HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lee, J. M. Articles by Roche, J. R. Search for Related Content PubMed Articles by Lee, J. M. Articles by Roche, J. R. Agricola Articles by Lee, J. M. Articles by Roche, J. R. Related Collections Best Management Practices Grazing Management Turfgrass

PASTURE MANAGEMENT

Effect of Defoliation Severity on Regrowth and Nutritive Value of Perennial Ryegrass Dominant Swards

^a Dexcel Limited, Private Bag 3221, Hamilton 2020, New Zealand
^b Tasmanian Inst. of Agric. Res., Univ. of Tasmania, P.O. Box 3523, Burnie 7320, Tasmania, Australia

^* Corresponding author (julia.lee{at}dexcel.co.nz).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The height or mass to which swards are defoliated can potentially affect regrowth. A field study was undertaken to determine the response of perennial ryegrass (Lolium perenne L.) dominant swards to defoliation severity over repeated defoliations during a period of low water-soluble carbohydrate (WSC) accumulation (late spring to mid-autumn due to active leaf growth and relatively high respiration). Five defoliation severities (defoliation to a residual stubble height [RSH] of 20, 40, 60, 80, or 100 mm) were replicated five times in a Latin square design. During a 6-mo period, treatment plots were defoliated seven times using a rotary lawnmower. Analysis of data indicated a quadratic relationship between RSH and total herbage production, with total yields of 12,190, 13,440, 13,730, 13,320, and 11,300 kg DM ha^–1 for swards defoliated to 20, 40, 60, 80, and 100 mm, respectively. Regression analyses identified 56 mm as the optimal RSH for herbage production, but there was little biological significance between 40 and 80 mm RSH. Total WSC content per tiller was reduced with increasing defoliation severity. The relationship between WSC content per tiller and subsequent herbage yield was quadratic, with peak herbage yield at 9.4 mg tiller^–1 (60 mm RSH). The data indicate that between September (spring) and April (autumn), herbage production of temperate perennial ryegrass-dominant swards is maximized when defoliation severity results in post-grazing stubble heights of 40 to 80 mm.

Abbreviations: ADF, acid detergent fiber • CP, crude protein • DM, dry matter • DMD, dry matter digestibility • ME, metabolizable energy • NDF, neutral detergent fiber • RSH, residual stubble height • WSC, water-soluble carbohydrate

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Received for publication March 21, 2007.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
THE SEASONAL VARIATION in herbage production and animal requirements experienced in most temperate regions of the world results in potential differences between feed supply and demand in seasonal grazing systems (Parsons, 1988). If herbage production does not meet animal requirements then options such as manipulation of the environment (e.g., irrigation or fertilizer application), feeding supplements and/or possibly altering the herbage supply through grazing management could be considered. However, while it is important to maximize herbage production, it is important that this does not occur at the expense of the forage nutritive value.

The height or mass to which swards are defoliated, i.e., the postgrazing residual, can potentially affect regrowth. However, published effects have been inconsistent. Some researchers have concluded that less severe defoliation (leaving residual leaf, >1500 kg dry matter [DM] ha^–1, >40 mm RSH) will result in quicker regrowth of grass swards (Smith, 1974; Booysen and Nelson, 1975). Contrasting results (Bryant and Blaser, 1961; Reid, 1962; Binnie and Harrington, 1972) have been reported, with greater herbage accumulation and growth rates occurring with a shorter grazing residual (<1500 kg DM ha^–1, <40 mm RSH).

One possible reason for this inconsistency is the confounding effect of defoliation frequency and severity, making it difficult to determine the true effect of defoliation severity. In some studies, swards were defoliated at precise pregrazing heights (Bryant and Blaser, 1961; Reid, 1962) or after a certain length of time (Binnie and Harrington, 1972; Booysen and Nelson, 1975), taking no account of plant physiology or leaf regrowth stage. This may have led to herbage being defoliated before emergence of the second new leaf, inadvertently reducing herbage yields for reasons other than defoliation severity (Fulkerson and Donaghy, 2001). Furthermore, some studies were undertaken in glasshouses or controlled environments (Smith, 1974; Booysen and Nelson, 1975) removing any interaction that may have existed between defoliation severity and the environment.

