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Interest in intercropping semi-leafless field peas (Pisum sativum L.) is increasing as a means of weed control in organic production. We evaluated field pea (cv. CDC Amarillo) grown alone or intercropped with three seeding rates of either barley (Hordeum vulgare L.), mustard (Brassica juncea L.), or oat (Avena sativa L.). A full seeding rate of field pea was used in each instance, resulting in an additive intercropping design. Each crop combination was conducted in a separate experiment, three times over two years (2019 and 2020) in Carman, MB. Measurements included crop and weed biomass production, grain yield and quality, and net return. Intercrops reduced weed biomass at maturity from 17% to 44% with barley and oat being more suppressive than mustard. Intercrops also reduced field pea yield from 6% to 26%, but increased field pea seed mass. Barley at the high seeding rate provided the most weed suppression per unit of field pea yield loss (2.62 kg of weed suppression per kg of field pea yield loss) compared with oat (1.29) and mustard (0.87). Barley and mustard intercrops decreased net return compared with monoculture field pea. Under low weed pressure (1150 kg·ha−1 weed biomass at maturity) and earlier seeding, oat intercrops reduced net return. However, under weedy conditions (2649 kg·ha−1) and later seeding, field pea-oat intercrops significantly increased net return. In conclusion, while all three intercrop mixtures reduced weed biomass, reductions in field pea yields were observed, and net return benefits were observed only in certain circumstances.

AAC Oravena is a white-hulled spring oat (Avena sativa L.) cultivar selected and developed under organic management. AAC Oravena yields well under organic and conventional production systems, compared with check cultivars. AAC Oravena has good milling quality. AAC Oravena was registered (Reg. No. 7561) by the Variety Registration Office, Canada Food Inspection Agency, on 3 July 2014.

Fall-seeded rye (Secale cereale) is known to suppress weeds through physical and allelopathic properties. This study examined the effects of fall rye cover crops on weed and dry bean (Phaseolus vulgaris) productivity over four site–years in Manitoba. In addition to rye, we tested early versus late spring rye termination times as well as herbicide use in a factorial experiment with four replicates. In the absence of herbicides, rye reduced early-season broadleaf and grassy weed plant populations by 44%–72% and 43%–88%, respectively. Terminating rye at the four-leaf stage (∼1100 kg dry matter ha−1) provided the same level of weed suppression as termination at booting (∼3100 kg dry matter ha−1). Early rye termination increased bean plant populations (significant at three out of four sites), bean development (four out of four sites), bean biomass (two out of four sites), and bean yield (three out of four sites) compared with later termination. Lower bean yield with rye at one site–year was attributed to dry early season conditions, where rye reduced soil water content. While the rye cover crop provided multiple benefits to bean production, early termination resulted in the best agronomic outcome. Rye was beneficial to weed control even when herbicides were used.

Greater seeding depths are often used in organic production to compensate for drier soil conditions caused by pre-seeding tillage. We hypothesized that reduced crop performance from deeper seeding could be compensated through larger seed. Field experiments were conducted in Carman, Manitoba, Canada, in 2015 and 2016. Barley (Hordeum vulgare) and oat (Avena sativa) seed lots were sieved using standard industry sieves (from 0.08 cm to > 0.32 cm × 1.91 cm in barley seed lots and from 0.08 cm to > 0.28 cm × 1.91 cm for the seed lots of oats) and classified into small, medium, and large seed sizes for each seed lot. The proportion of small, medium, and large seeds varied depending on farmer seed lot. Seed lots were sown at shallow (2.5 cm) and deep (6.4 cm) depths in organic fields. Deeper seeding and use of small seed size resulted in decreased grain yield and increased weed biomass. This trend occurred in both years but was only significant in 2015. No seed size by seeding depth interactions were observed for crop emergence, weed biomass, grain yield, or dockage for oat or barley over the 2-year study. In two instances, crop biomass was greater with larger compared with smaller seed at shallow seeding depths. This research indicated that large seed did not compensate for lower crop productivity and higher weed biomass owing to deep seeding, but that large seed and shallow seeding independently led to more positive outcomes for organic barley and oat production.

Intermediate wheatgrass yielded 519 and 446 kg seed ha−1in years one and two after establishment. Autumn grazing increased seed yield compared with post-harvest residue removal or chopping. Inter-seeding legumes (alfalfa (Medicago sativa), sweet clover (Melilotus officinalis), and white clover (Trifolium repens) did not affect intermediate wheatgrass seed production.

Smallholder farmers in sub-Saharan Africa (SSA) are under increasing pressure due in part to climate change and soil degradation, with many farming households unable to achieve even basic food self-sufficiency. Conservation Agriculture (CA) is a possible solution to these challenges, but the lack of sufficient biomass for mulch has limited wide-scale adoption, and many farmers who practice CA resort to adding supplemental mulch to their CA plots. Legume intercropping would not only provide biological and nutritional diversity, it may also provide an in situ cover, thereby reducing the amount of mulch required for soil and water conservation. Farmer managed research experiments were used in two semi-arid areas of Zimbabwe to test whether intercropping a cereal crop [maize (Zea mays)] with a legume [cowpeas (Vigna unguiculata), lablab (Lablab purpureus) or pigeon pea (Cajanus cajan)] could increase the total amount of biomass produced. The experimental design included two replicates with legume species and presence or absence of mulch cover as factors in the design. Maize yields were increased more by adding mulch than by legume intercrops in the absence of mulch. Therefore, intercrops were not a substitute for mulch. However, adding intercrops did significantly increase the amount of total biomass (maize and intercrop dry matter) produced at the sites and therefore, in addition to contributing protein rich grains, intercrops may reduce the amount of mulch required for soil and water conservation in CA systems. Farmer participation allowed the research to be conducted in the context of small-holder CA. Key words: Intercropping, cowpea, lablab, pigeon pea, soil conservation, farmer-based research.

Most non-genetically modified (GM) soybean ( Glycine max Merr.) cultivars are bred and performance-tested under conventional conditions and have rarely been tested in organic production. Twelve non-GM soybean cultivars were evaluated in weed-free and weedy conditions on 5 organic farms and 1 transitional farm in southern Manitoba in 2014 and 2015. The mean cultivar yield ranged from 1384 to 1807 kg ha −1 . Weed biomass at soybean maturity ranged from 1289 to 2553 kg ha −1 and was significantly affected by cultivar. Significant site–cultivar interactions were observed for soybean biomass, height, and yield. Site accounted for 72.4% of yield variability; cultivar accounted for only 1%. Our hypothesis that cultivars with greater early season height are more competitive with weeds was not supported. Yield loss due to weeds ranged between 20 and 44%; lower yield loss was associated with timely weed management. Partial least squares regression was used to assess the main factors controlling grain yield. Higher soil nitrate (N) status negatively impacted final grain yield in this study, suggesting that soil nutrient status impacted the soybean cultivars’ competitive ability against weeds. Results suggest that weed management and soil N status are of equal importance to cultivar choice for successful organic soybean production in Manitoba.

