Timothy Cultivars Research Articles

Genotype × environment interaction patterns of dry matter yield in meadow brome, orchardgrass, tall fescue, and timothy evaluated at harsh winter sites

AbstractBackgroundGenotype × environment interaction (GEI) slows genetic gains and complicates selection decisions in plant breeding programs. Forage breeding program seed sales often encompass large geographic regions to which the cultivars may not be adapted. An understanding of the extent of GEI in perennial, cool‐season forage grasses will facilitate improved selection decisions and end‐use in areas with harsh winters.MethodsWe evaluated the dry matter yield of nine meadow brome (Bromus biebersteinii Roemer & J. A. Schultes), nine orchardgrass (Dactylis glomerata L.), seven tall fescue (Lolium arundinaceum (Schreb.) Darbysh.), and 10 timothy (Phleum pratense L.) cultivars or breeding populations at seven high latitude and/or elevation locations in Canada and the United States from 2019 to 2021.ResultsFor each of the species, we found significant differences among the genotypes for dry matter yield across environments and found significant levels of GEI. Using site regression analysis and GGE biplot visualizations, we then characterized the extent of the interactions in each species. Except for tall fescue, there was little evidence for the broad adaptation of genotypes across locations.ConclusionsThis research adds further evidence to the limitations of perennial, forage breeding programs to develop widely adapted cultivars and the need to maintain regional breeding efforts.

Frost survival and gene expression in timothy (Phleum pratense L.) cultivars as affected by age and selection in diverse field environments.

The sustainable production of perennial grasses in Northern Norway is at risk due to the ongoing climate change. The predicted increase in temperatures and variable weather patterns are further expected to create challenges for winter survival of timothy (Phleum pratense L.). Knowledge about the molecular mechanisms underlying freezing tolerance is crucial for developing robust cultivars. The current study is aimed at identifying genes involved in freezing stress response of timothy and studying gene expression differentiation due to field selection in contrasting environments using RNAseq. Four timothy cultivars were field tested for three years in Tromsø and Vesterålen, in Northern Norway. The surviving material from the field tests, along with plants raised from the original seed lots, were subjected to freezing tests. LT50 values varied across cultivars and materials. Many genes coding for transcription factors and proteins known to play an important role in freezing tolerance, like dehydrins, c-repeat binding factors, and late embryogenesis abundant proteins were upregulated with decreasing temperatures. Moreover, genes associated with glycolysis/gluconeogenesis, TCA cycle, glutathione metabolism, proteasome pathways and genes encoding autophagy-related proteins, plasma membrane-associated proteins, sugar and amino acid transporters had elevated expression in field survivors compared to plants raised from the original material. The lower freezing stress tolerance of field survivors despite the elevated expression of several stress-responsive genes might be due to a combination of selection in the field and the age effect. Furthermore, differences in freezing stress response between northern and southern adapted cultivars and surviving material from two field trial locations are discussed.

Phenotypic Diversity in Domesticated and Wild Timothy Grass, and Closely Related Species for Forage Breeding.

Timothy grass (Phleum pratense L.) is one of the most important forage crops in temperate regions. Forage production, however, faces many challenges, and new cultivars adapted to a changing climate are needed. Wild populations and relatives of timothy may serve as valuable genetic resources in the breeding of improved cultivars. The aim of our study is to provide knowledge about the phenotypic diversity in domesticated (cultivars, breeding lines and landraces) and wild timothy and two closely related species, P. nodosum (lowland species) and P. alpinum, (high altitude species) to identify potential genetic resources. A total of 244 accessions of timothy and the two related species were studied for growth (plant height, fresh and dry weight) and plant development (days to stem elongation, days to booting and days to heading) in the field and in a greenhouse. We found a large diversity in development and growth between the three Phleum species, as well as between the accessions within each species. Timothy showed the highest growth, but no significant difference was found between wild accessions and cultivars of timothy in fresh and dry weight. However, these two groups of accessions showed significant differences in plant development, where timothy cultivars as a group reached flowering earlier than the wild accessions. This suggests that there has not been a strong directional selection towards increased yield during the domestication and breeding of timothy; rather, timothy has been changed for other traits such as earlier heading. Principal component analysis and cluster analysis based on all traits revealed distinct clusters. Accessions falling within the same cluster showed similarities in the development and growth rather than the type of accession. The large diversity found in this study shows the potential of using timothy accessions as genetic resources in crosses with existing cultivars. Also, accessions of P. nodosum with favorable traits can be candidates for the domestication of a novel forage crop, and the high-altitude relative P. alpinum may be a source of genes for the development of more cold and stresstolerant cultivars.