Lee et al. (2007) defoliated perennial ryegrass dominant swards to one of two residual masses (1260 ± 101 or 1868 ± 139 kg DM ha^–1, severe or lax, respectively) on one occasion during winter. Herbage accumulated over the 49 d of regrowth (time taken for three new leaves per tiller to fully emerge) was similar across grazing treatments, averaging 726 kg DM ha^–1. However, the stubble WSC concentration was high (>150 g kg^–1 DM) in both treatments, probably a result of low ambient and soil temperatures, and resultant reductions in respiration and growth rate. This WSC concentration was sufficient for regrowth to proceed unhindered (Alberda, 1966).

Plant WSC concentrations are highly dependent on growth rate and prevailing environmental conditions (Troughton, 1957; White, 1973). These result in marked seasonal fluctuations in WSC reserves, with concentrations tending to reach nadir in late spring/summer, following rapid growth and/or high minimum temperatures and maximal loss of WSC content through respiration (Pollock and Jones, 1979; Thom et al., 1989). A decreased WSC store may result in plants becoming more susceptible to stress, such as increased defoliation severity during these periods, and may have contributed to the widespread death of ryegrass plants following severe defoliation (25 mm RSH; Brougham, 1960).

The objectives of this study were to (i) determine the morphological, physiological, and production responses of perennial ryegrass-dominant swards to defoliation severity over repeated defoliations where plants were given sufficient time to replenish WSC reserves (i.e., removing any confounding effect of defoliation frequency), and (ii) quantify the effect of defoliation severity on location of perennial ryegrass WSC storage within the stubble.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The field study was conducted at Elliott Research Station, Burnie, Tasmania, Australia (41°04' S, 145°46' E; elevation, 148 m) between September 2005 and April 2006. A 5-yr-old predominantly perennial ryegrass sward (70% on a DM basis) was used, which also contained white clover (Trifolium repens L.), orchardgrass (Dactylis glomerata L.), and prairie grass (Bromus willdenowii Kunth). All plots were sprayed with 2-methyl-4-chlorphenoxyacetic acid (1%) before the first treatment harvest (H₁) to eradicate broadleaved weeds. Perennial ryegrass seed (cv. Impact; 20 kg ha^–1) was then broadcast over all plots to ensure adequate plant density (minimum of 150 plants m^–2), and lightly covered with soil to prevent removal by birds and/or pests.

The soil type was a red ferrosol (Isbell, 1996), or in soil taxonomic terms, a Humic Eutrodox (Soil Survey Staff, 1990). Analysis of soil before the study (75-mm sampling depth) revealed mineral concentrations of 17.3 mg P kg^–1 (Olsen), 67.5 mg S kg^–1 (MCP; PO₄^3– extraction), 209 mg K kg^–1 (HCO₃^– extraction), and a pH (H₂O) of 6.2. Following soil test results, the experimental site was fertilized with 40 kg N ha^–1, 145 kg P ha^–1, and 102 kg K ha^–1 to ensure these nutrients would not limit herbage production. Further applications of 40 kg N ha^–1, 10 kg P ha^–1, and either 30 (following H₁) or 60 kg K ha^–1 (following H₂ to H₆) were applied immediately after each treatment harvest to replace nutrients removed.

Five defoliation severities (defoliation to a RSH of 20, 40, 60, 80, or 100 mm) were replicated five times in a Latin square design. Treatments were randomly allocated to plots (2 x 3 m) within each row and column as specified by the Latin square design. Plots were defoliated to a RSH of 50 mm using a rotary lawnmower and the resultant herbage DM yields recorded for use as a covariate (9 Sept. 2005). Following emergence of the third new leaf (32 d later), all plots were defoliated to the allocated treatment RSH (H₀) in preparation for H₁ (1 Nov. 2005). Subsequent treatment harvest dates were: 29 Nov. 2005 (H₂), 28 Dec. 2005 (H₃), 23 Jan. 2006 (H₄), 16 Feb. 2006 (H₅), 14 Mar. 2006 (H₆), and 19 Apr. 2006 (H₇). Throughout the study, the decision to defoliate was based on the full emergence of three new leaves per ryegrass tiller (n = 10) or before canopy closure, whichever occurred first. This was assumed to be the optimal time for defoliation (Fulkerson and Donaghy, 2001).

