.) were isolated, quantified and identified in a field study that compared crop rotations (3 to 6 yr in length) and soil management (CONV, conventional; CONS, conservation) for dry bean, potato, sugar beet (Beta vulgaris L.) and spring wheat. Populations of culturable endophytes ranged from 2.83×103 to 7.65×103 colony-forming units g−1 of root dry matter. The populations and diversity of the endophytes were greater with CONS than CONV soil management, and tended to be greater in longer than shorter rotations. The community structures of the endophytes were different between CONV and CONS soil management. A terminal-restriction fragment length polymorphism assay targeting the 16S rRNA gene, and its sequencing, showed that CONS management systems contained more Proteobacteria than CONV management systems, and vice-versa for Acidobacteria. Bacteriodetes were found only in long CONS rotations. This phylogenetic characterization of potato endophytes is important for further studies on their effects on the host plants.

Khakbazan, M., Grant, C. A., Finlay, G., Wu, R., Malhi, S. S., Selles, F., Clayton, G. W., Lupwayi, N. Z., Soon, Y. K. and Harker, K. N. 2013. An economic study of controlled release urea and split applications of nitrogen as compared with non-coated urea under conventional and reduced tillage management. Can. J. Plant Sci. 93: 523–534. To evaluate the use of controlled-release urea (CRU) as a beneficial management practice for nitrogen management of wheat, barley, and canola, a multi-location study was conducted from 2004 to 2006 in a range of agro-environments across western Canada. The objective was to evaluate the relative economic performance of CRU and non-coated urea (NCU) for their effects on seed yield and quality, costs and net revenue (NR) using conventional tillage (CT) and reduced tillage (RT) management under varying environmental conditions. The NR was estimated as the income remaining after paying for all cash costs, ownership costs on machinery and buildings, and labour. The main factor affecting crop yield and NR was N application rate. In general, application of NCU produced similar or higher net revenues than that of CRU, split fertilizer applications or a blend of NCU and CRU. There were some limited situations where the use of split applications, CRU or CRU in a blend with the NCU increased crop yield as compared with NCU; however, the increased yield was not sufficient to cover the extra costs of CRU or the split application. The impact of tillage system on crop yield and NR was not consistent. Net revenue was higher under CT than RT for certain crops in some regions, but not in all regions or for all crops. Overall, NR analysis indicated that use of CRU did not provide an economic benefit over the use of NCU.

Increased irrigated production of potato (Solanum tuberosum L.), dry bean (Phaseolus vulgaris L.), and sugar beet (Beta vulgaris L.) in southern Alberta in the 1990s prompted a 12 yr (2000–2011) st...

Although dry bean (Phaseolus vulgaris L.) is a legume capable of fixing nitrogen, fertilizer N is usually recommended for its production in Canada because it is believed to be an inefficient N fixe...

Growing Bt crops reduces the use of insecticides applied to them, but these crops could affect soil microorganisms and their activities. We evaluated the effects of Bt ( Cry1Ab ) corn ( Zea mays L.) and deltamethrin ([S]-α-cyno-3-phenoxybenzyl [1R, 3R]-3-[2,2-dibromovinyl]-2,2-dimethylcyclopropane-1-carboxylate) insecticide application on soil microbial biomass C (MBC), β-glucosidase enzyme activity (final season only), bacterial functional diversity, and bacterial community-level physiological profiles (CLPPs) in corn monoculture in five seasons. We also determined if growing Bt corn in crop rotation would alter these effects. Statistical analysis of pooled data across seasons did not show any effects of Bt technology, insecticide application or crop rotation on soil microbial biomass or diversity even though differences between seasons and between the rhizosphere and bulk soil were observed. Annual analyses of results also showed that neither the Bt technology nor insecticide application affected soil MBC, enzyme activity, or functional diversity of bacteria in corn rhizosphere, but shifts in bacterial CLPPs due to Bt trait were observed in one year. Crop rotation effects on soil microbial properties were not observed in most cases. Where effects were observed, Bt corn grown in rotation resulted in greater MBC, enzyme activity and functional diversity than Bt corn grown in monoculture or conventional corn grown in rotation, and these effects were observed only in bulk soil. Therefore, the Bt technology is safe with respect to the non-target effects measured in this study. However, the effects of repeated use of Bt crops over many years on the soil environment should continue to be monitored.

There is considerable interest in using straw for industrial fibre or biofuel (ethanol) production. Removing straw from farm fields could have detrimental effects on soil quality. The objective of this work was to evaluate the role of above-ground vs. below-ground crop residues on soil organic C content, soil microbiological and physical properties, and crop yields. In a barley ( Hordeum vulgare L.), field pea ( Pisum sativa L.), wheat ( Triticum aestivum L.), canola ( Brassica napus L.) crop rotation from 2007 to 2010, we varied straw inputs by removing or retaining straw, with or without N fertilization, and also by fallowing some treatments in some years. Grain yields were unaffected by straw management or crop residue input, probably due to soil moisture deficits in three of the four years. Soil nitrate accumulation was consistently higher in fallow and N-fertilizer treatments, and grain N uptake was reduced after three years of retaining straw on the surface, indicating probable net N immobilization. The coarse (>0.5 mm) light fraction of soil organic matter was reduced by fallowing the preceding year or disking in the straw, and was significantly correlated with the most recent input amounts of straw or total residue (root plus straw) dry matter (DM). The fine light fraction did not correlate with those residue inputs. Soil aggregation was indicated by mean weight diameter and was not affected by straw management. Non-rhizosphere soil microbial biomass C and β-glucosidase enzyme activity were consistently lowest in the control (no cropping) treatment and the treatment with straw incorporated by disking, but the amounts of C and N mineralized were not affected by straw treatments. Non-rhizosphere soil MBC was strongly correlated with cumulative total residue DM input. However, because crop yields did not vary much with straw management, they did not correlate with soil quality parameters. Therefore, varying above- and below-ground crop residue inputs, as well as tillage (disking in straw), over four years affected some early indicators of soil quality but not crop yields.

Wood ash has the properties to be an effective liming material, and research is needed to compare its effectiveness relative to agricultural lime on acidic agricultural soils. Wood ash at a calcium carbonate rate of 6.72 t ha−1 was compared with an equivalent rate of agricultural lime on a clay loam soil with an initial pH of 4.9. Replicated plots were managed under a barley (Hordeum vulgare L.)–canola (Brassica rapa L.)–pea (Pisum sativum L.) rotation for 4 yr (2002–2005). Soil pH increased in the order of: wood ash = lime > control (without lime or wood ash). Available soil P increased in the order of: wood ash > lime ≥ control. The effect of wood ash and lime application on pH and available P was greatest in the 0- to 5-cm depth, less but still significant in the 5- to 10-cm depth, and not significant below 10 cm. The effect on soil aggregation was: wood ash > lime > control. Averaged over 4 yr, application of wood ash increased grain yields of barley, canola, and pea by 49, 59, and 55%, respectively, compared to a corresponding increase of 38, 31, and 49% by agricultural lime. The increase in crop yield with wood ash compared with lime is attributed partly to increased P availability in wood ash-amended plots. It is concluded that wood ash applied at rates equivalent to agricultural lime improved some soil chemical and physical properties and increased crop production relative to agricultural lime.

