Carbon isotope discrimination (∆) has been shown to be negatively related to water use efficiency (WUE) in several C3 crop species and has been proposed as a criterion to select for improved WUE in plant breeding programs. This study was conducted to determine if ∆ is related to WUE in crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes] and AItai wildrye [Leymus angustus (Trin.) Pilger] and to evaluate the influence of drought on the magnitude of genetic variability and broad‐sense heritability of ∆ among clones of crested wheatgrass. In a greenhouse pot experiment, ∆ was negatively related to WUE in crested wheatgrass (r = −0.73**, significant at P < 0.01) and Altai wildrye (r −0.81**). In field studies, a line‐source sprinkler system operated in conjunction with an automated rainout shelter imposed a continuously variable water application on 29 vegetatively propagated clones of crested wheatgrass. Three water levels along the water application gradient were selected for sampling and forage dry weights and ∆ values were determined for two harvests in 1986 and one harvest in 1987. In the field experiment, ∆ declined as less water was applied and was positively associated with forage yield at each of the three harvests (r = 0.59**, 0.44**, and 0.80**, respectively). Significant variability for ∆ was detected among the clones for the two peak‐season harvests, hut not for the late‐season harvest in 1986. Broad‐sense heritability for ∆ was 0.49 in the analysis of data combined over harvests and water levels. Genetic variances and broad‐sense heritabilities (H) for ∆ were generally greater at the high (H = 0.52) and intermediate (H = 0.52) water applications than at the low water application (H = 0.37), and coefficients of variation for ∆ were typically less than 4.5%. Selection for ∆ appears to be a promising screening tool for the development of crested wheatgrass populations that are productive and make efficient use of limited water resources.

Long-term assessment of management of an annual legume green manure crop for fallow replacement in the Brown soil zone. Can. J. Plant Sci. 84: 11-22. In the Brown soil zone of western Canada summerfallowing (F) is traditionally used to reduce the water deficit associated with cereal production, but frequent use of this practice results in soil degradation and reduces the N-supplying capacity of soils. Some scientists suggest that an annual legume green manure crop (LGM) could be used as a partial-fallow replacement to protect the soil against erosion and increase its N fertility, particularly when combined with a snow-trapping technique to replenish soil water used by the legume. We assessed this possibility by comparing yields, N economy, water use efficiency, and economic returns for hard red spring wheat (W) (Triticum aestivum L.) grown in rotation with Indianhead black lentil (Lens culinaris Medikus) green manure (i.e., LGM-W-W) vs. that obtained in a traditional F-W-W system. Further, we assessed whether a change in management of the LGM crop (i.e., moving to earlier seeding and earlier turn-down) was advantageous to the overall performance of this practice. The study was conducted over 12 yr (1988-99) on a medium-textured Orthic Brown Chernozem at Swift Current, Saskatchewan. Wheat stubble was left tall to trap snow, tillage was kept to a minimum, and the wheat was fertilized based on NO 3 soil tests. When we examined results after 6 yr, we concluded that by waiting until full bloom to turn down the legume (usually late July or early August) so as to maximize N 2 fixation, soil water was being depleted to the detriment of yields of the following wheat crop. The change in management of the LGM crop since 1993 resulted in wheat yields following LGM equaling those after fallow (due to improved water use efficiency), a gradual and significant increase over time in grain protein and in N yield of aboveground plant biomass of wheat in the LGM-W-W compared to the F-W-W system, plus a gradual decrease in fertilizer N requirements of wheat in the LGM system accompanying an improvement in the N supplying power of the soil. These savings in N fertilizer, together with savings in tillage and herbicide costs for weed control on partial-fallow vs. conventional-fallow areas, and higher revenues from the enhanced grain protein, more than offset the added costs for seed and management of the LGM crop. Thus, our results imply that, if producers seed the LGM in April and turn it down in early July, an annual LGM-cereal rotation is a viable option in the semiarid Canadian prairies; however, one negative consequence of adopting this management strategy is the possibility of enhancing NO 3 leaching.Key words: Nitrogen yields, grain protein, green fallow, summerfallow substitute, economic returns, NO 3 leaching Zentner, R. P., Campbell, C. A., Biederbeck, V. O., Selles, F., Lemke, R., Jefferson, P. G. et Gan, Y. 2004. Évaluation à long terme d'un engrais vert annuel de légumineuses en remplacement de la jachère dans la zone des ...

