Leaf number as a criterion for determining defoliation time for Lolium perenne: 2. Effect of defoliation frequency and height

The object of this study was to determine the importance of frequency and height of defoliation on regrowth potential of Lolium perenne. Defoliation interval was based on stage of the regrowth cycle, as indicated by leaves per tiller.
Simulated swards of Lolium perenne cv Yatsyn were grown as individual plants in a glasshouse kept at a day/night temperature of 25°C/15°C.
Treatments imposed were defoliation at 2, 5 or 12 cm residual height, and low and high water soluble carbohydrate (WSC) level obtained by varying defoliation interval, i.e. defoliating at the 1-leaf or 3-leaf stage of the regrowth cycle. Regrowth after frequent short defoliations was only 65% of the less frequently defoliated plants taken over the full regrowth cycle. This was associated with a lower stubble WSC content (2·15 vs 17·5% in stubble) and a twenty-seven-fold difference in the amount of WSC in the stubble per plant. This difference in total WSC was a combined effect of more and heavier tillers and higher WSC content in stubble of plants defoliated less frequently at the end of the regrowth cycle. The regrowth of plants with WSC levels depleted by frequent defoliation when defoliated at 2 cm was significantly below that of those defoliated at 5 and 12 cm.
The results indicate the desirability of defoliating plants at the 3-leaf stage of the regrowth cycle. This not only allows the full regrowth potential to be expressed in that growth cycle, but also in the next cycle, by allowing the replenishment of WSC reserves and optimizing tiller status. The potential to regrow appears then to be based more on the total amount of WSC than the proportion of WSC in stubble.     

Infrequent and intense defoliation benefits dry-matter accumulation and persistence of clipped Arrhenatherum elatius

The objective was to determine how the frequency and intensity of defoliation of tall oat grass [Arrhenatherum elatius (L.) Presl.], affected (i) annual dry‐matter (DM) accumulation, (ii) seasonal distribution of the accumulated forage, and (iii) morphological traits related to persistence and vigour. Data were collected twice a year throughout three growing years, beginning the second year after establishment. Two frequencies (A: each time modal height of plants reached 20 cm; B: each time modal height of plants reached 40 cm) and two defoliation intensities (I: 5 cm; II: 10 cm stubble) were arranged in a completely randomized block design with a fully factorial combination and four replicates. Measurements were made of annual DM accumulation, seasonal distribution of accumulated DM and morphological traits related to persistence and vigour, i.e. number of tillers m^?2, number of tussocks m^?2, crown diameter, and crown area of tussocks. The infrequent defoliation (B) increased annual DM accumulation besides maintaining levels of persistence and vigour. The most productive treatment (BI) had a significantly higher annual DM accumulation than treatments AI and AII. Frequent and severe defoliations (treatment AI) led to plant depletion, which reduced crown diameter, number of tillers m^?2 and crown area at the end of the third year compared with infrequent but severe defoliation (treatment BI). Annual DM accumulation was intermediate for less intense defoliations (AII), which produced forage during winter, but resulted in less vigorous plants by the end of the experiment. Crown area was a good indicator of tiller number, particularly under frequent defoliation.     

The effect of defoliation practice in Western Australia on tiller development of annual ryegrass (Lolium rigidum) and Italian ryegrass (Lolium multiflorum) and its association with forage quality

