The effects of sowing date and cutting stage on grain yield, biomass and leaf area were analysed in three spring triticale genotypes (× Triticosecale Wittmack) grown at three different sites in Spain during 1990/91. Results indicated that the most appropriate sowing date for grain yield in these environments seemed to be from the last 10 days in November to mid-December. Cutting reduced grain yield, biomass and leaf area at anthesis, and these decreases were greater in a drier environment (the only exception being cutting at Zadoks growth stage (GS)31 at Lleida), and when the cutting was done at GS31 rather than GS30. The significant relationships found between the percentage loss in grain yield and biomass and leaf area at anthesis after cutting suggest that genotypes intended for grain and forage production need to be able to regenerate leaf area rapidly after cutting.

Maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) were grown in five seasons, beginning in the long rains 1990 and ending in the short rains 1992, at Kiboko, Kenya under a range of different management conditions (N fertilization, irrigation, population density and intercropping). Seed weight was plotted against total dry weight to determine harvest index for both crops. For bean the intercept of this relationship for each experiment, with one exception, was not significantly different from zero, so that the slopes of the regressions were the harvest indices. Harvest indices for bean varied more between seasons (0·38–00·85) than from the effects of management practices (00·53–0·71). Over all seasons and treatments, the index for bean did not vary systematically with crop weight, and averaged 0·50. By contrast, a similar analysis for maize over all seasons and treatments, showed that the harvest index varied with crop dry weight, approaching an asymptotic value as dry weight increased. The regression intercepts for the different experiments were significantly different from each other, and in three cases differed significantly from zero. Therefore, although the slopes for the different experiments were parallel, they did not always represent the harvest index.

Field trials in commercial cereal crops were carried out over three growing seasons between 1988 and 1991 on farmland near Basingstoke, Hampshire to monitor the effects of reduced agrochemical use on crop quality. The lack of highly competitive weeds on the study sites gave little benefit in yield from the use of herbicide. In some cases no weed control or half rate applications gave significantly better yields than the full recommended rate. Herbicide applied at the full recommended rate significantly increased grain N in two of the experiments, despite no notable yield benefit from weed control. Grain N was the only aspect of grain quality to show a consistent decline with even moderate reductions in N application rate.

Wheat and sunflower plants were grown in a temperature-controlled glasshouse in Melbourne, Australia (37° 50′ S, 145° 00′ E), from 9 August to 2 October 1991, in cylinders containing two soils (Walpeup loamy sand (LS) and Gombalin clay loam (CL)) of low and moderate N status, respectively. Nitrogen fertilizer was applied by immersion of leaves in 0·18 M urea solution (10·5 atom% 15N).

Plants were N-deficient in the Walpeup LS but not in the Gombalin CL soils. Both species had higher root: shoot ratios, and higher proportions of foliar-absorbed N were transferred to the roots, in the Walpeup LS plants. Plant N derived from the fertilizer and root or shoot dry matter were significantly correlated only when plants were N-deficient.

In the Walpeup LS soil, N-fertilized wheat harvested 33 days after sowing (DAS) took up significantly less soil N compared with unfertilized plants, whereas significantly more soil N was taken up by N-fertilized sunflower compared with unfertilized plants harvested at 54 DAS. The fertilizerinduced response in uptake of soil N was directly related to the observed response in production of root biomass for both species. The different responses were related to the severity of the N deficiency and the limited effectiveness of foliar applications of urea in ameliorating the deficiency.

