Morphogenetic and structural characteristics of fieldgrown timothy cultivars differing in maturity G. B6langer Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by 3.236.55.199 on 06/12/20 For personal use only. Asricutture and Aori-Food Brunswick' canada c721d7#i::f!,3ilTa[;?;!!Jr#it!;::30,,{:,'?g'New timothy cultivars differing in maturity' can' Belanger, G. 1996. Morphogenetic and structural characteristics of field-grorvn interception depends on morphogenetic radiation subsequently, grasses and, of plant. development Sci. 76: 27'7-2g2. The leaf area J. appearance offield-grown timothy and processes such as leafextension and appearance._No ditailed studies ofleafextension and appearance offield-grown Leafextension literature. in the reported been have in maturity (phleum pratense L.) cultivars differing size per tiller and tiller densileaf as such timothy cultivars differing in maturity and their impact on sward structural characteristics cultivars was greater early-maturing of rate extension leaf The 1992. and l99l of spring growth in the ty were studied during primary rates appearance in leaf no differences were lT1e.cutthan that of late-maturing cultiv'ars during primary growh of timothy. There In 199.2,^latecultivars. late-maturing than size alarger.leaf developed cultivars of early-maturing tivars. Hence, individual tillers for-the smaller leaf size' Different maturing cultivars had a greater tiller iensity thin early-maturing'cultivarJwhich compensated outcome in terms of LAI' similar in a resulted cultivars tlimothy late-maturing and of early size characteristics tiller density-tiller Key words: Phleum pratense L., timothy, leaf extension, leaf appearance, tillering i de fl6ole des pr6s maturit6 diff6rente' B6langer, G. 1996. Caract6ristiques morphog6n6tiques et strutturales de cultivars I'interception du rayonnement depenpar cons6quent, Can. J. plant Sci. 76: Z7:.-2g2.Le d6veloppement de la surface foliaire et, pas d'6tudes ddtaill6es de I'elonn'existe Il feuilles. dei I'apparition et que l'6longation tels dent de processus morptrog-6netiques diff6rente et cultiv6s en champ' L.) dmatvrit6 pratense (phleum gation er de l,apparition de"s feuilies de culiivars de freole oes prei en champ, et leur effet sur cultives et diff6rente pr6s miturit6 a fl6ole des de cultivars de feuilles L,6longation et l,appantion des printemps de 1991 et.l992' primaire des croissance la les caract6ristiqu", st u"tu.ales du couvert v6g6tal ont 6t6 6tudi€ei lors de la croissance primaire lors de tardifs cultivars des que grande celle plus ituit fiatir, cultivars des La vitesse d,6longation foliaire entre les cultivars. Ainsi, les talles indide la fl6ole des pres. ll n,y avait pas de diff6rence de vitesse-d'apparition des feuilles tardifs' En 1992' les cultivars tardifs cultivars des que gandei celles plus feuilGs des ont d6velopp6 viduelles des cultivars hatif, lews plus petitesfzuilles'.Ces compenser permis de qui a avaient une densit6 O. iuff.r pfur 6lerr6e que t.r.uttiu*s n"atlts, ce ont toutefois produit un r6sultardifs et hdtifs cultivars des talles des la densitd et de la dimension caract6ristiques diff6rentes de tat similaire en ce qui atraitd I'indice foliaire. Mots cl6s: Phleum pratense L., fl',ole des pres, 6longation, apparition, tallage Radiation interception is one of three determinants of crop growth along with radiation-use efftciency and assimilate pariitioning between shoots and roots (Charles-Edwards 1982). The am-ount of PAR intercepted by the crop is a firnction of lg92). It is therefore hypothesized that the leaf extension rate of early-maturing cultivars will be greater than that of late-maturing-cultivars. The objeclives of this study were to determine the leaf extension and appearance rates during primary growth of field-grown timothy cultivars differing in maturity, and to determine the impact of those morphogenetic processes on sward structural characteristics. With the exception of the study of Ryle (1964)' no Two experiments were conducted at the Fredericton the LAI. The leaf area development and, subsequently, radiation