Reducing tillage in organic bean ( Phaseolus vulgaris ) production may be facilitated by strategic use of fall-seeded cover crops. This study characterized the effects of fall rye ( Secale cereal L.), barley ( Hordeum vulgare L.) and oat ( Avena sativa L.) cover crops on soil environment, weeds, and bean growth and development. It was repeated twice in Manitoba, Canada with cover crop type and tillage treatments in a factorial experiment. Cover crops were seeded in fall each year (2010 and 2011). Greater cover crop biomass and lower available soil N at bean planting for rye was attributed to rye spring growth. In the till managed treatment, cover crops were tilled immediately before bean planting. Cover crop management in the no-till treatment involved flail mowing (18 days after bean planting in 2011 and 11 days after bean planting in 2012) in the fall rye treatment and flaming immediately after bean planting in the frost-killed barley, oat and control treatments. Rye reduced soil temperature and early season bean development. Bean population density was unaffected by tillage or cover management despite 5604 kg ha −1 of rye biomass at planting. Green foxtail ( Setaria viridis ) populations were decreased with rye only in no-till plots. Dandelion ( Taraxacum officinale ) was unaffected by treatments, while redroot pigweed ( Amaranthus retroflexus ) and barnyard grass ( Echinochloa crus-galli ) populations were lower in no-till plots. Rye reduced weed biomass but not bean biomass at harvest; however, bean yield was lower with rye compared with other cover crops in both years. It was concluded while frost-killed cover crops did not provide sufficient weed suppression, fall rye provided too much competition against the bean crop. No-till management did not improve rye’s overall effectiveness.

Decomposition of cover crop mulches has received little attention in the scientific literature, particularly in the context of the organic rotational no-till systems adapted for the climatic conditions of the northern Great Plains of Canada. The objective of the study was to determine the effect of plant species and mulch application rate on cover crop decomposition and mulch quality parameters over time. Using the litter bag technique, six plant species and two mulch application rates were tested twice in field studies at Carman, Manitoba, Canada. Among the plant species tested, decomposition was the fastest with oilseed radish (Raphanus sativus L.) and the slowest with barley (Hordeum vulgare L.). The effect of application rate on mulch biomass was not consistent between experiments. Mulches released a large amount (46.4%) of their initial N content after only 30 days of field placement, for all levels of plant species and mulch application rates combined. Forty-four percent of initial N content still remained in the mulches by early May (Day 250), and may be available for the subsequent crops seeded in the spring or later in the crop rotation. This research provides us with valuable information on nutrient release, soil cover, and potential weed control from mulches.

Reducing tillage in herbicide-free cropping systems is a challenge for farmers and few studies have attempted to identify the limitations of organic no-till systems over a period of time greater than two years. The objective of the study was to determine the effect of tillage [no-till (NT) and conservation tillage (CT)] and management [organic (ORG) and conventional (CONV)] systems on mulch biomass, weeds, and crop productivity, over time. A six-year field study was conducted in Carman, MB, Canada, between 2008 and 2012. The crop rotation was barley (Hordeum vulgare L.)/hairy vetch (Vicia villosa Roth) cover crop in 2008, flax (Linum usitatissimum L.) in 2009, oats (Avena sativa L.) followed by a 4-species fall-seeded cover crop mixture in 2010, barley/hairy vetch cover crop in 2011, and spring wheat (Triticum aestivum L.) followed by fall-seeded cereal rye (Secale cereale L.) in 2012. From 2008 until mid-2010, the experiment design consisted of two tillage systems (NT and CT), both under ORG management. In mid-2010, the experiment was modified into a split-plot design to allow for the comparison between the ORG and CONV management systems, within each tillage system. In ORG NT, cash crops of flax and spring wheat were seeded into 4.5 and 4.7 Mg ha−1 of rolled cover crop mulch in 2009 and 2012, respectively. Differences in weed communities between treatments were statistically noticeable in the fifth year of the study only (2012), with higher weed biomass and weed species richness in the ORG management system. Crop yields were reduced in ORG NT in 2009 (flax) and 2012 (spring wheat). Little difference in weed and crop responses between ORG and CONV tilled systems were identified. Results suggest that additional innovative soil and weed management practices are needed to make organic continuous no-till cropping system productive for a period longer than six years, in a cool subhumid continental climate.

Changes in land management practices may have significant implications for soil microbial communities important in organic P turnover. Soil bacteria can increase plant P availability by excreting phosphatase enzymes which catalyze the hydrolysis of ester-phosphate bonds. Examining the diversity and abundance of alkaline phosphatase gene harboring bacteria may provide valuable insight into alkaline phosphatase production in soils. This study examined the effect of 20 years of no input organic (ORG), organic with composted manure (ORG + M), conventional (CONV) and restored prairie (PRA) management on soil P bioavailability, alkaline phosphatase activity (ALP), and abundance and diversity of ALP gene (phoD) harboring bacteria in soils from the northern Great Plains of Canada. Management system influenced bioavailable P (P < 0.001), but not total P, with the lowest concentrations in the ORG systems and the highest in PRA. Higher rates of ALP were observed in the ORG and ORG + M treatments with a significant negative correlation between bioavailable P and ALP in 2011 (r2 = 0.71; P = 0.03) and 2012 (r2 = 0.51; P = 0.02), suggesting that ALP activity increased under P limiting conditions. The phoD gene abundance was also highest in ORG and ORG + M resulting in a significant positive relationship between bacterial phoD abundance and ALP activity (r2 = 0.71; P = 0.009). Analysis of phoD bacterial community fingerprints showed a higher number of species in CONV compared to ORG and ORG + M, contrary to what was expected considering greater ALP activity under ORG management. In 2012, banding profiles of ORG + M showed fewer phoD bacterial species following the second manure application, although ALP activity is higher than in 2011. This indicates that a few species may be producing more ALP and that quantitative gene analysis was a better indicator of activity than the number of species present.

Bacterial transformation of phosphorus (P) compounds in soil is largely dependent on soil microbial community function, and is therefore sensitive to anthropogenic disturbances such as fertilization or cropping systems. However, the effect of soil management on the transcription of bacterial genes that encode phosphatases, such as phoD, is largely unknown. This greenhouse study examined the effect of long-term management and P amendment on potential alkaline phosphatase (ALP) activity and phoD gene (DNA) and transcript (RNA) abundance. Soil samples (0–15 cm) were collected from the Glenlea Long-term Rotation near Winnipeg, Manitoba, to compare organic, conventional and prairie management systems. In the greenhouse, pots of soil from each management system were amended with P as either soluble mineral fertilizer or cattle manure and then planted with Italian ryegrass (Lolium multiforum). Soils from each pot were sampled for analysis immediately and after 30 and 106 days. Significant differences among the soil/P treatments were detected for inorganic P, but not the organic P in NaHCO3-extracts. At day 0, ALP activity was similar among the soil/P treatments, but was higher after 30 days for all P amendments in soil from organically managed plots. In contrast, ALP activity in soils under conventional and prairie management responded to increasing rates of manure only, with significant effects from medium and high manure application rates at 30 and 106 days. Differences in ALP activity at 30 days corresponded to the abundance of bacterial phoD genes, which were also significantly higher in soils under organic management. However, this correlation was not significant for transcript abundance. Next-generation sequencing allowed the identification of 199 unique phoD operational taxonomic units (OTUs) from the metagenome (soil DNA) and 35 unique OTUs from the metatranscriptome (soil RNA), indicating that a subset of phoD genes was being transcribed in all soils.