Controlled release urea (CRU) has been shown to improve nitrogen fertilizer use efficiency in a number of production systems. However, the effectiveness of CRU will be strongly affected by the environmental conditions of the region. Research trials were conducted at five locations across four major ecoregions spanning 1600 km across the Northern Great Plains and Pacific Maritimes of North America from 2004 to 2006 to evaluate the effects of a single application of polymer-coated urea (CRU) or split applications of urea fertilizer as compared with non-coated urea for their effects on crop growth, crop N concentration, and crop N accumulation of wheat (Triticum aestivum L.), barley (Hordeum vulagre L.) canola (Brassica napus L.) and corn (Zea mays L.) across a wide range of environmental conditions. Urea applied as an in-soil band at the time of seeding was generally as or more effective than similarly placed CRU, split application of urea or blended urea and CRU in the semi-arid Mixed Grassland, moist Aspen Parkland or wet Boreal Transition ecoregions in increasing early season dry matter yield and seed or grain yield of canola, wheat or barley. Similarly, broadcast urea was as or more effective than broadcast CRU, split applications or blended applications in increasing corn dry matter yield under the wet conditions in the Lower Mainland ecoregion. There were some situations where use of split applications or use of the CRU in a blend with the non-coated urea resulted in increases in grain yield as compared to the non-coated urea, primarily under moist conditions in the Boreal Transition or Aspen Parkland ecoregions. Some yield losses occurred from use of the CRU as compared with the non-coated urea and were attributed to delays in release of N from the granule that limited early season N availability and crop growth, especially in corn with a high N demand. Effects on grain N concentration and accumulation of N in the crop at harvest were mixed, with the CRU, blended applications of CRU and urea or split applications occasionally producing higher grain N concentration and N accumulation in the crop than the non-coated urea. Benefits of CRU on grain N concentration were more frequent than benefits on grain yield, but were not large or consistent. Response of crop growth and N uptake to N management was generally similar under CT and RT, with occasional differences occurring due to changes in yield potential or N deficit associated with the differences in tillage management. Therefore, under growing conditions across a wide range of ecoregions in the Northern Great Plains and the Pacific Maritimes, the use of CRU or split applications do not appear to provide a consistent improvement in crop yield, N concentration in the grain, total N accumulation at harvest, or nitrogen use efficiency as compared to standard regional timing and placement of non-coated urea.

Cereal crops usually take up less than 50% of the N fertilizer applied. We hypothesized that, depending on application rate, the inorganic N in the soil could affect soil organisms. We investigated the effect of N applied to barley (Hordeum vulgare L.) at soil-test recommended rates (50–80 kg ha−1) in 2004–2006 in a Black Chernozem, and to corn (Zea mays L.) at recommended (80 kg ha−1) and higher (160 kg ha−1) N rates under no till (NT) and conventional tillage (CT) in 2004 and 2006 in an Orthic Gleysol, on soil microbial properties. Rhizosphere and bulk soil samples (0–7.5 cm soil depth) taken at flagleaf stage of barley growth and tasselling stage of corn growth were analysed for microbial biomass C (MBC), bacterial functional diversity and community-level physiological profiles (CLPPs). In barley, N increased MBC by 39% in bulk soil in one year. In corn, the response of MBC to N rate was quadratic, peaking at 80 kg N ha−1. The functional diversity of soil bacteria in the corn trial was not reduced even at the highest N rate. No-till in corn increased MBC by 30–102%, and also tended to increase bacterial functional diversity. The tillage effect was detectable in CLPPs although year-to-year differences were more prominent. Therefore, N applied at agronomically recommended rates either did not affect MBC and bacterial diversity or increased these microbial characteristics; N applied at higher rates reduced MBC. These results from two soil types, crops and climatic regions support our hypothesis that non-target effects of N fertilizer depend on the application rate. Soil testing to apply recommended amounts of fertilizer would reduce non-target fertilizer effects.

Including grain-legumes in cropping systems contributes to a reduction in greenhouse gas emissions and enhances agronomic and economic performance of cropping systems. The objective was to examine the potential for increasing the frequency of field pea (Pisum sativum L.) (FP) in a spring wheat (Triticum aestivum L.) (W)-based cropping system. Three crop rotations, continuous pea (C-Pea), W-FP, and W-W-FP, were evaluated over a 10-yr period (1998―2007) at Indian Head, SK. During the FPphase of C-Pea and W-FP, three starter N rates (5, 20, 40 kg N ha ―1 ) were applied. One rate of N (80 kg N ha ―1 ) was used in W. Rotation and N had similar effects on plant densities in either crop. Field pea grain yields were 25% lower with C-Pea than W-FP or W-W-FP but similar between W-FP and W-W-FP. Starter N had some effect on FP grain yields at the higher N rate in W-FP but not C-Pea. Spring wheat grain yields were 3% greater on FP than W stubble. Grain protein in FP was 3.1% higher on C-Pea than W-P or W-W-FP while grain protein in W was 1 g kg ―1 higher on FP than W stubble. Crop water use efficiency in FP and W was not affected by crop rotation. Based on the results of this study, we conclude that the frequency of FP in cropping systems in the subhumid and semiarid areas can be increased intermittently with only a 1-yr cereal break between FP crops when combined with proper integrated crop management practices.

Two field experiments were conducted to assess the effectiveness of polymer-coated urea (PCU) vs. conventional urea (urea) in minimizing nitrate accumulation in soil and nitrous oxide (N2O) emission while optimizing available N supply. The trials were located on Dark Gray Luvisols (Typic Cryoboralf) near Beaverlodge, Alberta (2004–2007) and Star City, Saskatchewan (2004–2006), in the north western Canadian Prairies. The treatments comprised of combinations of two tillage systems (conventional and no tillage), the two forms of urea (applied at commercial rates, 50–60 kg N ha−1), and time of application (side-banded in spring or fall). Tillage had little effect on the measured soil variables. Available N at the anthesis growth stage was higher with spring- than fall-banded N in three of four site-years, and with PCU than urea in two site-years. At seeding, nitrate in the soil layers to 60-cm depth, especially the top 15 cm, was mostly higher for fall- than spring-banded treatments but differed less between the forms of urea. Fall application, therefore, has greater potential for gaseous N and leaching losses early in the growing season when crops have low N requirements, and hence is not advisable. Nitrous oxide emission from spring to fall was higher with the fertilized treatments in three of five site-years and not different between fertilized and unfertilized treatments in the other site-years. At Beaverlodge, N2O loss was low in 2 years and showed few significant treatment effects. At Star City, N2O loss was 1.5- to 1.7-fold higher from urea than PCU treatments, and up to 1.5-fold lower from spring than fall application. It is concluded that although PCU can increase available N during the growth period and reduce N2O loss in some years compared with urea, the time of N application had a consistently greater effect than the type of urea in enhancing crop N recovery and reducing N loss to the environment.

The combination of high input costs and low commodity prices is forcing some farmers to consider reducing crop inputs like seed, fertilizer and herbicides. In a field trial in which different canola (Brassica napus L.) and barley (Hordeum vulgare L.) inputs were subtracted from a full package, or added to an empty package, we studied the effects of full or reduced fertilizer and herbicide inputs on soil microbiological characteristics at two sites from 2005 to 2008. The full package consisted of a high-yielding crop variety seeded at an optimum rate, with fertilizers and herbicides applied at recommended rates. The empty package consisted of a less expensive, low-yielding crop variety seeded at a low rate, with no fertilizer or herbicide applied. Between these two extremes were treatments in which fertilizers or herbicides were applied at 50% of recommended rates or not at all. Each treatment was repeated year after year in the same plot, i.e., treatment effects were cumulative. Fertilizer effects on soil microbial biomass C (MBC), β-glucosidase enzyme activity and bacterial functional diversity (based on community-level physiological profiles) were usually positive. Reduced fertilizer application rates reduced the beneficial fertilizer effects. Significant herbicide effects on soil microbiological properties occurred less often, were smaller in magnitude than fertilizer effects, and were mostly negative. Reduced herbicide rates reduced the deleterious herbicide effects. These significant fertilizer and herbicide effects were observed in canola more than barley, and mostly in the final year of the study, indicating the cumulative nature of treatment effects over time. Therefore, repeated applications of agricultural inputs like fertilizers and herbicides can have more significant effects on soil biology and biological processes than single applications indicate.