In a 14-year experiment conducted at Athalassa in the central plain of Cyprus, phosphorus was applied (0, 30 or 60 kg P/ha) annually over the first 5-year period to rainfed barley continually grown and cut for hay at the milk stage of the grain. The bicarbonate-extractable P content in the surface soil was 4 mg/kg at the start and increased to 16 and 25 mg/kg after the five annual applications of 30 and 60 kg P/ha, respectively. The residual effect of P was monitored in the following seven crop seasons, by the end of which soil P had dropped to below the recognised 6 mg/kg threshold value for response to P. The application of P was resumed in the last two experimental seasons (1992/93 and 1993/94). In two cropping seasons, rainfall was < 140 mm and no harvestable yield was obtained. In another two seasons, in which there was adequate rainfall in December and January, there was no response to P, but in the other seasons 30 kg P/ha was sufficient for maximum yield. Concentration of P in the dry matter (DM) harvested increased in proportion to the P applied.

A P balance sheet made after the first five P applications and taking into account the amount of P removed in the DM and the increase in soil bicarbonate-extractable P indicated that 29 and 26 % of the P applied with the 30 and 60 kg P/ha rates, respectively, was accounted for.

The data indicate that the established threshold value of 6 mg P/kg is valid. The soil tested 180 mg/kg exchangeable K. but application of 240 or 480 kg K/ha did not increase yield.

The influence of different drying conditions on the chemical composition, physical properties, in vitro organic matter degradability and fermentation kinetics of forages was investigated using young and old grass (Lolium perenne) samples (harvested on 15 June and 9 July 1992 at Lelystad, The Netherlands) and young and old maize (Zea mays cv. Scana) stem samples (harvested on 19 August and 30 September 1991 at Lelystad). The samples were either freeze-dried with a maximum sample temperature of 10 °C, dried in a vacuum at 20 °C or air-dried at 30, 50, 70 and 105 °C. The different drying methods had little effect on ash, acid detergent fibre (ADF), acid detergent lignin (ADL), crude fibre and crude protein (CP) contents and in vitro degradation of the forage samples. However, some effects were found for sugars and phenolic acids. The neutral detergent fibre (NDF) content in protein-rich samples and the fermentation kinetics in rumen fluid differed significantly according to drying method. In samples dried other than by freeze-drying, proteins were bound to the NDF content and in some cases an effect on the amount of soluble sugars was also seen. Physical properties of the samples were determined by differential scanning calorimetry (DSC) and differences were found between freeze-dried materials and those dried at 70 °C. The influence of age on the maize samples was very pronounced, whereas it had little effect on the characteristics of the grass samples, with the exception of a decreased CP content and an increased sugar content after acid hydrolysis.

Experiments on spring barley at Rothamsted over the years 1974–81 were used to study how sources of powdery mildew inoculum affected responses to fungicide sprays applied at different times. Reinfection of early-sprayed plots was generally faster where they were close to a potent source of inoculum than where they were not. Conversely, effects of sources on yield, although not always significant, occurred mainly in the later-sprayed plots. Sources thus had their most important effects before these later sprays were applied, and probably during the very early stages of the epidemic. This implies that if experiments are to approximate to fields, they should, initially, be part of a large, uniformly-susceptible area of crop.

Regression analyses showed that delaying the application of fungicide sprays after the optimum date caused smaller yield losses in plots near minimal sources of inoculum than in plots near more potent sources. There was no conclusive evidence for effects of inoculum sources on the optimum date to apply a fungicide spray but the tendency was for the optimum to become later as inoculum pressure increased.

Separating fungicide-treated plots with mildew-resistant barley resulted in larger treatment effects and smaller residual mean squares than where there was no separation. Judged by residual mean squares alone, precision was approximately doubled by separation.

