Light-fraction (LF) material, comprised largely of incompletely decomposed organic residues, may provide a sensitive indicator of the effects of cropping practices on soil organic matter. The objective of our study was to determine the influence of agronomic variables on soil LF content, and to evaluate the LF as a measure of labile organic matter. Soils from three long-term crop rotation studies in Saskatchewan, Canada, were analyzed for LF content and composition. The experiments, established at Indian Head (Udic Boroll), Melfort (Udic Boroll), and Scott (Typic Boroll), included wheat (Triticum aestivum L.) based rotations varying in fertilizer application, frequency of summer fallow, and cropping sequence. The LF of the surface soil (0-7.5 cm) accounted for 2.0 to 5.4%, 3.3 to 7.1%, and 7.1 to 17.5% of the organic C at Indian Head, Melfort, and Scott, respectively. Within each site, the LF content was generally highest in treatments with continuous cropping or perennial forages and lowest in those with a high frequency of summer fallow. Fertilizer application generally favored LF accumulation. Differences in LF content among sites and treatments were attributed to variable residue inputs and rates of substrate decomposition. The respiration rate and microbial N content of soils was strongly correlated with the LF content, suggesting that the LF is a useful indicator of labile organic matter. Nitrogen mineralization was also correlated with LF content, though the relationship was less consistent, presumably because the high C/N ratio of the LF induced temporary N immobilization. The LF content is a sensitive indicator of the effects of cropping on soil organic matter content and composition but, because of its transient nature, probably reflects primarily short-term effects. T HE ORGANIC MATTER CONTENT of a Soil IS profoundly influenced by the cropping system imposed on it. Numerous studies have demonstrated

Pulse crops discussed in this review include soybean (Glycine max L.), dry pea (Pisum sativum L.), lentil (Lens culinaris Medik.), dry bean (Phaseolus vulgaris L.) and chickpea (Cicer arietinum L.). Basic maturity requirements, yield relationships with rainfall and temperature, relative yield comparisons, water relationships, water use efficiency (WUE), crop management, tillage systems, and the rotational impact of these crops on productivity were considered. With the exception of soybean, maturity requirements for pulse crops are met in most locations within the northern Great Plains. Yield was more closely related to growing season precipitation than maximum temperature for all pulse crops except dry bean and lentil. The inability to effectively relate weather parameters to dry pea and lentil yield may indicate broad adaptation of these two pulse crops within the northern Great Plains. Correlation analyses showed the productivity of chickpea, dry pea, and lentil to be most closely associated with each other and for dry bean productivity to be most closely associated with that of soybean, effectively grouping pulse crops into their respective cool‐ and warm‐season classifications. Dry pea and chickpea had high WUE values, similar to spring wheat (Triticum aestivum L.). Examination of plant water relations of these crops revealed an ability for chickpea and dry pea to grow at lower relative water contents than spring wheat. Increased wheat grain yield and/or protein following pulse crops under widely different N‐limiting growth conditions indicated a consistent N benefit provided by pulse crops to wheat. Four general research needs were identified. First, comparative adaptation among pulse crops remains poorly understood. Second, best management practices and key production risks remain incompletely characterized. Thirdly, the knowledge of rotational effects of pulse crops in the northern Great Plains remains imprecise and inadequate. Fourth, genetic improvement for early maturity, increased yield, improved harvestability, and disease resistance requires attention. Pulse crops are poised to play a much greater role in diversifying cropping systems in the northern Great Plains but require that these key research areas be addressed so that their production potential can be realized.

Adverse changes in weed communities are a limiting factor for the adoption of conservation tillage practices. Predictions of an increased association of annual and perennial grasses, perennial dicot weeds, wind-disseminated species, and volunteer crops as weeds, and decreased association of annual dicot weeds in reduced-tillage systems were tested. Field experiments involving zero-, minimum-, and conventional-tillage systems were conducted in Saskatchewan from 1986 to 1990 at Ituna and Waldron, and from 1986 to 1988 at Tadmore. Weed community composition was analyzed for years 1988 to 1990 by canonical discriminant analysis. An increased association of perennial and annual grasses with zero tillage did not generally occur. Wind-dispersed species and volunteer crops were associated with reduced tillage and summer annual dicots with conventional tillage, but exceptions occurred. Species responded differently among sites or within a site over time. Within the time frame of this research, changes in weed communities were influenced more by location and year than by tillage systems, indicating fluctuational rather than directional or consistent changes in community composition.

Annual crop production in the Canadian prairies is undergoing significant change. Traditional monoculture cereal cropping systems, which rely on frequent summer‐fallowing and use of mechanical tillage, are being replaced by extended and diversified crop rotations together with the use of conservation tillage (minimum and zero‐tillage) practices. This paper reviews the findings of western Canadian empirical studies that have examined the economic forces behind these land use and soil tillage changes. The evidence suggests that including oilseed and pulse crops in the rotation with cereal grains contributes to higher and more stable net farm income in most soil–climatic regions, despite a requirement for increased expenditures on purchased inputs. In the very dry Brown soil zone and drier regions of the Dark Brown soil zone where the production risk with stubble cropping is high, the elimination of summer fallow from the cropping system may not be economically feasible under present and near‐future economic conditions. The use of conservation tillage practices in the management of mixed cropping systems is highly profitable in the more moist Black and Gray soil zones (compared with conventional mechanical tillage methods) because of significant yield advantages and substantial resource savings that can be obtained by substituting herbicides for the large amount of tillage that is normally used. However, in the Brown soil zone and parts of the Dark Brown soil zone, the short‐term economic benefits of using conservation tillage practices are more marginal and often less profitable than comparable conventional tillage practices.

