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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.

Aggregate stability (AS) was measured in the 25th year of a long-term organic — conventional comparison field study. Located in southern Manitoba, the study includes two, four-year crop rotations under conventional and organic management, plus a grassland. The forage-grain rotation includes alfalfa (Medicago sativa)–alfalfa–wheat (Triticum aestivum)–flax (Linum usitatissimum). The grain only rotation includes wheat–flax–oat (Avena sativa)–soybean (Glycine max); hairy vetch (Vicia villosa) is substituted for soybean in the organic system. Composted manure was added every 4 yr to half of the organic forage-grain rotation to correct a phosphorus deficiency. The wheat and flax phases were sampled at depths (0–10 cm; 10–20 cm) in spring 2017, and wet aggregate stability was measured using the Yoder method with stacked sieves. Mean weight diameter (MWD) was calculated. AS in the organic systems was never lower than that of comparable conventional systems, but had more large aggregates in only a few cases. Our hypothesis that including alfalfa would increase AS was supported in only a few instances. The largest aggregates (1–2 mm and 2–6.3 mm) and the fewest smallest aggregates (0.25–0.5 mm) were observed in the grassland. For the intermediate aggregate size class (0.5–1 mm), the organic forage-grain systems had levels similar (P > 0.05) to the grassland. While adding manure increased plant growth by about 40% in the organic forage-grain rotation, no AS differences were observed. Limited AS response in the arable systems may be due to suboptimal soil C contents; only the grassland had a C content above the minimum 35 g·kg−1 postulated for Vertisols.

Grass-fed ruminant production does not have the convenience of feeding easily-storable grains during periods of low forage availability. This study examined the forage yield, quality, and utilization of warm- and cool-season annual forages grown under organic management during the mid-summer “feed gap” period. Annual ryegrass (Lolium multiflorum Lam. cv. Tetra Brand), winter triticale (× Triticosecale Wittmack cv. common), oat (Avena sativa L. cv. Souris), millet (Panicum miliaceum L. cv. Crown Proso), corn (Zea mays L. cv. BMR84 and CM440 Canamaize), and sorghum-sudangrass (Sorghum bicolor [L.] Moench × Sorghum sudanense [Piper] Stapf cv. common) were grown in Carman, Manitoba, over 3 site-years in 2018 and 2019. Combined forage and weed dry matter (DM) yield was 7159 kg·ha−1 for sorghum-sudangrass (29% weeds), 5506 kg·ha−1 for corn (36% weeds), 4687 kg·ha−1 for oat (45% weeds), 4617 kg·ha−1 for annual ryegrass (95% weeds), 4542 kg·ha−1 for millet (28% weeds), and 2945 kg·ha−1 for winter triticale (51% weeds); significant differences in crop and weed biomass were observed. All forage systems were palatable to sheep with utilization rates from 47% to 65%. When all quality parameters were considered, corn, winter triticale, millet, and oat displayed adequate quality for mid-summer grazing, while sorghum-sudangrass had suboptimal crude protein concentrations. Direct measurements of forage quality on weeds showed that weeds did not compromise forage quality. This Canadian first study demonstrated the potential of forage production for mid-summer grazing in an organic, grass-fed regime with oat, millet, and corn resulting in the best combination of yield and quality.

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.

The challenges associated with the global phosphorus (P) cycle are complex and multifaceted, from geological resource limitation, to P deficiency on arable farmland, to environmental contamination via excess P fertilization. Although no single solution can address all of the challenges associated with the P cycle, the principle of circularity provides a framework toward a more sustainable and food-secure P system. Phosphorus deficiency on farmland is widespread, particularly on organically managed farms due to negative P balances in low-input cropping systems. Recycled nutrient sources divert food and human wastes back onto farmland; they have the potential to ameliorate both the global-scale issues of phosphate rock depletion and environmental contamination and the farm-scale issue of P deficiency, particularly for organic farms. For recycled nutrients to act as viable alternatives to conventional nutrient sources, their ability to supply P and improve yields must be demonstrated. This paper provides an introduction to the importance of recycled fertilizer sources in the global P cycle, and the key role they can play on organic farmland in Canada.