Effects of nitrogen application rate on productivity, nutritive value and winter tolerance of timothy and meadow fescue cultivars

AbstractFinnish N fertilizer application regulations for forage grasses are based on field experiments mainly conducted in the 1960–1970s with cultivars and management practices typical of the time. In order to update the yield response function of N, to make it better suited to current grassland farming, field experiments were conducted at two sites in 2015–2017 with two cultivars of timothy (Phleum pratense L.) and one of meadow fescue (Festuca pratensis Huds.). Dry matter (DM) yield, nutritive value and N balance were evaluated, with N application levels 0, 150, 200, 250, 300, 350, 400 and 450 kg N ha−1 year−1. The grasses were harvested three times per season. The data indicate that the DM yield response was significantly stronger, and N was used more efficiently for DM production than earlier without compromising the nutritive value, especially during the first two years. The third harvest produced on average 23% of the annual yield, utilizing N efficiently. N application rates below 350 kg N ha−1 year−1 did not cause substantial overwintering losses or lodging. The data indicate that with changing climate and improved cultivars and management practices, there is a need to modify the rates and timing of N application. The results suggest that N application levels could be increased by at least 50 kg N ha−1 year−1 from the current maximum accepted rate (250 kg N ha−1 year−1) without too high NO3‐ or CP concentrations in feed, or too high N balance that indicates increasing risk of N leaching.

Vernalization, gibberellic acid and photo period are important signals of yield formation in timothy (Phleum pratense)

Timothy (Phleum pratense) is a widely grown perennial forage grass in the Nordic region. The canopy consists of three tiller types, of which the stem forming vegetative elongating (ELONG) tiller and generative (GEN) tillers contribute the most to dry matter yield. In this study, the regulation of tiller formation by vernalization, day length (DL) [12 h, short day length (SD); 16 h, long day length (LD)] and gibberellic acid (GA) was investigated in two timothy cultivars. Vernalization resulted in a shift of ELONG to GEN tillers. No vernalization was required for the development of ELONG tillers but SD strictly arrested stem elongation. Vernalization is an important regulator of tiller development but it seemed to be upstream regulated by DL. LD was essential for floral transition and could not be substituted by GA and/or vernalization treatments. Genotypic variation was found in the development of GEN tillers. The ability to produce GEN tillers was associated with significant upregulation of PpVRN3. PpVRN1 expression peaked at the time of vegetative/generative transition, and PpVRN3 after the transfer to LD, suggesting them to have similar functions with cereal vernalization genes. PpVRN1 alone was not sufficient to activate flowering, and upregulation of PpVRN3 possibly together with PpPpd1 was required. Although vernalization downregulated PpMADS10, this gene did not act as a clear flowering repressor. Our results show that flowering signals alter the tiller composition, so they have important effects on yield formation of timothy.

Influence of harvest time and storage location on the longevity of timothy (Phleum pratense L.) seed