Climatic Measurements
Throughout the study, 24 h maximum and minimum air temperatures (°C; 1.1 m above ground level), 24 h rainfall (mm), and radiation (MJ m^–2) were recorded at 0900 daily at a weather station <500 m from the experimental site. Two dataloggers (each containing two sensors; M.K. Hansen Co., Wenatchee, WA) located within 100 m of the experimental site monitored soil water potential at a soil depth of 300 mm. The experimental area was irrigated when the average reading from all four sensors declined below –35 kPa, returning the soil to –10 kPa (field capacity; McLaren and Cameron, 1996). Mean monthly maximum and minimum temperature, radiation, evaporation, total monthly rainfall, and irrigation water are presented in Table 1 .

Immediately before H₄ and H₇, plants from each plot were destructively harvested for WSC analysis using a scalpel. Five individual ryegrass plants were randomly selected from each plot and harvested to ground level no later than 3 h after sunrise to negate the confounding effect of diurnal fluctuations in WSC content (Fulkerson et al., 1994). Five plants were deemed to be sufficient to provide suitable sample mass for WSC analysis based on previous studies (three plants had previously been used by Donaghy and Fulkerson [1997; 2002]). After harvesting, cut plants were trimmed to the appropriate treatment RSH, to quantify stubble WSC reserves at the end of one regrowth period that would be carried forward to the next regrowth period. Each stubble sample was stored on ice to minimize loss of WSC reserves through respiration and samples were then frozen at –20°C for 48 h before freeze-drying. Following freeze-drying, the number of tillers per plant were recorded and all five plants bulked. The stubble samples were then dissected into 20–mm increments (0 mm = ground level), ground to pass through the 1–mm sieve, and analyzed for WSC content. The WSC concentration (mg g^–1 DM) was determined by cold extraction in a reciprocal shaker for 1 h using 0.2% benzoic acid–water solution, and hydrolyzation of the cold water carbohydrates extracted by 1 mol L^–1 HCl to invert sugars. This solution was heated to 90°C, the sugar dialyzed into an alkaline stream of potassium ferricyanide, and reheated to 90°C before determining WSC concentration using an autoanalyzer (420 nm; Technicon Industrial Method number 302–73A; modified from the method described by Smith [1969]).

After each sampling, the entire plot was defoliated to the treatment RSH using a rotary lawnmower. The fresh weight of this sample was recorded on a hanging scale (Salter, Victoria, Australia) suspended from a tripod in the field. Herbage yield was calculated by multiplying the sample fresh weight by the DM content of the herbage from each plot.

One week after H₇, a 1–m² grid consisting of 100 squares (100 x 100 mm) was randomly placed in each plot. Ryegrass plant numbers were counted in each square, providing an estimate of ryegrass plant density.

Root Measurements
At H₇, three soil cores were taken from each plot to determine perennial ryegrass root mass. The corer (70 mm diam.) was placed over the center of a randomly selected clump of perennial ryegrass plants and each core was taken to 300 mm depth. The top 50 mm of each core was cut and separated from the rest of the core. Roots were washed free of soil in both portions using a series of sieves with graduated mesh size (Hubbard Scientific, Fort Collins, CO) and dried at 78°C (for approximately 24 h) to determine root DM yield.

