Persistence Of Perennial Ryegrass Research Articles

Effects of heading date and Epichloë endophyte on persistence of diploid perennial ryegrass (Lolium perenne). 1. Heading date

Context Data are lacking on the effects of heading date of perennial ryegrass (Lolium perenne L.) on ryegrass persistence. Aim We aimed to determine the impact of heading date on perennial ryegrass persistence. Method Two mid-heading (Samson, Bronsyn) and two late-heading (One50, Rohan) cultivars, infected with Epichloë endophytes (AR37, nea2/6 or standard toxic), were established in a replicated plot study grazed by cattle in a subtropical environment of the upper North Island of New Zealand. Persistence characteristics were quantified at least five times per annum, over 4 years. Key results Late-heading cultivars had higher yield, nutritive value, perennial ryegrass content in pasture dry matter, ground cover and tiller density than mid-heading cultivars. There were large seasonal impacts on all ryegrass characteristics, with a major decline over summer and recovery during late autumn into early spring, with less recovery in the final year. Overall, there was a strong linear decline in ryegrass content measured during spring (2018–21). Conclusions The two late-heading cultivars were more persistent than the two mid-heading cultivars, although persistence declined over 4 years for all cultivars. Implications Results support industry recommendations of choosing late-heading cultivars for improved pasture quality and persistence.

A review of grass species yields and growth rates in Northland, New Zealand

ABSTRACT Pastoral farming is a major land use in New Zealand's Northland region, with 3,171 farm holdings and a total area of 637,500 hectares in 2022. The region's pasture grasses include temperate (C3) and subtropical and tropical (C4) grasses which support dairy, and sheep and beef production from grazing. In lowland areas, C3 and some annual C4 grasses are prevalent where cultivation occurs, while perennial C4 grasses dominate areas with low soil fertility and summer dry conditions. Grass-based pasture growth rates (kg dry matter/ha/day) from published and unpublished sources were assembled into the AgYields database. Among the resident and sown grasses tested in Kaitaia, Kaikohe, Whangarei and Dargaville, perennial ryegrass represented ∼60% of the total data points. Dominant kikuyu pastures represented 23% and the remaining species represented 17%. Rates of growth ranged from 5 to 120 kg DM/ha/day, being lowest in late autumn-winter and highest in early summer. Data were compared and agronomic traits (i.e. drought tolerance, biomass production and tillering) are discussed to assess species suitability for the Northland environment. The medium-term prospect suggests an urgent need to improve research into management of cocksfoot and tall fescue-based pastures to provide viable alternatives to overcome the decreasing persistence of perennial ryegrass.

Persistence of perennial ryegrass, tall fescue and cocksfoot following annual sowings: influence of grass species, ryegrass cultivar and pasture age on yield, composition and density

Persistence is an important component of perennial pasture-grass productivity. Defining traits that affect persistence is essential for improving pasture longevity through plant breeding and for identifying persistence traits that should be included in cultivar ranking indices. Compared with conventional longitudinal studies, where a single sowing is monitored over time, repeated annual sowings allow the effects on persistence of sowing year and the ensuing interactions between environment and age of pasture to be identified. An experiment was commenced in 2015 under sheep grazing in Canterbury and in 2016 under cattle grazing in Waikato, where eight cultivars of perennial ryegrass representing different ploidy, flowering date, and cultivar age (release date), and one cultivar each of tall fescue and cocksfoot were sown in four randomised complete blocks in autumn each year. This paper reports interim data on spring and autumn pasture yield, composition, and density of 3-year-old, 2-year-old and 1-year-old pastures exposed to the same environmental conditions within the same, single year. There were significant effects on yield, botanical composition, basal cover and tiller density due to cultivar, pasture age, and their interaction. When the confounding effect of year-to-year variation was removed by comparing each age cohort in the same year, the underlying differences among grass species and cultivars, and ages of pasture, is starting to reveal the nature of this influence on pasture persistence.