The challenges of soil degradation and low crop yield are being addressed in East Africa using a number of soil health-promoting farming systems including Conservation Agriculture (CA). CA is based on principles of minimal soil disturbance, continuous soil cover, and crop diversity, though implementation on farms may vary due to local circumstances. This study evaluated the effect of CA, as practiced by farmers, and compared farmer descriptions of soil health with scientific measures. CA and non-CA fields were compared in regions of Ethiopia (23 farms), Kenya (23 farms), and Tanzania (13 farms) with most fields repeatedly sampled for 2 to 3 years. CA and non-CA fields were located within meters, on soils with the same texture, growing similar crops. CA systems used precision planting, mostly with basins. Soil parameters were assessed using a participatory approach where farmers and field technicians collected data. CA practices improved qualitative soil characteristics as sensed by farmers (e.g., hoe-ability, crusting, smell, water infiltration), and this positive response was consistent across most fields. For qualitative data, the logarithm of the odds ratio estimates method was used to test the probability that CA would provide soil improvement. Fields under the CA treatment had a higher probability of rating better than non-CA fields. Quantitative measurements of pH and microbial respiration validated farmer assessments. CA-managed soils were weakly associated with darker colour, indicating higher soil organic matter. Sandy soils did not appear to improve with CA as dramatically as clay and loam soils, suggesting different CA strategies may be required. We discuss both benefits and drawbacks of this type of participatory, on-farm research. We conclude that farmer participation as citizen scientists will advance soil restoration in East Africa and increase the potential for farmer-to-farmer knowledge exchange of soil-improving practices.

Soil phosphorus (P) availability may be impacted by management practices, thereby affecting plant P uptake and plant response to P amendments. The aim of this study was to determine the effects of long-term management on soil P pools and to assess the response of P bioavailability, plant growth, and P uptake to mineral versus manure P treatments. Soils were collected from plots under organic (ORG), organic with composted manure (ORG + M), conventional (CONV), and restored prairie (PRA) management. Italian ryegrass (Lolium multiflorum L.) seedlings were grown in the greenhouse for 106 d in soils amended with various rates of manure or mineral P. The ORG soil had lower concentrations of labile P (resin-P and NaHCO3-P) compared with the CONV and PRA soils, as determined by sequential P fractionation prior to planting. Ryegrass biomass (root + shoot) and shoot P uptake from soils receiving no P were significantly lower for the ORG than all other management systems. Although apparent P use efficiency of the whole plant was increased by low P rate in the ORG management system, the source of applied P, manure > mineral, only influenced Olsen test P.

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.

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.

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.

Organic spring wheat (Triticum aestivum L.) breeding programs have been initiated, yet yield efficiency and N economy research is limited. We evaluated the performance of advanced lines selected from an organic breeding program initiated in 2003. Fourteen F8 and F9 lines in 2009 and 11 lines in 2010 were compared with commercial (check) cultivars. Field experiments were conducted under organic management at four site–years in Manitoba and Saskatchewan. Combined analysis showed no difference in biomass accumulation between organic lines and check cultivars; however, harvest index and grain yield were greater in organic lines compared with the checks. Organic lines were shorter than check cultivars, but yield efficiency, defined as kernel number per unit of crop biomass at anthesis, was higher (P

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...

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.

Land management practices affecting soil erosion risk on organic and conventional farms were described using a mail-out survey. Organic farmers had more forages and green manures in rotation than conventional farmers (66 vs. 46% and 84 vs. 6%, respectively). Organic farmers used more tilled summerfallow (52%) than conventional farmers (6%). Tilled summerfallow represents a risk to soil sustainability on organic farms; however, the net effect of common organic management practices (e.g., green manuring, composting and tillage) on soil erodibility is not known. Determing the combined effect of management practices as well as finding alternatives to tilled summerfallow should be research priorities.Key words: Soil erosion risk, tillage, crop rotation, summerfallow

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

The effects of farming system (organic vs. conventional) and crop rotation (annual grain vs. grain-forage) on the mineral nutrient content of wheat (Triticum aestivum) grain was tested in a long-term field study in Manitoba. Crop rotation affected phosphorus (P), manganese (Mn) and copper (Cu) concentrations, while system affected nitrogen (N) and sulphur (S) concentrations. Interactive effects were observed for N, P, S, and zinc (Zn). This preliminary study demonstrates that differences in nutrient content between organic and conventional wheat depend on crop rotation and suggests that crop rotation should be considered in studies comparing the quality of organic and conventional produce.Key words: Crop rotation, organic crop production, mineral nutrient content, wheat

