Search

The world acreage of organic crop production systems is increasing, but the soil microbial dynamics in these systems are not fully understood. We studied the composition and functioning of soil microbial communities in 4-year organic or conventional rotations. The organic systems were tilled to control weeds, and N2-fixing legumes or compost supplied nutrients. The conventional systems were managed under no-till; herbicides controlled weeds, and compost or fertilizers supplied nutrients. Soil microbial biomass C (MBC), the diversity and composition of bacterial communities, and activities of enzymes that mediate C, N, P, and S cycling were determined. The bacterial classes Gemmatimonadetes, C0119 (phylum Chloroflexi), and Thermomicrobia (phylum Chloroflexi) were more abundant in organic than conventional cropping systems, so were some genera from the class Actinobacteria. The bacterial β-diversity showed similar cropping system differences. However, acid phosphomonoesterase activity was greater in conventional than organic cropping systems, presumably because the soil P from the large amounts of compost applied in the organic system suppressed this enzyme. MBC, bacterial α-diversity, the relative abundances of the bacterial classes δ-Proteobacteria, γ-Proteobacteria, and Bacilli (phylum Firmicutes) were all greater in compost than no-compost treatments. The relative abundances of three genera from Actinobacteria class were negatively correlated with acid phosphomonoesterase activity due to the high relative abundances of these genera, but low acid phosphomonoesterase activities, where compost was applied in the organic system. Therefore, there were soil bacterial compositional differences between organic and conventional cropping systems, but only differences in the activities of a P cycling enzyme were detected.

Dry bean (Phaseolus vulgaris L.), potato (Solanum tuberosum L.), wheat (Triticum aestivum L.), and sugar beet (Beta vulgaris L.) are mainstays of irrigated crop production in southern Alberta. Concerns about soil quality and sustainability instigated a 12 yr (2000–2011) rotation study to compare conventional (CONV) with conservation (CONS) management practices (reduced tillage, narrow-row dry bean, compost addition, and cover cropping). Plant-available water (PAW) was measured using a neutron probe (10–16 count days·season−1, n = 148) on all phases of 4 yr (dry bean–potato–wheat–sugar beet) rotations under CONS and CONV management. A visual monitoring approach was used for irrigation scheduling. For dry bean and sugar beet, management allowable depletion (MAD) was exceeded on only 11%–15% of neutron probe count days over 12 yr. However, MAD was exceeded on 30% of count days for wheat and 43% for potato. Significant crop × management interactions showed that PAW was higher with CONS management most frequently on potato, followed by dry bean, wheat, and sugar beet. This order reflected the prevalence of CONS practices directly impacting each crop. Regression analyses showed that potato, wheat, and sugar beet yield increased significantly as mean growing season water table depth (WTD) increased. This was explained by yield suppression due to excessive soil wetness in seasons with high rainfall and shallow WTD. This study provided comparative soil water dynamics for four major irrigated crops in southern Alberta, over a 12 yr period, which included record high and low growing season precipitation.

Due to widespread adoption of no-till management and use of glyphosate-resistant transgenic crops, glyphosate is the most widely used herbicide worldwide. However, its effect on soil microbial communities is inconsistent. We studied the effects of glyphosate, tillage, and crop rotation on the diversity and composition of soil bacterial communities in wheat (Triticum turgidum var. durum Desf.) rhizosphere after 6 and 7 yr of glyphosate applications. In a 2 × 2 × 2 factorial design, there were two crop rotation treatments: continuous wheat (W–W) and wheat in rotation with field pea (Pisum sativum L.) (P–W); two tillage treatments: minimum tillage (MT) and no-till (NT); and two glyphosate treatments: no application or pre-seeding application at the recommended rate. None of the treatments affected wheat rhizobacterial α-diversity or the relative abundances of most bacterial groups. The most abundant phyla were Proteobacteria (25.1% relative abundance), Actinobacteria (21.7%), Acidobacteria (8.7%), Bacteroidetes (5.9%), Firmicutes (1.4%), Armatimonadetes (1.3%), and Verrucomicrobia (1.2%). Glyphosate reduced the relative abundance of Alphaproteobacteria in W–W rotation but increased it in P–W rotation, and it reduced the relative abundance of Opitutus spp. The W–W rotation had greater relative abundances of the classes Bacilli (Firmicutes) and Gammaproteobacteria, and genera Bacillus and Opitutus (Verrucomicrobia), than the P–W rotation. Compared with MT, NT increased the relative abundance of the phylum candidate division WPS-1, but it reduced that of Phenylobacterium spp. in W–W rotation. These treatment effects probably had implications for soil functioning, including nutrient cycling and biological disease/pest control.

Glyphosate (N-(phosphonomethyl)glycine) is broad-spectrum herbicide that is extensively used worldwide, but its effects on the soil microbiome are inconsistent. To provide a sound scientific basis for herbicide re-review and registration decisions, we conducted a four-year (2013-2016) study in which we consecutively applied glyphosate to a wheat (Triticum aestivum L.)-field pea (Pisum sativum L.)-canola (Brassica napus L.)-wheat crop rotation at five sites in the Canadian prairies. The glyphosate rates were 0, 1, 2, 4 and 8 kg ae ha

Forage mixtures containing legume out-yield monocultures, fix atmospheric nitrogen, and have lower carbon footprints. However, evidence-based information on creating forage mixtures by direct seeding legumes into existing pastures is limited, and information on bloat-free legumes is nonexistent. Traditionally, pastures requiring improvement in western Canada were fully replaced by breaking up the old stand and reseeding. With new and improved forage cultivars, better seeding equipment, and increased knowledge about pasture management, there is a growing interest among producers in rejuvenating pastures instead of replacing them. Pasture rejuvenation refers to the improvement in biomass productivity and (or) nutritional quality of existing pasture without removing the existing vegetation. This can be done through fertilizer application, which is generally expensive and causes negative environmental impacts. Amelioration of compacted pastureland via mechanical aeration is short-lived and can lead to weed problems. As an alternative, direct seeding of productive, nutritive and bloat-free legume species into existing pasture is an attractive option for pasture rejuvenation. For high performance grazing systems, identification of suitable bloat-free legumes and methods for direct seeding into old grass and legume stands will be essential strategies. This review includes information on the benefits of mixed pastures and seeks possible methods of introducing bloat-free forage legumes into existing pastures in western Canada for rapid improvement in productivity and quality while positively influencing animal, soil, and environmental health.

