Spring Regrowth Research Articles

(101) Effects of Fall Applications of Urea and Zinc Sulfate to `Bing' Sweet Cherry Spring Budbreak

While rest-breaking agents have become commonly used in California cherry production, application timing continues to involve a certain amount of uncertainty from year to year. In order to use any chilling model adequately and thereby schedule rest-breaking treatments, both the beginning point of dormancy and the beginning point of chill accumulation must be understood. One method of testing dormancy onset is tree defoliation, which may be used to alter the pattern of budbreak and regrowth in spring. Defoliation is used in many tropical and subtropical fruit-growing regions to promote budbreak and flowering in species that are not adapted to less than adequate chilling conditions. Recent trials in California compared hand defoliation to applications of urea and zinc sulfate to determine effects on budbreak and flowering of sweet cherry, as well as to better identify entry into dormancy. Chemical applications were at concentrations lower than those used to effect complete defoliation. We found that chemical applications tended to advance bloom and that the most effective timings were consistent, based on chill portion accumulation and the Dynamic Model. In one of two years, chemical treatments tended to decrease floral bud death and increase fruit set when compared to hand defoliation and untreated trees.

VSP accumulation and cold-inducible gene expression during autumn hardening and overwintering of alfalfa

This study describes the time-course of the accumulation of total soluble proteins (TSPs) and vegetative storage proteins (VSPs) and of the transcripts of cold-inducible (CI) and VSP-encoding genes in taproots of two alfalfa cultivars (AC Caribou and Europe) during their acclimation to natural autumn hardening and overwintering conditions in eastern Canada. The impact of a defoliation in September on these winter hardening-related changes was also assessed. Both concentrations and pools of VSPs increased significantly between early September and mid-October and remained unchanged thereafter, concomitantly with the disappearance of VSP-encoding transcripts. Other soluble protein constituents continued to increase later in the autumn and early winter and accounted for nearly 60% of taproot TSP pools in winter. As a result, VSP abundance relative to TSPs decreased markedly during the winter. The increase in the levels of CI transcripts was induced by lowering temperatures, and distinct patterns suggest differences in the regulation of their accumulation. RNA analyses revealed that the accumulation of VSP transcripts during the autumn precedes the accumulation of CI transcripts. Autumn defoliation interrupted the accumulation of both TSPs and VSPs during autumn hardening and repressed the transcript levels of two CI genes differentially between cultivars. The well-documented impact of autumn defoliation on the vigour of spring regrowth and long-term persistence of alfalfa could be related to its negative impact on the accumulation of VSPs and TSPs and on the expression of genes encoding CI proteins potentially involved in cold tolerance and pathogen resistance.

Nitrogen fertilizer application and developmental stage affect silage quality of timothy (Phleum pratense L.)

AbstractCrop composition at harvest affects the ensiling process and the resulting silage quality. The objectives of this study were to determine: (i) the effect of annual N‐fertilizer application (0, 60, 120 and 180 kg N ha−1) and developmental stage (stem elongation, early heading, late heading and early flowering) on the ensiling properties and silage quality of the spring regrowth of timothy (Phleum pratense L.) at two sites for 1 or 2 years, and (ii) the relationship between ensiling properties of the forage and the quality of the resulting silage. Laboratory silos with wilted forage at approximately 350 g dry matter (DM) kg−1 of fresh matter were prepared at each harvest and opened 150 d later for silage analysis. Higher rates of N‐fertilizer application decreased the concentration of water‐soluble carbohydrates (WSC), increased the buffering capacity (BC) and nitrate concentration, and decreased the ratio of WSC:BC, primarily in the early stages of development. The ensiling properties of timothy were, therefore, less favourable when high rates of N fertilizer were applied. Silage pH generally increased with increasing rates of N‐fertilizer application; this increase was particularly evident at the first three developmental stages at one site in 1 year. Non‐protein N (NPN) and soluble N concentrations of the silages increased with increased rates of N‐fertilizer application at the first three developmental stages but decreased at early flowering. Ammonia‐N concentration in the silages increased by 0·85, 0·56 and 0·67 when rates of N‐fertilizer application were 60, 120 and 180 kg ha−1, respectively, compared with that when no N fertilizer was applied. Significant correlations between the composition of the forage ensiled and silage quality variables were found at sites in individual years but, when all data were combined, WSC concentration and BC, and their ratio in the forages, were not correlated with pH, and soluble‐N and ammonia‐N concentrations of the silages, and were weakly correlated with NPN and free amino acid‐N concentrations of the silages. Silage quality was reduced by increased N‐fertilizer application, primarily at the early developmental stages, and this can be attributed to a reduction in WSC concentration and an increase in BC of the forage. Water‐soluble carbohydrate concentration, BC, and their ratio, however, were poor predictors of silage quality.