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

Diversification and intensification of the cropping systems in the traditional wheat-fallow area of the semiarid Canadian prairie is necessary to improve sustainability. Selection of alternate crops to include in cropping systems requires information on production risks with different climate regimes. To understand water use/yield relationships of alternate crops, three pulse crops (leguminous grain crops) [chickpea (Cicer arietinum L.), pea (Pisum sativum L.) and lentil (Lens culinaris Medik.)], three oilseed crops [canola (Brassica napus L. and B. rapa L.) and mustard (B. juncea L.)], and one cereal crop [wheat (Triticum aestivum L.)] were studied under varying water regimes: during 1996–1998 under well-watered, rainfed, imposed drought conditions, and in 2001 under rainfed conditions. Generally, the relative ranking between crops for water use was maintained across water regimes, such that the crops separated into three general groups of water users (high: wheat, B. napus, mustard; medium: chickpea, B. rapa, lentil; low: pea) with pea using an average of 34 mm and 13 mm less water than high- and medium-water-using crop groups, respectively. The exceptions included desi chickpea, which tended to use less water and B. rapa, which tended to use more water relative to the other crops as water use decreased. Generally, pea and wheat produced the most grain and biomass, had the highest water use efficiency, and had moderately high to high harvest indices. Wheat and pea are well adapted to variable rainfall amounts inherent in semiarid climates. Desi chickpea and lentil produce good grain yields under dry conditions, and grain yields relative to those of other crops can be increased by some drought stress, especially mid- to late-season stress. Therefore, because of their relatively good performance under water-stressed conditions, they are also well adapted to semiarid climates. Conversely, the Brassica oilseeds yielded relatively poorly compared with wheat and pulse crops under severe water-stressed conditions, so they are not as well adapted to the semiarid climate. In 2001, grain yield of wheat and pulses seeded on stubble was ≥30% of the yield on fallow, whereas stubble-seeded Brassica oilseeds yielded only about 10% of that on fallow. Compared with stubble seeding, production of Brassica oilseeds on fallow will decrease the risk of very low yields under drought. We found little indication that mustard was more drought tolerant than B. napus. Key words: Yield, water use efficiency, oilseeds, pulse, semiarid prairie

International audience; AbstractReduced tillage is increasingly promoted to improve sustainability and productivity of agricultural systems. Nonetheless, adoption of reduced tillage by organic farmers has been slow due to concerns about nutrient supply, soil structure, and weeds that may limit yields. Here, we compiled the results from both published and unpublished research comparing deep or shallow inversion tillage, with various categories of reduced tillage under organic management. Shallow refers to less than 25 cm. We found that (1) division of reduced tillage practices into different classes with varying degrees of intensity allowed us to assess the trade-offs between reductions in tillage intensity, crop yields, weed incidence, and soil C stocks. (2) Reducing tillage intensity in organic systems reduced crop yields by an average of 7.6 % relative to deep inversion tillage with no significant reduction in yield relative to shallow inversion tillage. (3) Among the different classes of reduced tillage practice, shallow non-inversion tillage resulted in non-significant reductions in yield relative to deep inversion; whereas deep non-inversion tillage resulted in the largest yield reduction, of 11.6 %. (4) Using inversion tillage to only a shallow depth resulted in minimal reductions in yield, of 5.5 %, but significantly higher soil C stocks and better weed control. This finding suggests that this is a good option for organic farmers wanting to improve soil quality while minimizing impacts on yields. (5) Weeds were consistently higher, by about 50 %, when tillage intensity was reduced, although this did not always result in reduced yields.

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

Although integrated crop–livestock systems have been employed globally for millennia, in the past century, farmers in North America have tended toward increased specialization. There is renewed interest in reintegrating crops and livestock because of concerns about natural resource degradation, the profitability and stability of farm income, long-term sustainability, and increasing regulation of concentrated animal feeding operations. Integrated crop–livestock systems could foster diverse cropping systems, including the use of perennial and legume forages, which could be grown in selected areas of the landscape to achieve multiple environmental benefits. Integrated systems inherently would utilize animal manure, which enhances soil tilth, fertility, and C sequestration. Integration of crops and livestock could occur within a farm or among farms. Both scales of integration rely on farmers’ knowledge, motivation, and resources. Despite the numerous benefits that could accrue if farms moved toward on-farm or amongfarm integration of crops and livestock, the complexity of such systems could constrain adoption. However, farmers should expect that adoption of integrated crop–livestock systems would enhance both profitability and environmental sustainability of their farms and communities. The combination of system complexity and potential for public benefit justify the establishment of a new national or international research initiative to overcome constraints and move North American agriculture toward greater profitability and sustainability.