We identify P management strategies combining arbuscular mycorrhizal fungal (AMF) inoculation with rock phosphate or composted manure for intensive organic grain-production systems. We measured the response of plants traits and soil properties to the factorial combination of three rates of organic-approved P sources applied in rotation phase-1 of legume–flax cropping systems, and of granular AMF inoculant applied in the first, second, or both rotation phases, or not applied. Treatment combinations effects on the rhizosphere communities of AMF, fungi, and bacteria were tested by amplicon sequencing, in two pedoclimates. Inoculation had limited effects in both environments. Composted manure decreased lentil yield, but increased lentil N and P concentrations and soil P fertility on the Chernozem, while increasing pea productivity on the Luvisol. Composted manure applied in rotation phase-1 had a residual effect on flax productivity, N and P concentrations, and soil P fertility in both environments. Rock phosphate reduced soil P fertility and flax productivity on the Gray Luvisol. The β diversity of the rhizosphere communities was unaffected by treatments, while the α diversity of bacteria and AMF was altered by AMF inoculation and fertilization only in the Gray Luvisol. Correlations between microbial species and plant traits or soil properties were inconsistent, reflecting the complex relationships among microbial community, plant identity, and environmental conditions. Here, composted manure was more influential than AMF inoculation and rock phosphate. Given the influence of environmental conditions, small field trials are recommended before wide-scale adoption of their use.

Long-term manure application can build soil carbon and nutrient stocks and enhance enzyme activity, but its legacy on enzyme activity after discontinued application is unclear. We quantified soil microbial biomass carbon (MBC) and potential enzyme activities in fall, spring and summer in response to long-term manure application and its discontinuation under irrigated and rain-fed conditions. Relative to the non-amended control, 43 years of annual manure applications increased MBC by 38% and 33%, and β-glucosidase, β-N- acetyl-glucosaminidase (NAGase) and acid phosphomonoesterase activities by 35% and 33%, 137% and 135%, and 67% and 90%, in bulk and soybean rhizosphere soil, respectively, while arylsulphatase activity only increased in soybean rhizosphere by 13%. Fertilizer N had no effects on MBC or most enzyme activities, which were lowest in fall. In bulk and soybean rhizosphere soil, irrigation increased MBC, and NAGase and arylsulphatase activities by 17–33%, 19–54% and 39–57%, respectively, compared to rain-fed conditions, but β-glucosidase and acid phosphomonoesterase activities increased by 25 and 12%, respectively, only in soybean rhizosphere. Legacy effects of manure applied 13 years previously were observed for MBC and all enzyme activities in bulk and soybean rhizosphere soil except MBC in bulk soil and acid phosphomonoesterase in soybean rhizosphere. Legacy effects of manure applied 29 years previously were observed for NAGase and arylsulphatase activities in bulk soil, and NAGase in soybean rhizosphere. Manure legacy effects on enzyme activities decreased with the number of years without manure, following quadratic patterns, and the effects lasted longer than those on MBC.

Supplementing beef cattle with 3-nitrooxypropanol (3-NOP) decreases enteric methane production, but it is unknown if fertilizing soil with 3-NOP manure influences soil health. We measured soil health indicators two years after manure application to a bromegrass (Bromus L.) and alfalfa (Medicago sativa, L.) mixed-crop. Treatments were: composted conventional manure (without supplements); stockpiled conventional manure; composted manure from cattle supplemented with 3-NOP; stockpiled 3-NOP manure; composted manure from cattle supplemented with 3-NOP and monensin (3-NOP+Mon), a supplement that improves digestion; stockpiled 3-NOP+Mon manure; inorganic fertilizer (150 kg N ha-1 and 50 kg P ha-1 ); and an unamended control. Select chemical (K+ , Mg2+ , Mn+ , Zn+ , pH, and Olsen-P), biological (soil organic matter, active C, respiration, and extractable protein), physical (wet aggregate stability, bulk density, total porosity, and macro-, meso-, and micro-porosity), and hydraulic (saturation, field capacity, wilting point, water holding capacity, and hydraulic conductivity) variables were measured. The inclusion of monensin decreased soil Zn+ concentrations by 70% in stockpiled 3-NOP+Mon compared to stockpiled conventional manure. Active C and protein in composted conventional manure were 37 and 92% higher compared to stockpiled manure, respectively, but did not vary between 3-NOP treatments. 3- Nitrooxypropanol did not significantly alter other soil health indicators. Our results suggest that composted and stockpiled 3-NOP manure can be used as a nutrient source for forage crops without requiring changes to current manure management because it has minimal influence on soil health. This article is protected by copyright. All rights reserved.

Research indicates that not all crops respond similarly to cropping diversity and the response of triticale (× Triticosecale ssp.) has not been documented. We investigated the effects of rotational diversity on cereals in cropping sequences with canola (Brassica napus L.), field pea (Pisum sativum L.), or an intercrop (triticale:field pea). Six crop rotations were established consisting of two, 2-yr low diversity rotations (LDR) (continuous triticale (T-T_LDR) and triticale-wheat (Triticum aestivum L.) (T-W_LDR)); three, 2-yr moderate diversity rotations (MDR) (triticale-field pea (T-P_MDR), triticale-canola (T-C_MDR), and a triticale: field pea intercrop (T- in P_MDR)); and one, 3-yr high diversity rotation (HDR) (canola-triticale-field pea (C-T-P_HDR)). The study was established in Lethbridge, Alberta (irrigated and rainfed); Swift Current (rainfed) and Canora (rainfed), Saskatchewan, Canada; and carried out from 2008 to 2014. Triticale grain yield for the 3-yr HDR was superior over the LDR rotations and the MDR triticale-field pea system; however, results were similar for triticale-canola, and removal of canola from the system caused a yield drag in triticale. Triticale biomass was superior for the 3-yr HDR. Moreover, along with improved triticale grain yield, the 3-yr HDR provided greater yield stability across environments. High rotational diversity (C-T-P_HDR) resulted in the highest soil microbial community and soil carbon concentration, whereas continuous triticale provided the lowest. Net economic returns were also superior for C-T-P_HDR ($670 ha–1) and the lowest for T-W_LDR ($458 ha–1). Overall, triticale responded positively to increased rotational diversity and displayed greater stability with the inclusion of field pea, leading to improved profitability and sustainability of the system.

