Leaf number as a criterion for determining defoliation time for Lolium perenne, 1. Effect of water-soluble carbohydrates and senescence

This study sought to define the optimum defoliation interval for Lolium perenne , with the maximum interval being determined by the onset of senescence, as reflected by the number of fully expanded leaves, and the minimum interval set by the replenishment of water-soluble carbohydrates (WSCs).
In a glasshouse set at 13°C/23°C night/day temperature and at a plant spacing of 94 m⁻² (3290 tillers m⁻²), the accumulation of dry matter against leaf number and days was exponential to the four-leaf stage of the regrowth cycle. Senescence commenced at the 3·5-leaf stage.
WSCs in roots, stubble and leaf showed a very significant linear relationship with leaf number. Levels of WSCs in leaves were restored to predefoliation values by the one-leaf stage, after which WSCs accumulated preferentially in the stubble, rising to 22% at the four-leaf stage.
Regrowth after 6 d was significantly greater for plants defoliated at the three-leaf stage than at the one-leaf stage, but this difference disappeared at the end of the regrowth cycle. This questions the importance of WSCs in determining the yield of ryegrass under normal rotational grazing management.
Regrowth at 6 d was related positively to stubble WSCs (r²= 0·66) and to stubble DM per tiller(r²=0·71)     

Effects of defoliation and fertilizers on root competition between Dactylis glomerata and Lolium perenne

Dactylis glomerata and Lolium perenne were grown in single-species stands and in mixed-species stands in boxes for 1 year. Plants were grown in paired rows in each box with full competition below ground, but aerial partitions prevented shoot competition. The rows were cut either frequently (six cuts) or infrequently (three cuts). In single-species stands, frequent defoliation reduced the root competitive ability of D. glomerata plants, when growing with infrequently defoliated plants, though this occurred only if no N fertilizer was applied. Frequent defoliation did not affect the root competitive ability of L. perenne plants, in single-species stands, whether or not N fertilizer was applied. In mixed-species stands, the root competitive ability of D. glomerata was always greater than that of L. perenne, though N fertilizer applications and frequent cutting both reduced the root competitive ability of D. glomerata relative to L. perenne. Mixtures of frequently cut and infrequently cut plants, in unfertilized single-species stands, always yielded more than the mean of the uniformly treated stands (frequently or infrequently cut); they usually yielded more than the highest-yielding uniformly treated stand. Mixtures of frequently and infrequently cut plants, in fertilized single-species stands, always yielded less than the mean of uniformly treated stands. Mixed-species stands usually yielded more than the mean yield of the component species, and sometimes yielded significantly more than the highest yielding component. This effect generally increased with time. Relative yield totals (RYT) were consistently greater than 1·0, in both single-species and mixed-species stands, when no N fertilizer was applied. RYT were greatest (1·2–1·6) when neither N nor P fertilizer was applied, and generally increased with time. The results are discussed in relation to the effects of cutting on root competition and the probable value of mixed-species stands.     

The effect of time of initial defoliation and height of defoliation on the productivity of perennial ryegrass swards

Over a 3-year period the productivity of perennial ryegrass ( Lolium perenne L., cv. S24) swards as influenced by variations in the time of initial defoliation and close (2·5 cm) and lax (8 cm) defoliation was studied. Treatments with initial defoliations in the early vegetative stage, stem elongation and flowering stages of growth gave higher annual yields than treatments in which the initial defoliation was taken at an intermediate stage of growth when the majority of the stem apices had just been elevated above the height of defoliation. Initial defoliation treatments which removed a high proportion of apical meristems while the yield at the initial defoliation was still low produced the lowest annual yield. Consistent lax defoliation reduced yield by 14·5% compared with continual close defoliation. However, taking an initial lax defoliation followed by subsequent close defoliations produced a slight yield advantage of 4·8% over consistent close defoliation. The results are discussed in relation to other research findings and the practical implications commented upon.     