Statistical Analysis
All data were analyzed using the statistical package GenStat 7 (VSN International Ltd, 2004). Repeated measures data were analyzed as a Latin square, with row and column included as blocking variables, and RSH as a fixed effect that was partitioned into linear and quadratic contrasts. This analysis was done using the AREPMEASURES procedure, which produces an analysis of variance (ANOVA) for repeated measures with Greenhouse–Geisser adjustment. When significant harvest x treatment interactions occurred, the data was investigated further by analyzing at individual time points using ANOVA. There were no significant interactions with harvest on linear and quadratic contrasts of RSH on WSC content (mg tiller^–1 and mg plant^–1), therefore data from H₄ and H₇ were combined. Preexperimental DM yield and botanical composition were used as a covariate. Statistical significance was determined at P < 0.05 unless otherwise stated.

	RESULTS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
A quadratic relationship (P < 0.01; R² = 0.99) between RSH (mm) and total herbage production over the 6–mo experimental period was evident and can be described by the equation:

However, the effect of RSH on individual harvest yield tended to be inconsistent (Table 2 ). At H₁, herbage yield increased linearly (P < 0.001) with increasing RSH, with defoliation severity explaining over 99% of the variation in herbage yield. In general, however, the effect of defoliation severity on herbage yield was nonlinear, with herbage yield declining with RSH less than 40 mm and greater than 80 mm. The quadratic effect of defoliation severity on total ME yield was similar to the effect on herbage yield, peaking at 57 mm (Table 2; P < 0.001; total ME yield (MJ ha^–1) = –16.9(RSH)² + 1920.6RSH + 115,266; R² = 0.96).

View larger version (17K): [in this window] [in a new window]   Fig. 1. Total water-soluble carbohydrate (WSC) content remaining in the residual stubble of the (a) plant and (b) individual tiller following defoliation to 20, 40, 60, 80, or 100 mm residual stubble height (RSH) over seven sequential harvests. Data presented are averages from the fourth and seventh harvests (n = 10) for each RSH. The standard error of the difference was (a) 21.8 mg plant–1 and (b) 1.16 mg tiller–1.

View larger version (13K): [in this window] [in a new window]   Fig. 2. The quadratic relationship between water-soluble carbohydrate (WSC) content (mg tiller–1; H4) and subsequent herbage yield (kg DM ha–1; H5) following defoliation to 20 (filled circle), 40 (open circle), 60 (filled triangle), 80 (open square), or 100 mm (filled square) residual stubble height over seven sequential harvests. Each data point indicates an individual replicate. The standard error was 412 kg DM ha–1.

	DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Total herbage production in the current study was maximized in swards defoliated to 60 mm, although there was little difference in herbage yield between swards defoliated across the range of 40 to 80 mm. This result was consistent with previous research indicating that a 60 mm RSH was optimal (over a range of 20–120 mm; Wilson and Robson, 1970), while Fulkerson et al. (1994) and Parsons and Chapman (2000) both concluded that maximal herbage production will occur in swards defoliated to 50 mm.

In the current study, repeated lax defoliation reduced total herbage production. Laxly defoliated plants retain greater residual leaf area than severely defoliated plants, potentially providing plants with a greater capacity for photosynthesis, and therefore regrowth (Booysen and Nelson, 1975; Grant et al., 1981). However, the beneficial effect of residual leaf following defoliation has been debated. Contrasting research suggests that leaves remaining postdefoliation are generally older and less photosynthetically active, therefore unlikely to contribute substantially to regrowth (Gifford and Marshall, 1973; Woledge, 1977; Gay and Thomas, 1995). In the current study, during H₁ alone, herbage production and RSH were positively associated. This indicated that although it was likely that beneficial effects of residual leaf existed, the effects were only visible in the short term, before being outweighed by the detrimental impact of repeated lax defoliations.

In the long term, lax defoliation can actually result in reduced photosynthesis (Hernández Garay et al., 2000), partly through a loss in leaf area index in favor of pseudostem development, and partly through a reduction in photosynthesis per unit leaf area (Hernández Garay et al., 1999; Hernández Garay et al., 2000). Previous research with several crop plants suggested declining photosynthetic activity may be correlated with WSC accumulation (Azcón-Bieto, 1983; Goldschmidt and Huber, 1992). Therefore, the latter reduction may have been attributable to an end-product inhibition of photosynthesis, due to higher WSC content in laxly defoliated plants. Declining photosynthetic activity may also have been an artifact of the increased proportion of aging leaves in the laxly defoliated sward (Parsons et al., 1988), which may have been exacerbated in cases where WSC content had also increased with leaf age.