With the increasing resistance of wild oat (Avena fatua L.) to herbicides, there is a need to evaluate the potential of alternative cropping systems based on integrated weed management principles. A 5-yr field study at eight sites across Canada was used to evaluate the profitability of alternative cropping systems that have the potential to control wild oat using cultural practices in conjunction with herbicides. Cultural practices included twice the recommended seeding rates, fall-seeded winter crops, barley (Hordeum vulgare L.) silage, fallow, and alfalfa (Medicago sativa L.). Seven of the 14 cropping systems in this study did not include wild oat herbicide for three consecutive years, controlling wild oat entirely by cultural practices. Cropping system profitability varied by location. For many locations, combinations of barley silage and fall-seeded winter crops without wild oat herbicide application were as profitable as a system of canola (Brassica napus L.) and wheat (Triticum aestivum L.) with wild oat herbicide applied every year. Unprofitable systems generally included those with fallow, alfalfa, and fall-seeded winter crops in regions with rates of high winter kill. Wild oat control can be achieved with diverse cropping systems that are as profitable as conventional annual cropping that relies on herbicide control of wild oat.

Dry bean (Phaseolus vulgaris L.) is usually considered to be poor at biological nitrogen fixation (BNF), but large variations in this trait have been observed among bean genotypes. We evaluated 16 bean genotypes for N2 fixation ability in four N treatments: (i) uninoculated in low-N soil (30 kg N ha−1), (ii) inoculated with commercial Rhizobium leguminosarum bv. phaseoli inoculant Nitrastik-D® in low-N soil, (iii) inoculated with commercial R. leguminosarum bv. phaseoli inoculant Nodulator® in low-N soil, and (iv) uninoculated in high-N soil (100 kg N ha−1). There were differences between genotypes in all the plant parameters that were measured, but only nodulation was affected by N treatment. The 100 kg N ha−1 treatment suppressed nodulation. Seven genotypes nodulated well with either inoculant, two genotypes nodulated better with Nitrastik-D than with Nodulator, three nodulated better with Nodulator than with Nitrastik-D, and four nodulated poorly with either inoculant. Cultivars AC Redbond, Island, and Resolute, all currently commercially grown, did not fix much N2 at flowering (4–8 kg N ha−1) or maturity (19–34 kg N ha−1). By contrast, germplasm lines PI 136692 (red bean), GH-196 (pinto bean), and LEF2RB (carioca bean) had high BNF capability at flowering (10–11 kg N ha−1) and especially at maturity (60–72 kg N ha−1), in addition to high seed yield (2778–2897 kg ha−1), indicating their superior ability to support both of these economically important traits throughout plant growth. These three genotypes would be valuable to breeders for the genetic improvement of BNF in dry bean cultivars.

Relating soil microbial properties to crop productivity is important to appreciate the value of soil microbial activities in sustainable agriculture. Over a 10-year period, we evaluated the effects of conservation (CONS) management practices on soil microbial biomass carbon (MBC). The CONS practices included addition of composted cattle manure; reduced tillage; diverse crop rotations that comprised wheat (Triticum aestivum L.), potato (Solanum tuberosum L.), dry bean (Phaseolus vulgaris L.), and sugar beet (Beta vulgaris L.); and use of cover crops. The CONS management was applied to 3- to 5-year irrigated crop rotations and compared with conventional (CONV) management systems that did not have any of the CONS practices. Continuous wheat was also included. We then related MBC to wheat yields. Averaged over the 10-year period, CONS management overall increased MBC in wheat rhizosphere and bulk soil by 18% and 34%, respectively. When rotations of the same length were compared, CONS management in 3-year rotations increased rhizosphere MBC by 18% and bulk soil MBC by 30%; the corresponding increases in 4-year rotations were 13% and 36%. Regressions between soil MBC and wheat yields were quadratic, with MBC in wheat rhizosphere associated with increasing wheat yields up to 720 mg C kg soil. The corresponding value for MBC in bulk soil was 645 mg C kg soil. These effects were related to the compost and crop C inputs to the soil, which impacted soil organic C contents. Therefore, CONS management resulted in a cycle of high MBC and high wheat yields.

Recent canola acreage and production in western Canada have reached record high levels. Field experiments were conducted from 2014 to 2016 on land previously seeded to continuous canola for 6 yr at three Canadian Prairie sites. We determined that more intensive seed inputs, fertilizer, fungicide, tillage, or chaff removal could increase continuous canola yields compared with a “standard practice” (SP) treatment or match yields compared with canola in rotation. Recommended or 50% higher fertility levels alone or in combination with a higher seeding rate, tillage, chaff removal, or additional fungicide were applied to the same plots in three successive years to determine effects after 1, 2, and 3 yr of treatment imposition. In continuous canola, blackleg incidence and severity were both reduced by fungicide treatment. In rotations where canola was preceded by wheat, blackleg incidence and severity were much lower than in continuous canola. None of the treatments improved continuous canola yields compared with SP after a single year of treatment imposition. In subsequent years, canola yield increases compared with SP usually occurred as a result of additional fertilizer, seed, or fungicide. In the final year, canola yield loss due to continuous canola was largely rescued by additional seed and fertilizer. Without additional inputs, and when preceded by a different crop, canola yields averaged 11% greater than the average of all continuous canola treatments. High fertility regimes generally reduced oil content and increased protein content relative to standard fertility in continuous canola or relative to canola preceded by wheat.