Soil microorganisms mediate many important biological processes for sustainable agriculture. The effect of a polymer-coated controlled-release urea (CRU, ESN®) on soil microbial communities was studied at six sites across western Canada from 2004 to 2006. Fertilizer treatments were CRU, urea and an unfertilized control. Timing of fertilizer application (fall vs. spring) was studied in 9 of the 18 site-years (combinations of sites and years). Wheat (Triticum aestivum L.), canola (Brassica napus L.) and barley (Hordeum vulgare L.) were grown in rotation at five sites, and silage corn (Zea mays L.) was grown in all 3 years at one site, under conventional tillage (CT) or zero tillage (ZT). The fertilizers were side-banded at 50–60 kg N ha−1 for wheat, barley and canola, and broadcast at 150 kg N ha−1 for corn. Microbial biomass C (MBC) and bacterial functional diversity and community-level physiological profiles (CLPPs) were determined at about the flowering stage of each crop. In situ CO2 evolution (soil respiration) was measured, and microbial metabolic quotient (qCO2) determined, at one site in 2 years. In the rhizosphere, fertilizer effects on MBC and functional diversity were observed in 1 and 5 of 18 site-years, respectively; and in bulk soil in 4 site-years each. These effects were usually positive relative to the control. CRU increased MBC or functional diversity more than urea in 3 site-years, but the opposite was observed in 1 site-year. Time of fertilizer application affected MBC in 1, and functional diversity in 2, of 9 site-years in the rhizosphere, and no effects were observed in bulk soil. Fall-applied fertilizer increased MBC more than spring-applied fertilizer, but the opposite was observed for functional diversity. Tillage affected MBC and functional diversity in 4 and 5 of 18 site-years, respectively, in the rhizosphere, and in 3 and 4 site-years in bulk soil. Tillage effects were usually in favour of ZT. There were no treatment effects on CO2 evolution, but an interactive effect of fertilizer and tillage on qCO2 was observed in 1 year when qCO2 in the control treatment was greater than that in either fertilizer treatment under CT, but urea increased qCO2 relative to the control under ZT. Shifts in CLPPs were sometimes observed where the treatment effects described above were not significant. Notwithstanding the limitations of culture-dependent CLPPs, most fertilizer effects on soil microbiological properties were not statistically significant. Therefore, these fertilizers probably did not adversely affect most soil biological processes.

Field experiments were conducted on Dark Gray Luvisolic soils (Typic Cryoboralf) from 2004 to 2006 (wheat-canola-barley rotation) near Star City, Saskatchewan, and from 2004 to 2007 (barley-canola-wheat-barley rotation) near Beaverlodge, Alberta. The aim was to compare the effects of controlled-release urea (CRU) vs. conventional urea (hereafter called urea) on seed yield and N (i.e., protein) concentration, and N use efficiency (NUE). The treatments were combinations of tillage system [conventional tillage (CT) and no tillage (NT)], and N source (urea, CRU and a blended mixture), placement method (spring-banded, fall-banded and split application) and application rate (0-90 kg N ha-1). There was no tillage × fertilizer treatment interaction on the measured crop variables. Seed yield and crop N uptake and, to a lesser degree, seed N concentration generally increased with N application to 90 kg N ha-1. Fall-banded CRU or urea generally produced lower crop yield and N uptake than spring-banded CRU or urea. Split application of urea (half each at seeding and tillering) resulted in higher seed yield and N concentration in at least 3 of 7 site-years than did CRU and urea applied at a similar rate. A blend of urea and CRU was as effective as spring-banded CRU (at Star City only). Seed yield, N recovery and NUE were higher with spring-banded CRU than urea in 2 site-years, and similar to urea in other site-years. We conclude that for boreal soils of the Canadian prairies, spring-banded CRU is as effective as urea, and in some years more effective, in increasing crop yield and N recovery; however, urea split application can be even more effective in addition to having an advantage in managing risk.Key words: Controlled-release urea, Gray Luvisol, nitrogen source, nitrogen recovery, nitrogen use efficiency, tillage systems

Intercropping can enhance yields and reduce pest infestations, but investigations of intercropping regimes using crop species common to the large-scale monoculture production systems of western Canada have not examined these diverse elements. Intercrops of canola (Brassica napus L.) and wheat (Triticum aestivum L.) were established at three sites in Alberta, Canada in 2005 and 2006 to determine interactions between intercropping regimes and crop grain and biomass yield, crop quality characteristics, soil microbial community biomass and diversity, flea beetles (Phyllotreta spp., Coleoptera: Chrysomelidae), and wheat leaf diseases. The study also investigated effects on flea beetles and soil microbial communities of a canola seed treatment containing a neonicotinoid insecticide and fungicides. Crop yields were comparable between intercrops and monocultures of canola and wheat. Crop quality characteristics and flea beetle feeding damage to canola seedlings had variable responses to intercropping. Flea beetle feeding was reduced with the inclusion of the seed treatment by between 1 and 20% damaged leaf area, although only one site-year had damage levels great enough to overcome plant compensatory abilities in untreated plots. The first true-leaf stage of canola development experienced the greatest flea beetle damage. Proportions of pathogen-infected wheat leaf tissue were up to 2.5 times greater in intercrops than wheat monocultures but tended to decrease as the proportion of canola in the intercrops increased. Soil microbial parameters were unaffected by factors investigated. Although intercrop yields approximated those of monocultures, additional benefits of canola-wheat intercrops determined in this study appear insufficient to recommend this system for widespread adoption.

More than 90% of acid soils in western Canada are in Alberta, yet the use of agricultural lime is limited because it is expensive. Wood ash, a by-product of pulp and lumber mills, can be used for liming acid soils. We investigated the effects of amending an acid Luvisol with wood ash or lime on soil microbiological properties at Beaverlodge, Alberta. Both soil amendments were applied at a calcium carbonate rate of 6.72 t ha-1, which was 8.40 t ha-1 for wood ash and 7.47 t ha-1 for lime, in 2002. Soil microbial biomass C (MBC) and the functional diversity and community structures of soil bacteria (indicated by substrate utilization patterns) were measured from 2002 to 2005 under barley (Hordeum vulgare L.), canola (Brassica napus L.), field pea (Pisum sativum L.), and timothy grass (Phleum pratense L.). In the rhizosphere, wood ash increased soil MBC between 2.4-fold in 2002 and 1.3-fold in 2005, and lime increased MBC from 3.2-fold in 2002 to 1.3-fold in 2005. In bulk soil, the increases in MBC ranged from 3.0-fold in 2003 to 1.8-fold in 2005 for wood ash, and from 4.9-fold in 2002 to 2.0-fold in 2005 for lime. Crop effects on MBC were not consistent. Because annual crops were grown in rotation, it is possible that the results obtained in one crop were confounded by effects of the preceding crop. In 2003 and 2004, both amendments increased Shannon index (H’) of bacterial functional diversity in the rhizosphere, and similar results were observed in 2005 in bulk soil. Shifts in the functional structure of bacterial communities due to soil amendment were observed in bulk soil, and shifts due to crop effects were observed in the rhizosphere. In 2003, the average soil pH(CaCl2) increased from 4.91 in control treatments of different crops to 6.60 in lime-amended plots and 6.70 in wood ash-amended plots. In 2004, both wood ash and lime significantly increased soil C mineralization (up to 10 d incubation), but basal respiration (11-24 d incubation) was not affected. The large effect (up to about fivefold) of soil amendments on MBC implies that soil acidity is a major limiting factor for biological processes and the productivity of some Luvisolic soils in Alberta. Wood ash could be used to alleviate these limitations. Key words: C mineralization, microbial diversity, microbial biomass, soil amendment, soil acidity