A constant rate of change in harvest index (dHI/dt = k) has recently been incorporated into several crop simulation models, so that final grain yield can be calculated from final biomass and the duration of grain growth. Implicit is the assumption that dHI/dt is conservative across treatments and environments. This assumption was tested using data from five experiments grown in the United Kingdom (1973, 1978, 1994) and New Zealand (1992, 1993). The experiments included commercial spring and winter wheat cultivars introduced during the last 100 years and nitrogen, irrigation, sowing date, temperature and CO2 treatments. In all cases, the time course of harvest index (HI) had an initial lag phase, a linear phase and a maturation phase. The linear phase was stable in field-grown crops, except for a reduction in slope after lodging in some crops. Values for dHI/dt, taken as the slope of the linear phase, varied with variety and available nitrogen, were stable for a given variety among years, and were unaffected by water stress. Variation in dHI/dt among varieties was independent of their year of introduction, although those with the Rht2 semi-dwarfing gene generally achieved a higher final HI due to a reduced lag phase. Differences in the duration of the linear phase also caused differences in the final HI after drought. The upper and lower limits of dHI/dt for fieldgrown crops were 1·37 and 0·64% d-1 but, under normal fertility conditions, the variation was between 0·90 and 1·19 % d-1. Results indicated that dHI/dt could provide an effective semi-empirical relationship for predicting grain yield in simulation models. The consistent, linear nature of this relationship suggests a physiological maximum for dHI/dt, for a given species and variety. It may be possible to exploit varietal differences in dHI/dt, and in the lag phase, for yield improvement.

Mass selection (MS) and bulk selection of a single character (CS) were used for the improvement of a base population, Bl, which was composed of Tai Gu male-sterile progenies of ten high protein content and four high yielding parental lines of wheat (Triticum aestivum L.), transferred by 6–10 backcrossing generations, with equal numbers of plants from each line. Backcross mass selection (BS) was used for the improvement of a second base population, B2, which was formed by Tai Gu malesterile plants of four high yielding parental lines, again with equal numbers of plants from each line. Three cycles of selection were conducted for both population Bl and B2. Direct genetic advances of sterile plants for six traits were studied. The results indicated that use of the Tai Gu male-sterile single dominant gene is effective for recurrent selection of wheat. For improvement of a single character, CS was the most effective method, of which the selective effect in the first cycle (Cl) was greater than in the second (C2) and the third cycle (C3), although multivariate analysis snowed that the CS method was not conducive to the maintenance of variation in a population. The greatest response to selection was found in C2 with the MS method. Multivariate analysis also indicated that both the MS and BS methods increased the variation in the population, but MS was found to be the best selective method as judged by the mean response over three cycles of selection.

Nineteen populations of Lolium perenne were grown near Aberystwyth as small plots (sown in 1988) in the field, and as pot plants (sown in 1989) in the glasshouse and controlled environment (CE). In the summer of 1989 they were subjected to drought, and then rewatered. Herbage growth and water relations characters were measured. There was significant diversity between populations (narrowsense heritability) for: herbage production and yield stability before, during and after drought; tillering; osmotic potential and adjustment; tissue water content; and membrane stability (MS) following heat shock. There were no such differences in leaf water conductance, MS following desiccation shock, or chlorophyll stability under osmotic stress. The range of expression of characters was very different in the three environments, as was the ranking of populations, emphasising the danger of working in unnatural environments. Correlation analysis revealed no relationships between growth and physiological characters that were consistent across environments. Nevertheless, hierarchical cluster analysis indicated that some populations having a ‘hay-type’ morphology performed well over all three environments, and merit further study.

Iron toxicity is a nutrient disorder associated with high concentrations of iron in soil solutions. Deficiencies of other nutrients, such as P, K, Ca, Mg and Zn, have been implicated in its occurrence in rice plants. Field experiments were carried out in 1992 and 1993 in Ivory Coast to evaluate the iron toxicity tolerance of promising rice cultivars available in West Africa, and to provide additional information for selecting breeding materials. Two sites, differing in their potential to cause iron toxicity, were used. Glasshouse and field studies were also conducted to test the role of other nutrients in the occurrence of iron toxicity. The results showed that genetic tolerance to iron toxicity can significantly improve rice production in iron-toxic soils, with some cultivars producing yields in excess of 5 t/ha. The application of N, P, K and Zn in the field decreased the uptake of iron in rice tops, and this can be a significant factor in the iron-toxicity tolerance of the cultivars.