A black medic (Medicago lupulina L.) cover crop produces a persistent seed bank and self-reseeds each year in North America, but its effects on soil microbial communities are not clear. A field trial was established in 2003 with the following experimental treatments: (a) black medic or no medic, (b) a 3-year crop rotation of flax (Linum usitatissimum L.)-oats (Avena sativa L.)-winter wheat (Sativum aestavum L.), and (c) fertilizer N applied to the rotation crops at three rates: 20, 60 and 100% of the recommended N based on soil testing. In 2011, soil bacterial communities were characterized by pyrosequencing. Black medic increased Shannon and Simpson indices of diversity, and both indices increased linearly with increasing N rate. Sixteen phyla were observed and the most abundant (in bulk soil and rhizosphere, respectively) were: Actinobacteria (39.6 and 37.0%), Proteobacteria (34.0 and 32.9%), Acidobacteria (10.8 and 13.8%) and Bacteroidetes (6.2 and 6.7%). Black medic increased the abundance of Proteobacteria, but decreased the abundances of Actinobacteria and Firmicutes in bulk soil, and Acidobacteria in the rhizosphere. Bacteroidetes increased, but Actinobacteria decreased, with increasing fertilizer N rate in bulk soil. Therefore, the two predominant soil bacterial phyla, Actinobacteria and Proteobacteria, had opposite responses to black medic and fertilizer N, presumably due to differences in their ecological classifications. Soil bacterial community structures were shaped by medic. The bacterial phyla in bulk soil that were most associated with medic treatments included Proteobacteria and Bacteroidetes and those associated with no-medic treatments included Actinobacteria, Chloroflexi and Planctomycetes. The rotation crop effects were inconsistent. However, fertilizer N suppressed medic growth, so a black medic cover crop in this semi-arid region would be beneficial only in low-N or organic farming systems.

Long-term field trials are ideal for characterising soil microbial communities because lasting communities in a given cropping system evolve over a long time. However, the soil microbiome has not been characterized in most long-term trials. We used a field trial established in 1911 to identify the core soil bacteria and their functioning in century-old wheat rotations, and how soil moisture deficit affected them. We collected soil samples from three wheat rotations: continuous wheat (W), fallow-wheat (FW) and fallow-wheat-wheat (FWW), all with or without N + P fertilizer, and incubated them with or without soil moisture deficit. The crop rotation effects on microbial biomass C (MBC) were in the order: W > FWW = FW. Fertilizer increased soil MBC by 21%. The activities of β-glucosidase (C cycling), N-acetyl-β-glucosaminidase (C and N cycling), and acid phosphomonoesterase (P cycling) followed similar trends, as did soil N supply measured in the field. The α-diversity of the soil bacteria was lower in continuous wheat than in the other rotations, and decreased with fertilizer application. Actinobacteria and Bacteroidetes were more abundant in continuous wheat than other rotations, and the relative abundance of Bacteroidetes increased with fertilizer application. By contrast, Acidobacteria were less abundant in continuous wheat than in other rotations. Soil moisture deficit during incubation had no effects on the soil microbiome. The core bacterial genera present in 90% of the soil samples were Bradyrhizobium, Rubrobacter, Friedmanniela and Marmoricola. β-diversity analysis revealed that the bacterial community structure in continuous wheat with fertilizer application was different from the structures in the other treatments. These and previously-published soil organic C, N and wheat yield results suggest that microbe-mediated nutrient cycling enabled sustainable continuous wheat cropping when fertilizer was applied.

Arbuscular mycorrhizal fungi (AMF) inoculation and preceding crop identity have been widely reported to affect crop performance and root-associated microbiomes. However, the underlying relationship between the resulting crop performance and the dynamics of root-associated microbiomes is still poorly explored. In this study, the interaction of AMF inoculant and preceding crop was tested in wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) based rotation systems under three fertilization levels. Effects on agronomic traits, root-associated microbiome, and the relationship between root-associated microbiome and crop productivity were investigated. Higher crop yields were produced following a pulse crop (i.e., Fabaceae harvested for dry seed) than a canola crop. Better yields were at least partially due to higher plant N and P uptake, possibly mediated by certain taxa of the root-associated microbiome, such as N2-fixing and H2-oxidizing bacteria. Some differential rhizosphere zOTUs between canola and pulse crops were significantly related to succeeding crop yield. The structure of the communities of AMF, fungi and bacteria responded differently to the influence of geographical location, plant identity and microecological zone (i.e. root and rhizosphere). Results showed that the microbial communities in belowground microecological zones have specific patterns of sensitivity to driving factors, and the dynamics of certain taxa belonging to some N2-fixing and H2-oxydizing bacterial groups may be involved in the effect of crop rotation on the productivity of wheat and flax.

Potato and sugar beet, which are widely grown in southern Alberta, may degrade soil quality because they return little C to the soil, and their harvesting methods cause soil disturbance that increases erosion risk. To reverse these effects, a 12-yr study was established to evaluate soil conservation (CONS) management systems for rotations that included potato, sugar beet, dry bean and wheat. These systems, comprising addition of feedlot manure compost, reduced tillage, diverse crop rotations and use of cover crops, were applied to 3- to 5-yr crop rotations. They were compared with conventional (CONV) management systems that did not have any of the CONS practices. In the final year of the study, pyrosequencing was used to determine differences in soil bacterial community profiles between the two systems (CONS vs. CONV) in wheat rhizosphere and bulk soil. Thirteen phyla were observed, and the most abundant were Proteobacteria (39.6%), Actinobacteria (19.1%) and Acidobacteria (14.9%). Soil bacterial α-diversity increased under CONS relative to CONV management. However, whereas the relative abundances of Bacteroidetes and Firmicutes were greater under CONS than CONV management, the reverse was observed for Acidobacteria and Gemmatimonadetes. Proteobacteria were also more abundant under CONS than CONV management, but only in bulk soil. The community structures of the bacterial communities were in agreement with the differences in relative abundances. These differences were consistent with the ecological classification of soil bacteria as copiotrophic or oligotrophic. Therefore, CONS management systems altered the soil bacterial community profiles and increased the productivity of these soils.