The fungicide vinclozolin and insecticide λ-cyhalothrin are widely used to control canola (Brassica spp.) diseases and insect pests, respectively, in Canada. We investigated non-target effects of these pesticides, applied at recommended rates, on soil microbial biomass, functional bacterial diversity and functional community structure of soil bacteria (by evaluating patterns of C substrate utilization) in canola rhizosphere and bulk soil at three locations in Alberta from 2002 to 2004. Experimental treatments were (a) untreated control, (b) vinclozolin fungicide foliar application, (c) λ-cyhalothrin insecticide foliar application, and (d) vinclozolin and λ-cyhalothrin applications. No significant pesticide effects on soil microbial biomass or functional bacterial diversity were observed, but the functional structures of soil bacteria were altered. In 1 of 12 cases, the control treatment had a different soil bacterial community structure from the 3 pesticide treatments. The fungicide treatment had different bacterial community structures from the control or insecticide treatments in 3 of 12 cases, the insecticide treatment had different community structures from the control or fungicide treatments in 4 of 12 cases, and the combined fungicide and insecticide treatment had different community structures from the other treatments in 3 of 12 cases. Therefore, evaluating soil bacterial functional structures revealed pesticide effects that were not detected when bacterial diversity or microbial biomass were measured in canola rhizosphere or bulk soil.

Pea (Pisum sativum L.) varieties can differ in morphology, N2 fixation and straw N content. A study was conducted over 3 site-years to evaluate the influence of pea variety and inoculation with Rhizobium on N release from decomposing pea residues. The litterbag technique was used to measure N release over a 52-wk period starting from the time of pea harvest in one season through part of the following season when wheat was grown. Experimental treatments comprised factorial combinations of three pea varieties and either inoculation with 5 kg ha-1 of a granular inoculant or none, arranged in a randomized complete block design. Neither pea variety nor inoculation affected amounts or patterns of N released. Patterns of N release over time showed mostly net N mineralization in two of 3 site-years, and some net N immobilization in one site-year. The percentages (up to 19 to 24% over time) and amounts (up to 2.3 to 7.5 kg N ha-1) of N released were low, probably due to the combination of low N concentrations (mostly < 1%) in the residues and below-normal rainfall in all 3 site-years. Soil NO3-N and NH4-N (0- to 80-cm depth) in the fall after pea harvest (20 to 39 and 27 to 55 kg N ha-1, respectively) and in spring before wheat seeding (23 to 51 and 16 to 40 kg N ha-1, respectively) were not affected by pea variety or inoculation. However, soil NO3-N was mostly higher after peas than after barley (the control). There is need to measure patterns of N release over several subsequent crops to check if more N is released in the long term. Key words: Crop residue, N mineralization, Rhizobium inoculation, soil inorganic N

Adoption of glyphosate-resistant canola (Brassica napus L.) has increased glyphosate applications to this crop, and concerns have been raised about unintended consequences of these multiple applications. A field trial was conducted to evaluate the effects of pre-seed and in-crop glyphosate and alternative herbicides on soil microbial community functional structure, diversity and biomass. Pre-seed treatments were 2,4- D, glyphosate and 2,4- D + glyphosate, and in-crop treatments were glyphosate applied once, glyphosate applied twice, ethalfluralin, ethalfluralin + sethoxydim + ethametsulfuron + clopyralid, and sethoxydim + ethametsulfuron. Rhizosphere and bulk soil was collected at flowering stage of canola and analyzed for bacterial community-level substrate utilization patterns and microbial biomass C (MBC). Where differences were significant, pre-seed application of both 2,4-D and glyphosate altered the functional structure and reduced the functional diversity of soil bacteria, but increased MBC. These effects were not necessarily concurrent. The reduction in functional diversity was due to reduction in evenness, which means that the soil where both pre-seed herbicides had been applied was dominated by only few functional groups. In 1 year, two in-crop applications of glyphosate also reduced the functional diversity of soil bacteria when applied after pre-seed 2,4-D, as did in-crop sethoxydim + ethametsulfuron following pre-seed glyphosate. Even though significant differences between herbicides were fewer than non-significant differences, i.e., there were no changes in soil microbial community structure, diversity or biomass in response to glyphosate or alternative herbicides applied to glyphosate-resistant canola in most cases, the observed changes in soil microbial communities could affect soil food webs and biological processes.

Placing N in the form of urea with the seed allows seeding and fertilizer application to be accomplished simultaneously with minimal soil disturbance. However, seedling damage can occur from excess seed-placed urea. The objective of this study was to compare the effects of seed-placed and side-banded N (urea) applied at different rates on barley (Hordeum vulgare L.) density, maturity, and yield and wild oat (Avena fatua L.) fecundity, and to investigate if increasing the barley seeding rate would improve the ability of barley to overcome urea-induced injury and compete better with wild oat. A field experiment was conducted at three locations in western Canada over 3 yr. Nitrogen was applied as urea at five rates (0, 30, 60, 90, and 120 kg ha -1 actual N), either directly with the seed or as a side-band, at three barley seeding rates (200, 300, and 400 seeds m -2 ). When N was placed with the seed, barley plant density decreased, while time to maturity and wild oat fecundity increased as N rate increased. Barley yield also decreased but only at N rates above 60 kg ha -1 . Placing N as a side-band did not reduce barley density, resulting in shortened time to maturity, increased barley yield, and lower wild oat fecundity as compared to seed-placed N. Increasing the seeding rate increased barley density and reduced time to maturity and wild oat fecundity but did not affect barley yield.

Three field experimentswere conducted in northwestern Alberta to assess the influence of pea (Pisum sativum L.) cultivars on the N economy and the performance of the sequent wheat (Triticum aestivum L.) crop. Three pea varieties and two levels of Rhizobium inoculant (none and 5 kg ha-1), in factorial combination, were tested at each site; overall, four pea cultivars were tested with barley (Hordeum vulgare L.) as the check. All plots were seeded to wheat in the second year. All but one experimental year had below-average growing season rainfall. Dinitrogen fixation decreased in the following order among pea cultivars: Grande > Carerra ≥ Eiffel ≥ Swing, the same order as net productivity: the correlation between fixed N and shoot dry matter at harvest was highly significant (R2 = 0.982; P < 0.001). Only Grande pea resulted in balanced soil N (exported N = fixed N); the deficit in the N balance, in kg N ha-1, was 7–38 for Carrera, 20–37 for Swing and 18–37 for Eiffel. However, even where the soil N balance was negative, wheat follow ng pea mostly had higher seed protein content and yield than wheat following barley due to a high correlation between the yield of the sequent wheat and pea-fixed N. Rhizobium inoculation increased nodule formation and N2 fixation in only one of the experiments; however, it did not affect the yield of the sequent wheat as compared with uninoculated soil. We conclude that selection of a high net productivity pea cultivar should typically result in greater N and yield benefits to the sequent cereal crop than a low net productivity cultivar. Key words: N budget, Rhizobium inoculation, wheat, pea varieties, N2 fixation