Late season catch crops could be an effective tool to conserve highly available N after grazing of green manures. An experiment was established to investigate the productivity and N capturing abilities of barley (Hordeum vulgare cv. Cowboy) and oilseed radish (Raphanus sativus L.) crops seeded after a grazed green manure. Green manure was a mix of forage pea (Pisum sativum cv. 40–10), soybean (Gylcine max cv. Prudence) and oat (Avena sativa cv. Legget). The experiment was repeated twice in Carman, Manitoba in 2010 and 2011. Catch crops were seeded in late summer either no-till or after soil cultivation of the grazed plots. Wheat (Triticum aestivum cv. Waskada) was seeded in the second year as a test crop for both experiments. Catch crop productivity and N uptake was influenced by season (greater in the wetter year) and catch crop type (barley and radish produced 1990 and 1490 kg ha−1, respectively) but not tillage system. The catch crops had their greatest overall effect on soil NO3-N content in 2010 under conditions of high autumn precipitation when N leaching was more severe. Here, the catch crops significantly reduced NO3-N at all depths. Under drier conditions in 2011, catch crops only reduced NO3-N in the top 30 cm. There was average 57 and 12 kg ha−1 more soil NO3-N in plots with no catch crops than plots where catch crops were grown in 2010 and 2011, respectively. Wheat N uptake at maturity was reduced around 25% when grown after catch crops. Similarly, wheat grain yield was 12–31% less after catch crops than no catch crops. This study showed that catch crops can be used to capture excess nutrients after grazing, but N release from the selected catch crops in the following year was not in synchrony with the wheat N demand.

Studies comparing crop agronomic response in organic production systems under contrasting tillage practices are lacking. The objective of the study was to compare the effect of organic rotational no-till and two organic tilled systems on the basis of mulch biomass, soil chemical properties, weed control, and subsequent crop productivity. A field study consisting of two-year sequences was conducted three times at three close sites in Carman, Manitoba, Canada (2009–2010 at site A, 2010–2011 at site B, and 2011–2012 at site C), on Chernozem soils. Three management systems of cover crops were tested, in a randomized complete block design. A barley ( Hordeum vulgare L.)/hairy vetch ( Vicia villosa Roth) cover crop was grown in the first year of the study and terminated by rolling (no-till), rolling and tillage (Roll + Till), or haying and tillage (Hay + Till). Flax ( Linum usitatissimum L.) was seeded the following year. Our first hypothesis that a full-year growth of barley/hairy vetch cover crop allows the production of between 6 and 8 Mg ha −1 of mulch biomass for the subsequent crop was confirmed in two of three years. Flax was no-till seeded into 6.7, 7.7, and 4.2 Mg ha −1 of mulch at sites A, B, and C, respectively. At two of three sites, flax seed yields were significantly higher in no-till than in the two tillage treatments. There was no penalty on flax seed yield for haying the cover crop in mid-summer instead of incorporating it into the soil by tillage, across all three sites. There was an overall trend towards lower contents of soil nitrate-N in no-till, although it did not greatly influence total plant nitrogen uptake at two of three sites. This corroborates our second hypothesis that while flax N uptake would be reduced by the reduced soil N status in no-till, there will be sufficient N for optimum flax yield. The third hypothesis that barley/hairy vetch cover crop mulches have the ability to provide adequate weed control was generally supported, though there were important exceptions when insufficient mulch biomass was produced. Success of flax crop grown in an organic rotational no-till system in southern Manitoba depended on weather, mulch biomass production (>6.7 Mg ha −1 ), and weed species present. The fourth hypothesis that there is no yield penalty for eliminating tillage for 1.5 years in an organic flax crop in southern Manitoba held true only if that minimum mulch biomass benchmark of 6.7 Mg ha −1 was reached.

There is a need to design intensive cropping systems that can reap multiple benefits from annual forages including animal feed, soil fertility and weed control. Considering pea/oat (Pisum sativumcv. 40–10/Avena sativacv. Legget) as a standard green manure, this study investigated the productivity, weed competitiveness, utilization and nitrogen (N) benefit from grazed and ungrazed green manures to spring wheat (Triticum aestivumcv. Waskada) and fall rye (Secale cerealecv. Hazlet). A set of 3-year experiments was carried out in Carman, Manitoba, Canada in 2009, and was repeated in 2010 and 2011. Green manures were grazed by 2–3 ewes and 2–5 lambs for 24 h (1111–1667 sheep days per ha). Averaged over experiments pea/oat mix, hairy vetch (Vicia villosaL.) and sweetclover (Melilotus officinaliscv. Norgold) above-ground dry matter (DM) production were 5036, 5032 and 4064 kg ha−1, respectively. Lentil (Lens culinariscv. Indianhead), a mixture of seven species and soybean (Glycine maxcv. Prudence) produced the least amount of DM over 3 years; 3589, 3551, 3174 kg ha−1, respectively. Pea/oat and hairy vetch were the most weed-competitive species and, averaged over 3 years, contained less than 15% weed DM. Utilization of green manures by grazing animals varied little among species across years and ranged from 28 to 86% for individual species and years. When combined across experiments grazing increased N availability to the wheat crop. The grazing effect was significant for wheat DM production, N uptake and grain N, but not significant for yield across experiments. Averaged over 3 years, wheat took up 107 kg N ha−1from grazed plots versus 98 kg N ha−1from ungrazed plots. A significant species×management interaction for total (wheat+fall rye) N uptake in 2009 indicated that increasing the proportion of legumes in the green manure increased N benefit from grazing. Fall rye productivity was not affected by grazing. We recommend pea/oat and hairy vetch as two green manure species to enhance the overall system performance to achieve high level of DM production, good weed competition, utilization by sheep and provision of N benefit to the following wheat and fall rye crops.

Grazing green manures may improve N availability and productivity in integrated crop–livestock systems. We hypothesized that grazing green manures, compared with standard soil incorporation with tillage, would increase autumn soil profile NO3–N concentrations and grain yields in subsequent years. Three multiyear experiments were carried out for three years between 2009 and 2011 in Manitoba, Canada. For all three experiments, spring-seeded oat (Avena sativa cv. Leggett) and pea/oat (A. sativa/Pisum sativum cv. 40-10) green manure crops were grazed with sheep or left ungrazed in year one. Both treatments were soil incorporated with a tandem disk after grazing. Spring wheat (Triticum aestivum cv. Waskada) and fall rye (Secale cereale cv. Hazlet) test crops were grown in the second and third years, respectively. Biomass production was greater for pea/oat than oat in experiment 1; in experiment 2 pea/oat = oat; and in experiment 3 pea/oat

Field studies showed that hairy vetch (Vicia villosa) of “northern origin” produced more biomass than cultivars developed in milder climates. Hairy vetch biomass was greatest and weed biomass was l...

