Defoliation Frequency Research Articles

Root dry matter mass and distribution of Florico grass under different grazing strategies

Abstract: The objective of this work was to evaluate the variations in root dry matter mass (RDM) and the percentage distribution (PD) of the root density of Florico grass (Cynodon nlemfuensis) in the 0-40-cm soil layer, when managed under different grazing strategies. Two defoliation frequencies (90 and 95% light interception, as the criterion for allowing animals in the paddock) and two defoliation severities (post-grazing heights of 20 or 30 cm) were assessed. Four seasonal evaluations of the root system were performed between the winter of 2012 and the autumn of 2013, using the monolith and trench excavation technique, collecting 1-dm3 samples from soil surface down to a depth of 40 cm, in four sequential extracts of 10 cm each. Lower RDM values (0.69 g dm-3) were obtained in winter, with the four grazing strategies, whereas higher values were observed in spring (1.64 g dm-3), for the 30-cm post-grazing residue, and in autumn (1.63 g dm-3) for the 20 cm post-grazing residue, regardless of the light interception value. Between 52 and 66% of the RDM density was observed in the 10-cm layer, for all four grazing strategies, in all seasons.

Divergent effects of defoliation intensity and frequency on tiller growth and production dynamics ofPascopyrum smithiiandHesperostipa comata

Rotational stocking theoretically enables regrazing of regrowth, but regrowth may be limited in xerophytic vegetation. We tested the hypothesis that regrowth would be slow and fixed in Hesperostipa comata (a caespitose, drought-tolerant grass), while growth would be flexible in Pascopyrum smithii (a rhizomatous, less drought-tolerant grass) under increasing defoliation and moisture, by assessing tiller growth rates, population dynamics and plant yield on marked plants in a Dry Mixed Grass prairie. Plots were clipped in late summer to simulate a deferred control, or intermittently during the growing season (May–August) at high intensity–low frequency (HILF), low intensity–high frequency (LIHF) or high intensity–high frequency and crossed with two water treatments (ambient and addition) in both a xeric upland and a mesic lowland. Growing season defoliation increased tiller growth rates of P. smithii in the upland, whereas HILF and LIHF reduced growth in the lowland. All defoliation regimes increased tiller growth for H. comata. Tiller populations of H. comata increased with frequent defoliation, while tiller populations of P. smithii decreased regardless of defoliation regime. Frequent defoliation, regardless of intensity, reduced yield relative to the deferred control for both grasses. While water addition consistently increased growth rates and reduced differences in tiller number among defoliation treatments, the regrowth of both grasses remained similar under varied defoliation with ambient moisture. High moisture conditions also promoted regrowth more in P. smithii compared to H. comata. In summary, neither grass species displayed an inherently fixed or flexible tiller or plant yield response in response to defoliation or moisture.

Biomass flows and defoliation pattern of ryegrass grazed by supplemented heifers

To strategically define the best stocking rate management strategy for ryegrass, it is important to know the growth process of forage plants in detail. The study was conducted to analyze the leaf biomass flows and the defoliation intensity and frequency of Italian ryegrass (Lolium multiflorum Lam) grazed by heifers fed exclusively on pasture or on pasture and supplemented with corn or white oat grain. The experimental design was completely randomized following a repeated measures arrangement with three feeding systems and three area replications. Biomass flows (kg DM leaf blades ha1 day1) for leaf growth (40.6), leaf senescence (40.7), and leaf intake (29.7) were similar in the different feeding systems. Leaf blade intake adjusted to body weight was lower in supplemented heifers regardless of grain type. Actual and potential utilization efficiencies and ryegrass biomass net balance were not affected by feeding system. The leaf intake flow was 1.4 times lower than the growth flow, resulting in an actual utilization efficiency less than one (0.7), whereas the senescence flow was higher than the growth flow, resulting in a negative potential utilization efficiency (0.2). Leaf defoliation intensity was similar (54.4%) across feeding systems and defoliation frequency was higher in supplemented heifers. The 29.2% increase in stocking rate of heifers fed corn or oat grain as supplement did not affect the dynamics of ryegrass biomass flows, but reduced leaf blade intake adjusted to heifer body weight leading to alterations in the defoliation frequency of ryegrass pasture.