Field experiments were established at two locations in Manitoba in 2002 and 2003 to determine N contribution, moisture conservation, and weed suppression by alfalfa mulch applied to spring wheat (Triticum aestivum L). Mulch treatments included mulch rate (amount harvested from an area 0.5×, 1× and 2× the wheat plot area), and mulch application timing (at wheat emergence or at three-leaf stage). Positive relationships were observed between mulch rate and wheat N uptake, grain yield, and grain protein concentration. At Winnipeg, the 2× mulch rates (3.9 to 5.2 t ha-1) produced grain yields equivalent to where 20 and 60 kg ha-1 of ammonium nitrate-N was applied in 2002 and 2003, respectively. Where mulch and ammonium nitrate produced equivalent grain yield, grain protein in mulch treatments was often higher than where chemical fertilizer was used. N uptake was also observed in the following oat (Avena sativa L.) crop. The highest mulch rate (2×) produced higher N uptake and grain yield of second-year oat compared with ammonium nitrate treatments. N use efficiency of mulch-supplied N by two crops over 2 yr [calculated as (treatment N uptake – control N uptake)/total N added] was between 11 and 68%. Mulch usually suppressed annual weeds, with greater suppression with late- than early-applied mulch. Increased soil moisture conservation was observed with high mulch rates (≥ 4.3 t ha-1) at three sites. Alfalfa mulch holds promise for low-input cropping systems when used on wheat at the 2× rates. Key words: Legume N, low-input farming, integrated weed management, wheat protein

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.

Yield benefits of legume cover crops in winter/spring cereal systems have not been well documented in the Canadian prairies. The objective of this study was to evaluate the fertilizer replacement values (FRV) of relay-cropped alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.) and double-cropped chickling vetch (Lathryus sativus L.) and black lentil (Lens culinaris Medik. subsp. culinaris) to a subsequent oat (Avena sativa L.) crop. Field experiments were conducted in Manitoba on a clay soil at Winnipeg and a sandy loam at Carman. Alfalfa provided the highest FRV at Winnipeg (51–62 kg N ha-1), followed by chickling vetch (29–43 kg N ha-1), lentil (23–39 kg N ha-1), and red clover (24–26 kg N ha-1). FRV could not be established at Carman, where course-textured soil and low rainfall limited legume growth. Key words: Relay cropping, double cropping, cover crops

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

There are many economic and health reasons for reducing pesticide use in Canada. Herbicide use on field crops is by far the most common pesticide use in Canada. This paper is a review of four topics related to herbicide use reduction on field crops in Canada: (1) broad strategies and (2) specific tactics for herbicide use reduction; (3) factors affecting adoption; and 4) research approaches for improving the implementation of herbicide use reduction. Numerous tactics exist to use herbicides more efficiently and herbicides can sometimes be replaced by non-chemical weed control methods. Many of these tactics and methods have been investigated and demonstrated for use on field crops in Canada. However, herbicide use reduction is fundamentally dependent upon preventative strategies designed to create robust cropping systems that maintain low weed densities. Diverse crop rotation forms the basis of preventative strategies as it inherently varies cropping system conditions to avoid weed adaptation. There is evidence that residual weed densities resulting from herbicide use reduction are manageable within competitive cropping systems. A great deal of research has been done on herbicide use reduction on field crops in Canada, and most projects report definite possibilities for herbicide use reduction in field crop production in Canada. Synthesizing and extending this information and customizing it for use on individual farms remain challenges. Collaboration between researchers and farmers can help to build successful strategies for herbicide use reduction which reflect the context of modern farming, the will of farmers and the culture of technology adoption among farmers. Key words: Pesticide use reduction, low-input agriculture, integrated pest management, integrated weed management

