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Vegetative development of four annual clovers

H. Nori, A.D. Black and D.J. Moot

Field Service Centre, P.O. Box 84, Lincoln University, Canterbury, New Zealand. Email Hollena.Nori@lincolnuni.ac.nz

Abstract

A field experiment with 10 sowing dates quantified thermal time requirement for seedling development of arrowleaf, balansa, gland and Persian clovers. A base temperature (Tb) of 0oC was found for all species. Balansa and Persian clovers required ~213oC d from sowing to first leaf appearance compared with 231 oC d for arrowleaf and 221 oC d for gland clover. The phyllochron for these annual clovers was affected by photoperiod at emergence. For example, the phyllochron for balansa clover was 82 oC d when plants emerged into a 13.6 hour with decreasing photoperiod but only 44 oC d when plants emerged into a 15.6 hour with increasing photoperiod. These differences in phyllochron also affected the time of axillary leaf appearance. A slower phyllochron resulted in longer time to the first axillary leaf.

Key Words

Leaf appearance, Trifolium glanduliferum, T. michelianum, T. resupinatum, T. vesiculosum

Introduction

Annual clovers are used in dryland pastures to provide sheep grazing during late winter and early spring. Subterranean clover (Trifolium subterraneum L.) is the most widely used annual legume species in New Zealand. However, its seed burr means specialised machinery that can cause environmental damage is required for seed harvest, and none is currently produced commercially in New Zealand. Alternativley, top flowering species such as arrowleaf (Trifolium vesiculosum Savi), balansa (T. michelianum Savi), gland (T. glanduliferum Boiss.) and Persian (T. resupinatum L.) clovers may have potential for use in dryland pastures (Charlton and Stewart 2003; Dear et al. 2002; Evans and Mills 2008; Monks et al. 2008). These top flowering annual clovers are not widely used in New Zealand and little is known about the performance of these species under New Zealand conditions. Developmental characteristics in seedlings partially determine their success in a pasture sward. Specifically, leaf appearance rate (phyllochron) and timing of first axillary leaf affect canopy development and the consequent competitiveness of seedlings. Development processes such as leaf appearance can be quantified in thermal time (Tt).

Thus, the objective of this study was to quantify thermal time requirements for vegetative development of arrowleaf, balansa, gland and Persian clovers and relate this to temperature and daylength as the main drivers of seedling development.

Methods

The experiment was established at Lincoln University, Canterbury, New Zealand (43o 38’S, 172o 28’E, 11 m a.m.s.l.) on a Wakanui silt loam (Cox 1978) soil. A split-plot design with four replicates was initiated on 10 sowing dates (main plots) with four annual clover species (‘Cefalu’ arrowleaf, (‘Bolta’ balansa, ‘Prima’ gland and ‘Mihi’ Persian) sown in 6 m2 subplots.. The 10 sowing dates were: 26 Feb 10 (SD1), 30 Mar 10 (SD2), 4 May 10 (SD3), 3 Jun 10 (SD4), 7 Jul 10 (SD5), 14 Aug 10 (SD6), 25 Sep 10 (SD7), 9 Nov 10 (SD8), 20 Dec 10 (SD9) and 19 Jan 11 (SD10). Bare seeds of clover species were broadcast as pure stands at 6 kg/ha for ‘Cefalu’ arrowleaf, 4 kg/ha for ‘Bolta’ balansa and ‘Prima’ gland and 5 kg/ha for ‘Mihi’ Persian. All seeds were sown with Group C inoculants (ALOSCA Tech. Ltd.). Soil (10 mm depth) and air (1200 mm above ground) temperature were recorded hourly using a HOBO data logger to define daily maximum and minimum temperatures for thermal time calculations. Daily photoperiod was determined from geographic coordinates and includes civil twilight. Three 0.01m2 quadrats were placed in a fixed position on each subplot. The number of seedlings with spade leaf appearance was counted every alternate day until all seedlings within the quadrat had produced a leaf. The number of days to reach 50% of final first leaf appearance (t50) was determined from the Gompertz model, t50= M-ln[-ln(y/100)]/B where, M and B are constants. The base temperature and thermal time requirements for first leaf were defined using a linear model of development rate (1/t50) against mean temperatures as described by Angus et al. (1981) and Moot et al. (2000). The number of emerged leaves on the main stem and appearances of axillary buds were counted at 4-7 day intervals on 10 marked plants per subplot. The phyllochron was calculated from least squares regression of the number of leaves against thermal time accumulation across sowing dates and then analysed in relation to photoperiod at emergence. Quantification of thermal time to first leaf used soil temperature while phyllochron and axillary leaf initiation used air temperature based on the position of plant’s growing point (Jamieson et al. 1995).

Results and discussion

In each species, the number of days to first leaf appearance was ~41 days at the lowest temperature of 5.3oC (SD4) and then decreased with every increment of mean soil temperature (~11 days at 18.6oC (SD8)). In all species, Tb calculated was not different from 0oC. With Tb set to 0oC, to enable comparison among species (Moot et al. 2000), the Tt requirement for first leaf appearance averaged 213(9.4) oC d for both balansa and Persian clovers compared with 221(11.6) oC d for gland and 231(6.4) oC d for arrowleaf clovers. There was an interaction (P<0.001) between sowing date and species for the phyllochron (Table 1). The phyllochron exhibited a declining trend following each successive sowing date with the longest phyllochron from pastures sown on 26 February 2010 and the shortest for those sown on 9 November 2010.

Table 1. The phyllochron (oC d/leaf) of arrowleaf, balansa, gland and Persian clovers sown on different dates in Lincoln University, Canterbury, New Zealand.