In order to understand better the relationship between plant physical structure and rate of intake, twelve plant species were compared: Trifolium repens L., Medicago sativa L., Onobrychis viciifolia Scop., Desmodium intortum (Mill.) Urb., Brassica napus L., Spergula arvensis L., Lolium perenne L., Lolium multifiorum Lam., Festuca arundinacea Schreb., Chloris gayana Kunth, Cenchrus ciliaris L. and Zea mays L. The effects of early as opposed to late harvesting were compared. Plants were grown in a heated glasshouse in each of 2 years, examined for morphology, anatomy, neutral detergent fibre and digestibility, and fed to sheep for 1-min test periods to record rate of intake.

Rate of intake was in the order tropical grasses < temperate grasses < broad-leaved species < S. arvensis. The range was wide: from 4·6 g dry matter/min with C. gayana to 15·6 g with S. arvensis. The lowest rate of intake was associated with the possession of a large number of veins, close together, in parallel lines (tropical grasses); a rather higher rate was associated with fewer veins, further apart, in parallel lines (temperate grasses); the next to the highest rate was associated with broad leaves, which had a network of veins; the highest rate was associated with thin stems containing thin vascular bundles. L. perenne, L. multifiorum, C. gayana and C. ciliaris were similar in the thickness of large and small leaf blade veins and leaf sheath veins. F. arundinacea and Z. mays had rather thicker veins. T. repens, 0. viciifolia. D. intortum and B. napus were similar in the thickness of petiole vascular bundles. Neutral detergent fibre was lowest in B. napus and highest in C. gayana and C. ciliaris. In vitro digestibility was highest in B. napus and lowest in D. intortum.

Differences amongst wheat cultivars in the rate of reproductive development are largely dependent on differences in their sensitivity to photoperiod and vernalization. However, when these responses are accounted for, by growing vernalized seedlings under long photoperiods, cultivars can still differ markedly in time to ear emergence. Control of rate of development by this ‘third factor’ has been poorly understood and is variously referred to as intrinsic earliness, earliness in the narrow sense, basic vegetative period, earliness per se, and basic development rate. Certain assumptions are made in the concept of intrinsic earliness. They are that differences in intrinsic earliness (i) are independent of the responses of the cultivars to photoperiod and vernalization, (ii) apply only to the length of the vegetative period up to floral initiation (as suggested by several authors), (iii) are maintained under different temperatures, measured either in days or degree days. As a consequence of this, the ranking of cultivars (from intrinsically early to intrinsically late) must be maintained at different temperatures. This paper, by the re-analysis of published data, examines the extent to which these assumptions can be supported.

Although it is shown that intrinsic earliness operates independently of photoperiod and vernalization responses, the other assumptions were not supported. The differences amongst genotypes in time to ear emergence, grown under above-optimum vernalization and photoperiod (that is when the response to these factors is saturated), were not exclusively due to parallel differences in the length of the vegetative phase, and the length of the reproductive phase was independent of that of the vegetative phase. Thus, it would be possible to change the relative allocation of time to vegetative and reproductive periods with no change in the full period to ear emergence.

The differences in intrinsic earliness between cultivars were modified by the temperature regime under which they were grown, i.e. the difference between cultivars (both considering the full phase to ear emergence or some sub-phases) was not a constant amount of time or thermal time at different temperatures. In addition, in some instances genotypes changed their ranking for ‘intrinsic earliness’ depending on the temperature regime. This was interpreted to mean that while all genotypes are sensitive to temperature they differ amongst themselves in the extent of that sensitivity.

Therefore, ‘intrinsic earliness’ should not be considered as a static genotypic characteristic, but the result of the interaction between the genotype and temperature. Intrinsic earliness is therefore likely to be related to temperature sensitivity. Some implications of these conclusions for plant breeding and crop simulation modelling are discussed.

