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 wetter 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 wetter 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. Research Question Perennial forage crops are known to enhance sustainability of dryland cropping systems, hence, there is considerable interest in exploiting this traditional practice in modern agriculture. While there is considerable information on rotational benefits of forages from small plot research trials, there is no documentation of whether these rotational benefits are observed on commercial farms. Hence, the first objective was to determine whether producers perceive weed control and yield benefits from inclusion of perennial forages in their rotations, and to determine whether rotational benefits differ in the different agroclimatic zones of western Canada. The second objective was to determine whether producers' management practices are aimed at maximizing cycling of forage crops to capture rotational benefits, or whether they strive to maximize forage stand duration. Literature Summary There is a great deal of information about the benefits of including forage crops, especiall...

Variation in spring emergence periodicity (both before and after crop seeding) of summer annual weeds is a potentially exploitable attribute that may be applied to weed management in canola. Tillage intensity, which is decreasing in the Great Plains of North America, may influence emergence periodicity of summer annual weeds. Emergence periodicity of common lambsquarters, field pennycress, green foxtail, redroot pigweed, wild buckwheat, wild mustard, and wild oat were monitored during the spring of 2000 in 17 producers' canola fields across southern Manitoba, Canada. The fields represented a region of approximately 2 million ha and included a broad range of soil types, agronomic practices, environmental conditions, and seedbank distributions. Fields were grouped into one of two broad tillage classifications (conventional or conservation). For most species, except redroot pigweed and wild mustard, conservation tillage promoted earlier emergence than conventional tillage in terms of both thermal and chronological time. The differences were significant even though there was only a limited range of tillage intensity for the two tillage classes within this region. Onset of canola crop emergence preceded that of all but one weed species in the conservation-tillage fields and five weed species in the conventional-tillage fields. This suggests that canola seeded in conservation- vs. conventional-tillage systems may have a competitive advantage by way of an earlier relative time of crop emergence. The influence of tillage system on weed emergence periodicity is likely due to the influence of tillage on the vertical origin of weed seedling recruitment because measurements of soil temperature and soil moisture did not help to fully explain the differences in emergence periodicity between tillage systems. The results from this study will facilitate weed control timing decisions in canola and provide validation data for weed emergence models.

The role of alfalfa (Medicago sativa L.) in extracting NO3–N from deep soils of areas with cold, short growing seasons, such as western Canada, is not well understood. A study was established in 1990 to determine NO3–N extraction ability to 300 cm; initial soil NO3–N concentrations were high (>8 mg kg−1). Systems included continuous alfalfa; annual rotations of spring wheat (Triticum aestivum L.), field pea (Pisum sativum L.), and barley (Hordeum vulgare L.); a native‐grass system [big bluestem (Andropogon gerardi Vitman) and western wheatgrass (Agropyron smithii Rydb.)]; and continuous fallow. The annual rotation effectively lowered NO3–N to <2.3 mg kg−1 in the 30‐ to 90‐cm depth. By the 4th yr, alfalfa had reduced NO3–N concentrations to <3.8 mg kg−1 for the 30‐ to 240‐cm increment. The greatest NO3–N extraction benefits of alfalfa were realized in the 4th yr at a maximum soil depth of 270 cm. Subsoil NO3–N concentration increased in the continuous alfalfa between the 4th and 6th yr. Greater NO3–N extraction occurred with the native‐grass treatment compared with continuous alfalfa in the 0‐ to 120‐cm soil depth; however, similar extraction patterns existed below 120 cm. A system involving 4 yr of alfalfa followed by two wheat crops resulted in the lowest subsoil NO3–N concentration, even lower than the continuous alfalfa and native‐grass systems. It was concluded that subsoil NO3–N extraction with alfalfa was maximized when alfalfa was rotated with annual crops.