The effect of defoliation upon yield, flowering and vegetative spread of Holcus lanatus growing with and without Lolium perenne

Plants of Holcus lanatus L. and Lolium perenne L. were grown in monocultures and in 50:50 mixtures and cut at three heights and at three frequencies during 24 weeks. The higher the H. lanatus plants were cut the greater was their harvested yield but height of cutting did not affect the yield of L. perenne. Reduction in the frequency of cutting increased the total harvested yield of both species in monoculture. In mixture, H. lanatus dominated L. perenne , especially with high and infrequent cutting. Stubble yields generally followed harvested yields.
In a second experiment, H. lanatus plants were cut sequentially in spring; plants cut in early June produced very few panicles in the regrowth.
In a third experiment the growth of decumbent tillers in late summer on spaced plants of H. lanatus produced a stoloniferous growth habit. The production of lateral shoots and roots on these stolons was measured in spring on plants undergoing various types of defoliation. Regular cutting of the parent plant increased the production of lateral shoots on stolons but did not affect the production of lateral roots.
The significance of these results is discussed in relation to the manipulation of swards containing these two species.     

Canopy height measurements and non‐destructive biomass estimation of Lolium perenne swards using UAV imagery

In perennial ryegrass breeding programmes, dry‐matter yield (DMY) of individual plots is monitored destructively at the different cuts or derived from non‐destructive canopy height measurements using devices like rising plate meters (RPM). These approaches both have constraints. Destructive sampling implies low temporal resolution, restraining the study of dry‐matter accumulation rates, while RPM measurements are influenced by the canopy structure and limit intra‐field variability identification. We present a phenotyping methodology, based on the use of an affordable RGB camera mounted on an unmanned aerial vehicle (UAV), to monitor the spatial and temporal evolution of canopy height and to estimate DMY. Weekly flights were carried out from April to October above a field comprising a diverse set of accessions. To test the capacity of UAV imagery to estimate canopy height, 8 ground control points and 28 artificial height references were placed at different locations. Accurate flights with an RMSE as low as 0.94 cm were achieved. In addition, canopy height was recorded using an RPM and destructive biomass samples were collected. Different models (linear, multiple linear, principal components, partial least squares regression and random forest) were used to predict DMY, and their performance was evaluated. The best estimations were obtained by combining variables including canopy height, vegetation indices and environmental data in a multiple linear regression (R² = .81). All models built using UAV data obtained a lower RMSE than the one using RPM data. The approach presented is a possibility for breeders to incorporate new information in their selection process.     

Growth of individual tillers and tillering rate of Lolium perenne and Bromus stamineus subjected to two defoliation frequencies in winter in Argentina

The aims of the experiment were to (i) test whether the higher leaf elongation rate per tiller (LER_T) of Bromus stamineus D. than Lolium perenne L. at moderately low temperatures was maintained at high defoliation frequencies and (ii) explore responses in tiller dynamics during the onset of the cool season in the south‐east of the humid Pampas region in Argentina. The following treatments were applied: defoliation frequency at the 3·0‐leaf stage (i.e. one‐leaf lifespan), which is considered optimal, and higher defoliation frequency at the 1·5‐leaf stage (i.e. half‐of‐a‐leaf lifespan). The higher defoliation frequency reduced leaf elongation rate in both the species but it did not affect the leaf appearance rate. This confirms previous studies on several C₃ grasses, suggesting a similar pattern of response. Changes in tiller size are proposed as a possible mechanism to explain such long‐term defoliation effects on leaf elongation rates. Responses in tiller production depended on the species considered. The higher defoliation frequency caused a reduction in site‐filling which led to lower tiller production rates in L. perenne but not in B. stamineus. Thus, B. stamineus maintained the advantage in LER_T over L. perenne and its tiller production was not affected when defoliated at frequencies higher than those considered optimal.     