Nitrogen Reserves, Spring Regrowth and Winter Survival of Field-grown Alfalfa (Medicago sativa) Defoliated in the Autumn

The objective of the study was to characterize variations in proline, arginine, histidine, vegetative storage proteins, and cold-inducible gene expression in overwintering roots of field-grown alfalfa, in response to autumn defoliation, and in relation to spring regrowth and winter survival. Field trials, established in 1996 in eastern Canada, consisted of two alfalfa cultivars ('AC Caribou' and 'WL 225') defoliated in 1997 and 1998 either only twice during the summer or three times with the third defoliation taken 400, 500 or 600 growing degree days (basis 5 degrees C) after the second summer defoliation. The root accumulation of proline, arginine, histidine and soluble proteins of 32, 19 and 15 kDa, characterized as alfalfa vegetative storage proteins, was reduced the following spring by an early autumn defoliation at 400 or 500 growing degree days in both cultivars; the 600-growing-degree-days defoliation treatment had less or no effect. Transcript levels of the cold-inducible gene msaCIA, encoding a glycine-rich protein, were markedly reduced by autumn defoliation in 'WL 225', but remained unaffected in the more winter-hardy cultivar 'AC Caribou'. The expression of another cold-inducible gene, the dehydrin homologue msaCIG, was not consistently affected by autumn defoliation. Principal component analyses, including components of root organic reserves at the onset of winter, along with yield and plant density in the following spring, revealed that (a) amino acids and soluble proteins are positively related to the vigour of spring regrowth but poorly related to winter survival and (b) winter survival, as indicated by plant density in the spring, is associated with higher concentrations of cryoprotective sugars in alfalfa roots the previous autumn. An untimely autumn defoliation of alfalfa reduces root accumulation of specific N reserves such as proline, arginine, histidine and vegetative storage proteins that are positively related to the vigour of spring regrowth but poorly related to winter survival.

The consequences of lower nitrogen availability in autumn for internal nitrogen reserves and spring growth of Calamagrostis epigejos

The building and use of internal N stores in the grass Calamagrostis epigejos was investigated in context of complex ecological study focused on mechanisms underlying competitive ability of this highly successful invasive species. Induced changes in nitrogen availability in the course of two subsequent vegetation seasons were used as a tool for finding (i) to what extent high N availability in substrate is important for building N reserves in autumn that support spring regrowth and, (ii) if contrasting contents of N storage compounds may result in differences in growth in the next season. Plants were grown in solely inorganic substrate and received a nutrient solution containing 5 mol m−3 of NH4NO3. The nitrogen supply was reduced in a low nitrogen (LN) treatment to 0.25 mol m−3 in August whereas in high nitrogen (HN) treatment remained high till December. During the following growing season were plants from both treatments grown at the low N supply (0.25 mol m−3). An increase in the content of N storage compounds was observed from September to December in both treatments. Plants in the LN treatment showed significantly lower total N content and also N allocated to mobilizable reserves (20–50% of HN plants), namely due to a smaller accumulation of amino acids and soluble protein in autumn. External nitrogen availability in autumn is hence highly important for building N reserves in this species. A major portion of the nitrogen stored in HN plants during winter was taken up from growth medium in late autumn, whereas translocation from senescing shoots dominated in LN treatment. During the winter about 50% of N in plants was permanently present in shoots bearing several frost resistant green leaves. Spring regrowth was accompanied by a fast decrease of both total N and the content of N storage compounds in both treatments. Amino acids were identified as the most prominent source of mobilizable N during spring regrowth. Development of leaf area in LN plants was significantly slower in March and April than in HN plants namely due to smaller number of tillers and green leaves per plant. Low N availability in autumn, therefore, may result in restrictions of plant growth and development in the following season.