. 2000. Quantifying short-term effects of crop rotations on soil organic carbon in southwestern Saskatchewan. . Crop management practices can have a major influence on soil fertility and soil organic C (SOC) sequestration. We need to accurately measure and estimate changes in SOC in the short term (<20 yr). A 10-yr crop rotation experiment, conducted on a medium-textured Orthic Brown Chernozem at Swift Current, in southwestern Saskatchewan, was sampled in 1990 (3 yr after initiation of the study) and in 1993 and 1996, to measure SOC changes under nine crop rotation treatments. Minimum tillage practices were used. The stubble was cut high to enhance snow trap and N and P fertilizer applied based on soil tests. Grain and straw yields of the cereals, and hay yields of the crested wheatgrass (CWG) [Agropyron cristatum (L.) Gaeertn.] were measured annually. An empirical equation which uses two simultaneous first order kinetic expressions, one to estimate crop residue decomposition and the other to estimate soil humus C mineralization was used, together with crop residue (straw and estimated root) C inputs, to estimate SOC changes over the 1987 to 1996 period. The estimated SOC values for the 1990 to 1996 period were generally similar to the measured values (r 2 = 0.64, P < 0.0001). Significant (P < 0.10) changes in SOC were not observed below 15 cm depth, perhaps because shallow tillage (10-to 12.5-cm depth) is practiced. A change from cropland to CWG did not increase SOC, and this treatment, chemical fallow-winter wheat (Triticum aestivum L.)-spring wheat (F-WW-W), and F-high-yielding (Hy) Canada Prairie Spring (CPS) wheat-Hy (F-Hy-Hy) rotations, had the lowest SOC gains among the rotations. The CPS wheat had a higher harvest index (0.46) than hard red spring (HRS) wheat (0.39), but it increased SOC less than the comparable HRS wheat rotation between 1990 and 1996 indicating that higher grain yields do not always equate to higher SOC. Weather conditions were favourable for cereals from 1990 to 1996 and we measured significant increases in SOC (up to 5.5 Mg ha -1 in 6 yr). This is encouraging for producers who may be contemplating participating in "C trading", although this also suggests that periods of less favourable weather will limit gains in SOC. Summerfallowing once in 4 yr in this semiarid environment did not reduce SOC gains compared to continuous wheat (Cont W). For example, a F-W-W-W rotation gained 4.88 Mg C ha -1 in 6 yr while continuous wheat gained 5 Mg ha -1 . Growing Indianhead lentil (Lens culinaris Medikus) as a legume green manure crop (GM) with wheat in a GM-W-W rotation did not increase SOC more than F-W-W. The efficiencies of conversion of residue C to SOC were high, ranging between 9% for frequently fallowed systems to 29% for continuously cropped systems, likely due to the favourable weather conditions experienced.Key words: Carbon sequestration, legume green manure, crested wheatgrass, harvest index effect, C conversion efficiencies Campbell, C. A., Zentner, R. P., Selles, F., Biederbeck, V. ...

2001. Improving the nutritive value of timothy through management and breeding. Can. J. Plant Sci. 81: 577-585. Timothy (Phleum pratense L.) is a widely grown forage grass species in cool and humid regions of the world including northeastern and northwestern North America, Nordic countries, Russia, and Japan. The nutritive value of timothy decreases with time, phenological development, and increasing forage yield. This review paper summarizes methods of controlling or improving the nutritive value of timothy through management practices and genetic selection, while keeping in mind the importance of forage yield. Consequently, the nutritive value of timothy is considered in relation to the accumulation of forage yield. The ecophysiological basis for the decrease in nutritive value with increasing forage yield during a growth cycle is presented with the assumption that the forage is made of two components: metabolic and structural. The decrease in the proportion of the metabolic component with increasing forage yield reduces the nutritive value of timothy. The nutritive value is also affected by the N concentration of the metabolic component, and by the digestibility of the structural component. Harvest dates, growing seasons, N fertilization, and cultivars have an indirect effect on the nutritive value of timothy through increased forage yield and the change in the proportion of the metabolic and structural components, but they also have a direct effect on each component. The results presented demonstrate the possibility of dissociating yield and nutritive value by plant breeding and, therefore, to improve the nutritive value of timothy while maintaining forage yield. Nord, les pays scandinaves, la Russie, et le Japon. La valeur nutritive de la fléole des prés diminue avec le temps, le développement phénologique, et l'accumulation de rendement. Cet article de synthèse présente des façons de contrôler ou d'améliorer la valeur nutritive de la fléole des prés par la régie et la sélection génétique sans toutefois négliger l'importance du rendement. Ainsi, la valeur nutritive de la fléole des prés est considérée en relation avec l'accumulation du rendement fourrager. La base écophysiologique de la diminution de la valeur nutritive avec l'augmentation du rendement durant un cycle de croissance est présentée en faisant l'hypothèse que la biomasse aérienne est formée de deux composantes: métabolique et structurale. La diminution de la proportion de la composante métabolique avec l'augmentation du rendement réduit la valeur nutritive. La valeur nutritive est aussi affectée par la teneur en azote de la composante métabolique, et par la digestibilité de la composante structurale. Les dates de coupe, la saison de croissance, la fertilisation azotée et les cultivars ont un effet indirect sur la valeur nutritive de la fléole des prés via une augmentation du rendement et un changement de la proportion des composantes métaboliques et structurales, mais ils ont de plus un effet direct sur chacune de ces deux dernières composantes...