Interaction between water-soluble carbohydrate reserves and defoliation severity on the regrowth of perennial ryegrass (Lolium perenne L.)-dominant swards

A field-study was undertaken in Hamilton, New Zealand to determine if there was an interaction between water-soluble carbohydrate (WSC) reserve content and defoliation severity on the regrowth of perennial ryegrass-dominant swards during winter. Perennial ryegrass plants with either low or high WSC content were obtained by varying the defoliation frequency. At the third defoliation at the one-leaf stage and at the first defoliation at the three-leaf stage (harvest H₁), swards were mown with a rotary lawnmower to residual stubble heights of 20, 40 or 60 mm. All swards were then allowed to regrow to the three-leaf stage before again defoliating to their treatment residual stubble heights (H₂). Frequently defoliated plants contained proportionately between 0·37 and 0·48 less WSC in the stubble after defoliation, depending on the severity of defoliation. There was no interaction between WSC content and defoliation severity for herbage regrowth between harvests H₁ and H₂. Herbage regrowth was lower from swards containing low WSC plants compared with high WSC plants (2279 vs. 2007 kg DM ha⁻¹). Furthermore, swards defoliated to 20 or 40 mm had greater herbage regrowth compared with those defoliated to 60 mm (2266, 2249 and 1914 kg DM ha⁻¹ for swards defoliated to residual stubble heights of 20, 40 and 60 mm, respectively). Regrowth of perennial ryegrass was positively correlated with post-defoliation stubble WSC content within defoliation severity treatment, implying that WSC contributed to the defoliation frequency-derived difference in herbage yield. However, the effect of defoliation severity on herbage regrowth was not associated with post-defoliation stubble WSC content.     

Sward height, structure and leaf extension rate of Lolium perenne pastures when grazed by overwintering barnacle geese

Abstract The grazing of agricultural pastures during winter and spring by geese is considered an important agricultural problem in parts of the U.K. This study describes the sward structure, leaf extension and senescence rates of Lolium perenne‐dominated pastures that are frequently grazed by barnacle geese (Branta leucopsis) during winter in South‐west Scotland, as well as the conducting of a field experiment that simulated grazing to investigate the effects of defoliation. Gross leaf extension and senescence rates were strongly related to temperature, daylength and average tiller size, resulting in positive values of net leaf extension rate per tiller for most of the winter. Total tiller length declined from November to January but increased from January to April. Sward height, however, declined consistently from October to April, suggesting that swards were becoming trampled by repeated visits by flocks of geese over this time. The structure of individual tillers was found to vary slightly over the winter, with tillers becoming more dominated by younger leaves towards the end of the winter. Experimental defoliation of tillers suggested that absolute leaf extension rates did not respond in an under‐ or over‐compensatory manner, even when tillers were nearly completely defoliated. The results suggested that sward structure and leaf extension rates are not unduly affected by repeated grazing by overwintering geese and that short‐term depletion and trampling are the main impacts.     

Nitrogen studies in Lolium perenne grown for seed I. Level of application

In field trials in 1971–73, perennial ryegrass cv. S23 and S24 were given up to 200 kg ha^?1 nitrogen (N) and dry weight, seed yields and seed yield components measured. Optimum levels of applied N ranged from 80 kg ha^?1, where livestock had grazed the crop in the establishment year or where residual N levels were about 70 kg ha^?1, to 120 kg ha^?1 where residual N was low. Application of more than 120 kg ha^?1 did not increase yields further because of increased lodging and increased production of vegetative tillers. Seed set was 37–55% in S24 and 25–29% in S23 and was decreased by lodging.     

Nitrogen studies in Lolium perenne grown for seed. II. Timing of nitrogen application

The effects of applying nitrogen at different growth stages to S24 and S23 perennial ryegrass grown for seed were investigated in a series of field experiments from 1971 to 1976. These varieties of ryegrass were found to be insensitive to timing of nitrogen application from apex initiation to the stage when ears first emerged. However, if nitrogen application was delayed until about 30% or more of the ears had emerged, yields were lower compared with earlier applications, this effect being significant when nitrogen was delayed until 70–80% ear emergence because of a decrease in both numbers of fertile tillers and number of seeds per unit area. No advantages were found for splitting nitrogen applications between apex initiation and ear emergence.     