With 1 figure and 8 tables Abstract An important research question is whether wheat cultivars for organic production should be selected under organic field conditions. Yield, protein content and kernel weight (KWT) of seven populations of wheat (Triticum aestivum L.) selected in both organic and conventional growing conditions (termed selection environments) were compared at four organically and four conventionally managed sites (termed management environments). Selection environment was found to affect yield, protein and KWT in both management environments. At most sites, populations selected in organic environments had higher yields at organically managed sites relative to conventionally selected populations. When organically managed site-years were combined, the yields of organically selected populations were significantly higher than those of conventionally selected populations. Populations selected under organic management had higher protein content and KWT under both management environments. Direct selection in organically managed field conditions for genotypes targeted to organic agriculture offers advantages over indirect selection in conventionally managed field conditions.

Agricultural production systems that reduce the use of in-crop herbicides could greatly reduce risks of environmental damage and the development of herbicide-resistant weeds. Few studies have investigated the long-term effects of in-crop herbicide omissions on weed seedbank community size and structure. A crop-rotation study was sampled 10 yr after a strictly annual rotation and an annual/perennial rotation were exposed to different in-crop herbicide omission treatments. In-crop herbicides were applied either in all annual crops (control), omitted from oats only, or omitted from both flax and oats. Seedbank densities were greatest when in-crop herbicides were omitted from flax and oats, and this treatment also reduced crop yield. Shannon-Wiener diversity differed among crops in the annual crop rotation and among herbicide omission treatments in the perennial rotation. Herbicide omissions changed the weed-community structure in flax and in wheat and canola crops in the annual rotation enough to warrant alternate control methods in some treatments. The magnitude of the effects on the seedbank parameters depended largely on the competitive ability of the crop in which herbicides were omitted. No yield response to omitting herbicides in oats indicated that standard weed management practices have reduced weed populations below yield-loss thresholds.

Kirk, A. P., Entz, M. H., Fox, S. L. and Tenuta, M. 2011. Mycorrhizal colonization, P uptake and yield of older and modern wheats under organic management. Can. J. Plant Sci. 91: 663–667. Arbuscular mycorrhizal fungi (AMF) are important for plant nutrient uptake, and mycorrhizal dependence varies between wheat genotypes. Cultivar selection under fertilized conditions may have reduced mycorrhizal associations in modern cultivars. This study investigated AMF colonization, tissue P and grain yield of five modern (post 1990) and five older (pre 1970) spring wheat cultivars over 4 site-years in Manitoba. Older cultivars actually had significantly lower AMF colonization and grain yield than modern cultivars, but no tissue P concentration differences were observed. The two highest yielding lines were released after 2004, and one of these (FBC Dylan) was selected for suitability in organic farming systems.

Expansion of dry bean (Phaseolus vulgaris L.) production into saline soil areas of Manitoba has led to increased concern regarding its yield and quality response to soil salinity. The objective of this study was to evaluate the impact of salinity on dry bean productivity in southern Manitoba, including the application of a salt tolerance model for dry bean crops. Using a coulter-based sensor (Veris 3100, Veris Technologies, Salina, KS) to measure apparent soil electrical conductivity (EC a ), surveys of dry bean fields with five levels of soil salinity conditions (very low to very high salinity zones) were created for four sites over 2 yr. High values of EC a were associated with high values of soil saturation extract electrical conductivity (EC e ). Across all site years, average root-zone salinity (EC e ) values ranged from 0.77 to 11.16 dS m -1 . The lowest salinity zones resulted in greater crop biomass, grain yield, harvested seed weight, and grain number, and tended to have greater plant stand densities and grain protein content than the highest salinity zones. A 50% decrease in relative crop yield was caused by EC e values between 4.88 and 8.35 dS m -1 . EC a surveys were found to be an excellent tool for assessing the relative soil salinity status of study fields.

This study compared allelopathic effects of three winter cereals, winter wheat (Triticum aestivum), winter rye (Secale cereale) and winter triticale (Triticale hexaploide Lart.) on seed germination of redroot pigweed (Amaranthus retroflexus), green foxtail (Setaria viridis) and common bean (Phaseolus vulgaris). Extracts from field- and greenhouse-grown rye significantly inhibited germination of redroot pigweed and green foxtail, yet had no effect on the navy bean cultivar Envoy. In a second study, rye, wheat and triticale provided similar inhibition of weed seed germination; however, effects on bean germination differed between cereals. Bean seed germination was significantly reduced (P

Understanding the drought physiology of alternate crops is essential to assess the production risks of new cropping systems. We compared the water relations of dry (field) pea (Pisum sativum L.), chickpea (Cicer arietinum L.), canola (Brassica napus L.) and mustard (Brassica juncea L.) with spring wheat (Triticum aestivum L.) under different moisture availabilities in field trials conducted in 1997 and 1998 at Swift Current, SK. Stress experience and stress responses varied with crop type. In general, there were similarities in drought physiology between the two pulse crops and between the two oilseed crops. The mean predawn leaf water potential of pea was frequently lowest, while the mean midday leaf water potential of wheat was at least -0.40 MPa lower than for any other crop. The crops exhibited different strategies to overcome water stress. Wheat had the lowest osmotic potential at full turgor, except under drought when turgor was lowest for chickpea and wheat; the highest values were observed in Brassica spp. Mean midday pressure potentials were lowest in wheat (and mostly negative, indicating loss of turgor) and highest for the pulse crops. Mean midday pressure potential for canola was positive when well-watered, otherwise it was near 0. Despite lowering osmotic potential, wheat could not maintain positive turgor much of the time at midday. Pulse crops, with the contributions from both osmotic adjustment and cell elasticity, maintained positive turgor over a wider range of water potentials compared with the other crops. With regard to both osmotic adjustment and tissue elasticity, we ranked the crops from high to low ability to adjust to moderate to severe water stress as pulses > wheat > Brassica oilseeds. Key words: Leaf water, osmotic, turgor potentials, wheat, pulse, canola, semiarid prairie

The success of organic wheat (Triticum aestivum L.) production can be severely inhibited by weed and disease pressures. This study sought to determine the effectiveness of wheat intercrop mixtures in suppressing weeds and diseases and increasing grain yield and net return. Field experiments were conducted on organically managed land in 2004 and 2005 and three representative intercrop systems were tested: wheat with other cereals [oats (Avena sativa L.), barley (Hordeum vulgare L.), and spring rye (Secale cereale L.)]; wheat and noncereal seed crops (flax [Linum usitatissimum L.], field pea [Pisum sativum L.], oriental mustard [Brassica juncea L.]); and wheat and cover crops (red clover [Trifolium pratense L.], hairy vetch [Vicia villosa L.], annual ryegrass [Lolium multiflorum Lam.]). The cereal intercrop systems provided no consistent yield benefit over wheat monocultures. Results from noncereal-wheat intercrops were variable. Wheat-flax reduced the wheat crop to unacceptable levels but was capable of reducing wheat flag leaf disease levels. Wheat-field pea resulted in the lowest disease levels, yet had inconsistent yields, and more weeds than wheat monoculture. Wheat-mustard did not reduce weeds or diseases, but it was capable of high grain yields and net returns, though usually hampered by flea beetle (Phyllotreta cruciferae) attack. The effect of cover crops on wheat was affected by environment. Wheat-red clover and wheat-hairy vetch did demonstrate the ability to maintain high wheat grain yield in certain site-years. In conclusion, wheat intercrop mixtures provided little short-term benefit over monoculture wheat in this study.