Sowing date

Annual clover species

(SD)

arrowleaf

balansa

gland

Persian

26/2/2010

116

82

91

93

30/3/2010

96

77

87

93

4/5/2010

90

70

85

87

3/6/2010

83

70

74

78

7/7/2010

91

69

65

82

14/8/2010

80

55

50

77

25/9/2010

63

49

41

68

9/11/2010

53

44

33

61

20/12/2010

60

44

33

67

19/1/2011

62

46

36

67

 

SD

Species

SD*Species

P- value

<0.001

<0.001

<0.001

S.E.M.

1.3

0.6

2.2

Except when comparing means with the same level of SD

2.0

L.S.D. (5%)

3.7

1.8

6.1

Except when comparing means with the same level of SD

5.7

Note: Thermal time used air temperature (Tb = 0oC) and calculated starting from first leaf appearance. |
SD, Sowing date. S.E.M. Standard error of mean; L.S.D., Least significant differences.

The phyllochron responded to changes in the length and direction of photoperiod at seedling emergence. When seedlings emerged following the shortest day (21 June) into an increasing photoperiod up to 16 hours, the phyllochron decreased by 6 (0.9) oC d leaf-1 hour-1 for arrowleaf, 5 (0.9) oC d leaf-1 hour-1 for balansa, 7 (1.1) oC d leaf-1 hour-1 for gland and 3 (0.6) oC d leaf-1 hour-1 for Persian clover. Following the longest day, as photoperiod shortened to ~13 hours into the autumn, phyllochron rose rapidly by 21 (2.6) oC d leaf-1 hour-1 for both arrowleaf and gland, 14 (1.4) oC d leaf-1 hour-1 for balansa and 10 (1.0) oC d leaf-1 hour-1 for Persian clover. However, as photoperiod continued to decrease further into the winter, the phyllochron decreased by 9 (1.5) oC d leaf-1 hour-1 for arrowleaf , 4 (0.9) oC d leaf-1 hour-1 for both balansa and gland and 7 (0.9) oCd leaf-1 hour-1 for Persian clover.

The first axillary leaf was initiated in the axil of the spade leaf in balansa and Persian clovers and in the axil of the first trifoliate leaf in arrowleaf and gland clovers. For most sowing dates, the initiation of axillary leaf began after the appearance of four leaves on the main stem of balansa, gland and Persian clovers and five leaves on the main stem of arrowleaf clover. The time to axillary leaf appearance was affected (P<0.018) by a species by sowing date interaction. For example, in gland clover, the Tt requirement from sowing to axillary leaf appearance was 642 (49.1) oC d when sown on 30 March, 2010 (SD2), but it only took 320 (15.6) oC d (which is half of the Tt for SD2) to produce the first axillary leaf when seeds were sown on 9 November, 2010 (SD8) (Figure 1c).

Figure 1. Number of total (closed symbols) and main stem (open symbol) leaves of (a) arrowleaf, (b) balansa, (c) gland and (d) Persian clover plotted against thermal time after sowing (Tb = 0oC, air temperature) of SD2(_) and SD8(↵). Arrows indicate time of axillary leaf appearance. Error bars represent the maximum standard error for the final total leaf number.

The differences in timing of axillary leaf appearance among sowing dates were caused by the differences in the phyllochron at sowing. The phyllochron for gland clover was 87 (0.5) oC d/leaf in SD2 compared to 33 (0.1) oC d/leaf in SD8 (Table 1). Thus, the longer phyllochron resulted in a longer duration to the first axillary leaf appearance.

Conclusion

Phyllochron and axillary leaf appearance were quantified by thermal time when photoperiod at emergence was accounted for. Throughout all the sowing dates, phyllochron was fastest for gland (33 – 91oC d) and slowest for arrowleaf (53 – 116 oC d) compared with balansa (44 – 82oC d) and Persian (61 – 93oC d) clovers. To maximize dry matter production and seed yield, autumn sowing is recommended.

References

Angus J.F., Cunningham R.B., Moncur M.W., Mackenzie D.H. (1981) Phasic development in field crops. I. Thermal response in the seedling phase. Field Crops Research 3:365-378.

Charlton D., Stewart A. (2003) Pasture and forage plants for New Zealand Grassland Research and Practice Series 8: (October 2003).

Cox J.E. (1978) Soils and agriculture of part Paparua County, Canterbury. D.S.I.R: Wellington, New Zealand.

Dear B.S., Sandral G.A., Wilson B.C.D., Rodham C.A., McCaskie P. (2002) Productivity and persistence of Trifolium hirtum, T. michelianum, T. glanduliferum and Ornithopus sativus sown as monocultures or in mixtures with T. subterraneum in the south-eastern Australian wheat belt. Australian Journal of Experimental Agriculture 42:549-556.

Evans P.M., Mills A. (2008 ) Arrowleaf clover: potential for dryland farming systems in New Zealand Proceedings of the New Zealand Grassland Association 70:239-243.

Jamieson P.D., Brooking I.R., Porter J.R., Wilson D.R. (1995) Prediction of leaf appearance in wheat: a question of temperature. Field Crops Research 41:35-44.

Monks D.P., Moot D.J., Smith M.C., R.J. L. (2008) Grazing management for regeneration of balansa clover in a cocksfoot pasture. Proceedings of the New Zealand Grassland Association 70:233-238.

Moot D.J., Scott W.R., Roy A.M., Nicholls A.C. (2000) Base temperature and thermal time requirements for germination and emergence of temperate pasture species. New Zealand Journal of Agricultural Research 43:15-25.

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