Breeding CWG‐R Crested Wheatgrass for Reduced‐Maintenance Turf

Using reduced‐maintenance turfgrass as an alternative to current high‐maintenance turfgrass species would conserve resources, reduce labor, and potentially reduce pollutants in the environment. CWG‐R is an experimental population of crested wheatgrass [Agropyron cristatum (L.) Gaertn.] from Iran that has shown potential as a low‐maintenance turf. The objective of this research was to estimate the genetic variation for turf traits within the CWG‐R population when evaluated under a reduced‐maintenance regimen. Ninety CWG‐R clonal lines were established in 1998 near Logan, UT, as spaced‐plant plots in a RCB design with four replicates. Maintenance of 50% ET0 replacement, 97.74 kg of nitrogen ha−1 yr−1, and mowing at 7.62 cm was approximately 40% lower than typical for high‐input Kentucky bluegrass (Poa pratensis L.) turf. Critical turf traits, including spring regrowth, season‐long (March–October) and mid‐summer (June–July) turf quality, color, and rhizomatous spread were evaluated in 1999 and 2000. Significant genetic variation among clonal lines was evident with broad‐sense heritabilities of 0.65, 0.76, 0.45, and 0.76 for spring regrowth, season‐long turf quality, color, and rhizomatous spread, respectively. Several clonal lines remained green throughout the summer months and maintained acceptable turf quality and color ratings during the critical mid‐summer period. The high broad‐sense heritability estimates within this population indicate potential for successful improvement of critical turf traits by phenotypic selection. These results indicate that that CWG‐R could be an important low‐maintenance turf‐type crested wheatgrass germplasm.

Effect of Timing and Nitrogen Fertilizer Application on Winter Oilseed Rape (Brassica napus L.). II. Nitrogen Uptake Dynamics and Fertilizer Efficiency

AbstractField experiments were carried out on grey‐brown podzolic soil in the four consecutive growing seasons (1998–2001) at Krzeslice Farm, central‐western Poland. The effect of seven N fertilization treatments (in kg N ha−1): 80NF + 80CAN; 80NF + 50CAN + 30CN; 80CAN + 80CAN; 80CAN + 80CAN + 30CN; 80AN + 80AN; 80AN + 50AN + 30CN, where, NF – nitrofos NPK, CAN – calcium‐ammonium nitrate, AN – ammonium nitrate, CN – calcium nitrate and control (without N) on N uptake dynamics and N efficiency was studied. Mineral fertilizers were applied at the start of spring regrowth, beginning of stem elongation and at the flower‐bud‐visibility stage. The study revealed two distinct strategies of oilseed rape plants’ adaptation to timing and N fertilizer application sequences. Both strategies based on nitrogen uptake rate (NUR), were analysed at different plant growth stages. Ammonium nitrate (AN) applied in the two‐split system gave the highest NUR (387 mg m−2 day−1) during stem elongation (for comparison, a value of 166 mg m−2 day−1 was obtained in the control). In the case of calcium‐ammonium nitrate (CAN), a moderate level of NUR was obtained (304 mg m−2 day−1) but N uptake lasted 12 days longer compared with the AN treatment. Hence, N accumulation in leaves at the end of flowering explained about 81 % of yield variability. The second adaptation strategy was attributed to the three‐split N treatment. Plants fertilized with AN and CAN fertilizers showed an inconsistent pattern of NUR with time. Nitrogen accumulation in stems at the beginning of maturity, explained 69 % of yield variability. Nitrogen‐use efficiency did not show any response to N treatments.