The increasing acreages of crops like potato and sugar beet, which return little C to the soil, and whose harvesting methods cause soil disturbance, led to the establishment of a 12-yr study to evaluate soil conservation (CONS) management systems in southern Alberta. The CONS management systems, applied to 3- to 6-yr crop rotations, were compared with conventional (CONV) management systems that included wheat monoculture. The CONS management was a suite of practices that included addition of cattle manure compost, reduced tillage, diverse crop rotations and use of cover crops that CONV management did not have. In the last two years of the study (2010 and 2011), soil microbial biomass was measured in bulk soil and wheat rhizosphere using the substrate-induced respiration method and phospholipid fatty acid (PLFA) biomarkers. β-glucosidase enzyme activity was measured to evaluate soil functioning (C cycling). Total soil microbial biomass, and that of its components (fungi and bacteria), was significantly greater under CONS management than under CONV management. The total PLFA contents of 3- and 4-yr CONS rotations (15.24–34.69 nmol g −1 soil) were 84–193% greater than those in CONV management (33.45–63.66 nmol g −1 soil) when differences were significant, and fungal PLFA was up to 382% greater. β-glucosidase activity was 50% greater under CONS management than CONV management. Principal component analysis confirmed that the soil microbial community structures in the different rotations were shaped by management practices. These positive responses of soil microbial communities to conservation management will enhance biological processes including nutrient cycling and biological pest control.

Anthropogenic interventions play a key role in promoting positive feedback of soil–plant–environment interactions, but systematic reports on how anthropogenic activities influence soil physiochemical, microorganism-induced properties and soil health are still limited. Here, we assessed the impact of anthropogenic interventions, including crop diversification in rotations, soil physical disturbance, synthetic chemical inputs, and biofertilizer use on soil microbial community structure and function, and the consequential effects on agroecosystem productivity and environmental sustainability. Summarizing the results of over 160 medium- to long‐term experiments from various soil-climatic zones across the globe in this review illustrated that (1) increasing crop diversification in rotations could bring positive impacts on soil microorganisms and soil health, especially including legume crops in rotations. (2) However, monocultures such as continuous wheat cropping could negatively impact soil health by enhancing activities of host specific pathogens. (3) Physical agronomic practices such as tillage can alter soil microbial communities by shifting microclimate conditions. (4) Mineral nitrogen fertilizer use, a leading nutrient input, may have exceeded the planetary boundary of N cycling, and is causing soil acidification and decreasing microbial biomass. (5) Synthetic chemicals, essential for disease management (pesticides) and yield sustainability (fertilization) in conventional agroecosystems are often toxic to non-target soil microorganisms, while bio-fungicides and biofertilizers—a more sustainable approach—carry significant risks to trigger succession of the native soil microbial community, thus impacting soil health. The key is to establish a rational balance between anthropogenic activities for agroecosystem productivity and potential negative influences on the soil microbial community and long-term soil health.

El tizon tardio, causado por el oomiceto Phytophthora infestans (Mont.) de Bary, es una enfermedad devastadora en papa y tomate, y causa perdidas en rendimiento y calidad en todo el mundo. La enfermedad surgio primero en America Central y desde entonces se ha dispersado en Norteamerica, incluyendo los Estados Unidos y Canada. Recientemente han emergido varios nuevos genotipos de P. infestans, incluyendo el US-22, US-23 y el US-24. Debido al impacto economico y ambiental significativos, ha habido un interes en aumento en la identificacion rapida de los genotipos de P. infestans. Ademas de proporcionar detalles en relacion a varias caracteristicas fenotipicas, como la resistencia a fungicidas, preferencia de hospedante, y patogenicidad asociada a varios genotipos de P. infestans, la informacion relacionada al movimiento del patogeno y la recombinacion potencial tambien pudiera determinarse de los analisis geneticos. El analisis del polimorfismo de longitud de fragmentos de restriccion (RFLP) con el loci RG57 es uno de los procedimientos mas confiables usados para el genotipo de P. infestans. No obstante, el procedimiento de RFLP requiere propagacion y aislamiento del patogeno y relativamente grandes cantidades de ADN. El aislamiento del patogeno del tizon tardio algunas veces es imposible debido a la pobre condicion de los tejidos infectados, o por la presencia de residuos de fungicidas. En este estudio, describimos un procedimiento para identificar P. infestans a nivel molecular in planta, usando polimorfismo terminal de longitud de fragmentos de restriccion (T-RFLP) del loci RG57. Este ensayo de T-RFLP es lo suficientemente sensible para detectar y diferenciar genotipos de P. infestans directamente in planta sin la propagacion y aislamiento del patogeno, para facilitar la implementacion oportuna de las mejores practicas de manejo.

Soil surface cover (crop residue and fall-seeded cover crops) during the nongrowing season is an important tenet of sustainable agriculture, reducing wind and water erosion risk and enhancing soil water conservation. Expansion of irrigated row crop production, namely, potato (Solanum tuberosum L.), dry bean (Phaseolus vulgaris L.), and sugar beet (Beta vulgaris L.), in southern Alberta in the late 1990s prompted a 12-year (2000 to 2011) study to evaluate rotations and soil management systems for improved soil quality. The study compared conservation (CONS) and conventional (CONV) management systems in three- to six-year rotations. Conservation management included cover crops; reduced tillage; feedlot manure compost addition; and solid-seeded, narrow-row dry bean production. Beginning in the third year of the study (2002), surface residue cover was estimated each spring prior to tillage or seeding. Averaged over 10 years (2002 to 2011), residue cover was significantly higher on CONS (15.6%) versus CONV (7.1%) management. Cover was significantly higher where wheat (Triticum aestivum L.) was the previous crop (33.7%) compared to narrow-row dry bean (9.7%), which was significantly higher than potato and sugar beet (6.5% to 6.7%), which were in turn significantly higher than wide-row bean (3.6%). Inclusion of a fall rye (Secale cereale L.) cover crop after potato or dry bean increased residue cover close to or more than 30%, the threshold required to reduce wind erosion risk. Long-term replacement of cereals with lower residue-producing crops (e.g., potato, dry bean, and sugar beet) on irrigated rotations in southern Alberta should be considered judiciously in light of potential negative effects on surface residue cover.