Norwegian agriculture relies heavily on a safe supply of seed of winter-hardy timothy cultivars. To buffer variations in seed consumption and seed yields, seed companies keep stocks corresponding to 50–100% of average annual seed consumption. Such large stocks are risky to maintain as seeds lose germination over time. Our objective was to elucidate the effect of seed harvest time and seed storage location on the longevity of timothy seed. In 2003, the Norwegian timothy cultivars, ‘Grindstad’, ‘Vega’ and ‘Noreng’, were combined directly at three different seed harvest times corresponding to a seed moisture content (SMC) of 33–35% (H1), 26–28% (H2) and 16–20% (H3), respectively. Germination analyses were conducted before storage and after 12, 24, 36, 48 and 60 months of storage in a conditioned seed store at Landvik (4°C, 30% RH) or in unconditioned warehouses at three climatically different locations (Tynset, Holstad and Vaksdal). Seed harvest time became increasingly significant as time went by. After 60 months seed harvested at 16–20% SMC (H3) germinated, on average for storage locations and cultivars, 24% units better than seed harvested at 33–35% SMC (H1). Seed stored in the conditioned store at Landvik germinated, on average for harvest times and cultivars, 4, 15 and 47 units better than seed stored at Tynset (continental), Holstad (intermediate) and Vaksdal (coastal), respectively. A significant interaction emphasised the importance of storing seed combined at a high SMC under optimal conditions in order to avoid germination loss. This linkage between harvest time and storage conditions for timothy seed longevity has not earlier been reported. Probably due to larger seeds that were more susceptible to mechanical damage, seed of ‘Grindstad’ usually had the lowest germination. These new results suggest that appropriate adjustment of drum speed and concave clearance is especially important when harvesting ‘Grindstad’.

티모시의 품종에 따른 성숙종자 유래의 캘러스로부터 식물체 재분화

The present study was conducted to determine the optimum in vitro conditions for callus induction and plant regeneration from mature seed derived callus of four cultivars of Timothy. In order to investigate the effects of genetic variations of timothy in tissue culture, calli were induced from mature seeds of four varieties, 'Colt', 'Chair', 'Richmond' and 'Hokuo' and plant regeneration frequency was compared. Significant differences were observed among the cultivars in both callus induction and plant regeneration. Genotype 'Colt' consistently performed best in the callus subculture and plant regeneration. The complete plantlets were thereafter transplanted to grow under greenhouse condition. Regenerated timothy plants were morphologically uniform with normal leaf and growth pattern. (Key words : Callus, Plant regeneration, Timothy, Phleum pratense L.)

Modeling the Biomass and Harvest Index Dynamics of Timothy

Residual stubble, following harvest or the grazing of perennial grasses, is an important element of the C cycle in agricultural systems that has not been considered in most growth models. The stubble fraction from aboveground biomass can be quantified by predicting the harvest index (HI) of forage grasses, i.e., the amount harvested or grazed as a proportion of the aboveground biomass. A HI simulation module, using new functions to describe shoot apex height and plant weight density, was developed and integrated into the timothy (Phleum pratense L.) growth model CATIMO. The model was calibrated and validated using data from two timothy cultivars and different N fertilizer rates from five experiments conducted in eastern Canada. The root mean square errors (RMSEs) between simulated and measured values for HI (0.11), shoot apex height (7 cm), stubble biomass (25 g dry matter m−2), aboveground biomass (68 g dry matter m−2), and harvestable biomass (76 g dry matter m−2) were acceptable with normalized RMSEs (13–41%) compared with the coefficients of variation of measured data (13–30%). The HI also has implications for determining forage nutritive value. This improved CATIMO model provides a framework to explore options for optimizing yield and nutritive value and to quantify the stubble biomass of timothy within the context of C sequestration.

DNA Profiling of Seed Parents and a Topcross Tester and its Application for Yield Improvement in Timothy (Phleum pratense L.)

ABSTRACTAssessment of genetic diversity based on DNA profiling contributes to the selection of superior parents for heterosis. The objective of this study was to investigate how closely the yields of timothy (Phleum pratense L.) topcross progenies are related to the genetic diversity between their seed parents and the pollen tester parent ‘Aurora’, and to predict their yield potentials from the index based on simple sequence repeat (SSR) marker polymorphisms. Genetic diversity among 67 genotypes, which consisted of 16 plants of timothy cultivar Aurora, the pollen parent for topcross testers, and 51 clones derived from breeding populations was evaluated based on 28 SSR markers carrying 408 alleles. Genetic distance (GD) was estimated for all possible pairs of genotypes and then the mean of the GD estimates between each clone and Aurora (GDA) was also assessed to find the relationship between GDA estimates and yields of topcross progenies derived from all crosses between each clone and Aurora. The GDA estimates of the clones ranged from 0.653 to 0.756, and a correlation coefficient between the GDA estimates and yields of their topcross progenies was 0.675 (p < 0.001). These results strongly suggest that GD would provide reliable information on the yields of the assumed topcross progeny lines and that it will help breeders to accelerate yield improvements for a practical breeding program of timothy.