The effect of defoliation on the vegetative, early reproductive and inflorescence stages of tiller development, changes in the dry‐matter yield of leaf, stem and inflorescence and the associated changes in forage quality was determined on plants of annual ryegrass (Lolium rigidum Gaud.) and Italian ryegrass (L. multiflorum Lam.). The field study comprised seventy‐two plots of 1 m × 2 m, sown with one annual ryegrass and seven Italian ryegrass cultivars with a range of heading dates from early to late; defoliation commenced 6 weeks after germination. During the vegetative stage of growth, plots were defoliated when the tillers had three fully expanded leaves (three‐leaf stage). During the early reproductive stage of growth, to simulate a cut for silage, plots were defoliated 6–7 weeks after 0·10 of the tillers displayed nodal development. The subsequent regrowth was defoliated every 3 weeks. Assessments of changes in tiller density, yield and quality were made in the growth cycle that followed three contrasting cutting treatments during the winter–spring period (from 10 July). In treatment 1, this growth cycle (following closing‐up before a subsequent conservation cut) commenced on 7 August following two defoliations each taken when the tillers were at the three‐leaf stage. In treatment 2, the growth cycle commenced on 16 October following: for early‐maturing cultivars, two cuts at the three‐leaf stage, a cut for silage and an additional regrowth cut; for medium‐maturing cultivars three cuts at the three‐leaf stage and a cut for silage; and late‐maturing cultivars, five cuts at the three‐leaf stage. In treatment 3, defoliation up to 16 October was as for treatment 2, but the growth cycle studied started on 27 November following two additional regrowth cuts for early‐ and medium‐maturing cultivars and cut for silage for the late‐maturing cultivars. Tiller development for all cultivars was classified into three stages; vegetative, early reproductive and inflorescence. In treatment 1, in vitro dry‐matter digestibility (IVDMD) and crude protein (CP) content were negatively associated with maturation of tillers. IVDMD ranged from 0·85 to 0·60 and CP ranged from 200 to less than 100 g kg^–1 dry matter (DM) during the vegetative and inflorescence stages respectively. This large reduction in forage quality was due to an increase in the proportion of stem, inflorescence and dead material, combined with a reduction in the IVDMD and CP content of the stem. A high level of forage quality was retained for longer with later‐maturing cultivars, and/or when vegetative tillers were initiated from the defoliation of early reproductive tillers (treatments 2 and 3). However, 15 weeks after the closing‐up date in treatment 1, defoliation significantly reduced the density of inflorescences with means (±pooled s.e_m.) of 1560, 1178 and 299 ± 108 tillers m^–2, and DM yield of inflorescence with means of 3·0, 0·6 and 0·1 ± 0·15 t ha^–1 for treatments 1, 2 and 3 respectively. This study supports the recommendation that annual and Italian ryegrass cultivars should be classified according to maturity date based on the onset of inflorescence emergence, and that the judicious defoliation of early reproductive tillers can be used to promote the initiation of new vegetative tillers which in turn will retain forage quality for longer.     

Late defoliation and wheat yield: Little evidence of post-anthesis source limitation

The effect of source reduction on yield and protein content of bread wheat under well-watered and mild drought stress condition in a semi-arid climate was studied. Field experiments were conducted at the Tehran University research farm during 2003–2004 and 2004–2005 growing seasons. Mild drought stress was imposed when plants were at the second node stage by repeatedly withholding watering and re-irrigating when they showed symptoms of wilting or leaf rolling. Partial defoliations (all leaf lamina other than flag leaves were removed) were imposed at booting and anthesis; complete defoliation was imposed at anthesis (defoliation treatments were applied to all plants of each plot). Drought stress caused a significant increase in the remobilization of pre-anthesis reserves to the grain. Defoliation did not significantly affect remobilization. Grain yield and 1000-grain weight was reduced slightly by drought stress, but in most cases it was not significantly reduced by defoliation. Significant changes were not observed for grain protein content between defoliated and control plots. The results suggested that grain yield of the cultivar used under the condition tested is more controlled by sink than source strength.     