Effect of Timing and Nitrogen Fertilizer Application on Winter Oilseed Rape (Brassica napus L.). I. Growth Dynamics and Seed Yield

AbstractThe field experiments conducted on the grey‐brown podzolic soil in the four growing seasons (1998–2001) at Krzeslice Farm, central‐western Poland comprised seven fertilization variants: 80NF + 80CAN; 80CAN + 80CAN; 80AN + 80AN; 80NF + 50CAN + 30CN; 80CAN + 50CAN +30CN; 80AN + 50AN + 30CN (where NF – nitrofos NPK; CAN – calcium‐ammonium nitrate; AN – ammonium nitrate; CN – calcium nitrate) and control (without N) applied in split rates at the beginning of spring regrowth (80 kg N ha−1), stem elongation (80 or 50) and flower buds visible stages (30). The yielding effect of tested fertilization variants was significant in comparison with the control (2.24 t ha−1). The highest mean seed yield (3.64 t ha−1) was collected from 80AN + 80AN and 80CAN + 80CAN variants. Mean values of 4 years indicate that the second N rate division (80 + 50 + 30) decreased yield, although not significantly in comparison with these two N treatments. Plants grown on these treatments have developed different patterns of growth to yield the seeds. These patterns were characterized by very high crop growth rate during flowering (above 21 g m−2 day−1) and negative at maturation (down to −2.5 g m−2 day−1). Plants fertilized with ammonium nitrate (80AN + 80AN) reached maximum growth rate earlier (65 days), which lasted longer (20 days) than plants fertilized with calcium‐ammonium nitrate (71 days lasting 17.5 days). Plants grown on the control treatment reached the highest crop growth rate within 79 days (14.8 g m−2 day−1), which lasted 15 days.

Fine root dynamics of pedunculate oak and narrow-leaved ash in a mixed-hardwood plantation in clay soils

The minirhizotron technique was used to study the temporal dynamics of fine roots (diameter ≤2 mm) over a twelve-month period in pedunculate oak (Quercus robur L.) and narrow-leaved ash (Fraxinus oxyphylla Bieb.) trees growing in clay soil. The experiment was conducted in an eight-year-old mixed hardwood plantation established in northern Italy's Po lowlands on former farm land. Minirhizotron tubes were placed in mono-specific patches of oak and of ash and monitored from May 2000 to May 2001. Tubes were observed weekly from spring to fall and every two weeks during winter. The collected data for both species showed that while cumulative root length density of production (RLDp) and mortality (RLDm), as well as the RLDp's vertical and diameter distribution, did not differ statistically between them (RLDp was 7.6±0.89 and 7.31±0.74, RLDm 4.74±1.10 and 2.77±0.60 mm cm−2 yr−1 ± Standard Error for oak and ash, respectively), the seasonal course of root production and mortality markedly differed. The oak trees displayed a nearly steady rate of root production from early spring regrowth to mid-autumn and the ash produced most of its fine roots over a shorter period, from March to late May. The rate of root mortality peaked during winter in oak and in ash was fairly constant throughout the experiment. The coarse fine roots (e.g., root 1.1–2.0 mm in diameter) in ash were preferentially produced in June and their frequency increased with soil depth and in oak were produced simultaneously and with the same vertical distribution of the smaller roots. Root median longevity (Lm) was slightly higher for ash than for oak and for summer than for fall and winter root cohorts; that in both species Lm was negatively related with root diameter confirms that roots smaller than 1.0 mm are highly dynamic. These findings may be relevant for a better understanding of the ecology of mixed pedunculate oak and narrow-leaved ash stands in clay soil.

Untimely Fall Harvest Affects Dry Matter Yield and Root Organic Reserves in Field‐Grown Alfalfa

The regrowth interval between the last summer harvest and the fall harvest is a major determinant of alfalfa (Medicago sativa L.) persistence and spring regrowth. This study assessed the impact of the timing of a fall harvest on persistence, dry matter yield (DMY), and root carbohydrate and N reserves of field‐grown alfalfa. Two cultivars (AC Caribou and WL 225) were harvested either only twice during the summer or three times with the third harvest taken 400, 500, or 600 growing degree days (GDD) after the second summer harvest. Plant density was not affected by a fall harvest across three production years (1997 to 1999). The DMY of the first harvest in the second production year (1998) was significantly reduced by prior fall harvests taken at 400 or 500 GDD. However, the seasonal DMY in 1998 was higher with the 500 or 600 GDD harvest management than with the two harvest system. Root dry weight (DW) was generally reduced by a third harvest in the fall, especially when taken at 400 GDD. Amounts of root carbohydrate reserves (raffinose family oligosaccharides [RFO], sucrose, and starch), as well as the amounts of total amino acids and soluble proteins were significantly reduced by harvesting at 400 or 500 GDD. Untimely fall harvest reduced alfalfa spring regrowth by impeding the accumulation of both carbohydrate and N reserves. Seasonal DMY remained advantageous as long as an interval of 500 or 600 GDD was kept between the last summer and the fall harvests.

