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.     

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.     

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 use of growth regulator RSW0411 in seed crops of Lolium perenne L.

Field trials were conducted in 1985 and 1986 to assess the effects of the growth regulator RSW0411 on a Lolium perenne L. (perennial ryegrass) seed crop. Applications were made at spikelet and floret initiation, and at 1, 2, 3 and 4 kg active ingredient ha⁻¹.
Seed yield increases in 1985 were associated with increased reproductive tiller numbers and seed numbers, but in 1986 there were no seed yield responses.
Lodging was less severe in 1986, and there was less secondary filtering during seed maturation. In 1985, fertile tiller numbers were lower in control plots at harvest. These results are discussed in relation to the seasonal disparity in seed yield response.
RSW0411 application significantly decreased culm lengths by shortening the basal internodes, and this effect was greater with higher application rates. Stem width was increased in 1985 at the base and middle of the stem, and earlier applications increased the basal width by more than later applications.
Germination was not affected by RSW0411 treatment, except when applied at 4 kg active ingredient ha⁻¹ in 1985, when there was a small decrease. This was related to a low 1000-seed weight, and is discussed in relation to seed maturity at harvest.     

The effect of lodging on 14C-assimilate distribution after anthesis in Lolium perenne, CV. S24, grown for seed

Field experiments in 1981 and 1981 examined assimilate distribution in lodged and non-lodged plots of perennial ryegrass ( Lolium perenne) , cv. S24, grown for seed. Lodging was prevented either mechanically (1982 only) or chemically, by application of paclobutrazol (PP333) at 2 0 kg a.i. ha^-1. For each treatment, main-tiller ears, stems and leaves and subtending vegetative tillers were fed with ¹⁴CO₂ at 24 and 17 days after anthesis in 1981 and 1982, respectively, and the pattern of ¹⁴C-assimilate export from each fed part was determined.
Prevention of lodging increased assimilate movement to the ear from the flag leaf, although movement from main-tiller leaves was primarily downwards to vegetative tillers. Assimilate movement to the stem was also increased because the cessation of stem elongation was delayed, especially where lodging was prevented by PP333. Both increases were at the expense of the tillers, although their number was not reduced in non-lodged plots. Possible reasons for these changes in assimilate distribution are discussed.     

The effect of the growth regulator paclobutrazol (PP333) on the growth, development and yield of Lolium perenne grown for seed

Application at spikelet initiation of the growth retardant paclobutrazol (PP333) at a rate of 2.0 kg a.i. ha⁻¹ increased the seed yield of perennial ryegrass cv. S24 from 139 to 180 g m⁻² in 1981, and from 111 to 256 g m⁻² in 1982. Yield increases were associated with an increased production of fertile tillers in both years and with an increased number of seeds per spikelet in 1982. Other yield components were not changed. Seed yield increased with increasing PP333 application rate in both years. No significant yield difference was recorded between application at spikelet and floret initiation in 1981.
Lodging was prevented completely by the 2.0-kg rate, delayed until after anthesis by the 1.0-kg rate and began before anthesis with the 0.5-kg rate. PP333 reduced stem internode length and strengthened the base of the stem; total stem dry matter (DM) was reduced, but root DM accumulation was increased at all rooting depths. Leaf area duration was significantly increased in both years.
Vegetative regrowth after seed harvest was not significantly reduced by PP333 application, but soil residual properties were demonstrated.     

Dalapon resistance in Lolium perenne populations

The resistance often early, ten medium late and ten late flowering ryegrass populations to two rates of dalapon (2.8 and 5.6 kg ha^-1 acid equivalent) was measured in a box experiment. There was no difference in the mean effect of dalapon on the maturity groups at the time of greatest yield reduction, but the recovery of the late flowering population was, on average, better than that of the medium late group. There was a range of reaction to herbicide within all three maturity groups and, in general, the high yielding populations without dalapon were the most resistant, but there were exceptions. Assessment at 2.8 kg ha^-1 acid equivalent gave a similar ranking order to that using twice the amount of dalapon. The results of the current box experiment with seedlings were consistent with those obtained in the field at another location (Faulkner, 1974) for the eleven cultivars common to both trials. The resistance of a permanent pasture population was much lower than that of some cuttivars.     