Forage potential of winter‐hardy perennial ryegrass populations in monoculture and binary alfalfa mixture

AbstractPerennial ryegrass (Lolium perenne L.) is a cool‐season grass valued for its grazing characteristics and nutritive value. MSP3984 and MSP4029, breeding populations selected for winter‐hardiness, were evaluated for biomass and nutritive value in monoculture and grass–alfalfa mixtures (Medicago sativa L.). Plots were sampled at conventional hay harvest intervals at three Minnesota locations for two production years, 2017 and 2018. Persistence was evaluated in the spring of the 3rd year, 2019. MSP3984 and MSP4029 were compared to commercial cultivars of perennial ryegrass (Lolium perenne L.), meadow fescue (Festuca pratensis Huds.), tall fescue (F. arundinacea Schreb.), and orchardgrass (Dactylis glomerata L.). Location and year × location effects largely influenced grass monoculture yields (p < .001) and botanical composition of mixtures (p < .001). In general, perennial ryegrass monocultures yielded less and were less persistent (p < .05) compared to the other cool‐season grasses. Biomass, nutritive value, and persistence did not differ among MSP3984, MSP4029, and the perennial ryegrass check ‘Remington’. However, MSP4029 was less competitive in grass–alfalfa mixtures than ‘Remington’ (p = .01). Perennial ryegrasses had lower neutral detergent fiber (NDF) concentrations than meadow fescue (p = .001) and orchardgrass (p < .001). Perennial ryegrasses also had lower acid detergent fiber (ADF) values on average than the other grasses, but cultivar effects were influenced by a year × location interaction (p = .02). This research reinforces (a) the importance of evaluating cool‐season forage grasses across latitudinal and precipitation gradients, (b) the value of grass–legume mixtures for yield stability compared to monocultures across locations and production years, and (c) the sustained need to improve forage production and persistence of perennial ryegrass for cold environments.

Image‐based high‐throughput phenotyping for the estimation of persistence of perennial ryegrass (Lolium perenne L.)—A review

AbstractPerennial ryegrass (Lolium perenne L.) is considered the most important pasture species in temperate agriculture, with over six million hectares of sown area in Australia alone. However, perennial ryegrass has poor persistence in some environments because of low tolerance to a range of both abiotic and biotic stresses. To breed perennial ryegrass, cultivars with greater persistence and productivity may require evaluation of genotypes over a number of years. Persistence assessment in pasture breeding depends on manual ground cover estimation or counting the number of surviving plants or tillers in a known area. These methods are subjective and labour intensive, which may limit data collection in large‐scale breeding programs. With the rapid development of sensors and image processing algorithms, image‐based high‐throughput phenotyping (HTP) is becoming commonplace in the breeding of major food crops. Image‐based HTP approaches consist of the deployment of a wide range of sensors on ground‐based or airborne platforms and data analysed through image processing pipelines. Image‐based HTP shows high potential for use in pasture phenotyping in breeding programs and may be able to reduce timeframes for releasing new cultivars. Moreover, existing image‐based HTP approaches could be further developed to include precise tools for phenotyping pasture persistence traits such as pasture senescence, botanical composition, pathogen and pest resistance. In this study, we reviewed existing image‐based HTP approaches in precision agriculture and discussed their feasibility for perennial ryegrass persistence estimation in pasture breeding. Although the paper focuses on application in perennial ryegrass, the principles equally apply to other perennial forage species.

Persistence of perennial ryegrass, tall fescue and cocksfoot following sequential annual sowings: pasture yield, composition and density in three establishment years under cattle grazing in Waikato

Persistence is an important component of perennial pasture-grass productivity. Defining the traits that affect persistence is essential for improving pasture longevity through plant breeding and for identifying criteria that should be included in cultivar ranking indices. Compared with a conventional longitudinal study (a single study monitored over time), repeated annual sowings allow the effects on persistence of sowing year and the ensuing interactions between environment and age of pasture to be identified. An experiment commenced in 2016 in Waikato, in which eight cultivars of perennial ryegrass representing different ploidy, flowering date, and cultivar age, and one each of tall fescue and cocksfoot were sown each autumn in a randomised complete block design with four replicates in autumn 2016, spring 2017 and autumn 2018. This paper reports interim data on pasture yield, composition and density in the autumn following each sowing, and for the 2018 sowing only, in the 6 months after sowing. For the three successive autumn measurements there were significant effects due to cultivar, year of sowing and their interactions for all pasture variables. These differences in establishment may have consequences for the future resilience of these pastures under natural biotic and abiotic stressors.