Seedling Defoliation and Drought Stress: Variation in Intensity and Frequency Affect Performance and Survival

Our ability to restore rangelands is limited, and it is unknown if seedling herbivory on its own, or in interaction with other stressors, is a major contributor to restoration failure. To address this, we conducted two experiments: a No Defoliation (ND) experiment (n = 48), in which seedlings from three perennial grasses (crested wheatgrass [Agropyron cristatum {(L.} Gaertn.], bluebunch wheatgrass [Psuedoroegnaria spicata {Pursh} Á. Love], Sandberg bluegrass [Poa secunda J Presl]) were subjected to wet and dry water regimes for 4 mo, and a concurrent Defoliation (D) experiment (n = 95), in which seedlings were factorially assigned to two defoliation treatments—frequency (LOW, HIGH) and intensity (30% vegetation removal, 70% vegetation removal). Indicators of seedling performance were aboveground and belowground biomass (AGB and BGB), root:shoot ratio, tillering, and mortality. The effect size statistic, Hedge’s g, allowed for comparisons between performance measures. Water stress induced reductions in most performance measures: BGB (g = ND: –1.3; D: –1.6), root:shoot ratio (g = ND: n.s.; D: –0.2), and tillering (g= ND: –1.7; D: –1.2), though not significantly for all species. For ABG, water stress interacted with defoliation, reducing performance less at an intensity of 70% (g = –2.0) as opposed to 30% (g = –3.0), but not always significantly in the former. Water stress also caused less reduction in AGB when no defoliation occurred (ND: –0.8; g = D: –2.5). Intensity and frequency of defoliation interacted; seedlings were generally resistant to reductions in performance except at high frequency, 70% defoliation. Agropyron cristatum and P. spicata displayed similar sensitivity to treatments, mostly in terms of changes in AGB and BGB, while P. secunda also experienced increased mortality and reduced tillering. If these differences in sensitivity result in differential survival, herbivory could impact species postrestoration population demographics.

Changes in water‐soluble carbohydrates relative to crude protein in perennial ryegrass in response to defoliation frequency

AbstractThe water‐soluble carbohydrate relative to crude protein (WSC:CP) ratio in perennial ryegrass (Lolium perenne L.) has been postulated as a useful indicator of nitrogen (N) use efficiency in grazing dairy cows. A mini‐sward study was conducted to quantify the effects of defoliation frequency based on leaf stage on the CP fractions and the WSC:CP ratio in perennial ryegrass. Defoliation frequency corresponded to the time taken by ryegrass to develop 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 leaves per tiller. Plant growth dynamics and plant nutritive parameters related to N use efficiency were measured. The results showed that perennial ryegrass plants that were defoliated more frequently had reduced herbage mass accumulation, leaf elongation rate and total lamina length than plants defoliated less frequently in both growth cycles. Extending the defoliation frequency from the one‐ to five‐leaf stage resulted in a decline in WSC content, an increase in CP and buffer soluble CP and a decline in the WSC:CP ratio. Given the defoliation frequencies tested here, we concluded that plants defoliated too frequently have a potential risk of low N efficiency use by grazing animals, due to a low WSC:CP ratio. The best nutritional quality balance occurs when plants were defoliated at the 3.0‐leaf stage during the first growth cycle and at the 2.0‐leaf stage during the second growth cycle.

Tillering dynamics of Mulato grass subjected to strategies of rotational grazing management

SUMMARYPlants’ ability to rebuild their tiller population is affected by weather changes and management strategies. The hypothesis of the present study was that frequency and severity of defoliation alter Mulato grass (Brachiaria ruziziensis × Brachiaria brizantha cv. Marandu) sward development, and the proportion of aerial and basal tillers, interfering with sward stability. The objective was to evaluate aerial, basal and total tiller population density and changes in tillering dynamics. Treatments corresponded to strategies of rotational grazing characterized by combinations between two pre-grazing (95% and maximum canopy light interception during regrowth; LI95% and LIMax) and two post-grazing conditions (15 and 20 cm stubble height). The experimental period comprised four seasons of the year: summer 2008 (February–March 2008); autumn–early spring (April to mid-November 2008); late spring (mid-November–December 2008); and summer 2009 (January–March 2009). Density of aerial tillers decreased from summer 2008 to late spring. Tiller death decreased from summer 2008 to autumn–early spring. Aerial and total tiller death increased from late spring to summer 2009, mainly for the LI95% treatment. No differences were observed in the tiller population stability index of aerial tillers for LI treatments or post-grazing heights. The balance between tiller appearance and death for basal tillers remained relatively stable from summer 2008 to late spring. For aerial tillers the balance decreased to negative values from summer 2008 to autumn–early spring for both LI treatments. For total tiller population, the balance decreased to negative values from summer 2008 to autumn–early spring. Results indicated a strong seasonal effect on Mulato grass tillering and growth. Tillering dynamics were affected primarily by grazing frequency, which changed the relative importance of basal and aerial tillers. The results suggested that basal tillering was the predominant perennation pathway.