The concentration of nitrogen (N) within the emerging, youngest fully expanded and the youngest dead leaf laminae were examined in the grasses Lolium perenne, Agrostis stolonifera, Holcus lanatus and Poa trivialis in Devon, UK, in 1986 and 1987. Lamina growth, appearance interval and lamina utilization were also examined in each species. Marked tillers were measured in situ over 14–21 day periods in a continuously grazed permanent pasture under steady state management on plots receiving either zero (ON) or 400 kg nitrogen (400N) fertilizer/ha per annum. The concentration of N tended to be greatest in the distal half and least in the basal part of each lamina in each species. Total mass showed an opposite trend due in part to the shape of the lamina. Less than 40 % of the lamina N was lost through grazing either in the ON or 400N plots in the four species, except once in H. lanatus when more was lost. In absolute terms, because L. perenne and H. lanatus maintained larger and longer laminae than either A. stolonifera or P. trivialis, they lost more N through grazing. The four grass species recycled N from the senescing lamina with the same apparent efficiency; this meant that differences in lamina N concentration and carbon: nitrogen ratios were present in the dead laminae of the four species. L. perenne achieved the highest tissue growth rate per unit of N in the lamina in the ON plot, not only in comparison with the three other grasses but also compared with the 400N plot. This high N-use efficiency in L. perenne was not translated into an ability to either expand or maintain its population in the ON plot. L. perenne had a lower leaf appearance rate than the other species in both the 400N and ON plots, but this inherent characteristic of the species was particularly pronounced in the ON plot. A slower leaf appearance rate would limit the potential tillering capacity of L. perenne compared with the other species. A reduced tillering capacity, exacerbated by N deficiency, was probably the principal factor limiting the ability of L. perenne to exploit available niches in the ON pasture.

The effectiveness of chewing by sheep during eating in breaking a forage diet into particles was studied in twelve plant species over 2 years and related to the physical structure of the plants and their rate of intake. The twelve species were: Trifolium repens L., Medicago sativa L., Onobrychis viciifolia Scop., Desmodium intortum (Mill.) Urb., Brassica napus L., Spergula arvensis L., Lolium perenne L., Lolium multiflorum Lam., Festuca arundinacea Schreb., Chloris gayana Kunth, Cenchrus ciliaris L. and Zea mays L. In each case early harvesting was compared with later harvesting. The plants were grown in a heated glasshouse.

L. perenne and L. multiflorum were broken into a large number of particles per g dry matter; the particles were rather long and thin. F. arundinacea was broken into heavier, slightly shorter and slightly wider particles. C. gayana and C. ciliaris were broken into particles which were smaller, heavier and contained more vascular bundles than those of Lolium, reflecting the lower rate of intake, greater weight per unit area of leaf blade and greater proximity of bundles of the tropical grasses. Z. mays leaf blades broke into shorter, wider particles than the leaf blades of the other grasses, reflecting the much wider blades of Z. mays.

The leaflets of the four leguminous species and the leaf blades of B. napus were broken into particles with an average length:width ratio of c. 2:1, compared with an average ratio of c. 7:1 for particles derived from grass leaf blades other than those of Z. mays. The legume leaf petioles were broken into particles with an average length: width ratio of c. 13:1; many of the legume petioles were not split longitudinally during chewing. The stems of M. saliva and D. intortum were broken into particles similar in length and width to those from the stems of the tropical grasses, although the rate of intake of the legume diets was at least twice that of the tropical grass diets. The average length: width ratio of particles from B. napus petioles and stems was 5:1. A high proportion of particles from the B. napus and D. intortum diets had a rough surface. 5. arvensis was broken into more particles per g dry matter than the legumes and B. napus, despite its very high rate of intake. Many pieces of stem of S. arvensis were not split longitudinally during chewing.