High-Throughput Ground Cover Classification of Perennial Ryegrass (Lolium Perenne L.) for the Estimation of Persistence in Pasture Breeding

Perennial ryegrass (Lolium perenne L.) is one of the most important forage grass species in temperate regions of Australia and New Zealand. However, it can have poor persistence due to a low tolerance to both abiotic and biotic stresses. A major challenge in measuring persistence in pasture breeding is that the assessment of pasture survival depends on ranking populations based on manual ground cover estimation. Ground cover measurements may include senescent and living tissues and can be measured as percentages or fractional units. The amount of senescent pasture present in a sward may indicate changes in plant growth, development, and resistance to abiotic and biotic stresses. The existing tools to estimate perennial ryegrass ground cover are not sensitive enough to discriminate senescent ryegrass from soil. This study aimed to develop a more precise sensor-based phenomic method to discriminate senescent pasture from soil. Ground-based RGB images, airborne multispectral images, ground-based hyperspectral data, and ground truth samples were taken from 54 perennial ryegrass plots three years after sowing. Software packages and machine learning scripts were used to develop a pipeline for high-throughput data extraction from sensor-based platforms. Estimates from the high-throughput pipeline were positively correlated with the ground truth data (p < 0.05). Based on the findings of this study, we conclude that the RGB-based high-throughput approach offers a precision tool to assess perennial ryegrass persistence in pasture breeding programs. Improvements in the spatial resolution of hyperspectral and multispectral techniques would then be used for persistence estimation in mixed swards and other monocultures.

Effects of pasture age on the genotype and phenotype of perennial ryegrass

AbstractLimited persistence of perennial ryegrass (Lolium perenne L.) in dairy pastures is a significant issue in parts of New Zealand. The contribution of plant genetic background to this problem is not well understood. Temporal changes were investigated in genotypic and phenotypic composition of two perennial ryegrass cultivars (Nui SE and Alto AR37, older and newer cultivars respectively) sown as fields plots at three locations. Samples from survivor populations collected annually over 6 years from each location were established in a field nursery, analysed by simple sequence repeat (SSR) markers and assessed for vigour, leaf morphology and tiller number. SSR‐based estimates of the statistic G′ST indicated no significant (p > .05) genetic differentiation between survivor populations and plants grown from remnant seed (ex‐seed) after 5 years, and no significant change (p > .05) in within‐population genetic diversity for either cultivar at any location. SSR analysis of endophytic fungus (Epichloë festucae var. lolii) type revealed only limited ingress of off‐type ryegrass volunteers into plots at two locations. Vigour scores of survivor plants were not significantly (p > .05) different among plants collected from different locations and ex‐seed plants. Leaves on ex‐seed plants were longer (p < .001) than those on the survivor plants after four but not 6 years and may reflect a short‐term response to climatic conditions experienced in the field nursery. Our results suggest that the reported poor ryegrass persistence is not driven by changes in population genetic structure and that the sown cultivars survived and remained true to type.

An Object-Based Image Analysis Approach to Assess Persistence of Perennial Ryegrass (Lolium perenne L.) in Pasture Breeding

Perennial ryegrass (Lolium perenne L.) is one of the most important forage grass species in temperate regions of the world, but it is prone to having poor persistence due to the incidence of abiotic and biotic stresses. This creates a challenge for livestock producers to use their agricultural lands more productively and intensively within sustainable limits. Breeding perennial ryegrass cultivars that are both productive and persistent is a target of forage breeding programs and will allow farmers to select appropriate cultivars to deliver the highest profitability over the lifetime of a sward. Conventional methods for the estimation of pasture persistence depend on manual ground cover estimation or counting the number of surviving plants or tillers in a given area. Those methods are subjective, time-consuming and/or labour intensive. This study aimed to develop a phenomic method to evaluate the persistence of perennial ryegrass cultivars in field plots. Data acquisition was conducted three years after sowing to estimate the persistence of perennial ryegrass using high-resolution aerial-based multispectral and ground-based red, green and blue(RGB) sensors, and subsequent image analysis. There was a strong positive relationship between manual ground cover and sensor-based ground cover estimates (p < 0.001). Although the manual plant count was positively correlated with sensor-based ground cover (p < 0.001) intra-plot plant size variation influenced the strength of this relationship. We conclude that object-based ground cover estimation is most suitable for use in large-scale breeding programs due to its higher accuracy, efficiency and repeatability. With further development, this technique could be used to assess temporal changes of perennial ryegrass persistence in experimental studies and on a farm scale.