Effect of Lolium perenne sward density on productivity under simulated and actual cattle grazing

The objective of this study was to quantify the effect of perennial ryegrass (Lolium perenne L.; PRG) sward density on seasonal and total DM yield under simulated grazing and animal grazing by cattle, and to assess the effectiveness of visually estimated ground scores (GSs) for predicting sward PRG density. The study incorporated five different seeding rates of PRG, each replicated three times, to simulate swards ranging in PRG density typical of different ages and conditions. There was no significant difference between defoliation managements for total DM yield, but sward PRG density had a significant effect on both the seasonal and total DM herbage yield under both systems. Under simulated grazing, total DM yield ranged from 10·7 to 12·0 t DM ha^?1 with increasing sward PRG density at a GS range of 1·70–4·28 (mean of 2 years’ data, P < 0·01). Under animal grazing, the yield range was from 10·3 to 12·2 t DM ha^?1 for a GS range of 1·50–3·39 (mean of 2 years’ data, P < 0·01). The largest differences in DM yield occurred during the spring period. The relationship between sward DM yield and GS was significant (P < 0·001) for both simulated and animal‐grazed swards. Each unit increase in midseason GS (June) related to an average yield increase of 350 kg DM ha^?1 under simulated grazing and a 721 kg DM ha^?1 increase under cattle grazing. Every unit increase in the GS at the end of the grazing season (December) was associated with a 460 or 1194 kg DM ha^?1 increase under simulated and animal grazing, respectively. These results show that visual estimates of density were an effective tool in describing PRG density and that this could be related to DM yield potential. Further investigations may provide a threshold value below which the renewal of swards could be advised based on a visual GS of PRG.     

Nitrogen studies in Lolium perenne grown for seed. IV. Response of amenity types and influence of a growth regulator

In field trials in 1979–81, perennial ryegrass cultivars Royal and Majestic (amenity) and Morenne (agricultural) produced maximum seed yields at levels of applied N ranging from 40 kg ha⁻¹ to 160 kg ha⁻¹. Available soil N levels were estimated at 55 kg ha⁻¹; hence maximum seed yields were obtained at total nitrogen levels of 95–135 kg ha⁻¹ in Royal, 95–215 kg ha⁻¹ in Morenne, and 175–215 kg ha⁻¹ in Majestic.
Applied N at rates above 120 kg ha⁻¹ either reduced or did not significantly increase seed yield, decreased seed numbers per unit area and decreased spikelets per tiller and seeds per spikelet.
The use of a growth regulator increased seed yields by preventing lodging, but did so irrespective of nitrogen application rate. It is suggested that failure to increase seed yield at high N rates is a result not of poor pollination because of lodging, but seed abortion as a consequence of competition for assimilate supply by secondary vegetative tillers.     

The effect of frequency and height of defoliation on the production and persistence of 'Grasslands Matua' prairie grass

The performance of prairie grass ( Bromus willdenowii Kunth) cv. Grasslands Matua was examined under mowing at five defoliation intervals (10, 20, 30, 40 and 50 d) and two defoliation heights (3 cm and 8 cm). Annual and seasonal production of both the total herbage and of Matua, and the proportion of Matua in the sward, increased with less frequent defoliation. To a lesser extent, increasing the height of defoliation increased dry matter yield. Matua tiller numbers were increased by less frequent defoliation and were greater under the 8 cm than the 3 cm defoliation height. To increase prairie grass production and persistence, rest intervals between grazings of 40 to 50 d are recommended, or alternatively, a management involving silage or hay cutting offers scope.     

In vitro fermentation patterns and methane production as influenced by cultivar and season of harvest of Lolium perenne L.