Two heritage wheat cultivars, Red Fife and Marquis, along with two modern wheat cultivars, 5602HR and AC Barrie, were assessed in organically managed monocultures and mixtures to discern if mixtures provided a benefit to grain yield and disease and weed suppression in Manitoba over 3 site-years. 5602HR was the highest yielding sole cultivar, while Marquis and AC Barrie were the lowest yielding sole cultivars. Red Fife yielded similar to the modern cultivar 5602HR in several cases. Cultivar mixtures did not provide a yield advantage but did stabilize yields of mixtures containing disease susceptible cultivars. Key words: Cultivar mixtures, heritage cultivar, yield stability

Self-regenerating legumes such as black medic (Medicago lupulina L.) can play an important role as a low-maintenance cover crop in annual cropping systems, provided they produce a large quantity of seed, regenerate successfully from the seedbank, and produce a significant amount of biomass. Twenty-seven accessions of black medic, including the cultivar George, were grown at two locations and assessed for their potential as self-regenerating cover crops in prairie conditions, based on phenological and morphological characteristics. Five accessions with adequate seed production, survival and growth late in the season, large leaf size, and good ground cover capabilities were identified and will be the focus of further study. Key words: Medicago lupulina, black medic, legume cover crops, self-regenerating cover crops, Canadian prairies, germplasm screening

A 2-yr study was conducted to investigate the effects of application date, landscape position and a urease and nitrification inhibited formulation of urea on the efficiency of fall-banded N fertilizer under Manitoba conditions. To date, no studies have investigated how these factors interact to influence the efficiency of fall-banded N in western Canada. The effects of landscape position were apparent at three of the four sites, with significantly greater grain yields, straw yields and total recovery of N in the high landscape positions than in the low landscape positions. In the high landscape positions, there were no significant differences in crop response or recovered N among application dates in the fall and spring. However, in the low landscape positions, grain yields, grain yield increases and apparent recovered fertilizer N in the aboveground portion of the crop and in the soil (0–120 cm) were significantly greater for spring and late fall applications, when compared with early and mid-fall applications. At one site in the first year of the study, early fall-banded N with the urease and nitrification inhibitors produced greater increases in grain yield than early fall-banded N without the inhibitors in the low landscape positions. However, overall there was little agronomic benefit to the use of the additives, as there were few significant differences in crop yields or N uptake by the crop with the inhibitors than without, in either year or landscape position. The results demonstrate that selection of suitable timing for application of fertilizer N to optimize crop yields is much more critical for poorly drained areas within a field, or for poorly drained fields, than for better drained land. Key words: Fall-banded N, spring-banded N, landscape position, N-(n-butyl) thiophosphoric triamide (NBPT), Dicyandiamide (DCD), wheat (Triticum aestivum)

Combine harvesters have the potential to disperse weed seeds great distances. Reducing this dispersal may be important in an integrated weed management system. The objectives of this study were to determine the distance that wild oat seeds are dispersed by a combine harvester and the effect of chaff collection on combine harvester seed dispersal. This was measured by sampling wild oat seeds at varying distances behind a combine equipped with a removable chaff collection system after it passed through a wild oat patch. Chaff collection consistently reduced the amount and distance that wild oat seeds were dispersed. This occurred because more than 74% of the total wild oat seed that were ejected from the combine were in the chaff. Because most of the chaff falls in a row directly behind the combine, chaff collection only affected dispersal in this area. In 1996, chaff collection reduced wild oat seed dispersal past the wild oat patch to less than 10 seeds m−2at 45 m, whereas without chaff collection, there was greater than 10 seeds m−2up to 145 m. At distances beyond 145 m, chaff collection had no significant effect on seed dispersal. Chaff collection may be an important tool in an integrated weed management program because it may slow weed invasions and reduce the expansion of weed patches.

Pesticide Free Production (PFP) is a pesticide reduction system that removes in-crop pesticide use on a yearly basis. A long-term study was established in 2000 to investigate the effect of crop rotation and frequency of inclusion on the success of PFP, as well as the effect of PFP on subsequent crops in the rotation. The crop rotations being compared were linola–oat–canola–wheat and linola–oat–alfalfa–alfalfa. PFP occurred either once in the rotation (oat) or twice (linola–oat). Weed density and yield were measured in the crops that followed PFP. Oat was a more successful PFP crop than linola because it was better able to compete with weeds. Furthermore, PFP oat had a higher weed density when it followed PFP linola, but this did not influence PFP oat yield. Under the conditions of this study, PFP linola was more successful in the annual crop rotation. Inclusion of alfalfa hay crops in the crop rotation was not effective in lowering weed pressure and, in fact, may have contributed to an increase in weed density. It is concluded that weed species present influenced the effectiveness of alfalfa in facilitating PFP, because major weeds in the study are not effectively controlled by alfalfa. PFP did not have a negative effect on following crops in the rotation (i.e. canola–wheat or alfalfa), regardless of whether one or two consecutive years of PFP occurred in the rotation. No additional herbicide was necessary for weed control in the crops that followed PFP; however, alfalfa hay was weedier for the first year following PFP. This study indicates that PFP is a viable way to reduce herbicide use in a cropping system and that attention needs to be paid to PFP crop selection and crop rotation, particularly when the PFP crop is less competitive with weeds.

Knowledge of soil water use in different crops and among crop cultivars is useful in crop rotation planning. Net seasonal soil water depletion patterns in the 0- to 130-cm soil profile for semidwarf and tall cultivars of oat (Avena sativa L.) and wheat (Triticum aestivum L.) were compared at 3 site-years in Manitoba. Total soil water depletion was greater for oat than wheat (29–31 mm). This trend was consistent across site-years and N regimes. Greater water use for tall versus semidwarf oat was observed at one of three sites. Key words: Cultivars, oat, semidwarf, soil water depletion, wheat

Oat (Avena sativa L.) production has increased dramatically in the eastern Canadian prairies. The introduction of semidwarf oat cultivars to this region has resulted in the need for research regarding how a semidwarf oat performs relative to conventional tall oat cultivars. Split-split plot experiments were conducted at three site-years during 1999 and 2000 in Manitoba to examine cultivar responses of 'AC Ronald', a short-stature oat, and 'Triple Crown', a tall oat, under different crop rotations (grain legume or oilseed as a previous crop) and N fertilizer rates. Triple Crown had greater (P < 0.05) dry matter production than AC Ronald at anthesis (two of three sites) and maturity (one of three sites). At two of three sites, Triple Crown also displayed higher (P < 0.05) early season plant N uptake than AC Ronald, and Triple Crown always had higher (P < 0.05) kernel weight. However, averaged across sites, AC Ronald yielded 433 kg ha -1 greater (P < 0.05) than Triple Crown. Higher yield for the short-statured cultivar was attributed to greater (P < 0.05) panicle and kernel densities, and better assimilate partitioning (i.e., higher harvest index). Both cultivars were susceptible to lodging; however, Ha significant cultivar x site interaction indicated that under some conditions, AC Ronald experienced less lodging than Triple Crown. No significant cultivar effect was observed for evapotranspiration (ET) or water use efficiency (WUE). Both oat cultivars responded similarly to crop rotation and N fertilizer rate. While the grain yield advantage of AC Ronald appeared stable across treatment environments tested here, some differential cultivar responses for kernels per panicle and lodging resistance across sites were observed. This research supports an expansion of semidwarf oat production in the eastern Canadian prairies.