Effect of spring defoliation pattern on the mid‐season production and morphology of swards of perennial ryegrass cultivars of different maturity

The effect of three spring management treatments on the vertical distribution of dry‐matter (DM) yield and morphology of four cultivars of perennial ryegrass (Fennema, Corbet, Foxtrot, Melle) in mid‐season was investigated. The management treatments commenced with cuts on 15 February (Early), 1 March (Medium) and 29 March (Late), each followed by a 28‐day re‐growth period until the next cut and then further 21‐day re‐growth periods after each subsequent cut. This created four mid‐season measurement periods across the management treatments at cut 3 (5 April–17 May), cut 5 (17 May–28 June), cut 6 (7 June–19 July) and cut 7 (28 June–9 August). Tiller and sheath height and their ratio, and leaf lamina length, were measured prior to the four mid‐season cuts (cuts 3, 5, 6 and 7) when measurements of DM yield and proportions of leaf, stem and dead material in three herbage horizons (Lower, 0–8 cm; Middle, 8–15 cm; Upper, >15 cm) were made. There were significant responses in mid‐season to the management treatments involved complex interactions between management treatment and cutting date, which modified seasonal patterns in DM yield and leaf:stem ratio. There were significantly greater tiller heights, tiller:sheath ratios and leaf lamina lengths but lower sheath heights from the Early to Late management treatments. The greatest responses in morphological characteristics occurred in the Middle horizon compared with either the Lower (predominately stem and pseudo‐stem), or the Upper (predominately leafy) horizons. Distribution of DM yield between Middle and Lower horizons but not overall DM yields was significantly affected by management treatment. Morphological differences between cultivars were mostly in the Middle horizon and ranking of the cultivars was similar across the management treatments. The different responses of cultivars Fennema and Melle showed that genotype had a significant effect regardless of management. The leafiest mid‐season swards were achieved by delaying initial spring defoliation in the cultivar which had the lowest stem production.     

Differential red clover germplasm response to defoliation and fungicide application

A primary limitation to the use of red clover ( Trifolium pratense L. ) in the temperate zones is poor persistence. The objective of this research was to evaluate the effects of defoliation and fungicide application on the yield and persistence responses of twelve diverse red clover germplasms. Treatments consisted of reduced defoliation with the application of the systemic fungicide, propiconazole (RDF), reduced defoliation (RD) and a full-season defoliation control. Dry-matter yields were recorded for 3 years and stand density was determined during the third harvest year and again 2 years later. By the third harvest season, stand densities were 52% and 13·5% greater for treatments RDF and RD than the control. After 5 years, stand density on these two treatments was on average 68% greater than the control. RDF plots outyielded RD plots for the second and third harvest years, but both had lower forage yields than the control. Germplasm by treatment interactions were significant for stand density and yield by the third year. RD treatments out-yielded the control by the third year for only two germplasms, the experimental lines FL-MTC and FL6-EF. The treatments affected yield and persistence and enabled the identification of significant differences in germplasm response.     

Effect of regrowth interval on the productivity of swards defoliated by cutting and grazing

Over three grazing seasons (1984-1986) a sward of perennial ryegrass, cv. Talbot, which received a total of 336 kg N ha^-1 each season, was cut or grazed with ewes at 3- or 4-week intervals on a rotational basis.
Sward productivity was higher under cutting than under grazing irrespective of the interval between defoliations. Under cutting, mean herbage organic matter (OM) yields over both intervals were 8·66, 9·62 and 8·17 t ha-¹ in 1984, 1985 and 1986 respectively while under grazing the corresponding yields were 7·65, 8·63 and 7·50 t ha^-1. The mean annual yield of herbage defoliated at 3-week intervals was 7·50, 8·64 and 7 ·20 t OM ha^-1 compared with 8·80, 9·60 and 8·46 t OM ha^-1 for swards defoliated at 4-week intervals in the three years respectively.
The nitrogen (N) content of both the available and the residual herbage was consistently higher under grazing than under cutting. Available herbage contained 31·3 and 27·7 g N kg OM^-1 and residual herbage 26·1 and 22·7 g N kg OM^-1 under grazing and cutting respectively.
The mean yield of N under cutting was 284 kg ha^-1 compared with 304 kg ha^-1 under grazing. Defoliation interval had no effect on N yield, the overall mean yield being 294 kg ha^-1 under both 3- and 4-week defoliation intervals. The effect of the treatments on tiller population was slight and inconclusive.
The process of grazing reduced yield probably as a result of damage to the sward through trampling; the positive effect of excretal N on yield was minimal on account of the short grazing periods.     