Tolerance to frost and ice encasement in cultivars of timothy and perennial ryegrass during winter

AbstractIce encasement causes major winter damage in grasslands in coastal areas of Northern Scandinavia and may also affect grass performance in a future changing climate. Changes in ice‐encasement tolerance (LD50), frost tolerance (LT50) and water‐soluble carbohydrate (WSC) content were investigated in different cultivars of timothy and perennial ryegrass sampled at three sites with contrasting conditions. Timothy endured ice encasement for 40 d more than ryegrass (maximum LD50 63 vs. 20 d), and a cultivar originating from 69°N tolerated significantly longer periods in ice than a cultivar from 59°N. A similar relationship between cultivar origin and tolerance was observed for ryegrass. The higher LD50 in timothy compared with ryegrass seemed to be associated with a lower rate of change in WSC content during ice encasement, but no apparent relationship was found between WSC content at the start of encasement and plant survival in ice. A significant linear relationship was found between LD50 and LT50 of plants sampled in the field. A differing decline in frost tolerance during ice encasement for the species indicated that timothy is more resistant to dehardening under ice than ryegrass. This study contributes data and functional relationships needed to develop models of grass performance during winter.

Modelling cold hardening and dehardening in timothy. Sensitivity analysis and Bayesian model comparison

Timothy ( Phleum pratense L.) is the most important forage grass in Scandinavia and it is therefore highly interesting to study how it will perform in a changing climate. In order to model winter survival, the dynamics of hardening and dehardening must be simulated with satisfactory precision. We investigated an early timothy frost tolerance model (LT50 model), and an LT50 model for winter wheat. Based on the assumption that timothy has no vernalization requirement, unlike winter wheat, but does have the ability to adapt to cold temperatures in a process linked to stage of development, two alternative versions of the winter wheat model were also constructed. In total, these four candidate models were calibrated by a Bayesian approach for the timothy cultivar Engmo. The candidate models were validated using independent observations on LT50 in timothy at different locations reflecting differences in climate. A sensitivity analysis, using the Morris method, to identify important model parameters suggested that there is a connection between frost tolerance and stage of plant development, even if there is no vernalization requirement. The simplified winter wheat model was selected as the best candidate model for LT50 in timothy based on model selection criteria and its ability to capture the hardening and dehardening processes. The results from the Bayesian calibration suggest that there are no major regional differences in Norway calling for regional calibration. However, cultivar-specific calibration is probably required, since there are hardy and less hardy cultivars within the same species. A functional LT50 model would allow risk assessments to be made of future winter survival using specifically tailored and downscaled climate scenarios.

De‐hardening in contrasting cultivars of timothy and perennial ryegrass during winter and spring

AbstractScenarios of climate changes indicate longer and more frequent spells of mild weather during winter in northern latitudes. De‐hardening in perennial grasses could increase the risk of frost kill. In this study, the resistance to de‐hardening of different grass species and cultivars was examined, and whether the resistance changes during winter or between years, was tested. In Experiment 1, two cultivars of timothy (Phleum pratense L.) and perennial ryegrass (Lolium perenne L.) of contrasting winter hardiness were grown under ambient winter conditions, transferred from the field in January and April 2006 to the laboratory for 9 d with controlled de‐hardening conditions of 3°C, 9°C and 15°C. The timothy cultivars were tested at 3°C, 6°C and 9°C in a similar experiment (Experiment 2) in January 2007. De‐hardening, measured as decrease in frost tolerance (LT50), was less in timothy than in perennial ryegrass and increased with increasing temperatures. The northern winter‐hardy cultivar Engmo of timothy de‐hardened more rapidly than the less‐hardy cultivar Grindstad, but had higher initial frost tolerance in both experiments, whereas there was less difference between cultivars of perennial ryegrass in Experiment 1. Cultivar Grindstad of timothy lost all hardiness in early spring at all temperatures, whereas cultivar Engmo maintained some hardiness at 3°C. Cultivar Engmo de‐hardened at a lower rate in 2007 than in 2006, in spite of similar frost tolerance at the start of de‐hardening treatment in both years. This indicates that the rate of de‐hardening was controlled by factors additional to the initial frost tolerance and that autumn weather conditions might be important for the resistance to de‐hardening.