Cropping systems in the Northern Great Plains have shifted from fallow-based to legume-based systems. The introduction of grain legumes has impacted soil organisms, including both symbiotic and nonsymbiotic N-fixing bacteria, pathogens, mycorrhizae and fauna, and the processes they perform. These changes occur through effects of legume seed exudates, rhizosphere exudates, and decomposing crop residues. The legume-Rhizobium symbiosis results in dinitrogen (N 2 ) fixation that adds plant available N into the soil system. It is estimated that about 171 million kg N 2 was fixed by field pea (Pisum sativum L.), lentil (Lens culinaris Medik.), dry bean (Phaseolus vulgaris L.), and chickpea (Cicer arietinum L.) crops in the Canadian Prairies in 2004, representing 7% of the total fertilizer-N (2580 million kg) used by Canadian prairie farmers in that year. Similarly, an estimated 40 million kg N 2 was fixed by field pea, lentil, and dry bean (including chickpea) crops in U.S. agroecosystems in 2004. Some of the fixed N2 is recycled for the benefit of nonlegume crops grown after grain legumes. Many other associations benefit from the legume in a cropping system, including mycorrhizal associations that improve plant nutrient and water uptake, changes in the pathogen load and disease development, and overall changes in the soil community. Legumes contribute to greenhouse gas (N 2 O and CO 2 ) emissions during nitrification and denitrification of fixed N. However, because less fertilizer-N is used in legume-based cropping systems, overall greenhouse gas emissions are usually less than those in fertilized monoculture cereals. Therefore, grain legumes in Northern Great Plains have positive effects on agriculture by adding and recycling biologically fixed N 2 , enhancing nutrient uptake, reducing greenhouse gas emissions by reducing N fertilizer use, and breaking nonlegume crop pest cycles.

Field experiments were conducted at Fort Vermilion (58°23′N 116°02′W), Alberta, to determine phosphorus (P) release patterns from red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues in the 7th and 8th years of conventional and zero tillage. Phosphorus contained in crop residues ranged from 1.5 kg ha−1 in pea to 9.2 kg ha−1 in clover GM, both under zero tillage. The patterns of P release over a 52-week period sometimes varied with tillage, i.e., a greater percentage of GM residue P was released under conventional tillage than under zero tillage in the first 2–10 weeks of residue placement. Wheat residues resulted in net P immobilization under zero tillage, but the amounts immobilized were less than 1 kg ha−1. When net P mineralization occurred, the percentage of P released ranged from 24% of wheat P under conventional tillage to 74% of GM P under conventional tillage. The amounts of P released were 0.4 kg ha−1 from wheat, 0.8 kg ha−1 from canola, 0.4 kg ha−1 from pea and 5.1–5.6 kg ha−1 from clover GM residues. Therefore, only GM residues recycled agronomically significant amounts of P for use by subsequent crops in rotation. Phosphorus release was positively correlated with residue P concentration and negatively correlated with C/P and lignin/P ratios.

Information on which management practices can enhance soil organic matter (SOM) content and quality can be useful for developing sustainable crop production systems. We tested the influence of 12 years of no-till (NT) versus conventional tillage (CT), and four crop sequences on the organic C pools of a Grey Luvisolic sandy loam soil in northwestern Alberta, Canada. The crop sequences were: continuous wheat ( Triticum aestivum L.), field pea ( Pisum sativum L.)–wheat–canola ( Brassica rapa L.)–wheat, red clover ( Trifolium pratense L.) green manure–wheat–canola–wheat/red clover and fallow–wheat–canola–wheat. Soil samples from 1992, when the study was initiated, and 1996, 2000 and 2004 were analyzed for total organic C (TOC), the light fraction (LF) and its C content, and water-soluble and mineralizable C. Total organic C in the top 15 cm of soil was higher in the red clover rotation than either the pea or fallow rotation by 1996. The tillage effect became significant only in 2004 with NT having a higher TOC than CT. The LF dry matter (DM) increased from 6.9 g kg −1 soil in 1992 to a range of 10–13 g kg −1 in 2000 and 2004. It was higher under NT than CT in 2 of 3 years and in the red clover rotation than the pea or fallow rotation in 1 of 3 years. The LF C content exhibited a similar trend as LF DM. The water-soluble and mineralizable C pools were not affected by tillage but decreased with time. Among crop rotations, the red clover rotation tended to result in higher levels of hot water-soluble and mineralizable C. It is concluded that tillage had a greater influence than crop rotation on the LF DM and LF C (as indicators of C storage), whereas the converse effect applied to mineralizable C and, to a lesser degree, hot water-soluble C (as indicators of SOM quality).

As glyphosate-resistant (GR) crops are becoming common in agro-ecosystems, their effects on non-target soil organisms need to be monitored. We evaluated soil microbial biomass C (MBC), bacterial functional diversity and community structure, and dehydrogenase enzyme activity in a field experiment conducted at six sites on the Canadian prairies. Treatments consisted of a factorial arrangement of three GR wheat and GR canola crop frequencies and two tillage systems. GR crop frequencies were arranged in 4-yr wheat-canola-wheat-pea rotations, with GR wheat and GR canola in zero of four, two of four, or three of four possible GR crop frequencies. The two tillage systems were either low soil-disturbance direct-seeding (LDS) or conventional tillage (CT). MBC increased with increasing frequency of GR crops in two of 20 site-years in the rhizosphere, and had no effects in bulk soil. Depending on tillage, GR crop frequency also affected the functional diversity of rhizosphere soil bacteria in only two of 20 site-years, and had no effects in bulk soil. Shifts in the structures of bacterial communities related to GR crop frequency were detected, but they were few and inconsistent. In three of 22 cases (10 in rhizosphere+12 in bulk soil), the activity of dehydrogenase enzyme decreased with increasing frequency GR crops in both the rhizosphere and bulk soil. In five of 20 site-years, soil MBC in the rhizosphere was greater under CT than under LDS, regardless of GR crop frequency. In bulk soil, tillage affected soil MBC in five site-years, three of which had greater MBC under CT than LDS, and vice versa in the other two. Tillage affected the functional diversity of soil bacteria in the rhizosphere in three site-years, but the effects were not consistent. Similar inconsistent tillage-related patterns were observed in the community structures of bacteria. There were no tillage effects on bacterial diversity in bulk soil. Dehydrogenase enzyme activity was greater under LDS than under CT in three of four cases in which tillage had significant effects. Overall, GR crop frequency effects on soil microorganisms were minor and inconsistent over a wide range of growing conditions and crop management.

Adults of Sitona lineatus (pea leaf weevil, PLW) feed on foliage of several Fabaceae species but larvae prefer to feed on nodules of Pisum sativum L. and Vicia faba L. Indirectly, through their feeding on rhizobia, weevils can reduce soil and plant available nitrogen (N). However, initial soil N can reduce nodulation and damage by the weevil and reduce control requirements. Understanding these interactions is necessary to make integrated pest management recommendations for PLW. We conducted a greenhouse study to quantify nodulation, soil and plant N content, and nodule damage by weevil larvae in relation to soil N amendment with urea, thiamethoxam insecticide seed coating and crop stage. PLWs reduced the number of older tumescent (multilobed) nodules and thiamethoxam addition increased them regardless of other factors. Nitrogen amendment significantly increased soil available N (>99% nitrate) as expected and PLW presence was associated with significantly lower levels of soil N. PLW decreased plant N content at early flower and thiamethoxam increased it, particularly at late flower. The study illustrated the complexity of interactions that determine insect herbivory effects on plant and soil nutrition for invertebrates that feed on N-fixing root nodules. We conclude that effects of PLW on nodulation and subsequent effects on plant nitrogen are more pronounced during the early growth stages of the plant. This suggests the importance of timing of PLW infestation and may explain the lack of yield depression in relation to this pest observed in many field studies. Also, pea crops in soils with high levels of soil N are unlikely to be affected by this herbivore and should not require insecticide inputs.

