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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

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.

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

The objective of this experiment was to quantify the effect of landscape position and time of application on the agronomic efficiency of fall-banded urea [CO(NH 2 ) 2 ] for spring wheat (Triticum aestivum L.) grown in the eastern prairie region of Canada. Landscape positions in this experiment were defined as high and low based on their relative elevations to one another within the field. Fertilizer treatments included urea banded at three different times in the fall (early, mid-, and late fall), in the spring at planting, plus a control with no fertilizer N added. In the low landscape positions, grain yield, total crop N uptake, grain yield increases (GYI), and crop nitrogen use efficiency (NUE) for fall-banded urea (all relative to spring-banded urea) increased linearly with delayed application dates and declining soil temperatures on date of application. However, only crop N uptake and NUE were related to cumulative soil heat units (SHU) from date of fertilizer application until freeze-up, and no measure of crop response to N was related to cumulative nitrification heat units (NHU). In the high landscape positions, the performance of fallbanded urea was not related to any measures of time and/or soil temperature. These results can be used to predict the increase in crop response to fall-banded N as a result of delaying application in low areas of the landscape. Our study also shows that date of application and soil temperature are robust and practical indicators for determining the appropriate time to fall-band urea fertilizer in these areas.

Excess root zone soil moisture resulting from annual precipitation in excess of crop water requirements negatively affects crop yields. A field study was conducted in the 2005 and 2006 seasons on sandy loam soils to investigate the influence of berseem clover (Trifolium alexandrium L.) cover crop in oats (Avena sativa L.) on soil temperature, infiltration, and soil moisture redistribution within the growing season and during the fall to spring seasons. A 4-year crop rotation experiment to investigate farming with fewer chemicals was used to grow oats in a no-till cultivation system with and without the cover crop. The total and unfrozen water contents were measured in the field using neutron moisture meter and time domain reflectometry, respectively, at 0.2-m intervals from the surface to 1.8-m deep, plus a 0.1-m measurement depth. The cover crop significantly reduced soil moisture during the growing season resulting in significantly lower biomass yields (6146 kg ha-1 combined biomass for oats and berseem clover, vs. 7327 kg ha-1 for oats alone). By mid-August 2005, the cover crop treatment had 34.6% lower water content (0.17 vs. 0.26 m3 m-3) within the 0.0- to 0.7-m root zone depth compared to the non-cover crop. During the fall, the soil profile in the cover crop treatment was 3°C warmer, thus delaying soil freezing and leading to a shallower depth of the frozen soil layer (0.4 vs. 0.6 m) in March 2006. During the spring, the cover crop treatment warmed and thawed earlier enabling more snow melt infiltration and deep percolation. Areas experiencing excess soil moisture could use annual cover crops as a means for reducing excess soil moisture during the summer growing season and avoiding accumulation of soil moisture during the fall, winter and spring seasons.

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.

A goal in sustainable agriculture is to use fossil fuel energy more efficiently in crop production. This 12-year study investigated effects of two crop rotations and two crop production systems (organic versus conventional management) on energy use, energy output and energy-use efficiency. The grain-based rotation included wheat (Triticum aestivumL.)–pea (Pisum sativumL.)–wheat–flax (Linum usitatissimumL.), while the integrated rotation included wheat–alfalfa (Medicago sativaL.)–alfalfa–flax. Energy use was 50% lower with organic than with conventional management, and approximately 40% lower with integrated than with the grain-based rotation. Energy use across all treatments averaged 3420 MJ ha−1yr−1. Energy output (grain and alfalfa herbage only) across treatments averaged 49,947 MJ ha−1yr−1and was affected independently by production system and crop rotation. Energy output in the integrated rotation was three times that of the grain-based rotation; however, this difference was largely due to differences in crop type (whole plant alfalfa compared with grain seed). Energy output was 30% lower with organic than with conventional management. Energy efficiency (output energy/input energy) averaged to 17.4 and was highest in the organic and integrated rotations. A significant rotation by production system interaction (P

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

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

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

Interest is increasing in Uruguay in management practices that can store carbon in soils, such as the use of perennial forage crops. Previous studies on agricultural soils have focused on organic carbon in surface soil layers. However, due to the ability of perennial forages to develop extensive root systems, the potential exists for these crops to add carbon in the subsoil. A 38-year rotation experiment on a silty clay loam soil in southwestern Uruguay was used to examine the effect of a crop rotation including periods of pasture on total organic carbon (TOC) and particulate (>53 μm) organic carbon (POC) at soil depths of 20–40 and 40–60 cm. Analysis showed the pasture rotation had higher POC concentrations at both depths than an annual crop rotation. This may indicate increased addition of organic carbon in the pasture rotation and signal a future change in TOC and mineral-associated organic carbon levels. Total organic carbon was higher in the rotation including pasture at a P level of 0.14. These results present preliminary observations on the management effects of including perennial forages in rotations on subsoil carbon levels, using a long-term experiment resource to assess very slow changes.