The sowing of improved tropical forages in tree plantations can increase animal productivity considerably, but planted grasses often fail to persist under grazing, resulting in unstable pastures. An experiment was conducted in Brisbane, Australia during the summer of 1989/90 to investigate whether the failure of tropical grasses to persist in shade when regularly defoliated is related to their growth habit. Two shade-tolerant grasses of contrasting growth habit (prostrate Paspalum wettsteiniiv. erect Paspalum malacophyllum)were grown in simulated swards at light levels of 100, 50 and 20% of full sunlight and defoliated every 2 or 4 weeks. Shading and frequent cutting reduced total dry matter yield equally in the two grasses. Shading also reduced tiller density. Paspalum wettsteinii persisted poorly under frequent (2-weekly) defoliation in shade. Plant survival rate of this grass was 66% in the 2-weekly defoliation-20% light transmission treatment, compared with 94% in P. malacophyllum. The poor survival of P. wettsteinii was related to its high allocation of total yield to roots, low tiller density and low total nonstructural carbohydrate yield in residual biomass after defoliation. The inability of P. wettsteinii to adjust in shade to frequent defoliation led to a continual decline in photosynthetic area and light interception, resulting in the depletion of energy reserves, increased susceptibility to Rhizoctonia fungal infection and ultimately to death. It was concluded that growth habit per se cannot be used as a simple indicator for selecting tropical grasses for shaded environments. Instead, morphophysiological adaptation to defoliation in shade was critical for plant persistence.

Yields and hardseed breakdown of underground and aerial seeds in subterranean vetch (Vicia sativa ssp. amphicarpa) and lathyrus (Lathyrus ciliolatus) and aerial seeds of Medicago rigidula and M. noeana were compared at Tel Hadya, near Aleppo, in north Syria between 1990 and 1992. Underground and aerial seed and straw (mature herbage) yields were measured at maturity in the first spring, and hardseed breakdown over the following summer, autumn and winter. Regenerating herbage production was measured in the second spring.

In the establishment year (292 mm rainfall) the medics produced twice as much straw as the amphicarpic species. In contrast, seed yields were less than half: M. rigidula and M. noeana produced 412 and 110 kg/ha respectively, while subterranean vetch and lathyrus produced 1174 and 736 kg/ha. More than 95 % of the total seed yield of the amphicarpic legumes was underground. Underground seeds of the amphicarpic legumes were larger than aerial seeds, and almost 10 times as large as the medic seeds.

Seeds of all species were > 90% hard when newly set in summer. At the first seasonal rains > 95% of underground seed had softened, compared with 5 and 40% of the aerial seeds of vetch and lathyrus respectively. The medics remained > 90% hardseeded. In laboratory tests, embryo dormancy was observed in all species prior to the onset of first seasonal rains. For the amphicarpic legumes, but not for the medics, embryo dormancy persisted into winter. In the field, and after all germination events, 900–1430 seeds/m2 of subterranean vetch seed remained in the soil. This was considerably more than expected, based on the low levels of hardseededness and embryo dormancy observed in the laboratory. The results suggest that dormant seeds of the amphicarpic legumes need light to germinate.

In the second year (353 mm rainfall), regenerating M. rigidula produced 5·3 t/ha compared with 3·4 t/ha by the best subterranean vetch from approximately equal numbers of seedlings. The amphicarpic legumes germinated later and over a more extended period than the medics, indicating that they could become weeds in a cereal/pasture rotation. However, the results suggest that in drier areas or in drier years the vetches will compare favourably with the medics in most respects. Clearly, subterranean vetch and lathyrus have great potential for pasture improvement in dry areas.