Influence of defoliation regime on herbage production and characteristics of intake by dairy cows as affected by grazing intensity

Three contrasting defoliation regimes for dairy cows—four cuts annually, severe rotational grazing and lax rotational grazing integrated with cutting—were compared in terms of herbage production, selection and intake per cow. Lax and severe grazing were compared simultaneously and grazing intensity was characterized by means of changes in herbage mass and sward height during grazing.
Herbage growth and yield were similar under cutting, severe grazing and lax grazing/cutting (120 t organic matter (OM) ha⁻¹). Herbage quality and leaf production were highest with severe grazing, which also had a less marked seasonal pattern of growth. The herbage intake per cow was 111 kg OM d⁻¹ with severe grazing and proportionately (0-20) higher at lax grazing/ cutting. 050 of the herbage yield was harvested by cutting at lax grazing/cutting. Selectivity was described with high certainly by the nutrient content prior to defoliation and by the degree of defoliation. Models to quantify this are presented.
Grazing intensity could be described by the size and degree of utilization of the fouled area, and herbage intake was quantified by means of herbage height before and after grazing. Within the range of 80-240 mm sward height prior to grazing, height measurements led to realistic and more accurate estimates than those obtained by measuring organic matter disappearance.
Herbage utilization was depressed significantly by increasing maturity of herbage due to lower nutritive value, but in particular due to reduced green leaf content and increased reproductive development. If sward height did not exceed 250 mm at any time, good utilization by grazing could be obtained.     

The effect of height and frequency of mowing on the yield and composition of perennial ryegrass—white clover swards in the autumn to spring period

Ninety-six plots (3 × 2 m) of well-established perennial rye grass/white clover pasture were mown to heights of 2·7 (Low) or 3·96 (High) cm (rising plate meter) at 14-, 28-, 84- or 112-d intervals in autumn-winter. A 7-, 14- and 28-d mowing interval was superimposed in spring on each autumn–winter mowing interval treatment with the low and high mowing heights altered to 2·92 and 4·80 cm, respectively.
With the low cutting height, accumulated herbage DM was more than doubled (1806 ± 79 kg DM ha^-1) compared to a 'high' (754 ± 49 kg DM ha^-1) cutting height in autumn–winter and this was due to increased harvesting efficiency rather than growth as estimated by leaf extension. Although defoliation interval had no effect on DM yield, the grass component increased and clover decreased. The composition effect carried over into spring. On average, 3·5 tillers were produced over winter for each ryegrass tiller present in autumn and tiller densities were higher in spring. Tillers produced over autumn–winter contributed more than 60% of ryegrass growth by early spring.
In early spring (16–30 September), the low cutting height increased herbage DM yield, in mid-spring (1–14 October) it reduced DM yields particularly in combination with short defoliation intervals, while in late spring (14 October to 11 November) cutting height had no effect on DM yields.
Over the entire spring period there was a very marked effect of defoliation interval on DM yields.     

Effects of defoliation frequency and nitrogen fertilization on the production and potential for persistence of Dactylis glomerata sown in multispecies swards

Management decisions should facilitate the dominance of C₃ perennial grasses over annuals. This study examined the effects of defoliation frequencies and nitrogen fertilization on the productivity and potential for persistence of Dactylis glomerata L. (DG cocksfoot, perennial) in multispecies swards. Treatments were randomly applied to 24 mini‐swards of DG + Bromus willdenowii Kunth (BW prairie grass, annual/biennial) in a factorial design of four defoliation frequencies, based on number of leaves per tiller, by two nitrogen winter fertilization levels (N^? or N⁺). Regardless of fertilization, very frequent and repeated defoliations were related to decreases of about 43% of aboveground biomass and frequent defoliations with decreases of about 44% of vegetative tillers associated with horizontal space occupation and potential for persistence. Nevertheless, differences in DG aerial productivity or reserves were not detected between frequent and optimal defoliation frequencies. Combined effects of N⁺ and optimal frequency were related to root biomass increment of about 200%, compared with frequent defoliation, associated with competitiveness and survival of DG. Optimal defoliation frequency would have ecological but not production advantages, compared with frequent defoliations. The results are discussed in terms of more objective decision‐making in the management of multispecies swards.     