. 2005. Long-term effect of cropping system and nitrogen and phosphorus fertilizer on production and nitrogen economy of grain crops in a Brown Chernozem. Can. J. Plant Sci. 85: 81-93. Assessment of the long-term impact of fertilizers and other management factors on crop production and environmental sustainability of cropping systems in the semi-arid Canadian prairies is needed. This paper discusses the long-term influence of N and P fertilizers on crop production, N uptake and water use of hard red spring wheat (Triticum aestivum L.), and the effect of the preceding crop type [flax (Linum usitatissimum L.) and fall rye (Secale cereale L.)] on wheat grown on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan. We analysed 36 yr of results from eight crop rotation-fertility treatments: viz., fallow-wheat receiving N and P (F-W, N + P), three F-W-W treatments fertilized with (i) N + P, (ii) P only, and (iii) N only; two other 3-yr mixed rotations with N + P (i) F-flax-W (F-Flx-W) and (ii) F-fall rye-W (F-Rye-W); and two continuous wheat rotations (Cont W), one receiving N + P and the other only P. Growing season weather conditions during the 36-yr period were near the long-term mean, but the first 22 yr were generally drier than normal while the last 14 yr (1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)) had average to above-average growing conditions. This was partly responsible for grain and N yield being greater in the latter period than in the first 22 yr. The 36-yr average response of wheat grown on fallow to P fertilizer was 339 kg ha -1 , while the response to N fertilizer over this period was only 123 kg ha -1 . The 36-yr average response of wheat grown on stubble to N was 344 kg ha -1 for F-W-(W) and 393 kg ha -1 for Cont W. Neither flax nor fall rye influenced the yield response of the following wheat crops. Annualized grain production for F-W (N + P), F-W-W (+ N) and F-W-W (+ P) rotations were similar (1130 kg ha -1 yr -1 ); this was about 15% lower than for F-W-W (N + P), 40% lower than for Cont W (N + P), and 5% lower than for Cont W (+ P). Annualized aboveground N yield for Cont W (N + P) was 57% higher than for Cont W (+ P). Regressions were developed relating straw to grain yields for wheat, flax and fall rye. The amount of NO 3 -N left in the soil was directly related to amount of N applied and inversely to N removed in the crop. Thus, F-(W)-W (+ N) left about 28% more NO 3 -N in the rooting zone than F-(W)-W (N + P), while F-W-(W) (N + P) left 20% more than F-W-(W) (+ P), and Cont W (N + P) left 39% more than Cont W (+ P). F-Rye-W (N + P) left much less NO 3 -N in the soil than any other fallow-containing system and similar amounts to Cont W (N + P).

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. 1999. Climate change in the semiarid prairie of southwestern Saskatchewan: Late winter-early spring. Can. J. Plant Sci. 79: 343-350. Long-term weather and hydrological data were analyzed to study climate change during late winter-early spring within an approximately 15 000 km 2 area in the semiarid prairie near Swift Current, Saskatchewan. The climate has changed over the past 50 yr. Winter and spring maximum and minimum temperatures have warmed, snowfall amounts have decreased, and spring runoff has started earlier now than during past years. The percentage of precipitation as snow has decreased as temperatures have warmed. As well, even though temperatures have warmed, the date of the last spring frost has not gotten earlier with time. Nous avons scruté les données météorologiques et hydrologiques de longue durée pour étudier les changements climatiques survenus durant la période englobant la fin de l'hiver et le début du printemps dans un territoire d'environ 15 000 km 2 de la prairie semi-aride, situé aux abords de Swift Current en Saskatchewan. Le climat a effectivement changé au cours des dernières années. Les maximums et minimums de températures hivernales et printanières sont plus hauts, l'enneigement a diminué et l'écoulement des eaux de fonte printanière débute plus tôt que dans le passé. Le pourcentage de précipi-tations tombées sous forme de neige a diminué à mesure que la température se réchauffait. Par ailleurs, même si la température s'est relevée, la date de la dernière gelée printanière n'a pas évolué au cours de la période examinée.

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