Impact of frost and plant age on compensatory growth in timothy and perennial ryegrass during winter

AbstractTwo cultivars of each of two contrasting grass species, timothy (Phleum pratense L.) and perennial ryegrass (Lolium perenne L.), sown either in May or July, were sampled for dry matter (DM) weight of roots and herbage in late October (end of main growing season) and examined for regrowth when exposed to a frost treatment (−8 to −10°C in darkness for 48 h) in late January, early March and late April. The frost treatment caused compensatory root and herbage growth, and regrowth of roots in March and April was greater than regrowth of herbage. Early‐sown plants had higher DM weights of roots and herbage than late‐sown plants in October but had the lowest survival rate when exposed to the frost treatment in April. Compensatory growth of root and herbage in response to moderate frosts occurred in January and March in all cultivars, and in the most frost‐resistant timothy cultivar in April. Concentration of total carbohydrates increased from October to March with the greatest increase in the most winter‐hardy cultivar of each species, and then decreased in April. An indirect correlation between concentration of total carbohydrates and tolerance to moderate frost was indicated, and plant survival and ability for compensatory growth were also associated with differences in adaptation related to winter survival in the cultivars tested.

Effects of maturity stage, temperature and photoperiod on growth and nutritive value of timothy ( Phleum pratense L.)

The aim of this experiment was to investigate effects of temperature and photoperiod on growth characteristics, chemical composition and indigestible fibre (IaNDF) in timothy harvested at three defined maturity stages. Two cultivars of timothy, Engmo (69 oN) and Grindstad (59 oN) were grown in a controlled environment using a phytotron, and were exposed to two different temperature regimes (21/15 °C and 15/9 °C, 12 h/12 h) and photoperiods (18 and 24 h). Plants were harvested at beginning of heading (BH), full heading (FH) and anthesis (AN). Leaves and stems were separated prior to chemical analyses and ruminal in situ incubation for 288 h was used to determine indigestible aNDF (IaNDF) content. Plants grown at low temperature used almost twice the number of days to reach AN, compared to the highest temperature regime. This explained the lower leaf:stem ratio (LSR), higher aNDF content and lower crude protein (CP) content in low temperature plants. The effect of temperature was often dependent on maturity stage. However, the content of IaNDF and lignin(sa) was only affected by maturity stage at harvest. The content of IaNDF and lignin increased by 70% and 35% respectively from BH to AN. The lack of response in IaNDF and lignin(sa) content and dry matter digestibility to temperature was probably caused by a combination of direct and indirect temperature effects. Photoperiod affected growth characteristics, but had minor effects on chemical composition and IaNDF. Due to the lower LSR, Engmo had higher IaNDF and lignin(sa) content than Grindstad. This study showed a high positive correlation (0.93) between IaNDF and lignin(sa). Interactions between temperature and maturity stage affect the growth and nutritive characteristics of timothy. However, only maturity stage affected IaNDF and lignin(sa) content.

Split nitrogen application strategies in seed production of two contrasting cultivars of timothy (Phleum pratense L.)

