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1.
The impact of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on plant population density, ground cover and soil moisture in a hill pasture (annual grass dominated, with Australian native grasses being the major perennial species) were studied in a large‐scale field experiment from 2002 to 2006 in southern Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January each year), long‐term deferred grazing (no defoliation from October to the autumn break, that is the first significant rainfall event of the winter growing season) and optimized deferred grazing (withholding time from grazing depends on morphological development of the plants). These treatments were applied with two fertilizer levels (nil fertilizer and 50 kg P ha?1 plus lime) and two additional treatments [continuous grazing (control) and no grazing for year 1]. Deferred grazing increased (P < 0·05) perennial grass tiller density compared with the control. On average, the tiller density of the three deferred grazing treatments was 27–88% higher than the control. There was a negative (P < 0·01) relationship between perennial and annual grass tiller density. Fertilizer application increased (P < 0·05) legume plant density. The densities of annual grasses, legumes, onion grass (Romulea rosea) and broadleaf weeds varied between years, but perennial grass density and moss cover did not. The ground cover of the deferred grazing treatments in autumn was on average 27% higher than the control. Soil moisture differed between treatments at 15–30 cm depth, but not at 0–15 depth over autumn and winter. The results imply that deferred grazing can be an effective tool for rejuvenating degraded native pastures through increases in native grass tiller density and population and through improving farm productivity and sustainability.  相似文献   

2.
Little is known of the effect of selective plant defoliation at different intensities and frequencies in altering weed-forage dynamics in pasture. We conducted a field experiment to quantify Cirsium arvense responses to varying defoliation regimes of neighboring forage implemented for 2 years under high or low fertility conditions. Defoliation regimes were based on common grazing systems, and included: (1) high intensity–high frequency (HIHF) defoliation simulating continuous grazing, (2) high intensity–low frequency (HILF), (3) low intensity–high frequency (LIHF), and (4) deferred (DEF) defoliation to peak growth in late summer. All vegetation except C. arvense was defoliated during the growing season to examine weed responses to changes in neighboring forage abundance. Year-end C. arvense biomass at the end of the study was greatest in the HIHF treatment and lowest in the DEF, with the LIHF and HILF treatments intermediate in response. The HILF treatment also provided improved suppression of C. arvense biomass relative to the LIHF, although this response was inconsistent among sites. Trends in C. arvense shoot densities among defoliation treatments were similar to those for biomass. While weed abundance was lower in the absence of fertilization, rankings among defoliation treatments remained the same. Notably, trends in forage biomass among defoliation regimes followed a pattern opposite that of C. arvense, and are implicated in observed weed decreases. Our results indicate that defoliation regimes enhancing forage growth and biomass, particularly a DEF or HILF regime, reduce C. arvense the most. Grazing systems that employ these defoliation regimes are therefore likely to optimize the interspecific competitive suppression of C. arvense.  相似文献   

3.
The morphogenetic responses of individual tillers and the composition of tiller populations throughout regrowth in response to all combinations of two post‐grazing heights (35 and 45 cm) and two pre‐grazing conditions (95% and maximum canopy light interception during regrowth – LI95% and LIMax) were studied in swards of elephant grass (Pennisetum purpureum Schum. cv. Napier) from November 2011 to April 2012. Swards were subjected to the same treatments from January 2011 until measurements began, to enable them to adapt to the defoliation regimes. Treatments were allocated to experimental units (850 m2 paddocks) according to a 2 × 2 factorial arrangement in a randomized complete block design, with four replications. The total number of tillers (basal + aerial) was similar for both LI pre‐grazing targets. However, there was a change in the preferential growth pathway used by plants characterized by modification in the proportion of tiller classes in plant population. Swards managed with the LIMax target had a smaller population density of basal tillers and used the recruitment of aerial tillers as the main growth pathway. Although effective for maintaining stable rates of leaf elongation and senescence, such a strategy resulted in greater tiller death. Additionally, stem elongation, a consequence of the competition for light under those circumstances, resulted in differences in sward herbage mass and morphological composition with potential implications for herbage feeding value.  相似文献   