Knowledge of rotational N benefits of grain legumes can assist in crop rotation planning and N fertilizer management. Four annual grain legumes were tested in Manitoba field trials over 3 yr. Field pea provided the largest and most consistent apparent N benefit to a succeeding wheat crop; soybean provided relatively little N benefit. The apparent N benefits of chickpea and dry bean were inconsistent, although chickpea shows greater potential in dry conditions. Key words: Wheat rotations, N credit, crop rotation

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

Cropping records from 13 organic farms in the eastern Canadian prairies and one in North Dakota (1991 to 1996) were surveyed to determine crop rotation pattern, yields and soil nutrient status. Major crops included cereal grains, forages, and green manure legumes. Organic grain and forage yields averaged from one-half to almost double conventional yields. Soil N, K and S levels on organic farms were generally sufficient; however, levels of available soil P were deficient in several instances. Key words: Crop rotation, weeds, forages, green manure crops

Long-term weather data for 21 sites across Manitoba, Saskatchewan and Alberta were analyzed to evaluate the availability of late-season heat and water resources between time of winter wheat maturity and freeze-up. Thermal time during this period ranged from 159 to 754 growing degree days; precipitation ranged from 42 to 152 mm. Southern Manitoba appears to be best suited to relay and double cropping. Southern Saskatchewan receives significant thermal energy; however, lack of precipitation may limit late season plant growth. Key words: Legumes, no-till, cropping system intensity

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

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.

Herbicide application has been proposed as an alternative to tillage for termination of established alfalfa (Medicago sativa L.) stands but it may alter the pattern and amount of N released from alfalfa residues. A controlled environment study was conducted to investigate the effect of termination technique on the availability of N to four barley (Hordeum vulgare L.) crops. Four treatments consisting of a factorial combination of two termination methods (chemical, mechanical) and two methods of residue placement (surface, incorporated) were established. Nitrogen uptake by the four consecutive crops of barley was measured during a 125-d period after termination. Termination method, particularly residue placement, strongly affected N release from alfalfa residues. Nitrogen accumulation by the initial barley crop accounted for >60% of cumulative N uptake in incorporated treatments compared with 39% and 24% for herbicide and tillage treatments in which alfalfa residue was surface applied. Herbicide application also slightly increased N uptake by the initial barley crop. Nitrogen uptake by subsequent barley crops was not affected by termination method; however, cumulative N uptake remained substantially greater for incorporated treatments throughout the 125 d experiment. Effects of residue particle size on N release from alfalfa residues were small. These results suggest that herbicide termination in which residue is retained on the soil surface may reduce the short-term plant-available N supply. Provided that mineralization is sufficient to meet the N needs of subsequent crops, maintaining a smaller reservoir of soil inorganic N may be beneficial in reducing the potential for leaching or denitrification losses. Key words: Plant-available N, termination method, alfalfa, herbicide, tillage, growth chamber

Use of herbicide to terminate alfalfa (Medicago sativa L.), while reducing soil erosion, could conceivably enhance volatile N losses from alfalfa residues. A controlled environment study was conducted to determine the effect of termination method on the quantity of NH3 volatilized from residues of alfalfa. A factorial combination of two termination methods (chemical, mechanical) and two methods of residue placement (incorporated, surface applied) was applied to alfalfa. Treatments were incubated in a flow-through chamber in the greenhouse for 95 d during which NH3 and CO2 evolution was measured periodically. After 95 d, 8% of surface applied legume N was lost as NH3 in tillage treatments compared to 12% in herbicide treatments. These losses amounted to 3% and 4% of total legume N in tillage and herbicide treatments, respectively. Incorporation of alfalfa residue essentially eliminated volatile N losses. Termination method had comparatively less effect on NH3 evolution than residue placement although herbicide application tended to increase the proportion of alfalfa N lost via volatilization. Residue incorporation increased cumulative CO2 evolution regardless of termination method. Results of this study suggest that termination methods in which alfalfa residue is retained on the soil surface may result in significant volatile N losses which could diminish the fertilizer value derived from alfalfa residues. However, these N losses do not necessarily preclude the adoption of herbicide termination of alfalfa given the potential reductions in soil erosion and moisture loss which may be associated with this management practice. Key words: Volatile N losses, NH3 evolution, termination method, alfalfa, herbicide, tillage, greenhouse

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.