Effect of stubble height and irrigation management on the growth, botanical composition and persistence of perennial ryegrass, tall fescue and chicory swards in cool-temperate Tasmania

The profitability of dairying in south-eastern Australia can be improved by increasing pasture production during summer–autumn, when growth rates for the existing perennial ryegrass (Lolium perenne L.) feedbase are low. A study undertaken in cool-temperate north-west Tasmania examined the effect of stubble height and irrigation management on swards of perennial ryegrass, continental (summer-active) tall fescue (Festuca arundinacea Schreb.) and chicory (Cichorium intybus L.). Irrigation treatments included full irrigation (~20mm applied at every 20mm precipitation deficit), deficit irrigation (~20mm applied at alternate full-irrigation events) and rainfed (no irrigation). All species achieved greater summer–autumn yields when repeatedly defoliated to stubble heights of 35 or 55mm than when defoliated to 115mm, irrespective of irrigation treatment. Swards were managed under a common defoliation schedule of nine defoliation events in 12 months. Under full irrigation, second-year tall fescue achieved a greater summer–autumn yield than perennial ryegrass (by 10%, or 0.7 t DM ha–1), highlighting the potential role of tall fescue in north-west Tasmania. This was further demonstrated by the high marginal irrigation water-use index values (1.6–2.7 t DM ML–1) of tall fescue. By contrast, summer–autumn growth achieved by chicory was less than or equal to perennial ryegrass.

The measurement of perennial ryegrass persistence

Poor persistence in perennial ryegrass has been identified as a major limitation to pasture productivity, particularly in the upper North Island. Persistence can best be defined as the continuity of forage yield relative to a cultivar’s potential. Though there is limited evidence of differences in persistence between cultivars, there is interest in including persistence in the DairyNZ Forage Value Index. This requires an agronomically robust metric of persistence, measured over a suitable time frame and connected to economic value. Five candidates are evaluated: plant populations, tiller populations, basal cover, ground score and annual dry matter yield. Scarcity of long-term data is a major limitation to development of performance values for persistence, and must be addressed. The four abundance-based measures also lack a clear connection to economic values, from the limited data available. A persistence metric is proposed, that relates medium-term dry matter yield to short-term dry matter yield, for which perennial ryegrass functional type and cultivar differences are demonstrated.

Persistence of tall fescue in a subtropical environment: tiller survival over summer in response to flowering control and nitrogen supply

AbstractEnhancing pasture persistence is crucial to achieve more sustainable grass‐based animal production systems. Although it is known that persistence of perennial ryegrass is based on a high turnover of tillers during late spring and summer, little is known about other forage species, particularly in subtropical climates. To address this question, this study evaluated survival of grazed tall fescue tillers growing in a subtropical climate. We hypothesized that hard tactical grazing during winter to remove reproductive stems (designated as ‘flowering control’), and nitrogen fertilization in spring, would both improve tiller survival over summer, and thus enhance tiller density. This was assessed in two experiments. In both experiments, few tillers appeared during late spring and summer and so tiller density depended on the dynamics of vegetative tillers present in the sward in spring. In Experiment 2, flowering control and nitrogen fertilization both enhanced the survival of that critical tiller cohort, but the effects were not additive. Responses were similar but not statistically significant in Experiment 1, which had a warmer, drier summer and lower overall survival rates. Unlike grasses in temperate environments, persistence of tall fescue in this subtropical site appeared to follow a ‘vegetative pathway’; i.e., new tillers were produced largely in autumn, from vegetative tillers that survived the summer.

Evaluating perennial ryegrass cultivars: improving testing

The agronomic performance of a range of perennial ryegrass cultivar-endophyte combinations was compared in 16 trials conducted at sites throughout New Zealand. Each trial was run for 3 years according to seed industry evaluation protocols, measuring variables including: dry matter (DM) yield (total annual and seasonal DM yield), ryegrass ground cover at the end of 3 years, susceptibility to plant pulling, and rust incidence. The change in DM yield over the 3-year term of each trial was also analysed. There were significant differences among cultivars in total annual DM yield, and in seasonal DM yield for each of the five periods of the year among which yield was split (winter, early spring, late spring, summer, and autumn). Mean annual yield declined between Year 1 and Year 3 in all regions except Taranaki, by between 0.8 t DM/ha (Canterbury) and 5.3 t DM/ha (Waikato). There were significant region, year, region × year, and cultivar × year interactions in yield change. Significant differences in ground cover score for perennial ryegrass at the end of 3 years were recorded among cultivars. However, these differences did not mirror on-farm observations of ryegrass persistence in the Waikato during the drought of 2007/08, suggesting that the standard trial protocols currently used do not adequately test persistence. It is recommended that industry cultivar testing needs to more accurately assess perennial ryegrass persistence, using new protocols including running trials on commercial farms, for more than 3 years, and using mixed swards. Genetic differences in persistence could be generated more quickly by choosing sites known to challenge perennial ryegrass growth and survival. Keywords: perennial ryegrass, cultivar evaluation, DM yield, persistence testing, plant pulling, rust