In some European countries, the majority of annual enteric methane (CH₄) emissions by ruminants occur at pasture – a direct result of the predominance of grazing within ruminant production systems. However, there are only limited data available as to the effect of perennial ryegrass cultivar and season of harvest on CH₄ production. Using the in vitro gas production technique, the effect of perennial ryegrass cultivar on fermentation characteristics and CH₄ production was determined (Experiment 1) and the persistence of these traits throughout the growing season for two cultivars, identified from Experiment 1 as having either a high or low methanogenic potential, was examined (Experiment 2). In Experiment 1, organic matter (OM) digestibility and cumulative total gas production profiles were unaffected by cultivar but, with regard to the kinetics of CH₄ production, the asymptote value (A), cumulative CH₄ yield at 72 h, and the fractional rate (μ) of CH₄ production at both time of 0·5A(T)(μCH₄T) and at 48 h (μCH₄48h) were significantly (P < 0·05) different. The amount of digested OM, as a proportion of cumulative CH₄ production (DigOM/CH₄) at 24 and 72 h after commencement of inoculation, revealed that the amount of substrate required to produce 1 ml of CH₄ also differed significantly between cultivars (P < 0·01). In Experiment 2, regrowth number significantly modified the majority of measured samples (P < 0·01); cultivar effects were limited to the lag phase of the cumulative CH₄ production curve and DigOM/CH₄ at 8 h only (P < 0·05). These results suggest that differences exist between cultivars in how OM is partitioned following microbial fermentation and that these differences demonstrate persistency throughout the growing season. In the course of time it may be possible to exploit these differences through cultivar selection and plant breeding programmes, and thereby reduce enteric CH₄ emissions within pastoral production systems.     

Effect of defoliation management, based on leaf stage, on perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under dryland conditions. 2. Nutritive value

A field experiment was undertaken between April 2003 and May 2004 in southern Tasmania, Australia, to quantify and compare changes in the nutritive value of perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under a defoliation regime based on stage of leaf regrowth. Defoliation interval was based on the time taken for two, three or four leaves per tiller to fully expand. At every defoliation event, samples were collected and analysed for acid‐detergent fibre (ADF), neutral‐detergent fibre (NDF) and total nitrogen (N) concentrations and to estimate metabolizable energy (ME) and digestible dry matter (DDM) concentrations. Amounts of crude protein (CP) and metabolizable energy (MJ) per hectare values were subsequently calculated. There was a significantly lower (P < 0·001) NDF concentration for perennial ryegrass compared with prairie grass and cocksfoot, and a significantly lower (P < 0·001) ADF concentration for cocksfoot compared with prairie grass and perennial ryegrass, regardless of defoliation interval. The CP concentration of cocksfoot was significantly greater (P < 0·001) compared with the CP concentrations of prairie grass and perennial ryegrass. The estimated ME concentrations in cocksfoot were high enough to satisfy the requirements of a lactating dairy cow, with defoliation at or before the four‐leaf stage maintaining ME concentrations between 10·7 and 10·9 MJ kg^?1 DM, and minimizing reproductive plant development. The ME concentrations of prairie grass (10·2–10·4 MJ kg^?1 DM) were significantly lower (P < 0·001) than for cocksfoot (as above) and perennial ryegrass (11·4–11·6 MJ kg^?1 DM) but a higher DM production per hectare resulted in prairie grass providing the greatest amounts of ME ha^?1.     

Nitrogen studies in Lolium perenne grown for seed III. The effect of nitrogen and water stress

The effects of water and nitrogen (N) availabilities and their possible interactions on the seed yield and yield components of S23 perennial ryegrass grown in pots in the glasshouse were investigated. Increasing the N fertilizer from 0 to 5 g per pot more than doubled the seed yield but no further increase in seed yield was found by increasing N fertilizer from 5 to 10 g per pot. The main effect of increasing water availability was to increase both seed and straw yield. When N had been applied, accumulated evapotranspiration was linearly related to seed and straw yield. The component of yield having the greatest effect on yield was the number of fertile tillers and, although both N and water availability affected this component, N had the larger effect. Implications of these responses are discussed in relation to the potential yield of the crop and to the field situation.     