Effect of temperature regime on germination of seed of perennial ryegrass (Lolium perenne)

Perennial ryegrass ( Lolium perenne L.) is one of the most valuable temperate pasture grasses in the world. Understanding seed germination in response to temperature can help determine its optimal seeding times. Germination tests for two cultivars of perennial ryegrass (cv. 'Turfstar' and cv. 'Transtar') were conducted by applying thirty-six constant and alternating temperature regimes, ranging from 5 to 40°C (16 h night/8 h day). Responses in germination rate to these temperature regimes were then used to construct a quadratic response surface, giving estimated germination rates with confidence intervals at P  ≤   0·05 for both cultivars. Optimum germination rate occurred over a range of regimes: 15/25, 20/25, 20/30 and 25/30°C. Furthermore, a wide range in diurnal alternating temperatures resulted in maximum seed germination rate for cv. 'Transtar', while no constant temperature regime supported maximum germination rate for cv. 'Turfstar'. A temperature-dependent germination rate function for perennial ryegrass was developed which could be used in the future to predict location-specific optimum seeding times when national or regional monthly temperature data are available.     

A new descriptive scale for early reproductive development in Lolium perenne L.

Early reproductive development in Lolium perenne L. has been widely used for defining growth stages in spring, and this has been useful in managing seed crops and in trials involving the use of growth retardants.
A numerical scale for apical development based on morphological criteria, has been successfully used in research. The scale identifies eleven clearly recognizable stages of apical development, from the vegetative apex through to the immature, but completely-formed spike. It is intended that the key should be used to identify consistantly precise stages in apical development.     

Sward characteristics important for intake in six Lolium perenne varieties

An experiment was conducted to determine the genetic variation among diploid perennial ryegrass (Lolium perenne L.) varieties for sward structural characteristics considered to be important for intake by cattle. Assessments were made between June and September in 2000 and 2001. Six varieties (Abergold, Respect, Agri, Herbie, Barezane and Barnhem) were subjected to a cutting experiment where swards were cut after 3 to 4 weeks of regrowth during the growing season. The variables, measured in three 2‐week periods, were herbage mass of dry matter (DM), sward surface height (SSH), bulk density, proportion of green leaf, tiller density, tiller weight, extended tiller height, length of sheath and length of leaf blade. Significant differences among varieties were found in both years for herbage mass of DM, SSH, bulk density, proportion of green leaf, tiller density, tiller weight and length of sheath. The results show that there is significant genetic variation among diploid perennial ryegrass varieties for sward characteristics important for intake during grazing.     

The response of a perennial ryegrass (Lolium perenne L.) seed crop to nitrogen fertilizer application in the absence of moisture stress

Responses of perennial ryegrass (Lolium perenne L.) to nitrogen (N) fertilizer application rates and timings vary widely, because water is often limiting. Yield response to N fertilizer application during autumn, late‐winter and spring, and the associated efficiency of use of these inputs, was assessed under conditions of non‐limiting soil moisture during two, one‐year lysimeter studies in Canterbury, New Zealand. There were significant (P < 0·05) increases in seed and herbage yields with increasing N fertilizer application. Seed yields differed with year; greatest yields were 300 g m^?2 in 1996 and 450 g m^?2 in 1997. Seed head numbers (r²=0·77), seeds head^?1 (r²=0·92) and herbage yield (r²=0·92) were the major determinants of seed yield in both years. Irrigation required to maintain the soil between 70% and 90% of field capacity was directly related (r²=0·94 and 0·99 in 1996 and 1997 respectively) to increases in herbage yield. Seed yield, seed quality (thousand seed weight and percentage of seed > 1·85 mg), efficiency of water use, efficiency of N fertilizer use and apparent N fertilizer recovery were greatest when N fertilizer was applied at a rate of 50 kg N ha^?1, 50 or 100 kg N ha^?1 and 150 kg N ha^?1 in autumn, late‐winter and spring respectively; further increases in spring N fertilizer stimulated vegetative growth, but not seed yield. As a management strategy, applying N fertilizer to match the N requirements of the crop during the reproductive stage of growth will result in high yields of high quality seed while minimizing environmental impact.     

The effect of light intensity after anthesis on dry matter distribution and seed yield of Lolium perenne L.