Forage crops are widely grown in the mixed cropping system of southwestern Uruguay. There is renewed interest in the use of forages for soil improvement and carbon sequestration, but the root growth of forages has received little study. Field observations were made of the root systems of tall fescue (Festuca arundinacea Schreb.), alfalfa (Medicago sativa L.) and chicory (Cichorium intybus L.). Soil core samples were used to measure root count and biomass distributions to a depth of 1 m. Roots were detected to a depth of 1 m for all species, although half of the root biomass for each species was located in the top 20 cm of the soil. The distribution of root counts differed with the greatest number of root axes found above a depth of 20 cm for tall fescue and chicory, and below 20 cm for alfalfa. Key words: Carbon sequestration, perennial forages, subsoil, grasslands

We compared the growth and yield of five Brassica spp. genotypes [two B.juncea (L.) Coss., two B. napus L. and one B. rapa L.] in 11 environments spanning two degrees of latitude and longitude in southern Saskatchewan in 1996–1998. All entries were managed with three levels of N fertility at each site. Plant height for the canola-quality B. juncea breeding line J904316 was 21% greater than the mean of the other genotypes, but shoot biomass did not differ for the same comparison. Cutlass Oriental mustard consistently yielded greatest across all environments while the yield of J904316 was highly variable among environments. The mean seed yield of Cutlass was 12% greater than the highest-yielding B. napus cultivar and 32% greater than the B. rapa cultivar, and had a greater harvest index. Earlier genotypes yielded greater than late-flowering and maturing genotypes within B. juncea and B. napus, but the earliest genotype, Maverick (B. rapa), yielded lower than all other genotypes. All Brassica spp. genotypes were responsive to N fertilization, and high total available N (average = 109, range = 91 to 131 kg N ha-1) was generally required to maximize seed yield, but not shoot biomass, under the conditions of this study. Pod density was the primary yield component influenced by N level. This study illustrates the potential adaptive advantage of B. juncea on the semiarid northern Great Plains. Key words: Brassica, canola, genotype, mustard, N fertility, semiarid, northern Great Plains

This study investigates the relationship between seed dispersal and spatial pattern in a population of wild oats (Avena fatua L.), a common annual weed of arable fields in western Canada. Fractal analysis revealed that wild oats has an aggregated spatial pattern with statistically self-similar properties. Wild oats seed dispersal was successfully modelled using the fractal inverse power law. The estimated fractal dimension of the seed dispersal curve (D = 1.912) is strikingly similar to that of the population’s spatial pattern (D = 1.881), indicating that the observed spatial pattern is characteristic of the dispersal distribution. This result suggests that the dispersal curve of a given weed species may be used to successfully predict its pattern of invasion.

Single-year hay alfalfas (Medicago sativa L.), berseem (Trifolium alexandrinum L.) and red clovers (Trifolium pratense L.), chickling vetch (Lathyrus sativus L.) and lentil (Lens culinaris Medik.) were evaluated for rotational yield and N benefits to the following first-year wheat (Triticum aestivum L.) and second-year barley (Hordeum vulgare L.) crops. Field experiments were initiated in 1997 and 1998 on a Riverdale silty clay soil at Winnipeg, Manitoba. Yield and N content of the following wheat crop were increased following legumes compared to wheat following a canola control. Wheat yield and N content averaged 2955 kg ha–1 and 76.1 kg ha–1, respectively, following the chickling vetch and lentil, 2456 kg ha–1 and 56.4 kg ha–1 following single-year hay legumes, compared with 1706 kg ha–1 and 37.9 kg ha–1 following canola. Non-dormant alfalfas (dormancy rating of eight or greater) contributed to larger grain yields than the dormant alfalfas only in the first year of each experiment. The chickling vetch and lentil provided similar or higher subsequent crop yields and N content for 2 yr compared to a canola control or fallow treatment. This study shows that some increase in yield can be achieved by using a single-year alfalfa hay crop instead of fallow; however, exclusive green manuring of chickling vetch and lentil crops can produce the most increase in yield and N uptake in subsequent crops. Key words: Alfalfa (single-year), legumes (annual), green manure, nitrogen, cropping system

Development of early maturing short stature sunflower (Helianthus annuus L.) cultivars followed the success of semi-dwarf cereals. Although a number of breeding programs have recently released dwarf sunflower cultivars for production in western Canada, the drought adaptability of dwarf cultivars has not been studied. Therefore, field studies were conducted under rainfed conditions at two Manitoba locations during 1994 and 1995 to compare seasonal water relations of 'Sunwheat-103' (SW-103), a dwarf hybrid, and 'AC-Aurora' (Aurora), a dwarf open pollinated cultivar, with 'IS-6111', a standard height hybrid. The dwarf hybrid, SW-103, experienced less stress (up to 0.44 MPa higher leaf water potential) than the standard height hybrid, IS-6111. Genotypic variation for osmotic adjustment was observed in both 1994 and 1995. SW-103 and Aurora respectively had up to 0.42 and 0.39 MPa lower osmotic potential at full turgor compared with IS-6111. Aurora displayed greater osmotic adjustment per unit decrease in leaf water potential than other cultivars. All cultivars maintained positive pressure potential during the study and whenever significant differences in pressure potential were observed, SW-103 usually had higher pressure potential than other cultivars. IS-6111 maintained higher photosynthetic rate and stomatal conductance than the dwarf cultivars. These results suggest that under conditions of adequate water supply, the tall hybrid had the highest productivity despite experiencing the lowest leaf water potential and osmotic adjustment. The drought tolerance advantages of shorter statured cultivars identified here may be more important to productivity maintenance under limited soil water conditions.