The reduction in tiller density, demonstrated in the current study, also likely contributed to the detrimental impact of long-term lax defoliation. Increased stem development seen in laxly defoliated plants (Holmes and Hoogendoorn, 1983; Holmes et al., 1992) leads to diminished light penetration into the sward. This tends to reduce tiller density, by reducing tiller emergence and increasing tiller death (Kays and Harper, 1974; Ong, 1978; Ong and Marshall, 1979), potentially reducing herbage production.

Previous research has also demonstrated declining herbage production as defoliation severity increased (Smith, 1974; Booysen and Nelson, 1975; Leafe and Parsons, 1983). This trend was evident in swards defoliated to 20 mm RSH in the current study, and was likely due to several factors. Severely defoliated plants tend to be unable to meet postdefoliation demands for growth and respiration through photosynthesis (Davidson and Milthorpe, 1965), resulting in an increased reliance on WSC reserves to provide the necessary energy for regrowth. Once energy demands of the plant have been met, surplus WSC content is available for storage as reserves (Fulkerson and Donaghy, 2001). Replenishment of reserves in severely defoliated plants was likely to be slower than in laxly defoliated plants due to reduced WSC reserves, and may divert WSC content from other purposes, such as tiller initiation and root growth. In the current study, plants defoliated to 20 mm RSH did have a lower tiller density and less root mass between 50 and 300 mm depth than plants defoliated in the range of 40 to 80 mm, which supported that hypothesis.

The effect of increased reliance on WSC reserves was compounded by the fact that severely defoliated plants actually contained less WSC content. A significant proportion (48%) of WSC reserves were stored within the bottom 40 mm of stubble of tillers defoliated to 100 mm. This was similar to previous research conducted with ryegrass (45% in the bottom 50 mm of tillers defoliated to 100 mm; Delagarde et al., 2000), and prairie grass and orchardgrass (62% and 83% in the bottom 40 mm of prairie grass and orchardgrass tillers defoliated to 100 mm, respectively; Turner et al., 2007). These results confirmed that the quantity of WSC content stored in severely defoliated plants and the total storage capacity of these plants was likely to be reduced (Wilson and Robson, 1970; Davies et al., 1972), further decreasing the amount of energy available for tissue production. However, the small magnitude of difference in herbage production between swards defoliated to between 40 and 80 mm in the current study suggested that only plants defoliated below 40 mm had insufficient WSC reserves to initiate and sustain rapid plant growth immediately following defoliation. These data indicate a requirement for 6.5 mg WSC tiller^–1 to ensure uninhibited herbage growth.

The association between WSC content per tiller and subsequent herbage yield presented here supports the hypothesis that WSC reserves may influence regrowth, as suggested by Davies (1965) and Gonzalez et al. (1989). However, with differences in WSC content accounting for only 35% of the variation in regrowth, there are clearly additional factors involved, such as respiratory load and residual leaf photosynthetic capacity, which influence regrowth, although the extent and timing of the influence are unknown. It was not possible to quantify their effect in the current study.