4.
Nitrogen (N) inputs are recognised to maximise herbage mass (HM) in tropical perennial grasses, whereas less is clear on their impact on HM distribution and the effects on leaf mass (LM) and leaf area index (LAI) in the upper stratum. This 2 year study, carried out in Pirassununga, Brazil, assessed the HM distribution in the upper (>20 cm) and lower (<20 cm) strata in Urochloa hybrid ‘Mavuno’ grass maintained under similar pre- and post-cutting canopy heights with contrasting N fertilisation rates applied after each cutting (no-nitrogen, 15, 30, and 45 kg N ha−1). The relevance of specific leaf area (SLA), leaf N concentration (NLeaf), tiller weight (TW) and population density to the LM and LAI of the upper stratum were also examined. Mavuno grass expressed a stable HM < 20 cm (59%–71% during Year I and 66%–80% for Year II), and apparent N fertilisation impacts on HM > 20 cm were verified at specific regrowth cycles during Year II. Mavuno grass pastures expressed plasticity for adjustments on leaf, tiller and population attributes, which were modulated by both climatic conditions and N fertilisation. Under favourable growth conditions during Year I, fertilised pastures were able to sustain higher NLeaf and SLA but associated with lower TW, resulting in maximisation of LAI but not in LM in the upper stratum. During Year II, fertilised pastures expressed higher NLeaf, SLA, number of basal tillers, despite the lowest TW, which resulted in higher LAI and LM in the upper stratum compared with non-fertilised pastures. Our results highlighted that adjustments on leaf and population attributes within the canopy were driven to maximise the upper stratum LAI, being positively affected by N fertilisation.  相似文献   

5.
A field study was undertaken between April 2003 and May 2004 in southern Tasmania, Australia to quantify and compare changes in herbage productivity and water‐soluble carbohydrate (WSC) concentration of perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under a defoliation regime based on leaf regrowth stage. Defoliation interval was based on the time taken for two, three or four leaves per tiller to fully expand. Dry‐matter (DM) production and botanical composition were measured at every defoliation event; plant density, DM production per tiller, tiller numbers per plant and WSC concentration were measured bimonthly; and tiller initiation and death rates were monitored every 3 weeks. Species and defoliation interval had a significant effect (P < 0·05) on seasonal DM production. Prairie grass produced significantly more (P < 0·001) DM than cocksfoot and ryegrass (5·7 vs. 4·1 and 4·3 t DM ha?1 respectively). Plants defoliated at the two‐leaf stage of regrowth produced significantly less DM than plants defoliated at the three‐ and four‐leaf stages, irrespective of species. Defoliation interval had no effect on plant persistence of any species during the first year of establishment, as measured by plant density and tiller number. However, more frequent defoliation was detrimental to the productivity of all species, most likely because of decreased WSC reserves. Results from this study confirmed that to maximize rates of regrowth, the recommended defoliation interval for prairie grass and cocksfoot is the four‐leaf stage, and for perennial ryegrass between the two and three‐leaf stages.  相似文献   

6.
Soil occupation capacity via lateral expansion of tussocks in elephant grass (Pennisetum purpureum Schum.) may be associated with basal tillering. As grazing management alters the proportion of basal and aerial tillers in a tiller population, the hypothesis of this work was that grazing management affects tussock size and distribution with implications for plant population stability. The objective of this study was to evaluate the tiller population stability index, the proportion of basal and aerial tillers, tussock size, and the frequency of tussocks and bare ground in rotationally managed elephant grass cv. Napier. Treatments resulted from the combination of two post‐grazing heights (35 and 45 cm) and two pre‐grazing conditions (95% and maximum canopy light interception during regrowth – LI0·95 and LIMax) and were allocated to experimental units (850 m2 paddocks) according to a 2 × 2 factorial arrangement in a randomized complete block design, with four replications. Measurements were taken from January 2011 to April 2012. The post‐grazing height treatments affected the tiller population stability index, but did not influence the pattern of tussock distribution. On the other hand, the different grazing frequencies (targets of LI pre‐grazing) altered the pattern of tussock distribution and the proportion of bare ground. In general, the tiller population stability index and frequency of tussocks were higher and the frequency of bare ground lower on swards managed with the LI0·95 target relative to those managed with the LIMax target, regardless of the post‐grazing height used, indicating a larger soil occupation capacity of plants under the more frequent defoliation regime. Such responses were associated with larger population of basal tillers and highlight the importance of tiller category and perennation pathway in defining patterns of plant growth and tussock distribution.  相似文献   