interception, depend on morphogenetic processes such as leaf extension and appearance. In tum, the combination of leaf extension and appearance rates and the leaf life-span determine the sward sfuctural characteristics such as the size of the tillers and their densrty (Chapman and Lemaire 1993)' MATERIALS AND METHODS Research Cenffe of Agriculture and Agri-Food Canada (Lat. 45"55'N) on the primary growth of timothy in the spring of 1991 and 1992. ln both experiments, four cultivars were detailed studies of morphogenetic and structural characteristics of field-grown timothy (Phleum pratenseL') have been reported in the literature. As well, there are no reports on the established in a randomized complete block design with four replications. The plot size was 8 m x 1.25 m. morphogenetic and structural characteristics of early and late-maturing timothy cultivars. Ear emergence or heading of early and late-maturing cultivars of timothy varies by as much as 3 wk (Mika 1983; Surprenant et al. 1993). In other Abbreviations: LAI, leaf area index; LAR, leaf appearance rate: LER. leaf extension rate; PAR, photosynthetically active radiation; SEM, standard error of the mean grasses, the leafextension rate was greater during reproduc- tive growth than vegetative growth at similar temperatures (Peacock 1976; Parsons and Robson 1980; Gastal et al' 277 278 CANADIAN JOURNAL OF PLANT SCIENCE The experiments were previously described in detail Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by 3.236.55.199 on 06/12/20 For personal use only. @6langer and Richards 1995). Briefly, the cultivars for the first experiment (1991) were seeded in 1988 whereas the second experiment (1992) was conducted on an area established in 1990. Of the cultivars srudied in 1991, Champ, Nike and G reached the heading stage on 27 Jr:rre in 1990 and are referred to as early-maturing cultivars, whereas Farol reached the heading stage on I 1 July and is referred to as a latematuring cultivar. Of the cultivars studied n 1992. Clair and Axel reached the heading stage on 17 June in l99l and are referred to as early-maturing cultivars, whereas Farol and Hokushu reached that stage on 2 July and are referred to as late-maturing cultivars. Farol was the only cultivar studied in both 1991 and 1992. Before growth started, 168 kg N ha-l was applied.in I 99 I and 200 kg N ha-t n D92. In bo-th years, 50 kg P ha-l and 150 kg K ha-l were also applied at the time of N application. The rates of N, p, and K fertilization were chosen so that they were not limiting growth. Water received by rainfall in 1991, and by rainfall and irrigation n lgg2, war equal to or greater than potential evapotranspiration. Ten tillers per plot were tagged with a plastic-covered wire attached to a small stake on 13 May l99l and 6 May 1992.The tillers were chosen using a frame composed of lb equidistant needles moving vertically. The closest tiller to the intersection between the soil and the needle was chosen. The LER per tiller was obtained by measuring the length of every leaf on two successive dates. The measurements were taken on 14, 17,21,24,27 and 3l Mav 1991. and 7. I l, 15, 19,22,25 and 28 May 1992. The tengtn was measured between the tip of a leaf and the ligule of the preced_ ing leaf. The LER per tiller was calculated as the sum of the length increments of each leaf which was then divided bv the number of days between the two dates of mear*"rn"nf. The LAR per tiller was deterrnined on the same tillers bv calculating the increase in the number of leaves divided by the number of days between two dates of measurement. The thermochrome, i.e. the interval in degree-days between the appearance of two successive leaves, was estimated for Farol in l99l and 1992 by using a linear regression between the cumulative number of new leaves and cumulative degree-days ('C-d). The degree-days were based on the average of air and soil temperatwe (2 cm deep) using 0"C as the base temperature. In 1992, the numbei of tillers was corrnted weekly in an area of 0.3 by 0.3 m in each plot. Air (l m high) and soil (2 cm