Split nitrogen (N) application to seed crops of timothy (Phleum pratense L.) was evaluated in 20 field trials, 11 in the south-Norwegian cultivar ‘Grindstad’ (origin 59°N) and nine in the north Norwegian cultivar ‘Vega’ (origin 67°N) in southeast (58–61°N) and central (63–64°N) Norway during 1998–2000. Three N rates (25, 50 or 75 kg N ha−1) at the start of growth were combined with four N rates (0, 25, 50 or 75 kg N ha−1) at the start of tiller elongation (Z 31). On average for all trials, the highest seed yield was obtained when a total rate of 75 kg N ha−1 was split into a main application of 50 kg N ha−1 at the start of growth and a supplemental application of 25 kg N ha−1 at Z 31. In both cultivars, the optimal N rate at Z 31 was uncorrelated with soil mineral N (NO3+NH4) in early spring and only weakly correlated (r 2=0.16–0.17, p% = 2–5) with the N concentration of aboveground plant material at Z 31. In ‘Grindstad’, a better correlation (r 2=0.46, p% < 0.1) was obtained between the optimal N rate at Z 31 and measurements by the hand-held chlorophyll meter Hydro N-Tester™ on the last fully developed leaf. The equation (HTN model) Optimal N input (kg N ha −1 ) at Z 31 = − 0.37×measured HNT value at Z 31+156 was further evaluated in ten on-farm trials during 2001–2002. Compared to the fixed N levels 0, 25 or 50 kg N ha−1, the HNT model predicted optimal N rates at Z 31 in 2002, but not in 2001, when less rainfall caused less lodging than in 1998–2000 and 2002. Nevertheless, we conclude: 1) that the spring N rates to timothy seed crops should be split into an early and a late application, and 2) that the HTN model will help in adjusting the second N rate at Z 31 in ‘Grindstad’.

Agronomic Performance of Timothy Germplasm from Forage and Turf Sods under Two Harvest Managements

Cultivated timothy (Phleum pratense L.) is an important grass for hay production in temperate North America. It is underutilized in management‐intensive rotational grazing systems because of its poor persistence when frequently defoliated. The objective of this study was to compare families selected for forage yield under frequent defoliation, families derived from old turf sods, and cultivars for agronomic performance under frequent and infrequent harvest managements (four vs. two harvests per year). Forage timothy was generally superior to turf timothy for most traits. Forage selections averaged 9.4 and 4.9% higher forage yield compared with cultivars under infrequent and frequent harvest managements, respectively, indicating that selection for higher forage yield under frequent harvest improved forage yield under both harvest frequencies. There were differences among the four types of turf (golf course fairways and roughs, cemeteries, and lawn/roadways), but these differences were not closely related to mowing height or frequency, perhaps because of the small sample size. Some turf collections ranked high for net herbage accumulation under frequent harvesting, but most turf collections were also characterized by a high frequency of regrowth panicles under either or both harvest frequencies. Timothy germplasm from old turf sods may have value in developing new timothy cultivars with improved tolerance to frequent defoliation and efforts should continue to gather and evaluate collections from a range of turf types and locations.

Herbage yield and composition of Kentucky bluegrass (Poa pratensis L.) cultivars under two harvest systems

Although Kentucky bluegrass (Poa pratensis L.) is a naturalized species commonly found in the permanent grasslands of eastern Canada, its contribution to sward output is not well defined. Six Kentucky bluegrass cultivars originating from Norway, Germany and North America, and a timothy (Phleum pratense L.) cultivar, were grown under two harvest systems at two locations to determine yield and herbage composition. All cultivars persisted over 3 production years. Dry matter yields of bluegrass cultivars were similar to those of timothy, ranging from 7.87 to 9.76 t ha-1 in Charlottetown, Prince Edward Island, and from 3.64 to 4.79 t ha-1 in Normandin, Quebec. Yields of broadleafed genotypes from Europe were superior in year 1. However, the warm and dry growing conditions of year 3 favoured the narrow-leafed genotypes. Mean tiller density of Kentucky bluegrass was 6440 m-2; timothy had a mean tiller density of 3040 m-2. Forage quality attributes of Kentucky bluegrass were similar to those of timothy. Cultivar differences in fibre and mineral concentrations were consistent across years and locations and may provide selection criteria in breeding programs. Greater harvest frequency increased the total nitrogen concentration of herbage and tiller density but had no effect on yield. Kentucky bluegrass is a persistent, valuable forage grass species with good potential for use in pasture and as conserved forage in eastern Canada. Key words: Herbage composition, herbage yield, Kentucky bluegrass, Poa pratensis, Phleum pratense, tiller, timothy

Leaf and stem nutritive value of timothy cultivars of different maturity at an irrigated site in southwestern Saskatchewan