Assessing eight grass species for pasture by measuring etiolated spring regrowth

Grazing by herbivores can affect root carbohydrate reserves of grass species. A grazing study was conducted on an irrigated pasture near Outlook, Saskatchewan, Canada, during the summers of 1991 and 1992 t o determine etiolated regrowth after grazing of reed canarygrass ( Phalaris arundinacea L.), slender wheatgrass ( Elymus trachycaulus (Link) Gould ex Shinners subsp . trachycaulus), intermediate wheatgrass [ Thinopyrum intermedium (Host) Barkw. & D.R. Dewey subsp . intermedium], orchardgrass ( Dactylis glomerata L.), meadow bromegrass ( Bromus biebersteinii Roem. & Schult.), smooth bromegrass ( Bromus inermis Leyss.), tall fescue [ Festuca arundinacea (Schreb.) Wimm.] and timothy ( Phleum pratense L.) in order to eva luate the suitability of these species for grazing. All eight species were mob-grazed by sheep at a stocking rate of 30 animals ha-1. Carbohydrate reserves were estimated by determination of etiolated regrowth. Meadow bromegrass produced the greatest etiol ated regrowth and timothy the least. Based on production of etiolated regrowth the grasses were ranked into three groups - meadow bromegrass and intermediate wheatgrass ranked highest, smooth bromegrass, reed canarygrass, slender wheatgrass and orchardgra ss ranked intermediate and timothy and tall fescue ranked lowest. Key words:

Oxygen deficiency affects carbohydrate reserves in overwintering forage crops.

Anaerobic conditions developing under an ice cover affect winter survival and spring regrowth of economically important perennial crops. The objective was to compare, during a prolonged period of low (<2%) O2 at low temperature, the concentration of carbohydrates of four plant species contrasting in their resistance to oxygen deficiency. Four perennial forage species, lucerne (Medicago sativa L.), red clover (Trifolium pratense L.), timothy (Phleum pratense L.), and cocksfoot (Dactylis glomerata L.) were subjected to a progressively developing oxygen deficiency stress by enclosing potted plants in gas-tight bags in late autumn for overwintering in an unheated greenhouse. Timothy was previously reported to be more resistant to oxygen deficiency than the three other species. Non-structural carbohydrates increased and remained at a higher concentration in timothy than in the other three species under low O2 concentration. Concentrations of sucrose, fructose, glucose, and fructans increased in response to oxygen deficiency in timothy, whereas the concentration of soluble sugars decreased under the same conditions in lucerne, red clover, and cocksfoot. The gene expression of glyceraldehyde-3-phosphate dehydrogenase increased in response to low oxygen concentration in oxygen deficiency-sensitive lucerne while it remained unchanged in the oxygen deficiency-resistant timothy. It is concluded that timothy maintains higher carbohydrate reserves under oxygen deficiency, a specific feature that could favour its winter survival and spring regrowth.

Alfalfa Root Nitrogen Reserves and Regrowth Potential in Response to Fall Harvests