Differences in yield among annual forages used by the dairy industry under optimal and deficit irrigation

While perennial forages dominate the feed base on Australian dairy farms, poor persistence of perennial ryegrass (Lolium perenne L.) and relatively poor forage nutritive value of kikuyu (Pennisetum clandestinum Hochst. ex. Chiov.) and paspalum (Paspalum dilatatum Poir.) has led to an increasing interest in growing annual forages. Thus, this study was conducted to identify annual forage species that are more productive than the commonly used perennial pasture species. Seventeen annual forages were investigated under ‘optimal’ irrigation and two deficit irrigation treatments (nominally 66 and 33% of irrigation water applied of the optimal level) over 3 years at Camden, New South Wales, on a brown dermosol in a warm temperate climate. The forages evaluated were: Italian ryegrass (Lolium multiflorum Lam.), oats (Avena sativa L.), triticale (Triticosecale rimpaui Wittm), wheat (Triticum aestivum L.), balansa clover (Trifolium michelianum Savi), berseem clover (Trifolium alexandrinum L.), maple pea (Pisum sativum L.), Persian clover (Trifolium resupinatum L. var. majus Boiss.), subterranean clover (Trifolium subterraneum L.), forage rape (Brassica napus L.), forage radish (Raphanus sativus L.), maize (Zea mays L.), Japanese millet [Echinochloa esculenta (A. Braun) H. Scholz], pearl millet [Cenchrus americanus (L.) Morrone], sorghum [Sorghum bicolor (L.) Moench], cow pea [Vigna unguiculata (L.) Walp.] and lablab [Lablab purpureus (L.) Sweet]. There was more than a 4-fold range in annual yield between forages, but the length of the growing season and season of growth made direct comparisons difficult. Under optimal irrigation, maize produced the highest mean yield of 29.0 t DM/ha in only 125 days, which was over three times greater than cow pea (9.2 t DM/ha) grown in the same season yet requiring 190 days. Of the cool season annuals, wheat had the highest mean yield of up to 20.6 t DM/ha in 230 days, which was more than three times the yield of the lowest yielding forage, subterranean clover, at only 6.5 t DM/ha in 215 days. The forages which require harvesting generally had higher yields within a growing period of similar length than those that were defoliated to reflect being ‘grazed’. Combining annual forages in an annual cycle (e.g. maize and wheat) had the potential to produce up to 47 t DM/ha. Deficit irrigation reduced annual yield of all warm season-grown forages ranging from 8% for sorghum up to 48% for maize. In contrast, annual yield reductions were generally smaller for cool season forages, there being no reduction for forage rape, subterranean clover or oats, but up to 35% for Persian clover. However, while yield is an important criterion for choosing dairy forages, it is only one factor in a complex system, and choice of forages must be considered on a whole-farm basis and include water use efficiency, nutritive value, cost of production and risk.

Effects of spring grazing on dryland perennial ryegrass/white clover dairy pastures. 2. Botanical composition, tiller, and plant densities