Productive characteristics of the grass Digitaria umfolozi subjected to defoliation frequencies

An experiment was carried out to evaluate the dry matter production, total dry matter availability, daily dry matter accumulation rate, light interception, leaf area index, daily accumulation rate, dry matter availability of the morphological components (leaf blades, stems + sheaths and dead material), leaf/stem ratio, crude protein, neutral detergent fibre and acid detergent fibre of Faixa-Brancagrass under seven defoliation frequencies (14, 21, 28, 35, 42, 49, and 56 days). Longer defoliation frequencies reduced the percentage of leaf blades and increased the percentage of stems + sheaths. The defoliation frequency positively influenced the availability of leaf blades, stems + sheaths, dead material and total dry matter. In the range of 42 days of defoliation, light interception reached 95%. At frequencies of 14 and 21 days of defoliation, the crude protein content of the leaves was above 20%. The highest utilization efficiency of D. umfolozi grass is achieved when the forage is managed with cutting intervals of 40 to 46 days. Higher defoliation frequencies positively contribute to the increase in the number of total white band grass leaves and higher crude protein content of the leaf blades and stems + sheaths.

Timing and frequency are the critical factors affecting the impact of defoliation on long term growth of plantation eucalypts

Insect defoliation of plantation Eucalyptus sp. is a ubiquitous problem, not only in their native Australia but also in many other countries where Australian defoliators have invaded the introduced eucalypt plantations. Although eucalypts are very resilient to defoliation, their growth suffers and reduces the economic benefits of the resource. An artificial defoliation trial investigated the critical factors relating to patterns of insect defoliation that affect the long-term growth of the plantation eucalypt, E. nitens, in Tasmania, Australia. Current season’s adult-phase foliage was removed manually from two- to three-year-old trees to test four factors: severity (50% or 100% of current adult foliage, equivalent to 11% or 25% of total foliage); disbudding following defoliation (with or without disbudding), timing of defoliation (early or late in the summer) and frequency (for one or two consecutive years). Growth parameters of the trees were measured annually for four years after the initial defoliation, and again thirteen years later, before harvest. The most significant factors affecting the growth of the trees were timing and frequency of defoliation; severity of defoliation and disbudding did not have significant effects over the long term. Trees that received either light or heavy defoliation late in the season for two consecutive years were at least 17% smaller in diameter and MAI in diameter was reduced by at least 21% compared to untreated trees over one rotation. This means they would need to be grown for three to four more years to reach the same stand volume as undefoliated trees at harvest. This would have serious cost implications for plantation managers. To prevent these economic losses, an integrated pest management system should focus on protecting eucalypts from defoliation of 50% or more of current season’s adult foliage late in the summer, and in particular, preventing defoliation from occurring in concurrent years. In addition, the continual decline in growth rates of defoliated trees relative to undefoliated trees beyond the initial four years of measurement also suggests that defoliation impacts predicted by models based on short term studies may need to be treated conservatively.

<b>Efficiency of the use of ryegrass by heifers in response to the receival of supplement

The intensity and frequency of defoliation of ryegrass (Lolium multiflorum Lam.) by beef heifers exclusively grazing or receiving corn grain or extruded commercial product with fat as supplement were evaluated. The grazing method was put-and-take stocking. The experimental design was completely randomized following a repeated measure arrangement, three treatments and two area replications. The phyllochron of ryegrass was 140.1 and 303.4°GD the leaf lifespan. The intensity (67.0 %) and the frequency of defoliation (6.4 days) were similar, regardless of supply or no of energetic supplement for grazing heifers. The defoliation frequency indicates that the heifers can return about 3.3 times to the same tiller during the leaf lifespan. Considering the different categories of leaf blades, the supply of extruded fat causes the heifers to remove higher proportion (66.5 %) of expanding leaf blades. On ryegrass pasture, the efficiency of forage use is not modified when heifers receive energetic supplement.