The hardseededness and pattern of hard seed breakdown of 35 accessions of Medicago polymorpha, collected in Sardinia, were compared with Circle Valley, an Australian cultivar, near Sassari, northern Sardinia. The seed was produced in three consecutive years (1991–93), and the hardseededness measured at intervals in trie field during the summer following its production. The results were related to previously measured pod characteristics that separated the varieties polymorpha and vulgaris

The variety polymorpha, which had been collected mainly from coastal regions, was harder seeded than the variety vulgaris, which had been collected mainly from cooler, inland regions. Wherever the origin, hardseededness levels remained > 85% even in the year when seed softening was greatest (1992). In other years means of 94% (1991) and 97% (1993) of seed remained hard in late September. In 1992 and 1993 most hard seed breakdown occurred between early August and early September, while in 1991 hard seed breakdown occurred in September itself. There was little difference between varieties in the pattern of hard seed breakdown. Seedling emergence was related to the amount of seed that became soft during the previous summer. The results also confirmed that hard seeds soften sequentially from the proximal end of the pod (nearest the calyx) to the distal end.

The Australian cultivar was one of the hardest seeded accessions, showing very little hard seed breakdown during the experimental period. This result highlights the importance of selecting pasture legumes under the conditions in which they are to be used: in Australia, cultivar Circle Valley usually loses some 20% of its hardseededness in the first year, comparable with the softest Sardinian accessions in Sardinia. Even among the Sardinian accessions, most were probably too hard seeded in 1993. Nevertheless it is likely that material in this experiment will be released as commercial cultivars for Sardinia and other similar environments in the Mediterranean basin.

The impact of white clover on seasonal yield and nutritive value traits in perennial ryegrass was investigated using six ryegrass varieties which expressed contrasting levels of water soluble carbohydrate (WSC). These were sown in an upland environment at Syfydrin, near Aberystwyth, in mixtures with white clover and in monocultures. Plots were grazed by sheep and sampled during 1991–93. Grass yields in mixtures and monocultures were similar except during mid to late summer when clover contents were high. White clover had a considerably lower WSC content but a much higher crude protein (CP) content than the ryegrasses. The WSC content of grasses in mixed swards was consistently lower than in monocultures and markedly so during mid to late summer. Use of ryegrass varieties with a relatively high WSC content can compensate for this depletion. Consequently high WSC grasses may reduce the amounts of nitrogen excreted by ruminants grazing mixed swards by increasing the efficiency of protein use from clover.

The morphology of independent plants of ‘Grasslands Ruanui’ perennial ryegrass (Lolium perenne L.) and three cultivars of cocksfoot (Dactylis glomerata L.) (‘Grasslands Apanui’, ‘Grasslands Kara’ and ‘Grasslands Wana’) in mixed pastures under intensive sheep grazing was studied at Palmerston North, New Zealand during 1991/92.

Both perennial ryegrass and cocksfoot exhibited a similar pattern of clonal growth and population structure. Distribution of plants among various orders of branching showed a relatively stable pattern through most of the year except in spring, when stem decay and plant fragmentation exceeded apical growth and regeneration, causing an increase in the proportion of small plants and a corresponding decrease of larger plants. This pattern was similar to that previously reported for white clover (Trifolium repens L.). Nevertheless, seasonal variation in plant structure (number of leaves, tillers and stems per plant) was small, but variation in organ size (DW or length) was greater. Stolon formation through elongation of internodes occurred throughout the year, but was associated primarily with flowering.

Grazing management caused no differences in plant structure between species or among the cocksfoot cultivars, but did affect the size of organs, and hence plants. Cocksfoot plants were 50–60% heavier than perennial ryegrass under rotational grazing. Under set stocking, only perennial ryegrass and Wana cocksfoot exhibited sufficient phenotypic plasticity to survive, both Kara and Apanui cocksfoot failed to persist. The only consistent difference between the species was greater flowering in perennial ryegrass than in cocksfoot, in both the proportion of plants flowering, and the number of flowering tillers per plant. Both species produced stolons throughout the year, although perennial ryegrass and Wana cocksfoot had a higher proportion of plants with stolons than Apanui and Kara cocksfoot. Length and DW of stolons per plant were similar in both species.

As there was little variation in plant structure and plant density, length of stolons per unit area tended to parallel seasonal changes in pasture tiller density. The role of grazing management in the survival of tillers and plants, and subsequent performance of grass species in pastures is discussed.