Lax defoliation tended to have a detrimental effect on the nutritive value of the herbage by increasing the fiber concentration, while reducing CP concentrations, and DMD and ME content. These trends were also observed by Lee et al. (2007) in temperate ryegrass-dominant swards following defoliation to either 1260 or 1868 kg DM ha^–1. However, despite the variation in the nutritive value of the sward between harvests, the herbage harvested during the current study was considered to be good quality (>11.5 MJ ME kg^–1 DM, >750 g DMD kg^–1 DM, 380–450 g NDF kg^–1 DM; Kolver, 2000), regardless of defoliation severity. In a pastoral-based dairy system, animal production is partly a result of the quantity and nutritive value of the herbage provided, as is summarized by ME yield. In the current study, the impact of defoliation severity on ME content was minimal. As a result, total ME yield followed a similar trend to total herbage yield and peaked at 57 mm RSH. Interestingly, if total ME yield was divided by total herbage yield, average ME content of the herbage ranged between 12.1 and 12.3 MJ ME/kg DM over the entire experiment with no systematic decline at high or low RSH. The lack of substantial impact of lax defoliation on nutritive value of herbage in the current study may have been due to the fact that swards were mechanically defoliated to a uniform RSH. Under grazing conditions, lax defoliation to an average height of 80 mm may result in some areas of the sward being longer than 80 mm, enabling more stem and dead material to accumulate. This may increase the detrimental impact of lax defoliation on the nutritive value of the herbage subsequently produced.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The data indicate that between September (spring) and April (autumn), herbage production and nutritive value of temperate perennial ryegrass-dominant swards are maximized when defoliation severity results in a postgrazing stubble height of 40 to 80 mm. Although WSC content per tiller increases with increasing RSH, DM yield will be maximized provided there is 6.5 mg WSC tiller^–1.

	ACKNOWLEDGMENTS

 
The authors would like to acknowledge the statistical expertise of Barbara Dow and the technical assistance from Karen Christie, Scott Carlson, and Peter Chamberlain. The assistance of Dexcel management, the Tasmanian Inst. of Agric. Res. and the Univ. of Tasmania are gratefully appreciated.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