The distribution of NaHCO3-extractable nitrate-N, ammonium-N, phosphorus (P) and potassium (K) with soil depth (0 to 20 cm in 5-cm increments) at Fort Vermilion (58°23′N 116°02′ W), Alberta, was described in the 7th and 8th years of conventional and zero tillage following placement of red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues. Soil nitrate-N concentrations under zero tillage were greater than those under conventional tillage in the 0–5 cm soil layer, below which the concentrations were similar. Ammonium-N and K concentrations followed a similar pattern. However, soil P concentrations were usually not different between tillage systems in the 0–5 cm soil layer, but the concentrations decreased more under zero tillage than under conventional tillage at lower depths. A notable exception for soil phosphate was under canola residues, where the concentration was greater under zero tillage than under conventional tillage at all depths. Uptake of N, P or K by a subsequent wheat crop was usually greater (though not always significantly) under zero tillage than under conventional tillage, and there were no interactions between tillage and crop residue. Therefore, differences in nutrient stratification between the two tillage systems did not translate into differences in wheat nutrient uptake. Key words: Conservation tillage, crop rotation, nutrient uptake, soil nitrogen, soil phosphorus, soil potassium

Conservation tillage may increase the risk of leaf diseases for Alberta barley producers. A study was undertaken from 1995 to 1997 to assess the impact of the tillage system, crop rotation, and cultivar resistance on levels of scald [Rhynchosporium secalis] and net blotch [Pyrenophora teres] in commercial barley (Hordeum vulgare) fields. Scald and net-blotch levels were assessed in 99, 148, and 91 barley fields in 1995, 1996, and 1997, respectively, throughout Alberta. Fields were classified according to tillage regime (conventional, zero, and minimum tillage), cultivar resistance to both diseases, and crop rotation. The tillage system did not influence the probability of higher levels of scald or net blotch in all 3 years. The previous crop did influence the probability of higher levels of scald in 1995 and 1996; fields previously planted to barley were 3–4 times more likely to have greater scald severity than fields planted to a nonhost crop. The previous crop affected the level of net blotch in 1995 on...

Summary Legumes are an important source of protein for humans and livestock. Legumes have also been used for soil improvement for centuries because of their N and non-N rotational benefits to non-legume crops. The N benefits include N2 fixation and mineralization, sparing of soil inorganic N, and reduced immobilization of soil inorganic N. The non-N benefits include breaking pest cycles, improvement of soil structure, and the nutritional and disease-control effects of endophytic rhizobia. Therefore, optimizing the legume-Rhizobium symbiosis is important, and it can be done by selecting or modifying either (or both) symbiotic partner(s) for desirable traits related to N2 fixation. Rhizobium strains can be selected or genetically modified for traits like N2 fixation potential, nodulation competitiveness, persistence in soil, compatibility with inoculant carriers, and tolerance to environmental stress factors. Legume genotypes can also be selected, bred or genetically modified for N2 fixation potential, rest...

The litter-bag method was used in field experiments to determine nitrogen (N) loss patterns from decomposing red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues under conventional and zero tillage. Nitrogen contained in crop residues ranged from 10 kg ha-1 in wheat under both tillage systems to 115 kg ha-1 in clover GM under zero tillage. The patterns of N loss (i.e., release), particularly from GM residues, over 52-wk periods varied with tillage, i.e., residues lost N more rapidly under conventional tillage than under zero tillage in the first 5 to 10 wk after residue placement. Net N immobilization was sometimes observed, particularly under zero tillage. Where net N release occurred, it ranged from 22% of wheat N under conventional tillage to 71% for clover N under conventional tillage; it was positively correlated with residue N concentration and microbial activity, and negatively correlated with C:N and lignin:N ratios in one study period. The amounts of N released were 2 kg ha-1 from wheat, 10 to 25 kg ha-1 from canola, 4 to 18 kg ha-1 from pea, and 46 to 69 kg ha-1 from GM residues. Therefore, when grain is harvested, the remaining crop residues do not release much N to the soil in the first year of decomposition, but the N stored in soil is presumably released in subsequent years. Key words: Crop residues, crop rotation, N mineralization, organic soil amendments

Glyphosate-resistant (GR) crops are produced over large areas in North America. A study was conducted at six western Canada research sites to determine seed date and tillage system effects on weed populations in GR spring wheat and canola cropping systems from 2000 to 2003. Four-year wheat–canola–wheat–pea rotations were devised with varying levels of GR crops in the rotation. Weed populations were determined at pre– and post–in-crop herbicide application intervals in 2000 and 2003. Early seeding led to higher and more variable in-crop wild oat and wild buckwheat populations. High frequencies of in-crop glyphosate wheat in the rotation usually improved weed management and reduced weed density and variability. Canonical discriminant analysis (CDA) across all locations revealed that by 2003, green foxtail, redroot pigweed, sowthistle spp., wild buckwheat, and wild oat, all associated with the rotation lacking in-crop glyphosate. Similar CDA analyses for individual locations indicated specific weeds were associated with 3 yr of in-crop glyphosate (Canada thistle at Brandon, henbit at Lacombe, and volunteer wheat, volunteer canola, and round-leaved mallow at Lethbridge). However, only henbit at Lacombe and volunteer wheat at Lethbridge occurred at significant densities. Although excellent weed control was attained in rotations containing a high frequency of GR crops, the merits of more integrated approaches to weed management and crop production should also be considered. Overall, rotations including GR spring wheat did not significantly increase short-term weed management risks in conventional tillage or low soil-disturbance direct-seeding systems.

Soil biological properties can be significantly impacted by land management. Cattle manure, hog manure or inorganic fertilizers were applied annually or triennially in field trials conducted at two sites over 3 yr. A control treatment without manure or fertilizer was also included. Canola (Brassica napus) was grown in year 1, hulless barley (Hordeum vulgare) in year 2, and wheat (Triticum aestivum) in year 3. Where effects were significant, cattle manure increased soil microbial biomass C (MBC) by 26% to three-fold, hog manure by 31% to two-fold, and inorganic fertilizers reduced MBC by 20–64%. Similar effects, except the reduction by inorganic fertilizers, were observed for functional diversity of soil bacteria (Shannon index, H′ ). At one site, where crop yields were recorded for 3 yr, hog manure produced greater grain yields (75% increase over the control) than the rest of the treatments (49% increase by cattle manure) in year 1, but cattle manure out-yielded other treatments thereafter, when it increased yields by 25–50%. Cattle manure out-yielded other treatments even when nutrient uptake from inorganic fertilizers was the highest, implying that other factors also influenced crop yields. At the other site, crop yields were recorded only in year 1, and all soil amendments increased canola yields about three-fold relative to the control. Frequency of application usually had no effects on MBC or H′, but the triennial application rate of inorganic fertilizers or hog manure produced lower crop yields than annual applications in year 1. Key words: Functional diversity, Gray Luvisol, manure quality, NPK fertilizers, soil microbial communities

Field experiments were conducted to determine decomposition patterns of red clover (Trifolium pratense), field pea (Pisum sativum), canola (Brassica rapa) and wheat (Triticum aestivum) residues under zero and conventional tillage. Crop residue amounts produced in 2 trial years ranged from 1.6 t ha-1 for monoculture wheat to 6.05 t ha-1 for peas, and tillage had no effect. The extent of dry matter (DM) decomposition was usually less under zero than under conventional tillage, e.g., 31 to 41% of canola DM decomposed under zero tillage while 41 to 50% decomposed under conventional tillage in 12 mo. Corresponding percentages for other residues under zero and conventional tillage, respectively, were: 65 and 75% for clover, 43 and 45 to 55% for pea, and 27 and 40% for wheat. The rate and extent of DM decomposition were positively correlated with N and P concentrations, and negatively correlated with C/N, C/P, lignin/P and lignin/K ratios. These decomposition patterns have implications for nutrient release and soil cover. Rapid decomposition is not necessarily desirable because the nutrients released are subject to losses in soil. Key words: Biological soil quality, crop residue quality, crop rotation