oilseed crop produced in the USA, canola is the dominant oil crop in Canada. The cool climatic conditions Oilseed crops are grown throughout the semiarid region of the characteristic of the Canadian prairies provide an ideal northern Great Plains of North America for use as vegetable and industrial oils, spices, and birdfeed. In a region dominated by winter environment for Brassica spp. oilseeds and flax (Table and spring wheat (Triticum aestivum L. emend. Thell.), the accep-2) while the climate found in the USA is better suited tance and production of another crop requires that it both has an to the warm season crops like soybean and sunflower. agronomic benefit to the cropping system and improve the farmers' In the northern Great Plains, soybean is a relatively economic position. In this review, we compare the adaptation and new crop finding a place in semiarid cropping systems rotational effects of oilseed crops in the northern Great Plains. Canola with the development of early maturing, low heat-unit (Brassica sp.), mustard (B. juncea and Sinapis alba L.), and flax cultivars (Miller et al., 2002). As a result, the vast major-(Linum usitatissimum L.) are well adapted to cool, short-season conity of soybean production in both the USA and Canada ditions found on the Canadian prairies and northern Great Plains occurs in wetter regions east of the Great Plains. Howborder states of the USA. Sunflower (Helianthus annuus L.) and safflower (Carthamus tinctorius L.) are better adapted to the longer ever, for the other oilseed crops listed in Table 1, the growing season and warmer temperatures found in the northern and majority of production occurs within the northern Great central Great Plains states. Examples are presented of how agronomic Plains. practices have been used to manipulate a crop's fit into a local environ-Diversification within cereal-based cropping systems ment, as demonstrated with the early spring and dormant seeding can be critical to breaking pest infestations that are management of canola, and of the role of no-till seeding systems in common with monoculture (Bailey et al., 1992, 2000; allowing the establishment of small-seeded oilseed crops in semiarid Elliot and Lynch, 1995; Holtzer et al., 1996; Krupinsky regions. Continued evaluation of oilseed crops in rotation with cereals et al., 2002). Results of crop rotation studies in the Great will further expand our understanding of how they can be used to Plains revealed that where oilseeds are adapted, their strengthen the biological, economic, and environmental role of the region's cropping systems. Specific research needs for each oilseed

Previously published data were used to examine the N economy of pulse crops typically grown on the Northern Great Plains with the goal of assessing the potential contribution of field pea (Pisum sativum L.), lentil (Lens culinaris Medik.), chickpea (Cicer arietinum L.), common bean (Phaseolus vulgaris L.), and faba bean (Vicia faba L.) to soil N accretion. Incremental changes in soil N associated with the pulse crops (i.e., the nitrogen increment, Ninc), were strongly correlated to N 2 fixation and were highly variable. Data suggest that crops that can achieve relatively high levels of N 2 fixation, such as faba bean, field pea, and lentil are more likely to contribute positively to the overall N economy, particularly when a cropping system is evaluated over a long term. In contrast, pulse crops that typically achieve only modest levels of N 2 fixation such as desi and kabuli chickpea and common bean are more likely to be either N neutral or contribute to a soil N deficit. Because of extreme variability in levels of N 2 fixation achieved, presumably reflecting variability in soil productivity as well as variations in local climate and weather, the Ninc of pulse crops likewise is highly variable. Thus, the N contribution to a subsequent crop is difficult to predict with any certainty, particularly on a yearly or short-term basis.

Lafond, G. P., Loeppky, H. andDerksen, D. A. 1992

The malting barley (Hordeum vulgare L.) industry is often challenged by the availability of sufficient volume and quality to meet demand. Our objective was to evaluate the effects of agronomic practices on grain uniformity, protein concentration, yield, and yield components. Field experiments were conducted from 2005 to 2008 at eight rain‐fed locations in western Canada. The effects of two seeding rates (200 and 400 seeds m−2) and five N (0, 30, 60, 90, and 120 kg ha−1) rates on two two‐row barley cultivars (‘AC Metcalfe’ and ‘CDC Copeland’) were determined. Each experiment was conducted for 3 yr at each location (24 environments). CDC Copeland displayed some advantages over AC Metcalfe including higher grain yield, lower protein and more uniform kernels. For both cultivars, kernel weight, and plumpness were lower at the higher seeding rate; protein was also lower, maturity was earlier and kernels were more uniform. With increasing N rate, barley yield, kernel weight, and tillers plant−1 increased, but days to seed maturity and protein concentration also increased, and kernel plumpness and seed uniformity decreased. The increase in protein was less pronounced with CDC Copeland suggesting that there may be less risk with this cultivar of unacceptable protein levels at relatively high N rates. At many environments barley plant stand decreased while lodging increased with increasing N rates. To improve the likelihood that barley will be acceptable for malting growers should select low‐protein varieties, seed at relatively high rates and limit N application.