The adverse effect of fall harvesting alfalfa (Medicago sativa L.) during a critical rest period on persistence and the following spring regrowth has been historically attributed to a reduction in the concentrations of organic reserves, especially total nonstructural carbohydrates. However, recent reports highlight the determinant role of N reserves in overwintering and spring regrowth of alfalfa. This study was undertaken to assess the impact of fall harvest management on regrowth potential in relation to the quantitative changes in N reserves in alfalfa taproots throughout fall and winter. The experiment was conducted under simulated winter conditions in an unheated greenhouse with two alfalfa cultivars (AC Caribou and WL 225). The fall harvest treatments were no additional fall harvest (two harvests = control) or a third fall harvest applied at 400, 500, or 600 growing degree days (GDD) after the second harvest. Total N concentrations were significantly reduced in plants harvested at 400 or 500 GDD as compared with plants harvested at 600 GDD or harvested only twice. The striking accumulation of proline, arginine, and histidine observed in fall and winter was depressed by a fall harvest, especially in plants harvested at 400 or 500 GDD. The abundance of a major soluble protein of 32 kDa was reduced by harvesting at 400 or 500 GDD. Concentrations of major N components were correlated with shoot regrowth in spring in AC Caribou, but not in WL 225. However, the total amounts of major N components in taproots were correlated with spring regrowth in both cultivars. Our results point out that N reserves available in roots are determinant for spring regrowth in alfalfa under various fall harvest treatments.

Heterosis of Agronomic Traits in Alfalfa

Increasing forage yields remains a top priority of most alfalfa (Medicago sativa L.) breeding programs. Studies of crosses between dormant to moderately dormant M. sativa subsp. sativa and M. sativa subsp. falcata suggest a heterotic pattern for yield exists between the two subspecies. However, other agronomic traits need to be considered in addition to yield, especially when trying to develop breeding material from nonadapted sources. The objective of this study was to quantify the agronomic performance of sativa × falcata crosses (SFC) in relation to sativa × sativa crosses (SSC) and falcata × falcata crosses (FFC). Nine elite sativa clones and five falcata clones were crossed in a diallel mating design. Progeny were space planted in 1998 at Nashua and Ames, IA. During the 1999 growing season, winter injury, spring regrowth, vigor, growth habit, maturity, height, midseason regrowth, and autumn regrowth were measured. The 14 parental genotypes differed for general combining ability (GCA) for all traits; specific combining ability (SCA) was noted for height, maturity, winter injury, and vigor. Sativa × sativa crosses were superior to FFC for all traits except winter injury and vigor. Sativa × falcata crosses per se had slightly increased agronomic performance over the expected mid-subspecies for many traits. Most of the hybrids are intermediate to SSC and FFC, suggesting potential agronomic weaknesses of falcata germplasm in a breeding program. Improving regrowth, height, and growth habit of falcata breeding material would likely be needed to create commercially successful sativa–falcata semihybrid cultivars.

Alfalfa Root Carbohydrates and Regrowth Potential in Response to Fall Harvests

The adverse effect of harvesting alfalfa (Medicago sativa L.) during a critical fall rest period on the persistence and the following spring regrowth has been historically attributed to a reduction in the levels of root organic reserves, especially total nonstructural carbohydrates (TNC). Recent reports also pointed out the role of specific carbon (C) reserve components in winter survival. This study assessed the effect of the timing of a fall harvest on the regrowth potential in relation to quantitative changes in C reserves in alfalfa roots during fall and winter. The experiment was conducted under simulated winter conditions in an unheated greenhouse with two alfalfa cultivars (AC Caribou and WL 225) subjected to four fall harvest treatments: two summer harvests (control) and a third harvest taken in the fall at 400, 500, or 600 growing degree days (GDD) after the second harvest. Shoot regrowth was reduced by a fall harvest, especially when plants were harvested at 400 or 500 GDD. Root soluble sugar concentrations (sucrose, raffinose, and stachyose) measured during the overwintering period were higher in plants harvested in the fall than in those harvested only twice; these concentrations were also higher in the more hardy cultivar AC Caribou compared with WL 225. A fall harvest did not consistently affect root TNC concentrations, but decreased markedly the total amount of TNC in roots, especially in plants harvested at 400 GDD. In both cultivars, shoot regrowth in spring was correlated positively to the total amounts of root starch (r = 0.54 and 0.61) and TNC (r = 0.55 and 0.56), but not correlated to their concentrations. Our results suggest that the total amount of C organic reserves in alfalfa roots rather than their concentrations can be determinant factors of shoot regrowth.