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.

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

Strategies for pesticide use reduction have suffered from limited adoption. The impact of such strategies will be greater if they appeal to farmers with typical demographics and attitudes. A participatory, on-farm study was conducted to assess the potential of Pesticide Free Production TM (PFP) [Pesticide Free Production TM and PFP TM are registered trademarks of the University of Manitoba.] to be widely implemented on mainstream farms in Manitoba, Canada. PFP is a flexible, simple framework intended to appeal broadly to farmers who may not have adopted other pesticide use reduction initiatives. It may also provide a marketable food product label. This novel crop production system prohibits the use of in-crop pesticides and seed treatments during one crop year, as well as prior use of residual pesticides. Applications of nonresidual pesticides (such as glyphosate) are permitted prior to crop emergence. Synthetic fertilizer use is permitted at any time. The objectives of this study were: (1) to determine if the demographic and attitudinal characteristics of farms and farmers participating in a PFP pilot project varied depending on the level of PFP implementation; and (2) to compare the characteristics of farms and farmers participating in the pilot project with standards representing average farms and farmers in Manitoba. A total of 71 farmers, representing 120 fields and 11 crops, participated in the study. Fields and farmers were categorized into three groups, based on whether or not fields: (1) achieved PFP certification status and (2) were in transition to organic production. There were few demographic differences among groups. Demographic characteristics of participating farmers were typical for Manitoba, with the exception that participating farmers who were not in transition to organic production had higher levels of education than a random sample of Manitoba farmers. Attitudinal orientation (adherence to a conventional versus an alternative agricultural paradigm) of participants who were not in transition to organic production was similar to that of a random sample of Manitoba farmers. Fields and farms on which PFP was implemented were relatively large in the context of Manitoba averages. Participants indicated high satisfaction with certifiable PFP crops and high levels of interest in implementing future PFP. Pesticide free production demonstrates significant potential for broad adoption in this region.

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

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

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.

Because of their deep roots and high water demand, alfalfa (Medicago sativa L.) hay crops can reduce water available to crops following in the rotation. Recharging the soil water profile after alfalfa is, therefore, a high priority in dryland cropping systems. The objective of this study was to investigate effects of alfalfa crop termination date (late June, early August, and in spring immediately before spring wheat seeding) and method (herbicides, tillage, and herbicides plus tillage) on soil water conservation, and establishment, yield, and water use efficiency (WUE) of following spring wheat (Triticum aestivum L.) crop. Experiments were conducted over 5 site-years in a subhumid region of western Canada. Herbicide termination resulted in greater total water recharge and a faster rate of water recharge than treatments involving tillage. Greater efficiency of soil water recharge for herbicide termination after the first hay harvest (late June) appeared to cause deep water percolation at one site. Delaying termination until after the second hay harvest (early August) did not reduce soil water availability at spring seeding of the following wheat crop, hut increased reliance on overwinter soil water recharge. Delaying herbicide treatment until spring reduced water at seeding and wheat yields in some cases. Compared with treatments involving tillage, herbicide treatments resulted in higher levels of groundcover (i.e., greater soil erosion control), higher WUE, and higher grain yields. Herbicide termination after the second hay harvest produced the most favorable overall outcome; better than the traditional approach of tillage after the first hay harvest.

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.

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

Alfalfa ( Medicago sativa L.) has long been recognized as a source of N for the subsequent crops in a rotation. However, the relationship between symbiotically fixed N and soil mineral N sources, and the way they are partitioned into harvested hay or incorporated biomass, is not well understood. Calculating N budgets (i.e. estimating N input and output in a system) is useful for increasing our understanding of N dynamics in agro-ecosystems. Field experiments were initiated to develop a basic N budget for 1–3-year-old stands of alfalfa in a crop rotation. Changes in total soil N were monitored and N 2 fixation was measured using the 15 N isotope dilution technique. The total seasonal amount of N 2 fixed generally increased with each additional year of alfalfa, ranging from 174 kg N ha −1 for first year alfalfa to 466 kg N ha −1 for third year alfalfa. Alfalfa was also very effective at accessing deep-leached NO − 3 (i.e. soil NO − 3 greater than 1 m below the soil surface). The net soil N balance indicated that an average of 84, 148 and 137 kg N ha −1 was added to the soil system for 1-, 2- and 3-year-old alfalfa stands. The results of the budgeting process sugges that alfalfa stands as short as 2 years have the potential of making significant benefits to soil N status.