deep) temperatures were recorded every 15 min on the experimental site. The mean daily *d soil temperatures were calculated as the average of thL 1T l5-min values. These daily values were averaged over the period between two consecutive measurements of leaf length.All variables were subjected to analyses of varianie using Genstat (Genstat 5 Committee 1987). SEM were calculatedl Differences among cultivars were compared with orthogonal contrasts. RESULTS AND DISCUSSTON Leaf Extension There were no signifiganl (P > 0.10) cultivar differences in LER for each measurement interval in l99l (Table l). The Table l. LER ofcultivars differing in maturity in l99l and 1992 LER (mm titleFl d-r) 123456 l. Champ @)r 2. Nike (E) 3. G (E) 4. Farol (L) sEM 32.10 28.10 33.60 27.40 I99I 24.02 24.86 24.03 22.42 Intervalsz 33.10 48.10 30.10 49.20 32.90 42.10 30.50 39.90 2.t4 t.87 1.33 3.39 34.90 32.50 29.20 34.60 2.56 Contrast (signifi cance probability) NSI NS NS NS NS NS NS NS NS NS NS NS 10.9 13.2 16.0 - 4 vs. 1,2,3 3 vs. 1,2 I vs.2 T ("C)w (E) 2. Axel (E) 3. Hokushu (L) 4. Farol (L) l. Clair sEM I 992 t6.62 29.82 16.42 30.57 12.84 23.14 | 3.88 25.06 32.40 32.09 23.99 25.25 52.t2 NS NS NS 13.0 53.70 30.85 50.86 48.00 28.86 48.56 43.70 27.30 37.70 40.20 24.71 1.05 2.09 1.62 2.41 2.48 I .95 Contrast (sigrifi cance probability) 1,2 vs.3,4 I vs.2 3 vs.4 T ("C) zlntervals 0.015 0.017 0.001 0.007 0.006 0.079 NS NS NS NS NS NS NS NS NS O.OI I NS NS 9.3 12.6 | |.7 14.7 18.4 t 0.8 1,2,3,4, and 5 correspond to l4-l'l May, 17-21 May,2l-24 May,24-27 May, and 27-31 May 1991, respectively. In 1992, intervals I , 4 5, and 6 correspond to 7-l I May, I I-15 May, I 5-l 9 May, 1912 t May,22-25 May, and 25-28May, respectively. 2, 3, rE, early; L, late. rNS, not significant at P < 0.10. wT, average of air and soil temperature (2 cm) during interval. LER of the late-maturing cultivarFarol, however, was gener- ally less than that of early-maturing cultivars. In 1992, the LER of Farol and Hokushu, two late-maturing cultivars, were significanfly (P < 0.10) less than those of the early-maturing cultivars Clair and Axel. The early-maturing cultivars were in l99l and. 1992. This could explain the slight inconsistency of the maturity effect between the 2 years. In perennial ryegrass (Lolium perenne L.) and tall fescue different (Festuca arundinacea Schreb.), the potential LER was greater dwing reproductive growth than vegetative growth at similar temperatures (Peacock 1976; Parsons and Robson 1980; Gastal et al. 1992). Peacock (1976) concluded that this increase in LER associated with reproductive growth occurred at the onset of floral initiation. Heide (1982) reported cultivar differences in the critical dayleneth for floral induction of timothy. Hence, it is speculateA tnat the floral induction of the late-maturing cultivars was delayed com- pared to that of the early-maturing cultivars, and this resulted in lower LER of the late-maturing cultivars. The LER of grasses is closely related to temperature N is not limiting plant growth (Gastal et al. D92). In this study, high rates of N were applied so that N was not when limiting plant growth. Gastal et al. (1992) related the potential LER of tall fescue to the average of air and soil temperature. BELANGER_MORPHOGENET'CANDSTRTICTIIRALCHARACTERIST'CSOFTIMOTHY2T9 t"nf. Z. LAR ofcultivars differing in maturity in 1991 and 1992 LAR (leaves tillert d-') t23456 -o _40 g EJo 5u -20 E I99I (E)v 2. Nike (E) 3. G G) 4. Farol (L) 0'154 0'090 0'153 0.113 0.119 0' 105 0.123 0.086 0.117 0.lM 0.086 0'087 0.163 0.078 0.194 0.05 I 0.131 0.048 0.144 0.078 sEM 0.03s 0.028 0.030 L ChamP o/ /o o Intervalsz 0.034 0.017 Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by 3.236.55.199 on 06/12/20 For personal use only. LiJ o o o Contrast (signifi cance probability) NSX NS 4 vs. 1,2,3 NS NS 3 vs. 1,2 NS NS I vs.2 1992 1991 68rb1214161820 Meon doilY temPeroture ('C) Fig. 1. Potential LER of the late-maturing cultivar Farol in 1991 uotr lggZ as a function of the mean daily temperature (7)' Line represents the linear regression [LER = -t5.t + (l.S " 4, Rz = 0'74, P =0.001,n=101. The meristem zone, which is located near ground level, is the perception site of temperature for the leaf extension of g*rt". (Kleinendorst and Brouwer 1970; Peacock 1975b)' Feacock'(1975a) reported that the temperature in the hrst centimetre above ground level was intermediate between the air temperature measured at2 m high and the soil temperature at 10 cm. The LER of Farol, the only cultivar grown in both years, increased with an increase in mean daily temperature (Fig. 1). Using data from four spring regrowth cycles of tall i".irr", Gastal I 992 (E) 2. Axel G) 3. Hokushu (L) 4. Farol (L) 0.249 0.219 0.195 0.250 0.216 0.243 0.208 0.222 sEM 0.025 L Clair NS 3,4 0'168 0'140 0'156 0'187 NS NS NS NS NS NS 0.r1't 0.165 0.173 0.152 0.196 0.197 0.164 0.125 0.059 0.105 0.076 0.092 0.029 NS NS NS NS NS 0.076 NS NS NS and 5 correspond to l4-l'1 May, 17--21 May'2124 and 2711 Mav l99l , respectivelv' t1 ,t e.eJ'. intel{s 12T4, l,liv, zq-zi uuv, NS NS NS 0.027 0.025 0.022 Contrast (signifi cance probability) NS 1,2 vs NS NS 1vs2 NS NS 3vs4 "lnte.rtals NS NS NS } S,and 6'correspond to 7-l I May, I l-15 May' l5-19 May, 19-22 May,2225 May, and 2528May' respectively' YE, early; L, late. < 'NS, not significant at P 0'10' i,i,'i, et al. (199D found that the relationship between potential LER and temperature (average of air 9d soil temperature) was exponential at temperatures below 8oC and linear at temperatures above SoC. In this study, the mean daily temperatures for all the intervals were always greater than 9oC (Table 1). Hence, a linear regression was used to describe the relationship between LER and mean daily temperature (Fig. 1). tttir mbaet of potential LER is specific to a late-matwing cultivar since there were differences in LER between early and late-maturing timothy cultivars. The model only applies to the range of temperatures experienced in this study (10.9-16.0'C in 1991;9.!18.0'C lm1992) and to the primary growth of timothY. tively. The thermochrone of a late-maturing timothy cultivar is therefore much less than *rat of tall fescue, and relatively close to that of perennial ryegrass. The calculation of the thermochrone assumes a linear relationship between the cumulated number of new leaves and cumuiative degree-days (Fig. 2). This assumption is probably valid for relatively short periods such as those used io o* ttoOy (13-14 d)' B6langer (1990) and Onillon (1993)' however, boih reported that the LAR decreases during the regrowth cycle which would invalidate the assumption of a liriear relaiionship. The decrease in LAR with time was noticeable in the experiment conducted n 1992' The thermochrone should therefore be used with caution in growth models. Leaf Appearance There were no significant (P > 0.10) differences in LAR among cultivars in 1991 and 1992 (Table 2). Patel and Cooper (1961) also reported little cultivar differences for LAR in timothy, perennial ryegrass, and meadow fescue (Festuca pratensis L.). The interval between the appearance of two successive leaves of Farol was 131.5'C-d in l99l (17-31May) and 82.2"C-d n 1992 (15-28 May). There are no reports in the literature of the thermochrone for timothy. Values of 110 and 230'C-d were reported for perennial ryegrass @avies and Thomas 1983) and tall fescue (Lemaire 1985), respec- Leaf Life-sPan Leaf life-span along with leaf extension and appearance are the determinants of the three main structural characteristics of swards: leaf size, tiller density, and the number of leaves per tiller (Chapman and Lemaire 1993). The measurements in ttris stuay were not aimed specifically at determining the leaf life-span, but the data can be used to obtain an approximation oi the leaf life-span. In 1992' the senescence of the newly emerged leaf on the first measurement date started approximately 2I d (266"C'd) later for both early and latemituring cultivars. In 1991, because measurements were 280 CANADIAN JOURNAL OF PLANT SCIENCE o 1991 Y=O.0076X, D 1992 Y=O.O122X, a2. o o^ 3 1..5 o// 0. ,/ ,./ //2 -./-/ E l o Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by 