The Frequency and Persistence of Volunteer Canola (Brassica napus) in Québec Cropping Systems*

The presence of volunteer canola is becoming a significant agro-ecological concern, given the large-scale use of herbicide-tolerant varieties in some areas. Our goal was to estimate the frequency and persistence of volunteer canola in Québec cropping systems by surveying fields that included a single canola crop since 1995. A survey was conducted in 131 fields in the main canola-growing areas of Québec: in the Saguenay-Lac Saint-Jean region and the Québec City–La Pocatière area. Volunteer canola plants were counted in 0.25-m2 quadrats every 10 m along a W pattern, and every 15 m along the margins of 88 fields. Volunteer canola plants were found in 90% of the fields surveyed and in a wide range of crops, including cereal, corn, and soybean. Average densities of 4.9 and 3.9 plants/m2 were found 1 yr after canola production in fields and field margins, respectively. Volunteer canola densities decreased significantly over time. However, volunteer plants were still present at low densities 4 and 5 yr after production. Dense stands of volunteer canola were found before postemergence herbicide application in no-till fields (9.8 ± 4.1 plants/m2), suggesting that, contrary to what was suggested in the literature, seeds could become dormant in no-till as well as in tilled systems. A small proportion of the volunteer canola plants observed in no-till fields near Québec City and Ottawa included plants that had overwintered, either originating from fall-germinated seedlings, harvested adult plants that had grown new leaves before the onset of winter, or spring regrowth from the base of unharvested adult plants from experimental plots. The presence and persistence of low densities of volunteer canola may not have been a cause of concern until now. However, producers should be made more aware of the potential short-and long-term problems associated with potential gene flow between different herbicide-tolerant canola (HT canola) varieties and also between HT canola and related weed species.Nomenclature: Canola, Brassica napus L.; corn, Zea mays L.; soybean, Glycine max (L.) Merr.Additional index words: Herbicide-tolerant canola, oilseed rape, weed survey.Abbreviations: HT, herbicide-tolerant (canola).

Influence of summer sowing dates, N fertilization and irrigation on autumn VSP accumulation and dynamics of spring regrowth in alfalfa (Medicago sativa L.)

Herbage yield of alfalfa (Medicago sativa L.) depends on forage management or environmental conditions that change C and N resource acquisition, and endogenous plants factors such as root organic reserves and number of active meristems. The aim of this work is to study the influence of two sowing dates in summer (12 July or 9 August), N fertilization (0 or 100 kg ha(-1)) and/or irrigation applied during the first year of alfalfa establishment on (i) the accumulation of N organic reserves (soluble proteins and more specifically vegetative storage protein) in taproots during autumn, (ii) the number of crown axillary meristems present at the end of winter and (iii) the dynamics of spring shoot growth. Delaying the sowing date for one month reduced root growth and root N storage, especially vegetative storage proteins (VSP) during autumn. Irrespective of sowing dates, N fertilization did not affect root biomass, number of crown buds, total root N, root soluble protein or VSP concentrations. By contrast, water deficiency during alfalfa establishment in the early summer reduced both root growth and N reserve accumulation. When spring growth resumed, there is a significant linear relationship between leaf area development and soluble protein and VSP concentrations in taproots, and also the number of crown buds. The results showed that an early sowing date and adequate water status during the summer allowed alfalfa plants to accumulate N reserves by increasing taproot mass and soluble protein concentrations, especially VSPs. This resulted in rapid shoot regrowth rates the following spring.

Influence of summer sowing dates, N fertilization and irrigation on autumn VSP accumulation and dynamics of spring regrowth in alfalfa ( Medicago sativa L.)