7.
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.  相似文献   

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

9.
A well‐established canopy is crucial for a stable mixed grass–legume forage pasture. The aim of this study was to assess a defoliation intensity that can ensure the establishment of mixed pasture of brachiaria grass (Brachiaria brizantha) intercropped with forage peanut (Arachis pintoi). The treatments comprised four canopy heights: 10, 20, 30 and 40 cm, maintained throughout the first 3 years of pasture establishment. Canopy structure, morphogenetic and structural characteristics were measured. A block design was used with four replicates, and seasons of the year were considered using repeated measurements over time. Light interception during the experimental period was 86.3%, 95.9%, 97.6%, and 99.1% for 10, 20, 30 and 40 cm of defoliation respectively (p < .001). Competition for light in taller canopies (at 30 and 40 cm) caused etiolation of forage peanut (greater internode, petiolate and stolon lengths). This response promoted its upward growth, leading to a lower stolon density compared with 10 and 20 cm. The treatment at 10 cm displayed a predominance of forage peanut (up to 0.614), potentially compromising community stability. Overall, the 20 cm canopy height showed a desired botanical composition (from 0.20 to 0.45 of legume in forage mass) and thus was considered an ideal defoliation intensity for establishment of mixed canopies of brachiaria grass and forage peanut.  相似文献   

10.
This study utilized leaf stage‐based defoliation intervals to describe the concentrations and contents of water‐soluble carbohydrate (WSC) and nitrogen (N) in stubble and root reserves and their effect on the regrowth of prairie grass (Bromus willdenowii Kunth.) plants. The priority sequence for allocation of WSC reserves during the regrowth period was also investigated. There were substantially higher concentrations of WSC and N in the stubble compared with the roots following defoliation, confirming the stubble as the primary site for energy storage, with roots playing a lesser role. However, high R2 values for the relationships between WSC concentration in roots and regrowth variables suggested that plants of prairie grass were reliant on WSC reserves from the roots in addition to the stubble to meet the energy requirements of plants until adequate photosynthetic tissue had been produced. The sequence of priority for allocation of WSC reserves followed the order of leaf growth, root growth and tillering during the regrowth period. Although WSC reserves were identified as the primary contributor to plant regrowth following defoliation, there was also a strong relationship between stubble N concentration and regrowth variables.  相似文献   

11.
Growth rate, proportion of leaf and stem and nutritive value of sown tropical perennial grasses have not previously been documented for the dryland, frost‐prone summer‐dominant rainfall region of eastern Australia. An experiment was conducted in northern inland New South Wales with Chloris gayana (Rhodes grass) cv. Katambora and Digitaria eriantha (digit grass) cv. Premier, and compared to Sorghum bicolor ssp. bicolor x S. bicolor ssp. drummondii (forage sorghum). The grasses were harvested every 2 or 6 weeks and fertilized at five rates of nitrogen (N; 0–300 kg N ha?1) over two growing seasons (September–May), 2006–2007 and 2007–2008. Growing season rainfall was below median for both years of the experiment and growth rate was highly variable, reflecting variable rainfall. Sorghum generally had the highest growth rate. Digit grass generally had higher growth rates than Rhodes grass, was more responsive to growing season rainfall, commenced growth earlier and had a longer growing season. Nitrogen application extended the growing season of both perennial grasses. Growth response to N application was minimal when rainfall was low and response following significant rainfall was higher for fertilized than unfertilized grasses. In general, the proportion of green leaf was greater than green stem, although the proportion of stem increased when defoliation interval increased. Nutritive value of the perennial grasses was higher in leaf than stem and declined during the growing season. Differences between the grasses were slight, but indicated that fertilized digit grass defoliated at 2‐week intervals had higher growth rate and nutritive value than Rhodes grass.  相似文献   