ESTRUTURA E PRODUTIVIDADE DE CAPIM-TANZÂNIA SUBMETIDO A DIFERENTES FREQUÊNCIAS DE DESFOLHAÇÃO

Resumo Objetivou-se com este trabalho avaliar o efeito de diferentes frequências de desfolhação em períodos fixos sob as características estruturais e produtivas do dossel de capim-Tanzânia (Panicum maximum Jacq) em condições climáticas Am no ano de 2014. O delineamento experimental foi em blocos casualizados com seis tratamentos correspondentes a seis frequências de desfolhação (14; 21; 28; 35; 42 e 49 dias) e cinco repetições e os dados foram submetidos a análise de regressão. A interceptação luminosa (IL) aumentou (P<0,05) de maneira assintótica com o aumento dos períodos de descanso, no qual a máxima interceptação de luz foi de 98% e ocorreu aos 42 dias de rebrotação. O índice de área foliar (IAF) e o acúmulo de matéria seca, aumentaram (P<0,05) linearmente variando de 3,6 a 7,1 e de 880,3 a 4051,7 kg.ha-1 de matéria seca de forragem, nas frequências de 14 a 49 dias, respectivamente. A altura variou de 44 a 119 cm nas frequências de 14 a 49 dias, respectivamente. A frequência de desfolhação que representa uma IL de 95% está relacionada ao período de descanso de 29 dias, em que o dossel de capim-Tanzânia apresentou altura em torno de 63 cm, IAF crítico de 5,1 e acúmulo de matéria seca de forragem de 2.160 kg.ha-1.

Biomass flow and defoliation pattern in alexandergrass fertilized with nitrogen

The determination of biomass flows can assist on improving pasture fertilization techniques, contributing to identify the best management methods and, in relation the use of fertilizers. Nitrogen deficiency in pastures can reduce forage production. On the other hand, there is an environmental concern on nitrogen (N) losses when this nutrient is used in excess and this concern guides the search for new grazing systems that optimize its use. Leaf biomass flow, intensity and frequency of defoliation were evaluated in Alexandergrass ( Urochloa plantaginea (Link) Hitch) fertilized with Zero, 100, 200 or 300 kg/hanitrogen (N) as urea. The grazing method was put and take stocking in order to keep the forage mass at 3,000 kg/haDM. The experimental animals were Angus heifers with an initial age of 15 months and body weight of 241.5±5 kg. The experimental design was completely randomized following a repeated measure arrangement, with four treatments and variable number of experimental units. The highest growth of leaf blades was achieved with 100 kg/haN. Senescence and intake flows and defoliation intensity were similar among the N levels used. The frequency of return to the same tiller (days) was influenced by N levels and evaluation periods. Our findings recommend the use of 100 kg/ha N in Alexandergrass pasture.

Leaf morphogenesis influences nutritive-value dynamics of tall fescue (Lolium arundinaceum) cultivars of different leaf softness

The objective of this study was to compare the dynamics of neutral detergent fibre (NDF), and the 24-h in-vitro digestibility of NDF (NDFD) and dry matter (DMD) in leaf blades of two tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) cultivars of different leaf softness: a soft- and a tough-leaved cultivar. The experiment was conducted during the summer regrowth of three replicated, dense mini-swards per cultivar arranged in a completely randomised design, all grown under non-limiting water, nitrogen and phosphorus. Cultivars were harvested eight times over 14 weeks to measure morphogenetic traits and nutritive value in six predefined leaf-age categories (from growing to complete senescence). The leaf lifespan and leaf length of the first three successive leaves were measured on 30 marked tillers throughout the experiment. Following analysis of variance, linear regression models were fitted to describe variations of NDF, NDFD and DMD with increasing leaf age and leaf length. Similar leaf NDF contents were found for the two cultivars, which remained stable throughout the leaf lifespan and increased markedly during leaf senescence. Leaf NDFD and leaf DMD both declined with increasing leaf age and length for the two cultivars. However, owing to shorter leaf lifespan of the soft-leaved cultivar, this decline in leaf NDFD and leaf DMD was faster for the soft- than for the tough-leaved cultivar. These results suggest that the soft-leaved cultivar will require more frequent defoliations than the tough-leafed cultivar to prevent decreases in nutritive value.