The effect of light intensity after onset of anthesis on dry matter distribution, water soluble carbohydrate (WSC) concentration and seed filling in Lolium perenne was investigated in a pot experiment. Spaced plants of five clones were brought to flowering and exposed to four light intensities (24%, 57%, 100%, 115% of natural light) from 7 days after onset of anthesis onwards. The two oldest flowering tillers (i.e. the main and the first tiller) were separated from the rest of the plant and dissected after a seed-filling period of 450°Cd (temperature sum counting from 7 days after onset of anthesis). Their stem dry weight and WSC concentration were reduced at the lowest light intensity. WSC amount was more reduced in the first, younger, tiller. Seed yield per ear of the main tiller was reduced by 14% because seed set and average seed weight were lower at the 24% light intensity. Seed yield and seed number per ear of the first tiller were lowered by 21% and 17%, respectively, at the 24% light intensity, but average seed weight was not. The relative contribution of the seeds to total tiller weight was about 20% and was similar for both tillers and all light intensities. WSC concentration and WSC amount in the stem + rachis were reduced only at 24% light in the main tiller and at 24% and 57% light in the first tiller. It is inferred that seed yield was not limited by assimilate availability, but by the ability of the seeds to utilize fully the abundantly available reserves in the stem. The tiller can support seed yield under a wide range of tight intensities.     

Dry matter and quality of herbage harvested from Holcus lanatus and Lolium perenne grown in monocultures and in mixtures

The herbage dry matter (DM) harvested, N response and herbage quality of monocultures and mixtures of Holcus lanatus (local ecotype) and Lolium perenne (cv. S24) were compared in a field experiment. The species were seeded in the proportions 100:0, 75:25, 50:50, 25:75 and 0: 100; three rates of N were applied (150, 300 and 450 kg ha⁻¹) and five or six cuts were taken in each of four harvest years.
H. lanatus established poorly in the seeding year and in the first full harvest year L. perenne contributed 1, 54, 76, 89 and 99% of the total herbage DM harvested from the five sward types (mean of N treatments). Only a small decline in the L. perenne content of the swards occurred during the experiment.
Total amounts of herbage harvested were significantly lower for H. lanatus monoculture than for the other sward types in three of the four harvest years However, L perenne monoculture yielded significantly more total DM than mixtures with H lanatus in only one of the four harvest years. The five sward types did not differ overall in response to N fertilization. Nitrogen, phosphate and potassium content of the herbage was greatest for H. lanatus monoculture and decreased with increasing proportions of L perenne present in the mixtures.
Thus the presence of a high proportion of H. lanatus in mixture with L. perenne cv. S24 had     

Shoot characteristics of Trifolium repens grown in association with Lolium perenne or Holcus lanatus in pastures grazed by sheep

The morphological characteristics of Trifolium repens, grown in association with either Lolium perenne or Holcus lanatus and grazed by sheep to maintain sward surface heights of 3 cm, 5 cm and 10 cm, were measured. The lamina area, petiole length, internode length and internode weight of T. repens were significantly greater when H. lanatus was the companion grass than when L. perenne was the companion grass. All of these characteristics, together with the number of laminae per stolon, were also greater in the taller swards than in the shorter swards. The number of branches on each shoot did not vary significantly with either companion species or sward height treatment. Except for the effects of the treatments on the number of branches, the results are generally consistent with the known effects of variation in foliar shading on the morphology of T. repens.     

黑麦草生产能力及其抗热性评价

综述了黑麦草农艺性状及营养成分两方面的生产能力及差异,总结了黑麦草的育种方法,指出了高温胁迫对黑麦草的危害以及黑麦草抗热性的鉴定方法,提出了今后黑麦草抗热性育种的研究方向。     

Priority for allocation of water-soluble carbohydrate reserves during regrowth of Lolium perenne