A 3-year experiment (September 1999–August 2002) in south-western Victoria investigated spring grazing impacts on botanical composition, tiller densities (perennial ryegrass, other-grasses, clover growing points, and broad-leaved weeds), and perennial ryegrass plant frequencies of a pasture of perennial ryegrass (Lolium perenne L.)–white clover (Trifolium repens L.) pasture. Spring grazing treatments, applied annually from September to November were based on ryegrass leaf development stage with high (HF), medium (MF), and low (LF) grazing frequency being 2-, 3-, and 4-leaf stage, respectively, and post-grazing height as the grazing intensity with high (HI), medium (MI), and low grazing intensity being 3, 5, and 8 cm, respectively. Five combinations were used: HFHI, LFHI, MFMI, HFLI, and LFLI. A sixth treatment, rapid grazing (RG), maintained pasture between 1500 and 1800 kg DM/ha by grazing weekly during spring and a seventh and eighth treatment, simulating forage conservation for early-cut silage (lock-up for 6–7 weeks; SIL) and late-cut hay (lock up for 11–12 weeks; HAY), were also included. Perennial ryegrass content remained stable in the RG and HFHI treatments, averaging 78 and 75% DM, respectively, and declined in all other treatments. For example, perennial ryegrass content in LFLI declined from 75% (September 1999) to 50% DM (August 2002). RG and HFHI resulted in a slight increase in other grass (e.g. Holcus lanatus and Poa annua) content over time. SIL, LFLI, LFHI, and MFMI resulted in a higher other-grass content than RG and HFHI. LFLI, LFHI, and HFLI resulted in a stable dead (litter) pasture content over time, while SIL, HAY, HFHI, and RG resulted in a decline in dead pasture content over time. For RG and HFHI spring treatments the decline in dead pasture content was greater than LFLI, LFHI, and HFLI spring grazing. Data for white clover and broad-leaved weeds (e.g. Rumex dumosus and Taraxacum officinale) were inconsistent and could not be statistically analysed. While perennial ryegrass tiller density declined over time, RG and HFHI spring grazing resulted in a higher perennial ryegrass tiller density than low and medium grazing frequency treatments, and forage conservation treatments. Over time, tiller density of other grass increased, with MFMI, SIL, and HAY resulting in a greater increase than HFHI and RG treatments. During the experiment, white clover growing point density declined, while broad-leaved weed tiller data were inconsistent and not analysed. In October 2001, perennial ryegrass plant frequencies ranged from 12 (HAY) to 27 (RG) plants/m2. RG resulted in a higher perennial ryegrass plant frequency than medium and low spring grazing frequencies, and forage conservation (HAY). At the end of the experiment (August 2002), perennial ryegrass frequencies ranged from 15 (HAY) to 45 (RG) plants/m2 with RG resulting in a higher perennial ryegrass plant density than all other treatments. HFHI grazing resulted in a higher plant frequency than LFLI, SIL, and HAY, and HFLI a higher plant frequency than SIL and HAY. RG and HFHI spring grazing favoured perennial ryegrass persistence as it maintained botanical composition and perennial ryegrass tiller and plant frequencies relative to low and medium spring grazing frequency or high spring grazing frequency coupled with low intensity grazing and pasture locked up for forage conservation.

Selective elimination of perennial ryegrass by activation of a pro-herbicide through engineering E. coli argE gene

Perennial ryegrass is widely used for overseeding dormant bermudagrass on golf courses and sports fields in Southeastern United States to provide green color and improved playability. Late spring and summer persistence of perennial ryegrass may decrease the quality of the bermudagrass turf and reduce its winter hardiness. To help solve this problem, we developed a strategy to activate a pro-herbicide within the transgenic perennial ryegrass plants and to cause self elimination of the plants. An E. coli argE gene was introduced into perennial ryegrass by the biolistic method, which resulted in four independently transformed green plants. The mRNA of argE gene was detected in three of the plants by RT-PCR. Perennial ryegrass plants expressing the argE transgene were selectively controlled upon application of a pro-herbicide, N-acetyl-l-phosphinothricin (or N-acetyl-PPT), since the N-acetylornithinase encoded by argE gene is able to convert N-acetyl-PPT to the herbicide phosphinothricin (PPT). The non-transgenic bermudagrass plants were unaffected by the treatment. This approach provides a means to selectively remove a group of transgenic plants without affecting other plants growing with them.

Short Communication. Effects of endophyte infection on dry matter yield, persistence and nutritive value of perennial ryegrass in Galicia (North-West Spain)

Dry matter yield, persistence and three parameters of nutritive value were determined in two perennial ryegrass (Lolium perenne L.) genotypes either infected with a lolitrem B-free fungal endophyte or not infected, over a fouryear period at two different locations in north-west Spain. The endophyte did not influence the productivity or persistence of perennial ryegrass in the four years of study. Insufficiently stressful conditions could explain these results. The nutritive value of the plants was not influenced by endophyte infection, except for organic matter digestibility and water-soluble carbohydrates on some occasions (P

Effect of defoliation height and redefoliation interval on regrowth and survival of perennial ryegrass (Lolium perenne) in subtropical dairy pastures