ments toward minimum and zero tillage systems in many parts of the Canadian prairies and northern U.S. Great The opportunity to include late-season cover crops in northern Plains and significant reduction in the practice of sumcropping systems has been enhanced with the adoption of winter cereal production; however, cover crop feasibility has not been evaluated mer fallow. There is also increasing interest in alternain these regions. Field experiments were conducted at two sites in tive forms of nutrient management, particularly the role Manitoba in 1998 and 1999 to (i) assess establishment and dry matter of legumes in supplying N to nonleguminous crops (DM) production of legume cover crops that were relay-cropped through rotation and intercropping. [alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.)] The role of forage legume crops in improving agriculor double-cropped [chickling vetch (Lathyrus sativus L.) and black tural sustainability is well recognized. Benefits include lentil (Lens culinaris Medik. subsp. culinaris )] with winter cereals higher grain protein levels, higher yields, weed suppres[winter wheat (Triticum aestivum L.) and fall rye (Secale cereale L.)], sion, increased soil N, and improved soil properties (ii) assess the effect of relay cover crops on cereal grain yield, and

N by leaching not only increases the environmental hazard, but it reduces N available for assimilation by crops. The role of alfalfa (Medicago sativa L.) in extracting NO3‐N from The movement of NO3‐N through a soil profile is deep soils of areas with cold, short growing seasons, such as western directly linked to the movement of water through the Canada, is not well understood. A study was established in 1990 to determine NO3‐N extraction ability to 300 cm; initial soil NO3‐N soil profile (Nielsen et al., 1982). Preferential flow of concentrations were high (. 8m g kg 21 ). Systems included continuous soil water down structural pathways in the soil profile alfalfa; annual rotations of spring wheat (Triticum aestivum L.), field can also be responsible for the rapid movement of appea (Pisum sativum L.), and barley (Hordeum vulgare L.); a native- plied N fertilizers (Coles and Trudgill, 1985). Although grass system [big bluestem (Andropogon gerardi Vitman) and western NO3‐N movement is primarily downward, Boswell and wheatgrass (Agropyron smithii Rydb.)]; and continuous fallow. The Anderson (1964) indicated that upward movement of annual rotation effectively lowered NO3‐N to ,2.3 mg kg 21 in the NO 3‐N might also occur when evaporation exceeds pre30- to 90-cm depth. By the 4th yr, alfalfa had reduced NO3‐N concen- cipitation. Leaching of NO 3‐N is often greatest in wet

The effect of short periods of high temperature stress on the reproductive development and yield of three Brassica species were studied in a growth chamber experiment conducted for 2 yr. Two genotypes from Brassica juncea L. and one each from B. napus L. and B. rapa L. were grown under day/night temperatures of 20/15 °C till early flowering or early pod development, subjected to high temperature stress of 28/15 °C or 35/15 °C for 7 d and then allowed to recover at 20/15 °C. Species differed in optimum temperatures, with B. juncea and B. rapa having higher optimum temperature than B. napus. Dry matter was unaffected by moderate temperature stress, while it was reduced by high temperature stress. The 35/15 °C treatment was injurious to reproductive organs at different developmental stages of all three species. High temperatures at flowering affected yield formation more than high temperature at pod development. On the main stem, mean seed yield reduction due to heat stress was 89%, but partial compensation by pods on the branches reduced mean per-plant seed yield decrease to 52%. Reduction in fertile pods (not total pod number), thousand seed weight and seeds per pod were responsible for the reduced seed yield. Brassica rapa was more sensitive to heat stress than B. napus and B. juncea. Although observation did not indicate the exact developmental phase when the reproductive organs were susceptible to heat stress, pods that passed a critical threshold developmental phase tolerated heat stress, which explained the smaller effect of high temperature stress at pod development. A direct temperature effect on reproductive organs appeared to be responsible for the reduction in yield. All genotypes began to recover from the stress by continuing flowering after returning to 20/15 °C. Brassica napus was least able to recover from severe stress at flowering, as evidenced by the formation of many abnormal pods during recovery. Per-plant yield response of canola-quality B. juncea line J90-4316 was similar to oriental mustard Cutlass. Thus, heat stress effect depends on the growth stage of canola and mustard and Brassica species differ in heat stress response. Key words: Brassica species, napus, rapa, juncea, heat stress, yield, pod number

Avena fatua seeds remaining on the plant at harvest and taken into the combine harvester may be dispersed over large areas. The objective of this study was to characterize the development of A. fatua in comparison to spring Triticum aestivum. As part of this objective, the rate of seed shed in A. fatua relative to development of T. aestivum was determined. Avena fatua and T. aestivum had similar phyllochron intervals within locations but differed between locations. Plant development as measured by the Zadoks plant development scale was consistent within plant species between locations. Seed shed in A. fatua was also consistent between locations. Most of the seed shed occurred within 2 wk, and the cumulative seed shed followed a sigmoidal pattern. The seed shed occurred as T. aestivum was ripening, and the percentage of seed shed appears to be related to the water content of the T. aestivum spike. Because of this relationship, the proportion of seed remaining on A. fatua at harvest could be manage...

Alternatives to herbicides are needed for weed control. Field studies were conducted in 1994/1995 and 1995/1996 to investigate the nature of forage crop-weed dynamics and to test the effect of single year forage crops on the density and community composition of annual weeds in a following field pea (Pisium sativum L.) test crop. Five spring-seeded forage treatments were compared with wheat (Triticum aestivum L.) grain crops (with or without herbicides for grassy and broadleaved weeds): winter triticale (Triticosecale) (simulation grazed); spring triticale (silage); spring/winter triticale intercrop (silage, then simulation grazed); alfalfa (Medicago sativa L.) (hay); sorghum-sudangrass (Sorghum bicolor [L.] Moench × Sorghum sudanese [Piper]) (hay); and a weedy fallow (silage). A fall rye (Secale cereale L.) grain crop and a sweet clover (Melilotis officinalis L.)/winter triticale double crop (hay, then simulation grazing) were included in the 1995/1996 trial. All forage systems were at least as effective as the sprayed wheat control in suppressing wild oat (Avena fatua L.); however, effects on other weeds, especially broadleaved species, were variable. Biennial crops provided the best early season weed control, while long-season systems such winter triticale and the triticale intercrop provided the best late season weed control. Forages shifted the weed community composition away from wild oat and green foxtail (Setaria viridis L. Beauv.) to a similar or greater extent than herbicide-treated wheat. Forage systems that did not provide season-long crop competition tended to have more broadleaved weeds. Some forage systems increased pea grain yield the following year (relative to the sprayed wheat control); however, forages alone did not eliminate the need for herbicides in the pea crop. Annual forages may play an important role in integrated weed management, especially for wild oat, however further research to refine forage-based weed management systems is needed. Key words: Integrated weed management, alfalfa, intercropping, double cropping, organic farming

Herbicide application may provide an alternative to intensive tillage for the termination of alfalfa stands, but might alter N release and N availability to subsequent crops. Our objective was to determine, under field conditions, the effect of timing and method of termination on the pattern of N release from perennial alfalfa, and on N uptake and yield of subsequent wheat crops. Four field experiment, were initiated on perennial alfalfa (Medicago sativa I.,) in southern Manitoba in 1992 and 1993. A factorial of three methods (herbicide, tillage, herbicide + tillage) and two times of termination (early summer, after first alfalfa cut, and late summer, after second alfalfa cut) was arranged in a randomized complete block design. A spring-applied herbicide treatment was also included. Spring wheat (Triticum aestivum L.) was established after alfalfa termination. Soil NO 3 content, plant N uptake, and yield were then monitored for one to two years. In three of four experiments, plant-available N in the spring after termination was higher in tilled treatments than in treatments receiving only herbieides. Regardless of method, plant-available N in the spring after termination was reduced when termination was delayed from early to late season. Despite the lower short-term plant-available N supply in early- and late-summer herbicide treatments, wheat yields in herbicide treatments were similar to or greater than those in tillage treatments. Differences in the N content among treatments diminished with time: by the fall of the second growing season after termination, differences in the cumulative available N supply were no longer evident. These results suggest that termination of alfalfa with herbicides may improve the synchrony between N release and N demand of a subsequent spring wheat crop, thereby improving N use efficiency.