3.236.55.199 on 06/12/20 For personal use only. g ./- .0 800 .d 0) 600 -n 2' I z/ €z9( //E/ lrB ? f 400 o a) .,t)' sb { oll t""'--d o 200 E E .5 o (l) 1 R,=0.99, p<0.001 Ru=0.99, p<O.OOl 200 E € F roo ldo Forot (L) G (E) Nike (E) H lFd z6--lo 0 Cumulotive degree_doys (.C_d) Fig. 2. Cumulative number of new leaves of the late-maturing cul_ tivar Farol in I 991 and 1992 as a frrnction of the cumulatiue numbe, of growing degree-days. Lines represent the linear regressions. r0 2.O r -------a- 40 30 50 1200 E 1 000 -9 E00 () taken only over a period of I 7 d, no senescence ofthe newlv emerged leaf on the first measurement date was noticeable at the last measurement. Values of 330.C-d and 550.C_d have been reported for perennial ryegrass (Davies lggg) and tall fescue (Lemaire 1985), respectively. The leaf life-span of timothy is therefore closer to that of perennial ryegrass than that oftall fescue. Sward Characteristics Early-maturing cultivars had significantly (p < 0.10) wider and-longer mature leaves than late-maiuring cultivars in 1992 (Tables 3 and 4). However, in 1991. differences in width and length ofmature leaves between the late_maturing cultivar Farol and the three early-maturing cultivars wer6 not significant (P > 0.10). Cultivar differences in leaf width within a maturity group were observed in 1991. The width of mature leaves of the cultivar C was significantly (p < 0.10) greater than that of the cultivars Champ and Nike. The greater width and length of miture leaves of earlv_ maturing cultivars compared with those of late_maturing cultivars n 1992 is attributed to the fact that leaves of earlvl maturing cultivars extended faster than those of late_maturine cultivars but appeared at the same rate. The observed increase in width and length of successive leaves was also reported by Ryle (1964f on timothy and other grasses, and Davies (1971) on perennial ryegrasi. The precise reason for this increase with time is not fullv under_ stood but could be associated with the decrease in LiR with time, and the increase in LER. Because of the positive lin_ ear relationship benveen LER and temperatwe, the increase in temperature during the regrowth G;ble l) iesulted in an increase in LER. The total leaf length per tiller of the late-maturing cultivan was less than that of early-mahring cultivars inlggt anO 1992 (Fig.3). The LAI of the late-maturing cultivars, how_ ever, was similar to or greater than that of the other cultivars in both l99l and 1992 (B6langer and Richards 1995). The lower total leaf length per tilleiof late-mahring cultivars in ! ol {., o o e+l E o F Forot (L) Hokushu (L) Axet (E) o-€ 0+ o-+ r-rITf to 20 FA Doys from Moy Cloir I 50 40 T------- 50 1 Fig. 3- Total leaf length per tiller of timothy cultivars differing in maturity (E, early; L, late) in l99l and 1992. Bars indicate siandard error of the mean for each sampling date. 1992 was compensated by a greater tiller density. The tiller density of Farol and Hokushu was sipificantly (p < 0.05) grcater on the first four sampling dates than that of Clair and Hokushu (Table 5). Those four sampling dates correspond to the period during which LAR and LER were measured. Tiller density was not measured in 1991. Tiller density first increased and then decreased during the regrowth cycle. Langer (1958, 1959) also observed i decrease in tiller density prior to ear emergence in the spring. This decline was related to increased shading within the sward, and was aggravated by the subsequent onset of flowering (Langer et al. 1964). Langer et al. 1Le64y reporred a tiller density of approximately 3000 tillers m-2 for a timothy sward in its second production year. There was very little difference in the amount of inter- cepted PAR between early and late-maturing cultivars (B6langer and Richards 1995). The amount of intercepted PA& however, was detennined during a period (21 May-lg June l99l; 26 May13 June 1992) when the LAI was greater than 2 and most of the PAR was intercented. The measurements of morphogenetic and stucnral characteristics were taken earlier in the regrowth than those