Crop residue decomposition not only is mainly driven by, but also affects, soil microorganisms. However, soil microbial responses to legume crops are usually studied only in one subsequent crop. We compared the soil microbial effects of pea (Pisum sativa L.) and faba bean (Vicia faba L.) pulse crops (grown for seed) with faba green manure (GM) and chickling vetch (Lathyrus sativus L.) GM crops in three subsequent crops. Soil microbial biomass C (MBC), β-glucosidase enzyme activity, and bacterial physiological (C substrate utilization) diversity were measured in the summer (rhizosphere and bulk soil) and fall (bulk soil) in all subsequent crops: wheat (Triticum aestivum L.), canola (Brassica napus L.), and barley (Hordeum vulgare L.). Residues of faba bean (grown for GM, herein called faba GM, or for seed, herein called faba bean) usually resulted in the most soil MBC and β-glucosidase activity relative to the other residues. Faba and vetch GM residues increased bulk soil MBC or β-glucosidase enzyme activity more than pulse crop residues in the first and (or) third subsequent crops. Soil MBC and β-glucosidase activities were often positively correlated with initial crop residue N concentrations and negatively correlated with initial C:N ratios or C concentrations. Bacterial physiological diversity was the least responsive to crop residues and was affected differently by sampling time. β-Glucosidase activity was always greater in the fall after crop harvest than in summer. Therefore, β-glucosidase activity was a more sensitive and consistent biological indicator of crop residue effects, and perhaps soil health, than MBC or bacterial physiological diversity.

Sugar beet (Beta vulgaris L.) has a long history as an option for irrigated crop rotations in southern Alberta. A 12-yr (2000–2011) study compared conservation (CONS) and conventional (CONV) management for sugar beet in 4- to 6-yr rotations which also included dry bean (Phaseolus vulgaris L.), potato (Solanum tuberosum L.), and soft white spring wheat (Triticum aestivum L.). Oat (Avena sativa L.) and timothy (Phleum pratense L.) were included in the longest 6-yr rotation. Conservation management incorporated reduced tillage, cover crops, feedlot manure compost addition, and solid-seeded dry bean. Compared with a 4-yr CONV rotation (52.2 Mg ha−1), sugar beet root yield (averaged over the second 6 yr of the study, 2006–2011) was significantly higher, by 11%, on 4- and 5-yr CONS rotations (57.7–57.9 Mg ha−1), and by 8% on a 6-yr CONS rotation (56.1 Mg ha−1). Sugar beet impurity parameters were significantly affected by rotation in, at most, 3 of 12 yr. However, averaged over the final 6 yr of the study (2006–2011), a significantly higher K concentration (impurity) was found with CONS (2108 mg kg−1) vs. CONV (1958 mg kg−1) management. Integrating CONS management practices into sugar beet rotations led to significant yield benefits while effects on sugar beet quality were minimal.

Past agronomic practices, particularly cropping sequence and the balance between N applications and crop N removal, will influence soil N supply and crop yield potential. Nitrogen (N) fertilizer applications required to optimize crop yield and quality will be a function of the difference between crop N demand and the amount of N supplied by the soil. Therefore, assessment of the effect of past management practices on crop yield potential and soil N dynamics is important to accurately predict crop fertilizer N requirements. Field studies were conducted at seven locations representative of the varying soil types and ecozones across the Canadian prairies to determine the persistence of the effects of legume and non-legume crops and repeated N fertilizer applications on soil N supply and on the yield and N uptake of spring wheat ( Triticum aestivum L.) and canola ( Brassica napus L.) for two seasons after fertilization had ceased, corresponding to the fourth and fifth season after legume crop production. Field pea ( Pisum sativum L.), lentil ( Lens culinaris Medik.), faba bean ( Vicia faba L.), canola and wheat harvested for grain, and faba bean grown as a green manure were direct-seeded in 2009. Canola was seeded in 2010, barley ( Hordeum vulgare L.) in 2011, and canola again in 2012 with fertilizer N applied at 0, 30, 60, 90 and 120 kg ha −1 in each crop. Fertilizer N applications were then halted and spring wheat was grown in 2013 and canola in 2014, without fertilizer N applications. Very few effects of crops grown in 2009 were apparent on soil NO 3 -N supply, crop yield or crop N accumulation by 2013, which was the fourth year after crop growth, and no effects were observed in 2014. In contrast, fertilizer N applied from 2010 to 2012 had persistent effects, increasing soil NO 3 -N concentration, crop yield and crop N accumulation for two growing seasons after fertilization had ceased, although the magnitude of response varied considerably with location. By fall of 2014, effects of preceding fertilizer applications on soil NO 3 -N were no longer significant. Accumulation of N in wheat grain and straw was closely related (R 2 = 0.86) to soil NO 3 -N across locations while the relationship between soil NO 3 -N and N accumulation in canola seed was not as strong (R 2 = 0.60). Therefore, measurement of soil nitrate is a valuable tool for producers in this region to use when selecting fertilizer N application rates, but mineralization of N over the growing season will also contribute to crop N uptake. Residual effects of N fertilization can be substantial under prairie conditions, increasing N supply to crops for up to two years after the final application, and should be taken into account when assessing fertilizer use efficiency and N requirements for crop production.