A glasshouse study was undertaken to determine the priority within the perennial ryegrass (Lolium perenne L.) plant for leaf and root growth and daughter tiller initiation after defoliation, in relation to various levels of water-soluble carbohydrate (WSC) reserves at defoliation. Individual plants were arranged in mini-swards, and underwent varying defoliation frequencies and ambient temperatures before defoliation, and harvest heights at defoliation, to obtain a gradient of WSC content at H₁, the date when all plants were defoliated. Defoliation interval consisted of defoliating either three times at the one new leaf tiller^–1 stage (1-leaf stage) of regrowth, or once only at the 3-leaf stage, up to H₁, while night temperature in the week prior to H₁ was altered from 15°C to either 8 or 20°C. At H₁, plants were defoliated to a stubble height of either 20 or 50 mm. Plants were subsequently destructively harvested at days 4, 6, 8, 12, 18 and 27. Leaf and root extension and tiller dynamics were also measured. On a regrowth timescale, tiller initiation was most sensitive, root regrowth moderately sensitive, and leaf regrowth relatively insensitive to a decrease in WSC. The time of daughter tiller initiation also coincided with replenishment of stubble WSC levels. In contrast to this sequence of regrowth events following defoliation, the quantitative effects on growth were different, with elongation and survival of roots most affected by reduced WSC levels. A 30-fold difference in stubble WSC at H₁ between high and low WSC plants (1·52 vs. 0·05 mg tiller^–1) produced only a 4-fold increase in leaf dry matter (DM) after 27 d (2·2 vs. 0·6 g plant^?1), while tiller number plant^?1 increased 6-fold (138 vs. 23% increase in tiller number from H₁). Root elongation rate was 59 times higher in the high than in the low WSC plants (1·18 vs. 0·02 mm d^?1). From a pasture management perspective, the study confirms that defoliation, coinciding with the 3-leaf stage of regrowth and around a stubble height of 50 mm, optimizes persistence and productivity of perennial ryegrass. By allowing more rapid replenishment of WSC reserves, this optimal defoliation strategy enables a greater proportion of WSC to be allocated to maintain a more active root system, and promotes tillering, compared with more frequent and close defoliation.     

Dalapon resistance at an early seedling stage in Lolium perenne

The inhibitory effect of the herbicide dalapon on germination and shoot elongation was evaluated in two perennial ryegrass cultivars, Melino RvP and Cropper. These cultivars had been shown to be dalapon resistant and susceptible, respectively, in a previous comparison of 14-week-old plants. Dalapon (10^-2 and 10^-3 m) significantly reduced rates of germination and shoot elongation to the same extent in both cultivars. It is suggested that the effects of dalapon on germination and shoot elongation during the first 9 days of development are not indicative of levels of resistance in more mature plants.     

A comparison of the herbage productivity of Bromus wildenowii cv. Grasslands Matua with four cultivars of Lolium perenne when grown in association with Trifolium repens

In a small-plot trial five grass varieties bromegrass cv. Grasslands Matua, perennial ryegrass CVS. Melle (diploid) and Bastion, Condesa and Meltra (tetraploid) were established as grass/white clover swards with white clover cv. Menna. Productivity was measured under 6-weekIy cutting both without N fertilizer (N_o) and with 100 kg N ha^?1 applied in spring (N₁₀₀) Evaluation was made over 2 harvest years, 1986–87. Total mean annual production of herbage dry matter (DM) in the first harvest year at No and N_o was 5·07 t ha^?1 and 6·93 t ha^?1 respectively. In year 2, corresponding values were 11·81 and 12·67 t ha^?1. In year 1, Matua swards at N_o and N₁₀₀ yielded 5·08 and 6·65 t DM ha^?1 compared with 507 and 70 t DM ha^?1 for the mean of the four ryegrass varieties. In year 2, corresponding values were 12·90 and 12·29 for Matua and 11·54 and 12·78 for the four ryegrasses. In year 1, the digestable organic matter in the dry matter (DOMD) of the Matua swards was lower than that of Melle, Bastion and Condesa at N_O, particularly at the first cut. In year 2, differences in DOMD between treatments and varieties were not significant. The proportion of white clover was found to be higher in the N_o than the N₁₀₀ treatment, and also higher in year 2 in most treatments. For the _No treatment Matua swards had the highest proportion of white clover in year 1 (32% compared with 24% for the mean of the ryegrass varieties) but the lowest proportion in year 2 (27% compared with 60% for the ryegrasses). For the N_o treatment in year 1 clover production was also 43% higher, on average, from the tetraploid treatments than with Melle as the companion grass; for this comparison in year 2 the differences were not significant. It is concluded that Matua bromegrass/white clover swards receiving no N fertilizer may have a good potential under cutting management. However, the evidence from this trial is that in the second year the proportion of white clover is lower with Matua swards than with perennial ryegrass as the companion grass.     

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.