alfalfa or alfalfa-grass stands in Manitoba and Saskatchewan is 6.5 years (Entz et al., 1995). This exceeds the Herbicide application may provide an alternative to intensive tilleconomic optimum of 4 to 5 years reported by Jeffrey age for the termination of alfalfa stands, but might alter N release and N availability to subsequent crops. Our objective was to deter- et al. (1993) and the duration required to attain maximine, under field conditions, the effect of timing and method of mum N benefits (Hoyt and Hennig, 1971; Heichel et termination on the pattern of N release from perennial alfalfa, and al., 1984). However, successful adoption of shorter-term on N uptake and yield of subsequent wheat crops. Four field experialfalfa stands requires management practices that effecments were initiated on perennial alfalfa (Medicago sativa L.) in tively terminate alfalfa, but maximize the benefits prosouthern Manitoba in 1992 and 1993. A factorial of three methods vided to subsequent crops. (herbicide, tillage, herbicide ϩ tillage) and two times of termination Intensive tillage, the usual method of terminating al-(early summer, after first alfalfa cut, and late summer, after second falfa, leaves the soil prone to erosion and moisture loss. alfalfa cut) was arranged in a randomized complete block design. A An alternative is to apply herbicides, either in the previspring-applied herbicide treatment was also included. Spring wheat ous summer or in the spring immediately before estab-(Triticum aestivum L.) was established after alfalfa termination. Soil NO Ϫ 3 content, plant N uptake, and yield were then monitored for one lishment of a subsequent crop, and leave residue standto two years. In three of four experiments, plant-available N in the ing on the soil surface. Broad-spectrum herbicides allow spring after termination was higher in tilled treatments than in treatreliable, cost-effective termination of alfalfa, and simulments receiving only herbicides. Regardless of method, plant-available taneously control weeds. In addition, standing surface N in the spring after termination was reduced when termination was residues reduce soil erosion and moisture loss, and may delayed from early to late season. Despite the lower short-term plantincrease soil moisture by trapping snow (Bullied and available N supply in early-and late-summer herbicide treatments, Entz, 1999).wheat yields in herbicide treatments were similar to or greater than Although using herbicides in place of tillage has many those in tillage treatments. Differences in the N content among treatapparent benefits, herbicide termination might affect ments diminished with time; by the fall of the second growing season after termination, differences in the cumulative available N supply

Bacillus cereus UW85 inoculation effects on growth, nodulation, and N accumulation in grain legumes: Field studies. Can. J. Plant Sci. 82: 291-298. Bacillus cereus strain UW85 was assessed for growth-promotion effects on soybean and common bean in the presence and absence of rhizobial inoculation at two field sites in Manitoba in 1994. Growth promotions due to B. cereus UW85 occurred for soybean only, and only at one site. Promotions in plant emergence in soybean were apparent at 60 d after planting (DAP), but stimulations in shoot dry weight (DW), N concentration, and N content were not apparent until 90 DAP. At maturity (120 DAP), inoculation with UW85 resulted in stimulation of seed yield by 9% and seed N content by 14%. However, stimulation in growth and N parameters by UW85 treatment was proportionally greater in the absence of B. japonicum inoculation than in the presence of the rhizobial inoculant. These observations, in combination with the observations that nitrogenase activity was not stimulated by UW85 treatment, clearly indicate that the UW85-mediated stimulation of growth and N accumulation of soybean is via a generalized stimulation of plant growth, and not via a stimulation in the soybean-B. japonicum symbiosis per se. Overall, our study indicates that inoculation with UW85 has the potential of increasing soybean production in western Canada, but these effects are site specific and are not seen in common bean. Incidence de l'inoculation de Bacillus cereus UW85 sur la croissance, la nodulation et l'accumulation de N chez les légumineuses à graine: Études sur le terrain. Can. J. Plant Sci. 82: 291-298. Les auteurs ont essayé de déterminer les effets de la souche UW85 de Bacillus cereus sur la croissance du soja et du haricot commun, avec et sans inoculation de rhizobium. Les essais se sont déroulés à deux endroits, au Manitoba, en 1994. B. cereus UW85 n'a accéléré la croissance que du soja, à un seul site. La levée plus importante des plants était manifeste 60 jours après la plantation, mais la hausse du poids sec des pousses, de la concentration de N et de la teneur en N des graines n'est apparue qu'au bout de 90 jours. À maturité (120 jours après la plantation), l'inoculation de UW85 avait augmenté le rendement grainier de 9 % et la teneur des semences en N de 14 %. La stimulation de la croissance et les paramètres associés à l'azote étaient néanmoins proportionnellement plus importants sans inoculation de B. japonicum qu'avec cet inoculant. Ces observations et celle que l'administration de UW85 n'accroît pas l'activité de la nitrogénase indiquent clairement que la stimulation de la croissance et l'accumulation de N observées chez le soja après le traitement résultent d'une accélération générale de la croissance et pas d'une meilleure symbiose entre B. japonicum et le soja comme telle. Dans l'ensemble, l'étude révèle que l'inoculation de UW85 pourrait accroître la production de soja dans l'ouest du Canada, avec la réserve que de tels effets sont spécifiques au site et ne se reproduisent pas chez l...