The ability ofMedicago sativato suppress weed growth may provide a viable alternative to chemical weed control and allow crop producers to reduce herbicide inputs. Quantitative information regarding the suppressive effect ofM. sativaon weed populations in current cropping systems is lacking. A survey was conducted in Manitoba, Canada, in 1993 and 1994 to investigate weed populations in commercial cereal fields that had been preceded by eitherM. sativahay or cereal grain crops. A total of 117 fields were surveyed; approximately half from each field type. Principle component analysis indicated that the inclusion ofM. sativain crop rotations resulted in weed communities different from those of continuous cereal fields. Naturally occurring populations ofAvena fatua, Cirsium arvense, Brassica kaber, andGalium aparinewere lower in cereal fields that had previously containedM. sativathan in cereal fields that had been preceded by a cereal crop. Lower field uniformity values forC. arvenseandAvena fatuaindicated that these weeds were also more patchy in theM. sativarotations. Population differences between field types were nonsignificant forAmaranthus retroflexus, Chenopodium album, andPolygonum convolvulus, and although populations ofTaraxacum officinaleandThlaspi arvensewere greater inM. sativa/cereal fields than in continuous cereal crops. No consistent effect of field type onSetaria viridispopulations was observed. These results show thatM. sativaeffectively suppressed some, but not all, of the weeds found in the study area. IncludingM. sativahay crops in crop rotations can be part of an integrated weed management strategy for weeds such asA. fatua, B. kaber, andC. arvense.

Alfalfa (Medicago sativa) may contribute appreciable fixed N to subsequent crops, but the amount may depend on the method of stand termination. In a controlled-environment study, alfalfa was labelled by continuous, prolonged exposure to a 15N2-containing soil atmosphere to allow direct measurement of the fate of fixed N2 from growing and terminated alfalfa. The distribution of 15N in plant and soil components was measured 74 d after alfalfa establishment at the time of alfalfa termination, and again 33 d later following the growth of barley (Hordeum vulgare) for 4 wk. At time of termination, 88% of the 15N present was in alfalfa and 12% in soil (5% in root fragments, ∼5% in microbial biomass and 2% in root and microbial products). The distribution of 15N after alfalfa termination was primarily a function of residue placement rather than termination method. In herbicide treatments in which alfalfa topgrowth was retained on the soil surface, 1% of the 15N present was recovered in barley topgrowth, 8% in soil and 91% in residues; in tillage treatments in which alfalfa topgrowth was incorporated, 10% of the 15N present was recovered in barley topgrowth, 52% in soil and 38% in residues. Regardless of termination method, 10% of the 15N present in alfalfa roots was recovered in barley topgrowth, 30% in soil and 60% in residues. Although tillage and herbicide application result in a similar degree of N release from alfalfa root tissue, tillage accelerates mineralization of alfalfa topgrowth resulting in a larger short-term supply of plant-available N. These results suggest that termination management may provide a means of altering short-term N release from alfalfa, thereby improving synchrony between N release and N uptake by a subsequent crop.

Arbuscular mycorrhizal fungi are of particular interest in organic agricultural systems. We studied the effects of crop rotation and crop management system (conventional vs. organic) on mycorrhizal colonization of flax roots, in the 12th year of a long-term crop rotation trial. Colonization was higher in organic treatments than conventional, possibly due to decreased P availability. There was a highly significant rotation × management system interaction, which may be explained by differences in the abundance of mycorrhizal and non-mycorrhizal weed species between the two management systems. Further research is required before stronger conclusions can be made. Key words: Crop rotation, arbuscular mycorrhizal fungi, flax, wild mustard, host-plant dynamics, organic agriculture

It has been debated how different farming systems influence the composition of soil bacterial communities, which are crucial for maintaining soil health. In this research, we applied high-throughput pyrosequencing of V1 to V3 regions of bacterial 16S rRNA genes to gain further insight into how organic and conventional farming systems and crop rotation influence bulk soil bacterial communities. A 2×2 factorial experiment consisted of two agriculture management systems (organic versus conventional) and two crop rotations (flax-oat-fababean-wheat versus flax-alfalfa-alfalfa-wheat) was conducted at the Glenlea Long-Term Crop Rotation and Management Station, which is Canada’s oldest organic-conventional management study field. Results revealed that there is a significant difference in the composition of bacterial genera between organic and conventional management systems but crop rotation was not a discriminator factor. Organic farming was associated with higher relative abundance of Proteobacteria, while Actinobacteria and Chloroflexi were more abundant in conventional farming. The dominant genera including Blastococcus, Microlunatus, Pseudonocardia, Solirubrobacter, Brevundimonas, Pseudomonas, and Stenotrophomonas exhibited significant variation between the organic and conventional farming systems. The relative abundance of bacterial communities at the phylum and class level was correlated to soil pH rather than other edaphic properties. In addition, it was found that Proteobacteria and Actinobacteria were more sensitive to pH variation.

Timothy (Phleum pratense L.) is a bunch-type cool season perennial grass species grown in Manitoba primarily for seed production. The objectives of this study were to determine the effect of post-harvest residue management (straw removal-SR, straw and stubble removal-SSR and fall burning-Burn) on tiller production, yield components and seed yield of five timothy cultivars (Basho, Climax, Goliath, Hokuo and Salvo), and to better understand the association between yield components and final seed yield in timothy crops grown in the dry subhumid region of the Canadian prairies. Two experiments were conducted over four production seasons at Arborg, MB and one production season at St. Claude, MB. Tiller number per m2 in spring (TS) and at harvest (THV) were measured in 1990 at St. Claude and in 1990 and 1991 at Arborg. Residue management (RM) treatment ranking for TS was Burn −2 at harvest was also unaffected by RM. Seed yield was unaffected by RM in all instances, except at Arborg in 1989 where a significant RM × cultivar interaction was observed. The basis of the interaction was the greater sensitivity of Hokuo to the Burn treatment. Cultivar differences for seed yield were relatively consistent over years and between the two experiments, with Climax always ranking in the high yielding group and Salvo with the low yielding group. Based on analysis of yield components, it appeared that RM most affected early season growth (i.e. TS), while cultivar most affected later season growth (fertile tillers per unit area, seed yield per fertile tiller (SYFT)). Seed yield differences were most closely associated with SYFT (r2 = 0.97**) across cultivar treatments. Key words: Burning, straw removal, harvest index, yield components, forages