Effect of defoliation frequency and cutting height on growth,dry‐matter yield and nutritive value of Napier grass (Pennisetum purpureum (L.) Schumach)

Growth characteristics, dry‐matter (DM) yield, chemical components and in vitro dry‐matter digestibility (IVDMD) of Napier grass were studied in a randomized complete block design with three replications at Haramaya University, Ethiopia. The treatments were three defoliation frequencies (60, 90 and 120 d after Napier grass establishment) and five cutting heights (5, 10, 15, 20 and 25 cm above ground level). Except for leaf‐to‐stem ratio, all growth characteristics increased with decreasing frequency of defoliation. Similarly, DM yield of Napier grass increased as the frequency of defoliation decreased. Total ash, crude protein (CP), hemicellulose and IVDMD contents of Napier grass increased with increasing frequency of defoliation, whereas DM, acid detergent fibre, acid detergent lignin and cellulose contents increased with a decrease in defoliation frequency. In contrast, cutting heights had no significant effect on most chemical components and IVDMD contents, although total ash and CP decreased as the height of cutting increased. The CP yield per cut and per day was highest at an intermediate defoliation frequency. The results of this study indicated that Napier grass could be categorized under medium‐ to high‐quality herbage if defoliated at 90 d after establishment in the mid and highlands of Ethiopia.     

Effects of an autumn defoliation on overwintering, spring growth and yield of a white clover/grass sward

An established sward of binary mixtures of meadow fescue (Festuca pratensis) and white clover (Trifolium repens) (either AberHerald, Grasslands Huia or Sandra) was subjected to (A) no further defoliation, (B) a defoliation in late September or (C) a defoliation in late October after four harvests had been taken during the grazing season. About a tonne of dry matter (DM) was removed by the autumn defoliations. There were two levels of nitrogen application in spring, either 0 or 90 kg ha^?1. The development of grass and clover morphology and population sizes from early autumn until the first harvest the following year was followed by regular sampling of the above-ground material. Stolons were analysed for total non-structural carbohydrates (TNCs), and the temperature at stolon level was continuously recorded. There were no interactions between autumn defoliation, clover cultivar or nitrogen treatments on any of the parameters studied. White clover growing-point numbers and stolon morphological characteristics were reduced in size during the winter and did not recover during the spring. A defoliation in late September resulted in the greatest reduction, whereas there were no differences between the other two treatments. The grass tiller population increased from early autumn until the last sampling occasion in May, but both autumn defoliations resulted in a smaller increase. Defoliation in late September had the greatest impact. The TNC content of white clover stolons fell from about 350 g kg^?1 to 150 g kg^?1 DM from late autumn until late April. There were small differences between the treatments, but a defoliation in late September resulted in a significantly lower level in late autumn. The temperature amplitude at stolon level was consistently greater in plots defoliated in late September. Total DM harvested in spring was 4367, 2564 and 3536 kg ha^?1, of which 388, 352 and 460 kg ha^?1 was white clover, from treatments A, B and C respectively. It is concluded that an autumn defoliation may affect the overwintering of white clover negatively, but that the effect on the grass may be even more detrimental.     