Defoliation management of kleingrass (Panicum coloratum L. var coloratum) cv Verde

The defoliation frequency determines above and below ground biomass accumulation, pasture structure and nutritive value. Two defoliation experiments with Panicum coloratum were performed, from September to March. One of them was conducted in pots under greenhouse conditions, and the other one in field plots for three growing seasons (EC) at the Faculty of Agronomy, La Pampa, Argentina (36˚ 46' S; 64˚ 16' W). Defoliation frequency treatments were four cutting intervals (IC; 3, 4, 6 and 8 weeks). In greenhouse experiment, live leaf blade accumulation rates (TAL), tiller appearance (TAM) and death (TMM) rates, live leaf blade length (LL) and above and below ground dry matter (MS) accumulation were determined. In field plots tiller height, weight and tiller, crude protein (PB) and dry matter accumulation were determined. TAL and the TAM were 1.28 (0.1024 vs 0.0798 cm/tiller/°Cd; P

CARACTERIZAÇÃO MORFOLÓGICA EM PASTOS DE CAPIM-MARANDU SUBMETIDOS A FREQUÊNCIAS DE DESFOLHAÇÃO E NÍVEIS DE ADUBAÇÃO

Resumo Os perfilhos são as unidades básicas de crescimento das gramíneas forrageiras e o perfilhamento é responsável pela adaptação e reestabelecimento da gramínea após a desfolhação. Portanto, é importante conhecer as modificações morfológicas dos perfilhos em função do ambiente de desfolhação e da adubação, duas importantes estratégias de manejo das pastagens. Assim, objetivou-se com este trabalho caracterizar as respostas morfológicas dos perfilhos do capim-marandu, em resposta à adubação e à frequência de desfolhação, para melhor compreensão da plasticidade fenotípica dessa planta. O trabalho foi realizado em dois anos experimentais, em que foram avaliados distintos intervalos de corte (sete, 14, 28, 56 e 112 dias), utilizando-se o delineamento em blocos casualizados, com quatro repetições. No segundo ano, além dos mesmos intervalos de corte avaliados no primeiro ano, também foram estudadas duas condições de adubação, sendo uma baixa (21,5 kg.ha-1 de P e 75 kg.ha-1 de N) e outra alta (43 kg.ha-1 de P e 300 kg.ha-1 de N). No segundo ano, utilizou-se o esquema fatorial. Em ambos os anos, as respostas para comprimento de colmo, comprimento da lâmina foliar, espaço entre as lâminas foliares e área foliar e peso do perfilho foram crescentes com o intervalo de corte. No segundo ano, a alta dose de adubos proporcionou maior número de perfilhos vegetativos, espaço entre lâminas foliares, área foliar, peso de perfilhos, folhas e colmos mais compridos, em comparação à baixa dose de adubos. No segundo ano, houve maior densidade populacional de perfilho reprodutivo com o maior intervalo de corte. A desfolhação e a adubação nitrogenada e fosfatada causam modificações morfológicas nos perfilhos do capim-marandu, indicando a ampla plasticidade fenotípica desta gramínea.