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.

Including perennial forages in cropping systems is recognized as one of the best ways to enhance agricultural sustainability. While rotational benefits of forages have been established in small plot research trials, there is no documentation of whether these benefits are being observed on commercial farms, or whether producers manage forage stands to maximize rotational benefits. A survey of 253 Manitoba and Saskatchewan producers known to include forages in their crop rotations was conducted in 1992. The survey area was divided into six agroclimatic zones and correspondence analysis was used to test whether responses differed across the survey area. Sixty-seven percent of respondents indicated a yield benefit from including forages in the crop rotation, with the greatest yield benefit observed in welter zones of the survey area. Eighty-three percent of the respondents observe weed control benefits for one (11% of respondents), two (50% of respondents), or more (33% of respondents) years after forages. The majority of respondents indicated that their forage acreage would not increase in the future. Average forage stand duration varied significantly (P < 0.10) with agroclimatic zone, ranging from 3 to 5 yr in welter areas (south-central Manitoba) to 6 to 9 yr in the driest areas (south Saskatchewan). The two most common reasons cited for forage stand termination were reduced forage yield and damage by pocket gophers (presumably Thomomys talpoides and Geomys bursarius). Less than 12% of respondents cited rotational considerations as their primary reason for terminating forage stands, indicating that producers are not managing their forage crops to maximize rotational benefits. Producers relied heavily on tillage in both forage crop establishment and forage stand termination phases of the production system. It was suggested that decreasing the amount of tillage and fallow associated with forage-based cropping systems would not only facilitate increased cycling of forages in rotations, but also increase agricultural sustainability.

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

Field trials were conducted over 4 site-years in southern Manitoba to compare the response of Katepwa wheat, Westar canola and Victoria field pea to zero tillage (ZT). The experimental design was a split plot with tillage system as the mainplot (ZT vs. conventional tillage (CT)) and crop species as the subplot. All crops received protection from insect, weed and disease pests. Tillage system had only a limited impact on crop dry matter accumulation or grain quality. Where differences were observed, crop performance was enhanced under ZT. Seasonal evapotranspiration (ET) was either reduced or unaffected by ZT, while ET efficiency (ETE: kg ha−1 mm−1 ET) was either increased or unchanged by the shift from CT to ZT. Higher ETE under ZT was attributed to less soil water evaporation. Significant tillage system × crop species (T × S) interactions for growth parameters, ET and ETE indicated that field pea often benefitted more than wheat or canola from ZT. A significant T × S interaction at one of the four sites indicated that water extraction between 30 and 90 cm was higher for pea and canola in the ZT compared with CT treatment, while soil water extraction by wheat was reduced under ZT. At a second site, lower ET for all three crops under ZT was attributed to reduced water use between 90 and 130 cm. Despite some effects of ZT on crop growth and water use, no significant tillage, T × S, or site × tillage interactions were observed for grain yield. It was concluded that under the conditions of this study (i.e. precipitation and temperature conditions close to the long-term average), Westar canola, Victoria field pea and Katepwa wheat were, for the most part, equally suited to ZT production. Key words: Soil water extraction, evapotranspiration efficiency, crop quality, grain yield, canopy development

Orla Nazarko, Allison Schoofs, Rene C. Van Acker, Martin H. Entz, Doug Derksen, Gary Martens, and Todd Andrews discuss this Canadian initiative to reduce pesticide use.

Large wheat (Triticum aestivum L.) seed exhibits advantages over small seed in seedling growth and yield potential, but in seed processing, rigorous screening for large size may lead to unacceptably high screening losses. Studies were conducted to determine the effects of seeding rate (SR), N management, and foliar fungicide (FF) application on seed yield (yield of seeds above 0.094-in. sieve size) and cleanout (percentage of seeds below 0.094-in. sieve size), on the hypothesis that seed crop management could be altered to ensure a high proportion of large seed in a seed lot (...)