• Alberda, T. 1966. The influence of reserve substances on dry-matter production after defoliation. p. 140–147. In A.G.G. Hill (ed.) Proc. Xth Int. Grassl. Cong., Helsinki, Finland. Valtioneuvoston Kirjapaino, Helsinki, Finland.
• Azcón-Bieto, J. 1983. Inhibition of photosynthesis by carbohydrates in wheat leaves. Plant Physiol. 73 :681–686.[Abstract/Free Full Text]
• Binnie, R.C., and F.J. Harrington. 1972. The effect of cutting height and cutting frequency on the productivity of an Italian ryegrass sward. J. Br. Grassl. Soc. 27 :177–182.
• Booysen, P.V., and C.J. Nelson. 1975. Leaf area and carbohydrate reserves in regrowth of tall fescue. Crop Sci. 15 :262–266.[Abstract/Free Full Text]
• Brougham, R.W. 1960. The effects of frequent hard grazings at different times of the year on the productivity and species yields of a grass-clover pasture. N. Z. J. Agric. Res. 3 :125–136.
• Bryant, H.T., and R.E. Blaser. 1961. Yields and stands of orchardgrass compared under clipping and grazing intensities. Agron. J. 53 :9–11.[Abstract/Free Full Text]
• Corson, D.C., G.C. Waghorn, M.J. Ulyatt, and J. Lee. 1999. NIRS: Forage analysis and livestock feeding. Proc. N.Z. Grassl. Assoc. 61 :127–132.
• Davidson, J.L., and F.L. Milthorpe. 1965. Carbohydrate reserves in the regrowth of cocksfoot (Dactylis glomerata). J. Br. Grassl. Soc. 20 :15–18.
• Davies, A. 1965. Carbohydrate levels and regrowth in perennial ryegrass. J. Agric. Sci. 65 :213–221.
• Davies, I., A. Davies, A. Troughton, and J.P. Cooper. 1972. Regrowth in grasses. p. 79–94. In Rep. of the Welsh Plant Breed. Stn. for 1971. Plas Gogerddan, Aberystwyth, Wales.
• Delagarde, R., J.L. Peyraud, L. Delaby, and P. Faverdin. 2000. Vertical distribution of biomass, chemical composition and pepsin-cellulase digestibility in a perennial ryegrass sward: Interaction with month of year, regrowth age and time of day. Anim. Feed Sci. Technol. 84 :49–68.[CrossRef]
• Donaghy, D.J., and W.J. Fulkerson. 1997. The importance of water-soluble carbohydrate reserves on regrowth and root growth of Lolium perenne (L.). Grass Forage Sci. 52 :401–407.
• Donaghy, D.J., and W.J. Fulkerson. 2002. The impact of defoliation frequency and nitrogen fertilizer application in spring on summer survival of perennial ryegrass under grazing in subtropical Australia. Grass Forage Sci. 57 :351–359.
• Fulkerson, W.J., and D.J. Donaghy. 2001. Plant-soluble carbohydrate reserves and senescence – key criteria for developing an effective grazing management system for ryegrass-based pastures: A review. Aust. J. Exp. Agric. 41 :261–275.[CrossRef]
• Fulkerson, W.J., K. Slack, and K.F. Lowe. 1994. Variation in the response of Lolium genotypes to defoliation. Aust. J. Agric. Res. 45 :1309–1317.[Web of Science]
• Gay, A.P., and H. Thomas. 1995. Leaf development in Lolium temulentum L.: Photosynthesis in relation to growth and senescence. New Phytol. 130 :159–168.[CrossRef][Web of Science]
• Gifford, R.M., and C. Marshall. 1973. Photosynthesis and assimilate distribution in Lolium multiflorum Lam. following differential tiller defoliation. Aust. J. Biol. Sci. 26 :517–526.
• Goldschmidt, E.E., and S.C. Huber. 1992. Regulation of photosynthesis by end-product accumulation in leaves of plants storing starch, sucrose, and hexose sugars. Plant Physiol. 99 :1443–1448.[Abstract/Free Full Text]
• Gonzalez, B., J. Boucaud, J. Salette, J. Langlois, and M. Duyme. 1989. Changes in stubble carbohydrate content during regrowth of defoliated perennial ryegrass (Lolium perenne L.) on two nitrogen levels. Grass Forage Sci. 44 :411–415.[CrossRef]
• Grant, S.A., G.T. Barthram, and L. Torvell. 1981. Components of regrowth in grazed and cut Lolium perenne swards. Grass Forage Sci. 36 :155–168.
• Hernández Garay, A., C. Matthew, and J. Hodgson. 1999. Tiller size/density compensation in perennial ryegrass miniature swards subject to differing defoliation heights and a proposed productivity index. Grass Forage Sci. 54 :347–356.
• Hernández Garay, A., C. Matthew, and J. Hodgson. 2000. The influence of defoliation height on dry-matter partitioning and CO₂ exchange of perennial ryegrass miniature swards. Grass Forage Sci. 55 :372–376.
• Holmes, C.W., and C.J. Hoogendoorn. 1983. Some effects of grazing management in early lactation, and of topping on the growth and quality of pasture. p. 36–43. In Dairyfarming Ann. Massey Univ., Palmerston North, NZ.