12.
This glasshouse study aimed to determine the relative importance of water-soluble carbohydrates (WSC) and current photosynthate on root and top regrowth of perennial ryegrass (Lolium perenne L.). Individual plants were arranged in one of two miniswards (Experiments 1 and 2) and underwent varying defoliation frequencies designed to obtain a gradient of WSC content at the final harvest of each treatment (H1), when all treatments were defoliated. In Experiment 1, the plants were defoliated either three times at the one new leaf per tiller stage of regrowth (treatment 3 × 1), once at the two-leaf and again at the one-leaf stage (treatment 2, 1), once at the one-leaf and again at the two-leaf stage (treatment 1, 2) or once only at the three-leaf stage (treatment 1 × 3), up to H1. Leaf and root growth and other parameters were assessed over 6 d after H1 in sunlight, and over a 4-week period in darkness, and related to initial plant WSC content. In Experiment 2, plant defoliation treatments were: 3 × 1, 1, 2 or 1 × 3. Leaf regrowth was assessed for 36 d until the plants had three fully expanded new leaves per tiller. Leaf regrowth in both experiments was significantly related to stubble WSC (below 50 mm height). In Experiment 1, plants were almost fully reliant upon plant reserves for the first 3 d of regrowth, with reliance decreasing up to 6 d. When regrowth of plants was compared after 1 week in light or in darkness, it was estimated that one-third of leaf regrowth was due to plant WSC reserves and the remainder due to photosynthesis. However, the capacity to photosynthesize and to grow roots after H1 was also significantly related to stubble WSC content. In Experiment 2, there was a significant difference (P<0·01) between defoliation treatments on leaf dry matter (DM) yield at 12 d (×1 leaf tiller?1) of regrowth, and this was, as in Experiment 1, significantly positively related to WSC content in the stubble. However, after 36 d of regrowth, DM yield of plants defoliated at 2 or 3 leaves tiller?1 up to H1 were similar, and both were significantly higher (P<0·01) than regrowth of plants defoliated at the one-leaf stage. After defoliation, the period of reliance on WSC reserves may be substantially increased in situations of shading (canopy competition or cloud cover) or if the new regrowth shoot is removed by regrazing.  相似文献   

13.
Developing sustainable grazing management systems based on perennial species is critical to preventing land degradation in marginal land classes. A field study was conducted from 2002 to 2006 to identify the impacts of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on herbage accumulation, soil seed reserve and nutritive value in a hill pasture in western Victoria, Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January), long‐term deferred grazing (no defoliation from October to the autumn break) and optimized deferred grazing (withholding time from grazing commenced between annual grass stem elongation and seed head emergence and concluded in February/March). These treatments were applied with two fertilizer levels (with or without fertilizer at 50 kg phosphorus ha?1 and 2000 kg lime ha?1 applied in year 1 only) in a factorial arrangement and two additional treatments: continuous grazing (CG) and no grazing (NG) in year 1. The deferred grazing treatments on average produced herbage dry matter of 4773 kg ha?1, the NG produced 4583 kg ha?1 and the CG produced 3183 kg ha?1 in year 4 (2005–06) of the experiment. Deferred grazing treatments with and without fertilizer application produced an average of 5135 and 4411 kg DM ha?1 respectively. Averaged over 4 years, deferred grazing increased the germinable seed pool of perennial grasses by 200% and annual grasses by 50% (except optimized deferred grazing that considerably decreased the annual grass seed pool) compared with the CG. The best of the deferred grazing strategies increased the digestibility of pastures by 7% compared with the CG. The results demonstrated that deferred grazing from spring to autumn followed by rotational grazing could be an effective tool to increase herbage production and soil seed pool and improve the digestibility of native pastures in the steep hill country of southern Australia.  相似文献   

14.
This work analysed the regulatory structural mechanisms involved in the competitive interactions between the annual grass Bromus willdenowii Kunth. (BW = prairie grass) and the perennial C3 grass Dactylis glomerata L. (DG = orchardgrass) during pasture establishment. Four combinations of species (pure BW, pure DG, DG flanked by BW and BW flanked by DG plants), with and without winter nitrogen fertilization, were factorially arranged in a randomized complete block design. Data were recorded at two organization levels: tillers (three tiller age cohorts) and target plants. Annual neighbours caused a decrease in the number of living leaves in tillers of intermediate age of both species. This structural regulatory mechanism led to a decrease in tiller number per plant and, therefore, restricted the development of horizontal space occupation. Annual neighbours did not cause an increase in tiller size, measured as lamina length or pseudostem height, but decreased root biomass. As a consequence, annual neighbours did not lead the hierarchy in light capture, but limited species radical colonization and competitive ability for soil resources. Winter nitrogen fertilization only affected tiller size in older tillers. These findings emphasize the importance of the cultural decisions, as sowing densities and nitrogen fertilization, to optimize pasture floristic composition.  相似文献   