of LAI and radiation interception. They indicate that earlymaturing cultivars have greater LER than late-maturing cul- BELANGEB _ MORPHOGENETIC AND STRIJCTI//RAL CHARACTERISTICS OF Table 3, Maximurn width of msture leaves of cultivars differing in maturity on 31 May 1991 and I June 1992 Leaf width (mm) l. Champ (E)v 2. Nike (E) 3. G (E) 4. Farol (L) Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by 3.236.55.199 on 06/12/20 For personal use only. SEM 1991 7.27 7.27 8.07 7.02 0.26 Contrast (significance probability) NS' 4 vs. 1,2,3 3 vs. 1,2 I vs.2 l. Clair (E) 2. Axel (E) 3. Hokushu (L) 4. Farol (L) SEM 0.036 7.80 7.72 7.50 6.90 0.30 I vs.2 NS' NS ).J) l. Champ (E)r 6.92 7.5s 6.72 6.15 6.57 s.90 5.67 6.15 5.37 2. Nike (E) 3. G (E) 0.24 0.28 0.36 SEM NS NS NS NS NS 24t.6 254:1 264.8 256.1 t2.2 4. Farol (L) Contrast (signifi cance probability) NSx NS 3 vs. NS 4 vs. 1,2,3 1,2 lvs.2 250.6 250'3 237.5 213.0 4.75 6.35 5.95 4.90 4.22 (E) 2. Axel (E) 3. Hokushu (L) 4. Farol (L) 0.19 0.22 0.25 sEM 0.006 0.028 0.026 NS Contrast (signifi cance probability) 0.054 1,2 vs.3,4 NS' I vs. 2 NS 3 vs.4 6.88 6.78 NS NS NS NS is the leafpreceding the last emerged elongating leaf, and 4 are the preceding leaves' 5.25 4.45 0.01I and leaves early; L, late. tNS, not significant at P < 0.10. YE, tivars but a similar LAR. As a result of these differences in morphogenetic processes, sward structural characteristics of early and late-maturing cultivars differed. Early-manrring cultivars had a greater leaf size per tiller than late-maturing cultivars but, at least in 1992,the difference in leaf size was compensated by a greater tiller density of the late-maturing cultivars. As a result, there were no differences in LAI between early and late-maturing cultivars. CONCLUSION Differences in morphogenetic processes between early and length (mm) Leaf numbef 5.85 5.45 5.25 'Leaf I 2,3, NS NS I 992 Contrast (signifi cance probability) 0.094 1,2 vs. 3,4 3 vs.4 5.82 0.031 NS 1992 kaf 6.6'l NS ofmature leaves ofcultivars differing in maturity on 3l May l99l and I June Cultivars Leafnumber" Cultivars f"ft l. Length T'MOTHY 281 L Clair 11.35 r99I 9.0 187.5 189.0 172.0 163.3 10.9 NS NS NS NS NS NS 245.0 262.2 229.6 232.9 1992 261.4 182.8 160.7 134.3 t26.8 10.69 258.1 213.7 192.2 lr.9l 123.0 lll.0 rr3.7 103.2 21.7 NS NS NS 107.8 83.3 80.3 81.8 7.97 0.004 NS NS 0.001 NS NS NS 0.058 NS t*f preceding the last emerged elongating leaf, and leaves 2, it' th. 3, and 4 are the Preceding leaves. vf, sar'ly; L. late iNS, not significant at P < 0.10. "L."f I late-maturing timothy cultivars resulted in different sward of earlymaturing cultivars was greater than that of late-maturing cultivarl during primary growth of timothy. Since there were no differJnies in LRR among cultivars, individual tillers of early-maturing cultivars developed a greater leaf size than late-maturing cultivars. ln 1992,late-maturing cultivars had a $eater tiller density than early-maturing cdqyars which compensated for the smaller leaf size per liller' Different tilier density-tiller size characteristics ofearly and late-maturing timothy cultivars resulted in a similar out- structural c[aracteristics' Leaf extension rate come in terms of LAI. Table 5. Tlller density of cultivars differing in maturity during primary growth in 1992 Number of tillers Cultivars 12 May 9 June I 6 June 2225 22ll I 528 23 June 1744 I 875 1825 I 2 r08 t294 3245 2183 3245 3461 2450 1764 959 2374 269 344 255 335 282 266 NS NS NS NS NS NS Clair (E)z 2020 2. Axel (E) 3. Hokushu (L) 4. Farol (L) t'|72 2297 1975 2530 3395 2969 300 l. sEM 26May Contrast (signifi cance probability) 1,2 vs.3,4 l vs.2 3vs.4 0.022 NSY NS "E, early; L, late. YNS, not significant at P < 0.10. Sampling date 2 June 1945 1892 2't59 2945 l9 May 0.002 NS NS 0.024 NS NS 0.001 NS NS 833 I NS NS NS 282 CANADIAN JOUBNAL OF PLANT SCIENCE ACKNOWLEDGMENTS I thank J. O. Monteith and S. D. Coy for excellent technical assistance. I am also gateful to Dr. J. E. Richards and Dr. W. K. Coleman for their critical review of the manuscript. B6langero G. f990. Incidence de la fertilisationazoteeet de la saison sur la croissance, I'assimilation et la r6partition du carbone dans un couvert de f6tuque 6levde en conditions naturelles. DSc. Thesis, Universit6 de Paris-Sud, France. 