• Holmes, C.W., C.J. Hoogendoorn, M.P. Ryan, and A.C.P. Chu. 1992. Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass/white clover pastures. 1. Milk production in early spring: Effects of different regrowth intervals during the preceding winter period. Grass Forage Sci. 47 :309–315.
• Isbell, R.F. 1996. The Australian Soil Classification CSIRO Pub., Melbourne, Australia.
• Kays, S., and J.L. Harper. 1974. The regulation of plant and tiller density in a grass sward. J. Ecol. 62 :97–105.[CrossRef]
• Kolver, E. 2000. Nutrition guidelines for the high producing dairy cow. p. 17–28. In J. Lomas (ed.) Proc. 52nd Ruakura Dairy Farmers' Conf., 10 May 2000, Hamilton, NZ.
• Leafe, E.L., and A.J. Parsons. 1983. Physiology of growth of a grazed sward. p. 403–406. In Proc. XIVth Int. Grassl. Cong., Boulder, CO.
• Lee, J.M., D.J. Donaghy, and J.R. Roche. 2007. The effect of grazing severity and fertiliser application during winter on herbage regrowth and quality of perennial ryegrass (Lolium perenne L.). Aust. J. Exp. Agric. 47 :825–832.
• McLaren, R.G., and K.C. Cameron. 1996. The storage of water in soil. p. 71–86 In Soil science: Sustainable production and environmental protection. 2nd ed. Oxford Univ. Press, Auckland, NZ.
• Ong, C.K. 1978. The physiology of tiller death in grasses. 1. The influence of tiller age, size and position. J. Br. Grassl. Soc. 33 :197–203.
• Ong, C.K., and C. Marshall. 1979. The growth and survival of severely-shaded tillers in Lolium perenne L. Ann. Bot. (Lond.) 43 :147–155.[Abstract/Free Full Text]
• Parsons, A.J. 1988. The effects of season and management on the growth of grass swards. p. 129–177. In M.B. Jones et al. (ed.) The grass crop: The physiological basis of production. Chapman and Hall, London.
• Parsons, A.J., and D.F. Chapman. 2000. The principles of pasture growth and utilization. p. 31–89. In A. Hopkins (ed.) Grass: Its production and utilization. Blackwell Science Ltd., Oxford, UK.
• Parsons, A.J., I.R. Johnson, and J.H.H. Williams. 1988. Leaf age structure and canopy photosynthesis in rotationally and continuously grazed swards. Grass Forage Sci. 43 :1–14.
• Pollock, C.J., and T. Jones. 1979. Seasonal patterns of fructan metabolism in forage grasses. New Phytol. 83 :9–15.[CrossRef][Web of Science]
• Reid, D. 1962. Studies on the cutting management of grass-clover swards. 3. The effects of prolonged close and lax cutting on herbage yields and quality. J. Agric. Sci. 59 :359–368.
• Smith, D. 1969. Removing and analysing total non-structural carbohydrates from plant tissue. Res. Rep. 41 :1–11. Wisconsin Agric. Exp. Stn., Madison, WI.
• Smith, D. 1974. Growth and development of timothy tillers as influenced by level of carbohydrate reserves and leaf area. Ann. Bot. 38 :595–606.[Abstract/Free Full Text]
• Soil Survey Staff. 1990. Keys to soil taxonomy. 4th ed. SMSS Tech. Monogr. 19. USDA, Blacksburg, VA.
• Thom, E.R., G.W. Sheath, and A.M. Bryant. 1989. Seasonal variations in total nonstructural carbohydrate and major element levels in perennial ryegrass and paspalum in a mixed pasture. N. Z. J. Agric. Res. 32 :157–165.
• Troughton, A. 1957. The underground organs of herbage grasses. Commonwealth Agric. Bureaux, Farnham Royal, UK.
• Turner, L.R., D.J. Donaghy, P.A. Lane, and R.P. Rawnsley. 2007. Distribution of water-soluble carbohydrate reserves in the stubble of prairie grass and orchardgrass plants. Agron. J. 99 :591–594.[Abstract/Free Full Text]
• VSN International Ltd. 2004. GenStat 7 for Windows. Release 7.2. VSN International Ltd, Oxford, UK.
• White, L.M. 1973. Carbohydrate reserves of grasses: A review. J. Range Manage. 26 :13–18.
• Wilson, D.B., and M.J. Robson. 1970. Regrowth of S24 ryegrass and its relation to yield measurement of grazed swards. J. Br. Grassl. Soc. 25 :220–227.
• Woledge, J. 1977. The effects of shading and cutting treatments on the photosynthetic rate of ryegrass leaves. Ann. Bot. 41 :1279–1286.[Abstract/Free Full Text]

This article has been cited by other articles:

				J. M. Lee, D. J. Donaghy, and J. R. Roche Short Communication: Effect of Postgrazing Residual Pasture Height on Milk Production J Dairy Sci, November 1, 2008; 91(11): 4307 - 4311. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lee, J. M. Articles by Roche, J. R. Search for Related Content PubMed Articles by Lee, J. M. Articles by Roche, J. R. Agricola Articles by Lee, J. M. Articles by Roche, J. R. Related Collections Best Management Practices Grazing Management Turfgrass