ÍNDICE DE HORIZONTALIDADE E REMOÇÃO DE TECIDOS DO CAPIM-MARANDÚ

Resumo É possível que a maior disponibilidade de nutrientes no solo promova modificação mais acentuada da forma de crescimento da planta forrageira sob alta frequência de desfolhação. Para testar essa hipótese, caracterizaram-se as modificações na forma de crescimento da Brachiaria brizantha cv. Marandu syn. Urochloa brizantha cv. Marandu (capim-marandu) submetida aos intervalos de corte e à adubação, bem como avaliou-se o efeito dessas modificações sobre as forragens removida e remanescente do corte. O trabalho foi realizado em dois períodos experimentais. Em cada período, experimentos independentes, porém com natureza semelhante, foram realizados. No Experimento 1, de outubro de 2013 até fevereiro de 2014, o capim-marandu foi adubado com 70 kg.ha-1 de N e 50 kg.ha-1 de P2O5 e foram avaliados intervalos de corte (sete, 14, 28, 56 e 112 dias), em delineamento em blocos casualizados, com quatro repetições. No Experimento 2, de novembro de 2014 até março de 2015, além dos mesmos intervalos de corte avaliados no Experimento 1, também foram estudadas duas condições de adubação, sendo uma baixa (50 kg.ha-1 de P2O5 e de 75 kg.ha-1 de N) e outra alta (100 kg.ha-1 de P2O5 e 300 kg.ha-1 de N). No Experimento 2, utilizou-se o esquema fatorial, com dois níveis de adubação e cinco níveis de intervalos de corte, e o delineamento em blocos casualizados, com quatro repetições. No Experimento 1, os maiores índices de horizontalidade (IH) ocorreram (p<0,05) nas plantas sob intervalos de corte de sete, 14 e 28 dias, em relação às plantas cortadas a cada 56 e 112 dias. No Experimento 2, apenas a planta cortada a cada sete dias apresentou (p<0,05) aumento do IH (de 1,3 para 1,5) com a melhoria da alta condição de adubação. A massa de forragem remanescente aumentou (p<0,05) com o intervalo de corte, de 412 para 483 g.m-2 e de 412 para 571 g.m-2 nos Experimentos 1 e 2, respectivamente. No Experimento 2, ocorreu aumento (p<0,05) da massa de forragem remanescente (de 447 para 505 g.m-2) e da percentagem de colmo vivo (de 23 para 33%) com a adubação em todos os intervalos de corte. Em ambos os experimentos, os maiores intervalos de corte incrementaram (p<0,05) a massa de forragem removida (de 95 para 840 g.m-2 e de 44,8 para 843 g.m-2 nos experimentos 1 e 2, respectivamente) e o índice de área foliar (IAF) removido (de 1,0 para 4,3 e de 0,4 para 3,9 nos experimentos 1 e 2, respectivamente). No Experimento 2, a melhoria da condição de adubação resultou em aumento (p<0,05) da massa de forragem removida (de 261,3 para 391,8 g.m-2) e do IAF removido (de 1,6 para 2,1). No Experimento 2, quando a condição de adubação foi alta, houve (p<0,05) menor percentagem de folha viva removida nos dosséis sob cortes intermediários (28 e 56 dias). Quando a desfolhação é muito frequente, a maior disponibilidade de nutrientes no solo contribui para que o capim-marandu modifique sua forma de crescimento de ereta para prostrada, em comparação à condição de menor disponibilidade de nutrientes no solo. O aumento do intervalo de corte e a adubação incrementam a remoção da forragem do capim-marandu.

An initial investigation of forage production and feed quality of perennial wheat derivatives

Perennial cereals may offer a novel forage source in mixed farming enterprises while improving the sustainability of grain farming. There has been limited analysis of the quality of this forage type and its likely value to mixed grazing/cropping farming systems. This study evaluated the biomass and grain production of four wheat × wheatgrass hybrid experimental lines under four simulated grazing regimes; nil defoliation (grain only; D0), defoliate once (D1), defoliate twice (D2) and defoliate twice followed by a simulated hay cut (D3), and compared performance to a winter wheat, Wedgetail, and the perennial grass Thinopyrum intermedium. Early biomass production of the perennial entries was significantly less than Wedgetail (P = 0.01). Grain yield from Wedgetail was generally higher (P < 0.001) than all other lines. As defoliation frequency increased, the comparative difference in grain yield between Wedgetail and the hybrid entries decreased, with lines OK7211542 and 11955 exceeding the grain yield of Wedgetail in the D3 treatment. Cumulative annual biomass production of the hybrid lines exceeded that of Wedgetail, though the seasonal production differed markedly. Generally there was limited decline in perennial plant population between April and December in both years of the experiment. Defoliation had little impact on perennial plant survival; however, none of the hybrids could sustain a significant plant population beyond the second summer of the experiment. Yield declines of the hybrid entries was due to increasing plant mortality, rather than a predisposed yield limitation of the germplasm, as all hybrid entries either maintained or increased their grain yield on a per plant basis. In contrast, the perennial grass maintained a constant population for the duration of the experiment. Dry matter digestibility and energy content of all forages tested were high, averaging 80.2% and 13.3 MJ ME/kg DM, respectively. Crude protein was higher (P < 0.001) in Th. intermedium and the hybrid entries with 62% and 25% more crude protein than Wedgetail, respectively. All cereals had very high potassium : sodium and low calcium : phosphorus ratios, which indicated the need to provide mineral supplements to grazing animals to maintain growth rates and manage animal health disorders, similar to conventional grazing cereals. This paper discusses the role perennial cereals could play in a sustainable expansion of the cropping zone in south-eastern Australia.