We investigated the effects of field pea (Pisum sativum)-based crop rotations on endophytic bacteria in roots and surrounding soil of cereal and oilseed crops. Barley (Hordeum vulgare), wheat (Triticum aestivum) and canola (Brassica rapa) were each grown (a) following peas inoculated with Rhizobium leguminosarum bv. viceae, (b) following uninoculated peas or (c) in monoculture. At flagleaf (cereal) or flowering (canola) growth stage, populations of soil-extract agar (SEA)-culturable bacteria ranged from log10 7.12 to log10 7.82 cells g-1 soil dry weight in the bulk soil, log10 7.15 to log10 8.12 cells g-1 soil in the rhizosphere, log10 7.77 to log10 10.39 cells g-1 root dry matter (DM) on the rhizoplane, and log10 5.56 to log10 7.63 cells g-1 root DM in root interiors (endophytic bacteria). Differences between treatments in populations and functional diversity of bacteria depended on where the bacteria were sampled in the continuum from bulk soil to root interiors. This affected correlations with crop N and yield because these crop parameters were lowest in monoculture. Thus, populations of endophytic bacteria and functional diversity of rhizospheric bacteria were negatively correlated with crop N accumulation and yields. However, the diversities of endophytic and bulk soil bacteria were positively correlated with crop N and yields. Key words: Community-level physiological profile, crop rotation, substrates, endophytic bacteria, microbial functional diversity, rhizosphere

Greenhouse and field experiments were conducted to investigate the effects of herbicides on soil microbial C (microbial biomass), bacterial diversity and community structure. In the first greenhouse experiment, 12 herbicides were applied at recommended rates to a Gray Luvisolic soil contained in trays. Soil samples were collected 0, 1, 2, 3 and 4 wk after treatment and analysed for microbial C and bacterial diversity. The second greenhouse experiment was similar to the first, but only 6 of the 12 herbicides were applied to a Gray Luvisolic and Black Chernozemic soil. The same six herbicides were applied to the Gray Luvisolic soil at a field site near Fort Vermilion, Alberta, and to the Black Chernozemic soil at Lacombe, Alberta, in 2000. In the first greenhouse experiment, metribuzin, imazamox/imazethapyr, triasulfuron and metsulfuron methyl reduced microbial C compared with glufosinate ammonium and sethoxydim. In the second greenhouse experiment, microbial diversity as determined by Shannon index was lower after application of metribuzin, imazamox/imazethapyr and glufosinate ammonium than after application of glyphosate, but none of the herbicides altered microbial diversity relative to the control treatment. In the field experiments, herbicides had no effect on microbial C or diversity. In all experiments, examination of microbial community structure revealed herbicide-induced shifts in microbial composition even when diversity indices among treatments were not different. It was concluded that herbicides applied once at recommended rates did not have significant or consistent effects on microbial C or diversity. Key words: Environmental sustainability, substrate utilization, biological soil quality, community-level physiological profiles (CLPP)

Appropriate rhizobial inoculation and fertility management can increase field pea (Pisum sativa) seed yield and improve yield stability in western Canada. The objective of this study was to determine the effect of inoculation method and N fertilizer application on pea seed yield and quality. The effects of soil inoculant (granular) and seed-applied inoculant (peat powder or liquid) used with and without urea-N application on field pea were investigated in the Peace River region of Western Canada. At low applied N rates, field pea biomass was significantly higher for soil-applied inoculant as compared to seed-applied inoculant. Soil-applied inoculant resulted in 15, 18, 9 and 0% higher pea biomass yield at the flatpod stage than seed-applied inoculant at 0, 20, 40 and 80 kg N ha-1, respectively. Averaged over all N rates, soil-applied inoculant resulted in 17, 50, and 56% higher pea seed yield than peat inoculant, liquid inoculant, or the uninoculated check, respectively. Soil-applied inoculant increased the proportion of the biological yield converted to seed compared to seed-applied inoculant. Seed protein concentration increased by 12 and 15% when inoculant was soil-applied compared with seedapplied or uninoculated pea, respectively. Without N fertilizer, soil-applied inoculant increased field pea biomass, seed yield and protein concentration and contributed to increasing yield stability compared with seed-applied inoculant. Key words: Granular inoculant, Pisum sativum, field pea, inoculation, seed protein, seed yield

Endophytic rhizobia have been shown to improve the nutrition of nonlegume crops. The objective of this work was to investigate the effects of field pea (Pisum sativum)-based crop rotations on endophytic rhizobia in roots of cereal and oilseed crops. Barley (Hordeum vulgare), wheat (Triticum aestivum) and canola (Brassica rapa) were each grown (a) following inoculated peas, (b) following uninoculated peas or (c) in monoculture. At flag-leaf or flowering growth stage, populations of endophytic rhizobia were usually in the order: crop following uninoculated peas (up to 7244 cells g-1 root DM) > crop following inoculated peas (up to 1660 cells g-1 root DM) > crop grown in monoculture (< 10 cells g-1 root DM). At one of three sites, there were significant positive correlations between endophytic rhizobia and crop N and yield. Populations of rhizobia in bulk soil, rhizosphere, or rhizoplane of nonlegume roots were greater where nonlegume crops were preceded by peas (inoculated or uninoculated) than where they were grown in monoculture. Significant positive correlations between populations of these rhizobia outside roots and crop N or yields were observed at each site. Key words: Crop rotation, inoculation, nitrogen fixation, plant growth-promoting rhizobacteria (PGPR), rhizosphere

Field pea (Pisum sativum L.) acreage has expanded rapidly in the past 10 yr in the Peace River Region of Alberta as well as western Canada. Understanding nitrogen dynamics of Rhizobium inoculants and applied N will provide farmers opportunities to improve N nutrition of field pea. Field experiments were conducted (a) to compare the effects of soil inoculation using granular inoculant, and seed inoculation using peat powder and liquid inoculants with an uninoculated check, on field pea nodulation and N2 fixation, and (b) to determine whether starter N is required by field pea to enhance N2 fixation. The effects of inoculant formulation on nodule number, N accumulation and N2 fixation were in the order: granular > peat powder > liquid = uninoculated. Field pea, from soil-applied inoculant, accumulated more N prior to and during podfilling than field pea with seed-applied inoculant. Fertilizer N application rates < 40 kg N ha-1 had no significant effects on biomass N at flatpod, indicating that starter N was not necessary. Application rates greater than 40 kg N ha-1 reduced nodulation, but the total amounts of N accumulated by plants did not vary. The close proximity of a highly concentrated band of N fertilizer had a greater impact on nodulation and subsequent N2 fixation than the residual soil N level. Under field conditions, soil-applied inoculant improved N nutrition of field pea compared to seed-applied inoculation, with or without applied urea-N. Key words: Granular inoculant, Pisum sativum, Rhizobium, inoculation, field pea, nodulation, N2 fixation