15.
In the moist mid‐latitudes of eastern Australia, soil water dynamics, herbage production and water use efficiency (WUE) were monitored during 2006–2008, for five perennial pastures: digit grass (Digitaria eriantha), Rhodes grass (Chloris gayana), forest bluegrass (Bothriochloa bladhii), native grass (Bothriochloa macra and Rytidosperma bipartita dominant), lucerne (Medicago sativa); and two forage crops: oat (Avena fatua) and sorghum (Sorghum bicolor). Ground cover formed more quickly in Rhodes grass and lucerne (>70% ground cover in 120 and 175 days after sowing [DAS] respectively) than in forest bluegrass and digit grass (245 and 365 DAS respectively). Values of maximum extractable water (MEW) for Rhodes grass and lucerne were similar (180–242 mm), while values for digit grass and forest bluegrass (129–175 mm) were equal to or greater than those for native grass, and two annual forage crops (77–144 mm). Lucerne expressed the maximum root depth (1.46 m), while values for the tropical grasses (0.96–1.39 m) were greater than native grasses and forage crops (0.87–0.96 m). Native grasses (6.5–12 t DM/ha) had the lowest herbage production, which resulted in values of WUE that were significantly less than most other treatments (16–21 vs. 23–43 kg DM ha?1 mm?1). Digit grass (33–34 kg DM ha?1 mm?1) had higher WUE compared with the other tropical grasses (20–27 kg DM ha?1 mm?1). The data collected here suggest that a forage system comprising digit grass, lucerne and forage oat would provide high production and WUE in this environment.  相似文献   

16.
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.  相似文献   

17.
Subtropical pastures are an important alternative to increase forage yields to fulfil cattle nutritional requirements. Despite the increasing expansion of these pastures in the semiarid subtropical region of Argentina, there is very little information about their responses to grazing management. The aim of this study was to evaluate the effect of different defoliation regimes on morphogenesis, sward structure and leaf area index of one of the most expanded forage species in this region, Chloris gayana Kunth. A combination of two defoliation frequencies (300 and 500 GDD) and two defoliation intensities (1 and 3 green stubble leaves) was compared by a controlled experiment that comprised 1,500 GDD. Defoliation frequency significantly affected leaf elongation rate (LER) and leaf area index (LAI). Under the high defoliation frequency, LER and LAI resulted almost half than under low defoliation frequency (0.34 ± 0.08 vs. 0.67 ± 0.08 mm·tiller?1·GDD?1; 8.31 ± 2.27 m2/m2 vs. 13.27 ± 1.59 m2/m2, at 300 or 500 GDD respectively), regardless of the intensity. Defoliation frequency or intensity did not affect leaf appearance rate, leaf lifespan, leaf size, number of green leaves per tiller nor tiller density at the end of the experiment. We conclude that to maintain high LER and LAI in Chloris gayana Kunth cv. Épica INTA‐Pemán pastures, defoliation frequency could be of 500 GDD. Since leaf lifespan was 415 ± 110 GDD, under this defoliation frequency, a maximum accumulation of green leaf tissues with very little dead tissues may be achieved.  相似文献   