Impact of defoliation on yield of group IV soybeans in Mississippi

Field experiments were conducted during 2009 and 2010 to evaluate the effects of defoliation on maturity group IV soybeans, Glycine max (L.) Merr., grown in Mississippi. During each year, two locations were planted with maturity group IV soybeans that were subjected to various levels of defoliation during R3, R5, and R6 growth stages. Soybeans were subjected to various levels of defoliation within the upper 50% of the plant canopy, lower 50% of the plant canopy, and whole-plant canopy. There was greater yield loss from defoliation occurring in the upper plant canopy compared with the lower plant canopy during R3 and R5 stages, but no difference between canopy regions during R6 stage. Yield loss from whole plant defoliation was greater than upper or lower canopy defoliation. Results confirmed that soybeans during R3 and R5 stages are more susceptible to yield loss than during R6. However, yield losses were not significantly different between R 3 and R5 until defoliation exceeded 63%. Dynamic economic injury levels were determined for each growth stage based on yield loss equations, value of the crop, and cost of control and can be used as a basis for developing action thresholds in high-yielding soybean production environments.     

芝麻不同时期去叶对蒴果发育和产量的影响及保叶增产措施

采用定株观察，以芝麻生长正常单株为对照，研究不同生育时期，不同蒴果发育时期去叶，对芝麻农艺性状和单株产量的影响。结果表明，随着芝麻生育进程，终花期，封顶期，盛花期去叶减产值幅度递增。相同植株同天开花采取不同时期去叶所结蒴果分别与对照相比，去叶时间越早秕籽率越高，千粒重越低。同时还进一步研究出延长芝麻中上部叶片功能期，提高单株产量的技术措施。     

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.     

THE EFFECTS OF CHANGES IN HEIGHTS OF CUTTING AND GROWTH ON THE DIGESTIBLE ORGANIC MATTER PRODUCTION AND BOTANICAL COMPOSITION OF PERENNIAL PASTURE

Irrigated plots of a mixed sward of Lolium perenne, Paspalum dilatatum, Bromus unioloides, Dactylis glomerata and Trifolium repens were used in 2 experiments during 4 years. In the first experiment, die treatments comprised factorial combinations of heights of cutting of 3, 6 and 10 cm (1.2, 2.4 and 3.9 in.) above ground level, and heights of growth of 5, 13 and 20 cm (20, 5.1 and 8.0 in.) above the height of cutting. In the second experiment, 8 combinations of dose (3 cm or 1.2 in.) or lax (10 cm or 3.9 in.) cutting were applied at various times during each year. In the first experiment, DM production for cutting heights of 3, 6 and 10 cm was 50, 44 and 43 t/ha (198,17.5 and 171 ton/ac), respectively; the DOM production was 37, 32 and 32 t/ha (147, 12.7 and 12.7 ton/ac). DM production for growth heights of 5, 13 and 20 cm was 45, 46 and 48 t/ha (17.9, 183 and 191 ton/ac), respectively. DOM production, 34 t/ha (13.5 ton/ac), was not affected by height of growth. Percentages of protein (26, 22 and 20) and DOM (76, 72 and 71) declined as the height of growth was increased; but cutting height produced no significant effects in them. As cutting height was increased the percentage of clover declined (40, 31 and 23) and that of grasses increased (52, 66 and 72); diere were smaller changes with changes in height of growth. Hie second experiment showed that the difference between close and lax cutting became significant only when lax cutting was applied for at least half of the cuts each year. DM production was similar for treatments witii the same number of close or lax cuts, regardless of the time of year at which the two heights of cutting were applied.     

Effects of timing and intensity of defoliation on growth and development of white clover seedlings