There is little information on the effects of S management strategies on soil microorganisms under zero tillage systems o n the North American Prairies. Experiments were conducted to examine the effects of tillage and source and placement of S on soil microbial biomass (substrate induced respiration) and functional diversity (substrate utilization patterns) in a canola-wheat rotation under conventional and zero tillage systems at three sites in Gray Luvisolic and Black Chernozemic soils. Conventional tillage significantly reduced microbial biomass and diversity on an acidic and C-poor Luvisolic soil, but it had mostly no significant effects on the near-neutral, C-rich Luvisolic and Chernozemic soils, which underlines the importance of soil C in maintaining a healthy soil. Sulphur had no significant effects on soil microbial biomass, and its effects on microbial diversity were more frequent on the near-neutral Luvisol, which was more S-deficient, than on the acidic Luvisol or the Chernozem. Significant S effects on microbial diversity were observed both in the bulk soil (negative effects, compared with the control) and rhizosphere (positive effects) of the acidic Luvisol, but all significant effects (positive) were observed in root rhizospheres in the other soils. Sulphur by tillage interactions on acidic Luvisolic soil indicated that the negative effects of S in bulk soil occurred mostly under zero tillage, presumably because the fertilizer is concentrated in a smaller volume of soil than under conventional tillage. Sulphate S effects, either negative or positive, on microbial diversity were usually greater than elemental S effects. Therefore, S application can have direct, deleterious effects on soil microorganisms or indirect, beneficial effects through crop growth, the latter presumably due to increased root exudation in the rhizosphere of healthy crops. Key Words: Biolog, conservation tillage, microbial biodiversity, rhizosphere, soil biological quality, S fertilizer type and placement

Rhizobium inoculant products in North America are often prepared using non-sterile peat and may contain more contaminants than rhizobia. The effectiveness of sterile and non-sterile peat-based inoculants applied to alfalfa (Medicago sativa) seed using either traditional seed inoculation just before planting, or pre-inoculated and commercially coated, were evaluated for three years (eight harvests) at two sites in northwestern Alberta. Seeds inoculated just before planting had more rhizobia at planting time than pre-inoculated seed. When results from all the three years were combined, inoculation with Rhizobium, either seed-applied or pre-inoculated, significantly (P

Annual legumes are usually inoculated with rhizobia annually to ensure high nodulation, nitrogen fixation and crop yields. To assess the potential of establishing a highly effective population of soil rhizobia in a crop preceding the legume, the effect of passing the rhizobia through crop rhizosphere prior to planting peas was investigated in pot experiments. We inoculated pea seeds with soil obtained from (a) the rhizosphere of peas or wheat with or without rhizobial inoculation, and grown in potted soil, or (b) inoculated and uninoculated soil-only control pots (non-rhizosphere). Seeds and soil had been inoculated with Rhizobium leguminosarum bv. viceae strain NRG480 (also known as 128C56G, LiphaTech, Milwaukee, WI). Inoculation of peas with previously-inoculated soil sampled from wheat rhizosphere nor pea rhizosphere had no significant effect on nodulation and plant dry matter (DM) of peas. However, inoculating peas with previously-uninoculated soil (i.e., indigenous rhizobia) sampled from pea rhizosph...

Greenhouse and field experiments were conducted with field peas (Pisum sativum, L.) in soils of pH 4.4 to 6.8 to determine the best rate of inoculation with rhizobium and to evaluate pre-inoculated (coated) seeds as an alternative to the traditional seed inoculation method of using sticking agents. Inoculation rates higher than 105 cells seed–1 were usually required for high nodulation, nitrogen fixation and grain yields. Therefore, Canadian standards, which require that 105 nodulating rhizobia be delivered per seed for large-seed legumes like peas, may need to be increased. Counts of rhizobia on coated seeds were about 3 log units lower than those on freshly inoculated seeds, but coated seeds significantly outperformed standard seed-inoculated seeds in nodulation and crop yield in acid soils (pH 4.4 and 4.7). However, field pea yields were too low to have commercial value at these low pH levels. In soils with higher pH, standard inoculation resulted in greater nodulation and yield, but the differences were not always significant. It is concluded that the use of coated seeds provides a yield advantage for field pea grown on acid soils, but liming would probably be a better option. Use of coated seeds on other soils will depend on the trade-off between the time and money saved in inoculation in order to seed early and a possible reduction in yield due to insufficient numbers of rhizobia being applied. Key words: Nitrogen fixation, nodulation, Pisum sativum, pre-inoculated seeds

Reduced tillage of agricultural soils has been shown to result in greater macroaggregation, microbial biomass and microbial diversity. While it has been shown that macroaggregates contain more microbial biomass per unit soil mass than microaggregates, it is unclear how microbial diversity varies with soil aggregation. We investigated the functional diversity (catabolic potential) of bacteria, evaluated by calculating Shannon’s diversity index ( H ′), substrate richness ( S ) and substrate evenness ( E ) from potential substrate utilization patterns, in whole soil (i.e. not separated into different aggregate sizes) and aggregates of different sizes (2–4, 1–2, 0.5–1, 0.25–0.5, and 0.1–0.25 mm diameter) in loam and silt loam soils grown to barley and managed for 6 years under conventional tillage (CT) or zero tillage (ZT) systems in northern British Columbia. There were no significant tillage effects on bacterial diversity in whole soils. In soil aggregates, H ′ and E were significantly higher under CT than under ZT on the loam at barley planting time, with no significant aggregate size effects. However, at barley-heading stage, all diversity indices in both soils were significantly higher under ZT than under CT, and they tended to increase with increasing aggregate size. Cluster analysis and principal component analysis of substrate utilization patterns also revealed differences in bacterial community structures between CT and ZT, but the substrates that were utilized differently between the two tillage systems were not the same between soil types or sampling times. The results during the cropping cycle imply that deterioration of soil structure is probably one factor that explains the adverse effects of soil tillage on soil microbial biomass and diversity.

Alfisols, Vertisols, Inceptisols, Aridisols, Mollisols, and Entisols were sampled (0–30 cm) from 32 locations across Ethiopia. The soils were analyzed for copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) contents using 0.005 M diethylene triamine pentaacetic acid (DTPA), 0.05 M hydrochloric acid (HC1), and 0.02 M ethylene diamine tetraacetic acid (EDTA) extractants. EDTA extracted more of each micronutrient than DTPA, which extracted greater amounts than HC1. The quantities of EDTA and DTPA‐extractable micronutrients were significantly correlated, and were in the order: Mn>Fe>Cu>Zn. The order of HCl‐extractable micronutrients was Mn>Fe>Zn>Cu. Micronutrient contents of Mollisols, Vertisols, and Alfisols were usually greater than those of the other soils, and Entisols usually had the lowest micronutrient contents. The contents were mostly positively correlated with clay and Fe2O3 contents, but negatively correlated with soil pH and A12O3contents. While comparison of DTPA‐ and EDTA‐extractable ...

Crop production systems that include field pea (Pisum sativum L.) in rotation are important for sustainable agriculture on acid soils in northwestern Canada. Greenhouse experiments were conducted to compare the ability of liquid inoculant applied to the seed, powdered peat inoculant applied to the seed, and granular inoculant applied in a band with the seed to establish effective nodulation on field pea grown at soil pH(H2O) 4.4, 5.4 and 6.6. Plants were grown to the flat pod stage, and then total plant biomass dry weight, dry weight of nodules, number of nodules, plant nitrogen content, and proportion of plant nitrogen derived from the atmosphere (%Ndfa) were measured. Granular and powdered peat inoculants produced greater nodule numbers and weight, plant nitrogen content, %Ndfa and total biomass than liquid inoculant in at least two of the three experiments. Only granular inoculant was effective in establishing nodules at soil pH 4.4, but granular and powdered peat inoculants were effective at pH 5.4, and all three formulations were effective at pH 6.6. The results showed that granular inoculant has potential for effective nodulation of field pea grown on acid soil. Key words: Rhizobium, inoculant formulations, field pea, nodulation, acid soil