Carbohydrate and crude protein fractions in perennial ryegrass as affected by defoliation frequency and nitrogen application rate

AbstractThe objective of this study was to evaluate the effects of defoliation frequency (either at two‐ or three‐leaf stage) and nitrogen (N) application rate (0, 75, 150, 300, 450 kg N ha−1 year−1) on herbage carbohydrate and crude protein (CP) fractions, and the water‐soluble carbohydrate‐to‐protein ratio (WSC:CP) in perennial ryegrass swards. Crude protein fractions were analysed according to the Cornell carbohydrate and protein system. Carbohydrate fractions were analysed by ultra‐high‐performance liquid chromatography. Sward defoliation at two‐leaf stage increased the total CP, reduced the buffer‐soluble CP fractions and decreased carbohydrate fractions of herbage (P < 0·001). The effect of defoliation frequency was less marked during early spring and autumn (P < 0·001) than for the rest of the seasons. An increase in N application rate was negatively associated with WSC, fructans and neutral detergent fibre (P < 0·001), and positively associated with CP and nitrate (N‐NO3) contents of herbage. Nitrogen application rate did not affect CP fractions of herbage (P > 0·05). The fluctuations in CP and WSC contents of herbage resulted in lower WSC:CP ratios during early spring and autumn (0·45:1 and 0·75:1 respectively) than in late spring (1·11:1). The herbage WSC:CP ratio was greater (P < 0·001) at the three‐leaf than the two‐leaf defoliation stage and declined as the N application increased in all seasons (P < 0·001). The results of this study indicate that CP and carbohydrate fractions of herbage can be manipulated by sward defoliation frequency and N application rate. The magnitude of these effects, however, may vary with the season.

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

AbstractManagement 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.

Consequences of Repeated Defoliation on Belowground Bud Banks of Carex brevicuspis (Cyperaceae) in the Dongting Lake Wetlands, China

Despite the predominant role of bud banks in the regeneration of clonal macrophyte populations, few studies have examined the way in which clonal macrophytes adjust the demographic features of bud banks to regulate population dynamics in response to defoliation in wetlands. We investigated the density and composition of bud banks under repeated defoliation in the wetland sedge Carex brevicuspis C. B. Clarke in the Dongting Lake wetlands, China. The density and biomass of rhizome buds and shoots did not decrease significantly in response to repeated defoliation over two consecutive years. The composition of bud banks, which consisted of long and short rhizome buds, also did not change significantly in response to repeated defoliation. Nevertheless, the ramet height and the shoot, root, and rhizome mass of C. brevicuspis declined significantly under repeated defoliation. Our findings suggest that bud banks are a conservative reproductive strategy that enables C. brevicuspis to tolerate a certain amount of defoliation. The maintenance of large bud banks after repeated defoliation may enable C. brevicuspis populations to regenerate and persist in disturbed habitats. However, bud bank density of C. brevicuspis might decline in the long term because the amount of carbon stored in rhizome buds and plants is reduced by frequent defoliation.

Role of Herbivore Impact and Subsequent Timing and Extent of Recovery Periods in Rangelands

The productivity and stability of cattle production on rangelands depends on the maintenance of a dense and productive perennial grass−dominated resource base, which is contingent on appropriate grazing and recovery periods. We investigated the effect of simulated trampling, dung inputs, frequency of defoliation in the previous growing season (grazing history), and timing of recovery periods on various grassland functional responses in two experiments in western and northwestern Botswana. A field-based clipping experiment at the individual tuft scale demonstrated that perennial grasses are most productive when rested for a full growing season, but that productivity of the highly palatable soft leaved Brachiaria nigropedata Ficalho & Hiern. decreases exponentially with increasing clipping frequency in the previous season (a lagged effect of grazing history). This species was also more productive in the next season when rested during the early than late growing season. The less palatable needle-leaved Stipagrostis uniplumis Licht. ex Roem. & Schult. was less resistant to defoliation than B. nigropedata and decreased equally at each clipping frequency regardless of season. A second field-based experiment at the plot scale demonstrated that a full-season recovery period increased tuft densities while its combination with dung increased cover. The effects of hoof trampling on sandy nutrient-poor grasslands appear to be less significant compared with grasslands on fertile soils. Thus, optimal livestock management strategies should aim to promote season-long grazing of both palatable and unpalatable species to disadvantage the less grazing-tolerant unpalatable species and full growing season recovery periods to ensure optimal recovery and future productivity.