A cut plot study was undertaken on the subtropical north coast of New South Wales, Australia, to determine the effect of defoliation height and redefoliation interval on dry matter yield and persistence of perennial ryegrass (Lolium perenne L.) pastures. The pasture was established on 7 April 1998 and plots were irrigated to replace evapotranspiration loss. The study was a completely randomised block design with plots of 2 by 1 m and treatments replicated 3 times. In winter (commencing 13 July) plots were defoliated to 20, 50 or 120 mm stubble height and either not redefoliated or redefoliated at 3, 6 or 3 and 6 days after initial defoliation. In spring (commencing 28 October) plots were redefoliated as for winter but only to 50 mm stubble height. After imposition of the redefoliation treatments, the plots were allowed to regrow until the non-redefoliated treatments had regrown 3 new leaves per tiller (subsequently referred to as a regrowth cycle) and then again defoliated (regrowth cycle 1). Plots cut in winter were then halved with one half (A plots) continuing to be subject to the redefoliation treatment for 4 more regrowth cycles until regrowth cycle 1 in spring was completed on 24 November, while the other half (B plots) were a carryover comparison of redefoliation treatment in regrowth cycle 1. Both A and B plots continued to be subjected to the same defoliation height treatments as imposed in regrowth cycle 1. From 24 November to 30 March 1999, plots were defoliated at 50 mm height each time 3 new leaves per tiller had regrown.Plots defoliated to 20 or 50 mm height during regrowth cycle 1 in winter yielded 21% more dry matter than plots cut to 120 mm height while redefoliation at 6 or 3 and at 6 days produced 14% less dry matter than plots not redefoliated or redefoliated at 3 days. Continued redefoliation at 6 days (comparison within A plots) reduced dry matter yield by 63% compared with no redefoliation or redefoliation at 3 days, but only in plots defoliated to 20 or 50 mm height.Plant density in the autumn (March 1999) of the year after establishment was positively related to defoliation height over regrowth cycles 1–5 of the previous year (35, 55 or 77 plants/m2 for plots defoliated at 20, 50 or 120�mm, respectively). Plant density of plots not redefoliated or redefoliated at 3 days over regrowth cycles 1–5 was 63% higher (70 plants/m2) than for the other treatment combination (43 plants/m2) at P = 0.07 level of significance.Plants cut to 20 or 50 mm stubble height at the commencement of regrowth cycle 1 in winter had a stubble water-soluble carbohydrate content of 5.2%, decreasing to 2.3% at day 6 post-defoliation. The water-soluble carbohydrate content of plants cut to 120 mm were initially higher at 8% and fell to only 6.4% by day 6.The redefoliation treatments imposed in this study were designed to simulate the regrazing of regrowth shoots in an extended grazing bout at various defoliation heights. The results confirm the negative effects of redefoliation, at 6 days in the winter to spring period, on both dry matter yield and plant survival over the subsequent summer in the subtropics. In contrast to winter, redefoliation in late spring had no effect on dry matter yield or plant density. The results also indicate a compromise between the benefits of more lax grazing for persistence and harder grazing for pasture utilisation.

Selection for more persistent perennial ryegrass (Lolium perenne) cultivars for subtropical/warm temperate dairy regions of Australia