169 pp. B6langer, G. and Richards, J. E. 1995. Grofih characteristics of timothy cultivars differing in maturity. Can. J. plant Sci. 75: Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by 3.236.55.199 on 06/12/20 For personal use only. 64H48. Chapman, D. F. and Lemaire, G. 1993. Morphogenetic and structural determinants of plant regrowth after defoliation. proc. XVII Int. Grassl. Congr. 93-104. Charles-Edwards, D. A. 1982. physiological determinants of crop growth. Academic Press, London, U.K. l6l pp. Davies, A. 1971. Changes in growth rate and morphology of perennial ryegrass swards at high and low nitrogen levels. J. Agric. Sci.77: 123-124. Davies, A. 1988. The regrowth of grass swards. pages g5_l 17 rn M. B. Jones and A. Lazenby, eds. The grass crop. Thephysiological basis of production. Chapmam and Hall, London, U.K. Davies, A. and Thomas, H. 1983. Rates of leaf and tiller produc_ tion in young spaced perennial ryegrass in relation to soil iemperatures and solar radiation. Ann. Bot. 57: 591-597. Gastaf, F., B6langer, G. and Lemaire, G. lggl. A model of the leafextension rate oftall fescue in response to nihogen and temperature. Ann. Bot. 70: 437-442. Genstat 5 Committee. 1987. Genstat 5 reference manual. Oxford University Press, New York, Ny. Heide, O. M. 1982. Effects of photoperiod and temperature on growth and flowering in Norwegian and British timotiry cultivars (Phleum pratense L.). Acta Agric. Scand. 32: 241--252. Kleinendorst, A. and Brouwer, R. f970. The effect of temperature of the root medium and of the shoot on growth, water content and sugar content ofmaize leaves. Neth. J. Agric. Sci. 1g: l 40-14g. Langer, R. H. M. f958. A study of growth in swards of timothy and meadow fescue. 1. Unintemrpted growth. J. Agric. Sci. 5i: 347-352. Langer, R. H. M. 1959. A study of growth in swards of timothy and meadow fescue. 2. The effects of cutting treatments. J. AgriC. Sci.52: 273-281. Langer, R. H. M., Ryle, S. M. and Jewiss, O. R. 1964. The changing plant and tiller populations of timothy and meadow fescue swards. l. Plant survival and the pattern of tillering. J. Appl. Ecol. l:197--208. Lemaire, G. 1985. Cin6tique de croissance d'un peuplement de f6tuque elev6,e (Festuca arundinacea Schreb.) pendant i'hiver et le printemps. Effets des facteurs climatiques. DSc. Thesis. Universit6 de Caen, France. 96 pp. Mika, V. f 983. A comparison of the nutritive values of early and late varieties of timothy. Grass Forage Sci. 38: 67-71. Onillon, B. 1993. Effets d'une contrainte hydrique 6daphique sur la croissance de la fdtuque 6lev6e soumise d diff6rents niveaux de nutrition azotee. Etude d l'6chelle foliaire et ir celle du couvert v6gdal. D.Sc. Thesis, Universit6 de Poitiers, France. 123 pp. Parsons, A. J. and Robson, M. J. 1980. Seasonal changes in the physiology of S24 perennial ryegrass (Lolium perenne L.). l. Response of leaf extension to temperature during the transition from vegetative to reproductive growth. Ann. Bot. 46:435444. Patel A. S. and Cooper, J. P. 1961. The influence of seasonal changes in light energy on leaf and tiller development in ryegrass, timothy and meadow fescue. J. Br. Grassl. Soc. 16: 299-308. Peacock, J. M. 1975a. Temperature and leaf growth in Lolium perenne. I. The thermal microclimate: its measurements and relation to crop growth. J. Appl. Ecol. 12: 99-114. Peacock, J. M. 1975b. Temperature and leaf growth in Lolium perenne. IL The site of temperature perception. J. Appl. Ecol. 12: n5-123. Peacock, J. M. 1976. Temperature and leaf growth in four grass species. J. Appl. Ecol. 13: 225-232. Ryfe, G. J. A. 1964. A comparison of leaf and tiller growth in seven perennial grasses as influenced by nitrogen and temperature. J. Br. Grassl. Soc. 19: 281-290. Surprenant, J., Drapeau, R. and Fernet, C. 1993. Cultivar-byyield and quality caii- management interaction effects on timothy bration. Can. J. Plant Sci.73: 44H60.