Herbage yield of alfalfa ( Medicago sativa L.) depends on forage management or environmental conditions that change C and N resource acquisition, and endogenous plants factors such as root organic reserves and number of active meristems. The aim of this work is to study the influence of two sowing dates in summer (12 July or 9 August), N fertilization (0 or 100 kg ha −1 ) and/or irrigation applied during the first year of alfalfa establishment on (i) the accumulation of N organic reserves (soluble proteins and more specifically vegetative storage protein) in taproots during autumn, (ii) the number of crown axillary meristems present at the end of winter and (iii) the dynamics of spring shoot growth. Delaying the sowing date for one month reduced root growth and root N storage, especially vegetative storage proteins (VSP) during autumn. Irrespective of sowing dates, N fertilization did not affect root biomass, number of crown buds, total root N, root soluble protein or VSP concentrations. By contrast, water deficiency during alfalfa establishment in the early summer reduced both root growth and N reserve accumulation. When spring growth resumed, there is a significant linear relationship between leaf area development and soluble protein and VSP concentrations in taproots, and also the number of crown buds. The results showed that an early sowing date and adequate water status during the summer allowed alfalfa plants to accumulate N reserves by increasing taproot mass and soluble protein concentrations, especially VSPs. This resulted in rapid shoot regrowth rates the following spring.

The release of cell contents of fresh rye-grass ( Lolium perenne L.) during digestion in dairy cows: effect of the intracellular constituents, season and stage of maturity

The objective of the trial was (i) to measure the release kinetics of intracellular constituents (ICs) of fresh grass during eating and after a meal in dairy cows fed rye-grass ( Lolium perenne L .), (ii) to quantify the effect of the season (spring versus autumn) and the stage of maturity on the release of ICs, and (iii) to dissociate the effects of chewing during rumination from the effects of ruminal processes (microbial degradation of cell walls, ruminal mixing, osmotic shocks) in the release of ICs. In each season, four dairy cows fitted with a large ruminal cannula were fed indoors, during two 3 h periods, with fresh grass cut at 23 and 57 days of regrowth in spring, and at 34 and 68 days in autumn. The rumen of each animal was evacuated every 3 h during daylight (0, 3, 6 and 9 h after the beginning of the meal). Subsamples of ruminal contents were rinsed carefully and their IC contents compared with the IC contents of grass. To dissociate the effect of ruminal processes, ingestive boli were incubated in nylon bags in the rumen and rinsed at the same times as the rumen evacuations. The soluble carbohydrates were quickly released. More than 85% were released by the end of the meal and all the soluble carbohydrates disappeared from forage particles 6 h after the meal. The release kinetics did not vary very much between free sugars and fructans. The proportions of chlorophyll released were far lower. Only 45% of the chlorophyll was released by the end of the meal and an additional 45% was released 6 h later. The release of soluble carbohydrates was only marginally affected by the stage of maturity and season. The release of chlorophyll and fructans was lower for young grass in autumn. The release of chlorophyll was quicker in spring than in autumn. The release of soluble carbohydrates was almost complete before rumination began. The release kinetics of chlorophyll in ingestive boli incubated in nylon bags in autumn was parallel to the release kinetics measured in the ruminal contents, thus showing that chewing during rumination is not a major process in the release of ICs. However, the effect of rumination may have been more important in spring as suggested by the positive correlation between the unit ruminating time and the proportions of chlorophyll released. A high weight of ruminal contents may enhance the release of chlorophyll by increasing the ruminal pressure. These results clearly show that the release kinetics differs between chlorophyll and the other ICs and suggest that ingestive mastication and ruminal processes other than rumination are of major importance in the release of ICs.

Effects of nitrogen deficiencies on autumnal growth of oilseed rape

Several field experiments were carried out to define the effects of temporary N deficiency in autumn on the growth and yield of winter oilseed rape. N deficiencies are described in terms of nitrogen nutrition index (NNI) i.e. methodologies of Lemaire et al. (Proceedings of the XVI International Grassland Congress, Nice, France, 1989, p. 179) and Lemaire and Gastal (In: G. Lemaire (Ed.), Springer, Berlin, Diagnosis of the Nitrogen Status in Crops, 1997, p. 3). The growth components analysed were shoot and tap root biomass, leaf area index (LAI) and radiation use efficiency (RUE). In all the experimental conditions, N deficiencies were severe (NNI near 0.60) and had significant effects on all growth components. These growth variables and NNI were fitted by various functions. The effects of N stress on winter oilseed rape are discussed and compared to another crop. Despite severe autumn N deficiencies, no difference in yield was apparent because these deficiencies probably allow all the time enough growth in autumn to ensure sufficient regrowth in spring.