Three experiments were conducted in subtropical/warm temperate dairy regions of Australia to relate persistence of perennial ryegrass (Lolium perenne) to their response to temperature and defoliation. Experiment 1 was a small plot cutting study on a Krasnozem soil with 2 perennial ryegrass lines: LP31, a New Zealand Agriseeds Ltd experimental line; and Kangaroo Valley (KV), adapted to the south coast of New South Wales. They were defoliated at 1 (L) or 3 (3 L) leaves/tiller regrowth stage and at 20 or 60 mm stubble height. When defoliated at 3 L, LP31 was most productive (8839 v. 8481 kg DM/ha) and persistent (57 v. 49 plants/m2 surviving into the autumn of the second year) while the reverse was true at 1 L (5753 v. 6237 kg DM/ha and 27 and 54 plants/m2, respectively). In experiment 2, small plots were sown to 11 cultivars comprising the New Zealand Agriseeds Ltd experimental perennial ryegrass lines: F2 LP93045, F2 LP93026 (Dobson × Bronsyn), LP54, F2 LP92039 (Dobson × Jumbo), LP30 and the commercially available varieties: Bronsyn, Meridian, Dobson, Yatsyn1 and Impact. The plots were 'rotationally' grazed by Friesian heifers. Over the 25 months of this experiment Bronsyn was the most productive (7173 v. 5310 kg DM/ha) and persistent (17 v. 4 plants/m2 for Bronsyn and mean of the remainder, respectively) cultivar.In experiment 3, the 3 most persistent cultivars from experiment 2 (labelled 'Cas'), and 8 other cultivars, were grown as a mini-sward in a temperature-controlled glasshouse. The cultivars were grouped on the basis of persistence, origin and response to defoliation interval and temperature as follows: group 1 (persistent): Bronsyn, Bronsyn (Cas), F2 LP93026 (Dobson × Bronsyn) (Cas), Dobson; group 2 (persistent adaptive ecotype): Victorian; group 3 (not persistence): LP2551, Impact, F2 LP92039 (Cas); group 4: European. The treatments were 28/17°C (HT) or 21/10°C (LT) (day/night) temperature and 1 (1 L) or 3 (3 L) leaves/tiller defoliation interval. Yield (1.28 v. 0.77 g DM/plant) and water-soluble carbohydrate (WSC) content (127 v. 15 mg WSC/plant) were substantially higher in plants defoliated at 3 L compared with 1 L, respectively. The effect of temperature on yield was not significant but more WSC plant reserves accumulated (92 v. 60 mg/plant) at LT than HT. There was a significant (P<0.001) interaction between defoliation interval and cultivar group, with the cultivar, Victorian, being the highest yielding at a short defoliation interval (1.04 v. 0.71 g DM/plant for Victorian and the mean of the remaining cultivars, respectively) while group 1 cultivars (most persistent) were highest yielding at 3 L (1.45 v. 1.08 g DM/plant) and HT. In contrast, group 3 cultivars, were least productive at high temperatures, irrespective of defoliation interval.The results showed that the Australian adapted ecotypes Victorian and KV, which are not responsive to defoliation frequency, were only average yielding. In contrast, the newer cultivars such as Dobson and Bronsyn or crosses thereof are also persistent and are more productive but only when defoliated at an appropriate interval (3 leaves/tiller). In this group, growth was reduced at the higher temperature under frequent defoliation but promoted at infrequent defoliation. The more productive and persistent cultivars tended to have a higher content of WSC plant reserves.

The impact of defoliation frequency and nitrogen fertilizer application in spring on summer survival of perennial ryegrass under grazing in subtropical Australia

Abstract This field study investigated the effect of timing of nitrogen (N) fertilizer application in spring on the survival of grazed perennial ryegrass (Lolium perenne cv. Dobson and Yatsyn) over summer in a subtropical environment. There were five N fertilizer treatments: no applied N, 46 kg N ha−1 on 22 October or 22 November or 22 December, or on 22 October and again on 22 December. Water‐soluble carbohydrate (WSC) concentration of perennial ryegrass plants entering the summer was altered by varying defoliation frequency, with defoliation interval based on the number of leaves per tiller. Frequent defoliation was set at a regrowth level of one leaf per tiller and less frequent defoliation at a regrowth level of three leaves per tiller, over a total of two by three‐leaf per tiller regrowth periods. Application of N fertilizer was found to have no significant effect (P > 0·05) on survival of perennial ryegrass plants over summer. On the other hand, defoliation had a marked effect on perennial ryegrass persistence, with frequent defoliation decreasing ryegrass plant density (51 vs. 88 plants m−2; P < 0·001) and increasing the density of tropical weed grasses (99 vs. 73 plants m−2; P < 0·001) by autumn. Frequently defoliated plants had a lower stubble WSC content on a per plant basis than less frequently defoliated plants in spring (103 vs. 201 mg per plant; P < 0·001) and summer (59 vs. 101 mg per plant; P < 0·001). The lower WSC content was associated with a smaller root system in spring (1·50 vs. 2·14 g per plant; P < 0·001) and autumn (1·79 vs. 2·66 g per plant; P < 0·01), and this was reflected in 0·29 more plants being pulled from the soil by livestock between November 1996 and April 1997. Rhizoctonia fungus was associated with roots of pulled plants, but not with roots of seemingly healthy plants, indicating that this fungus may have a role in a weakened root system, which was more prone to sod pulling. Nitrogen applied in October and November resulted in a reduced WSC concentration, although the effect was restricted to 1 month after N application. The present study indicates that survival of perennial ryegrass plants over the summer in a subtropical region is prejudiced by frequent defoliation, which is associated with a lower WSC concentration and a shallower root system. Under grazing, sod pulling is a reflection of this weaker root system and contributes to plant mortality.