The effects of different defoliation regimes on the growth and development of three contrasting white clover cultivars (S184, Menna and Alice) were assessed in three experiments in the glasshouse. Experiment 1, with clover growing on its own, investigated the effects of three times of onset × two intensities of defoliation. In Experiment 2, clover was grown with grass and there were two times of onset × two heights × two frequencies of defoliation. Experiment 3, also with grass, investigated the effects of changing defoliation frequency at different intervals from sowing. All clover cultivars responded similarly to the various treatments and there were no interactions between time of onset and subsequent defoliation regimes in Experiments 1 and 2. Without competition from grass (Experiment 1), defoliating early at the three leaf-stage of clover decreased the number of growing points by 32% and stolon weights and lengths by 50% compared with delaying defoliation until the nine leaf-stage. Maintaining one compared with two leaves per growing point had similar effects. Over 17 weeks undefoliated seedlings produced ten times more stolon than early defoliated or intensively defoliated seedlings. In competition with grass (Experiment 2) delaying defoliation significantly decreased all aspects of stolon growth. Seedlings growing in swards defoliated frequently and closely had most growing points whereas those defoliated infrequently had least. Stolon lengths and weights were larger for seedlings growing in swards defoliated frequently than for those defoliated infrequently at both heights of cutting. Mean weight of stolon per unit length was greater when swards were defoliated at 6 cm than at 2 cm height. Changing defoliation from every 2 weeks to every week (Experiment 3) decreased stolon growth slightly when the change was made early but increased it when the change was made late, although similar amounts of stolon were produced by seedlings continuously defoliated throughout every week and every 2 weeks. The results are discussed in relation to the seedlings' leaf complements and growth habit; the over-riding influence of grass competition is highlighted. The possibility of devising optimal defoliation strategies and the need to test these in the field are also outlined.     

Frequency of defoliation of native and naturalized species of the Flooding Pampas (Argentina)

This study describes the effect of herbage mass of species on defoliation patterns in a multispecies temperate–subhumid natural grassland of the Flooding Pampas at low, medium and high sward herbage mass [761  ±  8·7, 989  ±  137 and 1591  ±  44·0 kg green dry matter (DM) ha^–1 respectively] maintained by continuous grazing of cattle at variable stocking rates. Four native and naturalized warm-season species were studied: the grasses Cynodon dactylon , Leersia hexandra and Paspalum dilatatum and the legume Lotus tenuis . Sward state of the four species was described in terms of sward surface height, herbage biomass and the number of individual grass tillers and legume stems per unit area. The defoliation pattern was monitored twice-weekly during an experimental period of 3 weeks on permanently marked individual plants. Proportions of individual plants defoliated and the ranking of species selected differed among sward treatments and species. The results showed that the density of the species was a major factor determining the pattern of species defoliation and suggest that, in continuously grazed mixtures, the pattern of defoliation might be more dependent on the abundance of a species in the plant community than on species preferences. The results show the importance of considering this structural characteristic of swards in understanding the process of species selection by large herbivores in multispecies vegetation.     

Comparative defoliation tolerance of temperate perennial grasses

The defoliation tolerance of cultivars of four temperate perennial pasture grasses, perennial ryegrass (Lolium perenne, cv. Yatsyn1), phalaris (Phalaris aquatica cv. Australian), tall fescue (Festuca arundinaceae cv. Demeter) and cocksfoot (Dactylis glomerata cv. Porto), was determined under controlled conditions over a period of 12 weeks. Undefoliated plants were compared with defoliated plants, where only half of one leaf was left intact at the initial defoliation, and leaf regrowth was harvested every 3–4 d. The growth responses measured were plant tiller number, dry weight, relative leaf regrowth rate, root:shoot ratio, sheath:stem ratio and specific leaf weight. All species showed morphological adaptations that potentially increased their ability to tolerate defoliation (e.g. increased allocation to shoot at the expense of roots and lower specific leaf weights) but cocksfoot was found to be the most defoliation‐tolerant and perennial ryegrass the least. The adaptation that favoured cocksfoot most strongly was high sheath:stem ratio, which, it is proposed, allowed it to maintain photosynthesis and a level of carbon supply sufficient to support regrowth throughout the experiment. The strategy of perennial ryegrass which favours leaf growth and leads to rapid leaf turnover rates made it particularly susceptible to defoliation under the conditions of this experiment. This highlights the likely importance of defoliation‐avoidance responses in explaining the well‐known grazing resistance of this species. Phalaris and tall fescue showed responses that were intermediate between the other two species. The importance of defoliation‐avoidance mechanisms and implications for grazing management are discussed.     

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.