Crop rotation and nitrogen (N) fertilization can influence soil N cycling, however, less is known about their interactive effects under varying soil and climatic conditions. We examined the interactive effects of preceding crops and N fertilizer rates on soil N cycling in canola (Brassica napus L.) and spring wheat (Triticum aestivum L.) cropping systems in no-till soils in the Canadian prairies. Field pea (Pisum sativum L.), lentil (Lens culinaris Medik), faba bean (Vicia faba L.; faba bean-seed), canola and wheat grown for grain, and faba bean green manure (faba bean-GRM) were the preceding crops and were direct-seeded at 7 and 6 locations in 2009 and 2010, respectively. Canola and wheat were seeded in 2010 and 2011 (2012 for wheat at one site), respectively with N fertilizer applied at 0, 30, 60, 90 and 120 kg N ha−1. Above-ground residue N returned was greatest for faba bean-GRM and lowest for canola and wheat. On average across sites, apparent in-crop N mineralization (ANM) under canola was greater following faba bean-GRM than all other preceding crops, except field pea, while under wheat, ANM was greater following all the legumes than following canola and wheat. Crop N uptake increased with N fertilizer rate, but the response was generally lower following faba bean-GRM and lentil. The N budget showed that 40–65% of crop N uptake (35–100% at highest ANM site) was possibly derived from ANM, more so following legumes, as compared to 35–60% from N fertilizer. The surplus and unaccounted N were particularly pronounced when canola and wheat were preceded by legumes rather than by canola or wheat. Our findings indicate that legumes can enhance soil N supply in no-till soils, and also highlight the importance of adjusting N fertilizer rates based on preceding crops to minimize the potential for N losses.

In western Canada, more money is spent on wild oat herbicides than on any other weed species, and wild oat resistance to herbicides is the most widespread resistance issue. A direct-seeded field experiment was conducted from 2010 to 2014 at eight Canadian sites to determine crop life cycle, crop species, crop seeding rate, crop usage, and herbicide rate combination effects on wild oat management and canola yield. Combining 2× seeding rates of early-cut barley silage with 2× seeding rates of winter cereals and excluding wild oat herbicides for 3 of 5 yr (2011 to 2013) often led to similar wild oat density, aboveground wild oat biomass, wild oat seed density in the soil, and canola yield as a repeated canola–wheat rotation under a full wild oat herbicide rate regime. Wild oat was similarly well managed after 3 yr of perennial alfalfa without wild oat herbicides. Forgoing wild oat herbicides in only 2 of 5 yr from exclusively summer annual crop rotations resulted in higher wild oat density, biomass, and seed banks. Management systems that effectively combine diverse and optimal cultural practices against weeds, and limit herbicide use, reduce selection pressure for weed resistance to herbicides and prolong the utility of threatened herbicide tools.

Aims Field pea (Pisum sativum L.) is an important rotation crop in agriculture on the Canadian prairies. Pea root rot is caused by a complex of soilborne pathogens, and can have a tremendous impact on reducing yields and removing fields from pea production. The objectives of this study were to: determine whether characteristics of the fungal and bacterial microbiome are associated with diseased or healthy sites within pea fields, and assess whether abiotic soil properties differed between these diseased or healthy sites. Methods Soil was collected from healthy and diseased sites within 5 fields across Alberta. Bacterial and fungal operational taxonomy units were determined using barcoded Illumina MiSeq of the 16S rRNA and internal transcribed spacer 1 (ITS) genes, respectively. Soil enzyme activities and soil physicochemical properties were also measured. Results Principal coordinate analysis showed that health status was an important determinant of bacterial communities in two out of five fields and fungal communities in all fields. Microbial communities also differed between locations. However, there was no clear relationship between specific fungal or bacterial families, enzyme activities or soil properties with root rot status. Conclusions Although root rot severity and fungal community composition varied between healthy and diseased sites within a field, there was no consistent correlation of disease severity with biotic or abiotic soil properties across locations.

This study evaluated the effects of a ferulic acid esterase (FAE) and a non-FAE-producing inoculant applied alone or in combination with exogenous fibrolytic enzymes (EFE) on the fermentation and nutritive value of mixed grain (barley, oats and spring triticale) silage. The mixed crop was ensiled in laboratory mini-silos either untreated (CON), or treated with a FAE inoculant (FAE), a non-FAE inoculant (NFAE) or NFAE + EFE. Inoculated silages were lower (P

Potato, dry bean, and sugar beet production have increased markedly in recent years on irrigated cropland in Alberta, Canada. Concerns exist about declining soil quality and increased soil erosion when these low-residue crops are grown in sequence in short-duration rotations. A 12-yr rotation study was conducted to determine the merits of adopting various conservation practices (reduced tillage, cover crops, composted manure) and longer-duration rotations to develop a more sustainable production system for these row crops. This article reports on weed density and weed seedbank data collected in the study. Weed densities recorded prior to applying postemergence herbicides indicated that conservation compared with conventional management treatments had greater weed densities in 30 to 45% of the cases in 3-, 4-, and 5-yr rotations. In contrast, a 6-yr conservation rotation that included 2 yr of timothy forage resulted in similar or lower weed densities than rotations with conventional management practices. Residual weed densities recorded 4 wk after applying postemergence herbicides were only greater in conservation than conventional rotations in 2 of 12 yr, regardless of rotation length. Weed seedbank densities at the conclusion of the 12-yr study were similar for 3- to 6-yr rotations under either conservation or conventional management. These findings indicate that implementing a suite of conservation practices poses little risk of increased weed populations in the long term. This knowledge will facilitate grower adoption of more sustainable agronomic practices for irrigated row crops in this region.

Irrigated processing potato production is an important part of southern Alberta’s agricultural economy. A 12-year (2000–11) study compared conservation (CONS) and conventional (CONV) management for potato in 3- to 6-year rotations which also included dry bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and soft wheat (Triticum aestivum L.). Oat (Avena sativa L.) and timothy (Phleum pratense L.) were added to the longest rotation. Conservation management included reduced tillage, cover crops, feedlot manure compost addition, and solid-seeded dry bean. Averaged over 12 years, a 5-year CONS rotation (potato–wheat–sugar beet–wheat–dry bean) resulted in 18 % higher marketable tuber yield than a 3-year CONV rotation (potato–dry bean–wheat). Reduced incidence of potato early dying was also found with CONS management. Results indicate that integration of CONS management practices led to yield and disease control benefits without negatively impacting tuber quality.