Winter hardiness in Lolium multiflorum Lam. II. The effect of defoliation and nitrogen application as assessed by low temperature response in a controlled environment

The effect of defoliation and nitrogen application on the cold tolerance of four varieties of Italian ryegrass was assessed using controlled environment chambers. Both defoliation and nitrogen fertilizer markedly reduced overall cold tolerance and this closely matched changes in winter hardiness induced by similar treatments applied to the same varieties in a field experiment. However, the relative response of individual varieties differed from that found under field conditions. Thus, RvP showed high levels of tolerance to low temperatures in the controlled environments and was also winter-hardy under field tests; by contrast Bb 1430, although previously shown to be winter hardy in the field, exhibited low tolerance of cold stress in growth chambers. Thus, results obtained in controlled environment tests cannot be entirely equated to winter hardiness in the field. Water-soluble carbohydrate (WSC) levels were reduced by both defoliation and nitrogen application and there were significant overall differences between varieties. It was not possible, however, to detect any clear relationship between these differences in WSC levels and cold tolerance. The significance of these results in relation to the use of controlled environment chambers for selecting for improved winter hardiness is discussed.     

Variation in inflorescence characters and inflorescence development in ecotypes and cultivars of Lolium perenne L.

A sufficient database of seed yield components is the prerequisite to predict which component contributes most to the seed yield complex and to dissect the biology of the complex quantitative trait seed yield. Phenotypic variation of eleven vegetative and reproductive traits was characterized for 2481 individuals from fifty Lolium perenne L. (perennial ryegrass) ecotypes and cultivars. Considerable levels of among‐ and within‐population variation were found across several inflorescence characters. Principal component and canonical variate analysis separated ecotypes from cultivars, and cultivars generally had later dates of ear emergence, better spring and summer growth, longer rachis length and more spikelets per spike than ecotypes. Strong positive relationships were seen between inflorescence characters using both correlation and regression analyses. The strong relationship between rachis length and other inflorescence characters suggested that rachis length could be used as a performance predictor for several other characters of the spike. This phenotypic study has helped to determine basic patterns of morphological diversity and correlations between characters. It is discussed in which way further developmental genetic studies can be directed.     

Interactions between leaf lifespan and defoliation frequency in temperate and tropical pastures: a review

In continuously stocked swards or pastures the frequency at which individual tillers and individual leaves are defoliated by ruminant livestock, relative to leaf lifespan of the grass species within the sward, determines the proportion of each leaf defoliated before senescence, and hence the efficiency of harvesting of herbage. In this paper, sets of data obtained in a range of climatic conditions and with a range of grass species are used in order to document this relationship. It is shown that the frequency of defoliation of individual tillers or individual leaves is closely linked to the average stocking density used within a period of time for maintaining a steady state sward or pasture height, herbage mass or leaf area index. Consequently, any decrease in herbage growth rate should lead to a decrease in the efficiency of harvesting of herbage and then to a more than proportional decrease in total herbage consumption by ruminant livestock. These effects will be more important for grass species having short leaf lifespan than for species with long lifespan. In rotational stocking, the link between herbage growth rate and frequency of defoliation of leaves can be broken by controlling the grazing interval, so any decrease in herbage growth would not be systematically associated with a decrease in efficiency of harvesting of herbage. Rotational stocking should be more efficient than continuous stocking in low herbage production conditions, while in high herbage production systems rotational and continuous stocking would have similar efficiency. The implications of these conclusions for the management of swards and pastures to meet different objectives are discussed briefly.     

Effects of Neotyphodium endophytes on growth, reproduction and drought-stress tolerance of three Lolium perenne L. genotypes

Three Lolium perenne L. genotypes collected from different natural habitats were tested for the effects of their fungal endophyte Neotyphodium spp. on plant growth and seed yield. Half the clones of the originally infected plants were subjected to fungicide treatment to eradicate the endophytes. In an experiment, the clones were planted separately into pots and were either watered adequately or subjected to drought stress. In the genotype collected from a dry site, the endophyte infection reduced plant growth at an adequate water supply, but increased regrowth under drought. In the genotype from a periodically either flooded or dry site, endophyte infection significantly promoted the development of reproductive tillers and seed production (effects which are associated with adaptation to drought). In contrast, the genotype that originated from a wet site showed higher sensitivity to drought stress when endophyte infection was present. The results suggest that environmental conditions in the original habitat of the plants may influence the symbiotic interaction between plant and fungus, probably through natural selection. However, endophyte‐induced increases in root dry weight and root/shoot ratio were recorded for all three genotypes. These features could be beneficial for plant persistence, especially on sites where water is the growth‐limiting factor.