18.
The objective of this work was to analyse the competitive interactions between Bromus willdenowii Kunth. (BW = prairie grass) and a perennial C 3 grass Dactylis glomerata L. (DG = cocksfoot) through morphogenetic traits, during pasture establishment. Four combinations of species (pure BW, pure DG, DG flanked by BW and BW flanked by DG plants), with and without winter nitrogen fertilization, were factorially arranged in a complete random block design. Data were recorded on three tiller age cohorts of the central target plant: the main stem and those that appeared 20 and 30 days after fertilization (daf). Leaf elongation rate (LER) of the older tillers was the only variable affected by nitrogen addition. Annual neighbours, which showed higher LER than perennial ones, caused a decrease in leaf lifespan in the younger tillers and a delay in the leaf appearance rate on the main stem and on 20‐daf tillers, and the tiller appearance rate. Annual neighbours controlled leaf and tiller dynamics and therefore restricted the vertical and horizontal space occupation of the target plant. These results reinforce the advantage of using a low seeding rate for the annual species to avoid negative effects on perennial grass establishment and persistence.  相似文献   

19.
Abstract This field study investigated the effect of timing of nitrogen (N) fertilizer application in spring on the survival of grazed perennial ryegrass (Lolium perenne cv. Dobson and Yatsyn) over summer in a subtropical environment. There were five N fertilizer treatments: no applied N, 46 kg N ha?1 on 22 October or 22 November or 22 December, or on 22 October and again on 22 December. Water‐soluble carbohydrate (WSC) concentration of perennial ryegrass plants entering the summer was altered by varying defoliation frequency, with defoliation interval based on the number of leaves per tiller. Frequent defoliation was set at a regrowth level of one leaf per tiller and less frequent defoliation at a regrowth level of three leaves per tiller, over a total of two by three‐leaf per tiller regrowth periods. Application of N fertilizer was found to have no significant effect (P > 0·05) on survival of perennial ryegrass plants over summer. On the other hand, defoliation had a marked effect on perennial ryegrass persistence, with frequent defoliation decreasing ryegrass plant density (51 vs. 88 plants m?2; P < 0·001) and increasing the density of tropical weed grasses (99 vs. 73 plants m?2; P < 0·001) by autumn. Frequently defoliated plants had a lower stubble WSC content on a per plant basis than less frequently defoliated plants in spring (103 vs. 201 mg per plant; P < 0·001) and summer (59 vs. 101 mg per plant; P < 0·001). The lower WSC content was associated with a smaller root system in spring (1·50 vs. 2·14 g per plant; P < 0·001) and autumn (1·79 vs. 2·66 g per plant; P < 0·01), and this was reflected in 0·29 more plants being pulled from the soil by livestock between November 1996 and April 1997. Rhizoctonia fungus was associated with roots of pulled plants, but not with roots of seemingly healthy plants, indicating that this fungus may have a role in a weakened root system, which was more prone to sod pulling. Nitrogen applied in October and November resulted in a reduced WSC concentration, although the effect was restricted to 1 month after N application. The present study indicates that survival of perennial ryegrass plants over the summer in a subtropical region is prejudiced by frequent defoliation, which is associated with a lower WSC concentration and a shallower root system. Under grazing, sod pulling is a reflection of this weaker root system and contributes to plant mortality.  相似文献   

20.
Dry matter (DM) production of multispecies swards compared to perennial ryegrass (Lolium perenne; PRG) swards under intensive grazing warrants investigation as it is relatively unknown. A 5 × 2 factorial experiment, with five sward types and two defoliation methods, was used to investigate the effect of grazing versus cutting on dry matter (DM) production of multispecies and PRG‐only swards. Five sward types were established namely: a PRG‐only sward, receiving 250 kg N ha?1 year?1 (PRG250), and a PRG‐only sward (PRG90), a two‐species sward with PRG and white clover (Trifolium repens; PRGWC), a six‐species sward (6S) and a nine‐species sward (9S), each receiving 90 kg N ha?1 year?1. Cutting plots measured 1.95 × 10 m and grazing plots measured 10 × 10 m. All plots were harvested concurrently every 21–30 days from April‐November for two years (2015 and 2016). A strip from the grazing plots was cut for DM yield determination prior to turning in cattle for grazing. There was an interaction between sward type and defoliation method (p < .01), whereby there was no effect of defoliation method on the PRG‐only swards, however, the annual DM production of PRGWC, 6S and 9S swards reduced under grazing compared to cutting (p < .001; on average 1,929 kg DM/ha lower). Multispecies swards had lower DM production under grazing compared to cutting, while the DM yield of PRG‐only swards was unaffected by defoliation method.  相似文献   

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