Pulse crops are grown on the Canadian prairies because of their agronomic, economic, and environmental benefits. They are recommended to be grown once every 4 yr, but N release from their residues is usually quantified over one crop season following their harvest. We estimated biologically fixed N and monitored patterns of C and N release from residues of green and forage pea (Pisum sativum L.), faba bean (Vicia faba L.), faba green manure (GM), and chickling vetch (Lathyrus sativus L.) GM in three subsequent crop years. Pulses fixed more N, particularly faba bean (184 kg N ha⁻¹) and forage pea (165 kg N ha⁻¹), than GM legumes (77 and 95 kg N ha⁻¹), and they contained more C (1839–2577 kg C ha⁻¹) than GM residues (1072 and 1240 kg C ha⁻¹). Vetch GM, faba bean, and forage pea residues contained the most N (129–153 kg N ha⁻¹), and green pea the least (65 kg N ha⁻¹). Green manure residues released > 80% of their C and N contents, and pea residues released 46 and 62% of their C and about 50% of their N in the first year, but pea residues released more C and N than GM residues in the second and third years. Faba bean residues released 70% and 63% of their C and N, respectively, in the first year. After 3 yr, 3–5% of GM residue organic C and N remained in the soil, compared with 9–18% and 13–16% of pulse crop C and N, respectively. Therefore, pulse and GM residues had different patterns of C and N release.

Soil microorganisms mediate many important biological processes for sustainable agriculture. However, correlations between soil microbial properties and crop productivity cannot always be demonstrated. We collected soil microbial data from a canola ( Brassica napus L.) study that was conducted at seven sites on the Canadian prairies about agricultural practices focused on increasing canola yields. The treatments consisted of two canola seeding rates (75 or 150 seeds m −2 ), two nitrogen rates (1× and 1.5× soil test recommendation) and three nitrogen form–fungicide (prothioconazole) combinations (uncoated urea, no fungicide; uncoated urea + fungicide; and 50% polymer-coated urea + fungicide) in a 2 × 2 × 3 factorial arrangement. Microbial biomass C (MBC), β-glucosidase enzyme activity and functional bacterial diversity (based on C substrate utilization patterns) were determined in canola rhizosphere and in bulk soil and related to canola yields. The effects of seeding rate, nitrogen (N) rate and N form on soil microbial biomass, enzyme activity or bacterial functional diversity were usually not statistically significant. In the few cases where significance occurred, doubling the seeding rate from 75 to 150 seeds m −2 usually increased these microbial properties in canola rhizosphere or bulk soil. Increasing N rate to 1.5× the recommended rate had mostly positive effects in canola rhizosphere and negative effects in bulk soil. The effects of N form (including addition of fungicide) were inconsistent. Soil MBC and β-glucosidase enzyme activity correlated positively with canola grain yield at the five sites where yields were −1 ( r = 0.51** to 0.76**), but no or weak negative correlations were observed at the two sites with yields >4000 kg ha −1 . The functional diversity of soil bacteria was not or was weakly negatively correlated with grain yields. Some of these relationships appeared to be influenced by canola root maggot damage because root damage was usually negatively correlated with the soil microbial characteristics, but the correlations were too weak to be relevant. These results suggest underground feedback interactions between crops and soil microbes, i.e., crop/soil management practices that enhance crop growth also enhance soil microbial communities and their activities, and vice versa.

Historically, soft white spring (SWS) wheat (Triticum aestivum L.) has been a crop choice in southern Alberta’s irrigation districts. A 12-yr (2000–2011) study compared conservation (CONS) and conventional (CONV) management for SWS wheat in 3–5-yr rotations with dry bean (Phaseolus vulgaris L.), potato (Solanum tuberosum L.), and sugar beet (Beta vulgaris L.). Conservation management incorporated reduced tillage, compost, cover crops, and narrow-row dry bean. Wheat was largely unresponsive to CONS management, with only 2 of 13 parameters showing significant positive effects: greater grain Ca (605 vs. 576 μg g−1 on CONV) and S concentrations (1137 vs. 1105 μg g−1 on CONV). Two parameters showed significant negative responses to CONS management: shorter plant height (82.8 vs. 84.8 cm on CONV) and higher take-all [Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker] severity (1.34 vs. 1.27 rating on CONV). The remaining nine parameters were unresponsive: plant density, days to maturity, grain y...

High costs of fertilizer in western Canada have generated interest in alternative N sources. Legumes produce N through fixation, and may increase soil residual and mineralizable N, thus reducing the need for fertilizer N in subsequent crops. Hybrid canola (Brassica napus L.) has a high N requirement for optimum yield, but knowledge of rotational effects of legumes on canola is limited. The objective was to determine the effects of legume and non-legume preceding crops on yield and quality of canola grown the follow ing year and malting barley (Hordeum vulgare L.) grown after canola. Field pea ( Pisum sativum L.), lentil (Lens culinaris Medik.), faba bean (Vicia faba L.), canola, and wheat (Triticum aestivum L.) harvested for grain, and faba bean grown as a green manure were direct-seeded at seven locations in 2009. Canola was seeded in 2010 and barley in 2011, with fertilizer N applied at 0, 30, 60, 90, and 120 kg ha –1 . On average, all legumes, except faba bean for seed, produced higher canola and barley yields than when wheat was the preceding crop. Faba bean green manure produced the highest yields, while canola on canola produced the lowest canola yield. The legumes had little negative effect on canola oil or barley protein concentration. Yields of both crops increased with increasing N rate, but canola oil concentration decreased, and barley protein increased. The results indicate that growing legumes for seed before hybrid canola can improve canola and subsequent barley yield without negatively affecting canola oil or malting barley protein.