Leaf and stem structural components contribute to variation in nutritive value among timothy (Phleum pratense L.) cultivars. Modelling timothy growth and nutritive value requires a better understanding of this variation. A trial of 11 timothy cultivars was conducted on irrigation at Swift Current, Saskatchewan from 1995 to 1997. Leaf:stem ratio, forage yield, days to maturity, N, P, acid detergent fiber (ADF) and neutral detergent fiber (NDF) concentrations, N/P ratio and P uptake of leaf and stem components were determined for spring growth forage. Two N fertilizer rates (100 and 150 kg N ha-1) did not consistently affect leaf and stem nutritive value. Cultivars differed in maturity, stem P, stem N, stem NDF, leaf NDF and leaf ADF in all 3 yr. Days to maturity was correlated to stem P concentration (r = 0.59, P &lt; 0.05, to 0.77, P &lt; 0.01) and leaf ADF concentration (r = 0.59, P &lt; 0.05, to 0.82, P &lt; 0.01) in all 3 yr but not to stem NDF concentration. Days to maturity was correlated to stem N concentration and leaf NDF concentration in 1995 and 1997 but not in 1996. However, days to maturity did not explain the observed variation among cultivars for stem NDF concentration and several other variables. While maturity differences among timothy cultivars must be taken into account when selecting for improved nutritive value or modelling growth and quality, additional variation for these traits was evident. Key words: Forage quality, Phleum pratense L., maturity, forage yield

Evaluating the performance of alfalfa cultivars in rotationally grazed pastures

Although alfalfa (Medicago sativa L.) is an important and reliable hay crop in eastern Canada, it is generally not considered suitable for pastures. However, local studies have shown that alfalfa is capable of superior yield in mixtures under rotational grazing. This study evaluates the performance of commercially available, locally adapted, hay-type alfalfa cultivars and new experimental, grazing-type alfalfa synthetics under hay and two rotationally grazed regimes. Ten alfalfa cultivars, including five hay-type and five grazing-type cultivars, were seeded with the timothy (Phleum pratense L.) cultivar, Richmond, in mixtures. The two pasture regimes consisted of grazing to low and high residual heights. Over two dry growing seasons, the pasture management with high residual grazing height was more productive than the low; on average lenient rotational grazing pressure (high residual heights) produced 20% higher yield than low residual heights. Alfalfa cultivars selected specifically for continuous grazing were not, on average, superior to those hay-type cultivars selected for general adaptability to soil and environmental conditions in Atlantic Canada. Differences among cultivars within alfalfa type were significant. Over 2 production years, mixtures containing the hay-type cultivar, Apica, and the grazing type, Alfagraze, produced more dry matter on average than three others in the study, regardless of management regime. Key words: Grazing height, cattle grazing

Timothy regrowth, tillering and leaf area dynamics following spring harvest at two growth stages

Timothy is the most widely grown grass species in Scandinavia. It is more winter-hardy than ryegrasses, but less tolerant to frequent cutting. Its intolerance to frequent defoliation is not well understood. This has hampered efforts to optimise the cutting regime, and made it difficult to develop and test mechanistic models for growth. In the present study, in order to identify the key determinants of regrowth capacity, we quantified time courses after cutting of physiological and morphological processes in timothy swards. In three consecutive years, field experiments were carried out with cv. ‘Grindstad’, the most commonly grown timothy cultivar in Norway. The sward was first cut either at a silage stage (early heading) or at a hay stage (full heading to anthesis). The effects of cutting time on tillering and leaf area dynamics were measured. Early cutting increased the length of the lag-phase of the sigmoid regrowth curve by more than 1 week on average, but once the sward entered the period of rapid biomass accumulation, growth rate was similar in both cutting treatments. Early cutting reduced the number of surviving tillers in the sward, leading to a slower rate of leaf area recovery. A lower carbohydrate concentration in the sward at the early cutting date, observed in 2 years out of 3, may also have contributed to this effect. Cutting time did not affect the chronological order in which the different processes contributed to recovery from cutting. The data assembled in this research will be used for testing a previously developed mechanistic model of timothy growth.