R.D. Sheldrick, R.H. Lavender and T.M. Martyn
Institute of Grassland and Environmental Research,
North Wyke Research Station, Okehampton, Devon, EX20 2SB, United Kingdom
Introduction
Materials and methods
Results
Discussion and conclusions
Acknowledgement
References
A major problem with the management of swards containing white clover in the temperate, maritime climate of the UK is the loss of clover stolon and reduction of growing point density over winter (Frame and Newbould, 1986; Woledge et al., 1990), leading to poor sward productivity the following spring (Collins et al., 1991). Selections from white clover material collected in Switzerland were shown to be more cold tolerant than standard cultivars, a character related to the stolon's content of non-structural carbohydrate (Collins and Rhodes, 1995). Two new cultivars bred from such material, AberCrest (small leaved) and AberHerald (medium leaved), have been released (Rhodes et al., 1994) and gained recognition on Recommended Lists (SAC, 1994; NIAB, 1994). An evaluation of these cultivars in comparison with white clover cv. Menna under 4-weekly cutting management commenced at North Wyke in 1989 (Sheldrick et al., 1993) and in 1991 it was decided to extend the assessment by establishing swards for a sheep-grazed experiment, reported here.
A ryegrass-dominant sward, originally sown to cv. Vigor in 1982 at North Wyke (50°51' N; 3°50' W) was cut for silage in mid May 1991 and afterwards oversown with white clover using a Hunter Rotary Strip Seeder (Pascal and Sheppard, 1985), creating 3 randomised blocks each containing 0.35 ha plots of cvs. AberCrest, AberHerald and Menna. Clover germination took 2-3 weeks. The swards were then grazed at intervals with young cattle, and later by sheep over winter 1991-92, before fencing the plots. Soil analyses suggested that pH (water) was adequate, ranging from 6.3 to 6.5, but P levels were low. Applications of 57 kg P and 126 kg K ha-1 were made in March - June 1991, and 33 kg P and 62 kg K ha-1 in February 1993. Swards were sprayed with chlorpyrifos in October 1991 to control Sitona weevils.
Plots were grazed with Suffolk × Masham ewe lambs, approximately 12 months of age at the start of each grazing season. Grazing took place between 24 March and 14 October 1992, and 11 March and 7 October 1993. Balanced groups of 8 ewe lambs (mean liveweight 44 kg) were allocated to each plot, and sward height assessed twice weekly. A temporary, electrified buffer fence was introduced across each plot and moved to keep the mean sward height of the area grazed by the core sheep in the range 4.0-6.0 cm. Additional ewe lambs were used to graze the sward behind the buffer fence to the same sward height criteria, on a "put and take" basis. Thus when the buffer fence was moved back to alleviate falling sward heights in the area for the core group, the sward incorporated was similar to it in structure, density and composition.
All core animals were weighed fortnightly. Shearing took place in June 1992 and 1993.
Shallow turf cores (diameter = 10 cm) were taken from each experimental plot in March and October each year, and the total length of clover stolon determined. Three circular ground level quadrats (area =0.1 m2) were cut from each plot in March, June or July and October of both years to determine the tiller density of ryegrass and other grasses, also dry matter (DM) yields of clover and grass, live or dead, leaf and stem. Weather data were available from a meteorological station c. 400 m from the experimental site.
The clovers established well, despite dry weather after sowing, and subsequent grazing management produced satisfactory swards. Details of liveweight gain per ha by the core sheep and the sward carrying capacity appear in Table 1; DM yields of white clover in the ground level quadrats and the stolon densities are shown in Table 2. Weather data are shown in Table 3.
Table 1. Sheep liveweight gain (LWG) (kg ha-1) and sward carrying capacity (C. Capacity) (t d ha-1), 1992 and 1993.
|
Clover cultivar |
1992
|
1993
|
||||
|
LWG |
C. |
LWG |
C. |
|||
|
Mar-Jun |
Mar-Oct |
Mar-Oct |
Mar-Jun |
Mar-Oct |
Mar-Oct |
|
|
AberCrest |
179 |
553 |
313 |
201 |
596 |
329 |
|
AberHerald |
113 |
477 |
302 |
185 |
502 |
279 |
|
Menna |
221 |
612 |
355 |
249 |
625 |
340 |
|
P value |
0.002 |
NS |
NS |
NS |
0.08 |
NS |
|
SED (4 dfs) |
12.1 |
80.4 |
29.7 |
29.8 |
40.5 |
28.6 |
The liveweight gains by the ewe lambs in the first half of the 1992 grazing season were greater on the cv. Menna sward (P < 0.01) than on the cv. AberCrest sward, which were greater in turn than on the cv. AberHerald sward (Table 1). However, these differences were not significant for the full year's results. In 1993 there was a tendency towards superiority of cv. Menna over cv. AberHerald, though not statistically significant at P = 0.05. Carrying capacity showed no statistically significant differences between the cultivars in either 1992 or 1993. Yields of clover DM from the quadrats cut in March both years were very low, but cv. AberCrest showed some recovery each year by October (Table 2). Both cvs. Menna and AberHerald showed recovery by October 1993, but in 1992 cv. AberHerald showed no recovery and cv. Menna yields declined sharply from mid-season. Clover stolon density was significantly (P < 0.05) greater for cv. AberCrest in October 1992, but not in 1993. Clover performance was not related to changes in grass tiller density.
Table 2. White clover DM yields (DMY) (kg ha-1) in ground level quadrats and stolen density (mm2) in turf cores, 1992 and 1993.
|
Clover Cultivar |
1992 |
1993 |
||||||
|
Clover DMY |
Density |
Clover DMY |
Density |
|||||
|
Mar |
Jul |
Oct |
Oct |
Mar |
Jun |
Oct |
Oct |
|
|
AberCrest |
73 |
139 |
176 |
67.9 |
40 |
68 |
190 |
47.5 |
|
AberHerald |
87 |
40 |
27 |
21.4 |
15 |
12 |
141 |
25.6 |
|
Menna |
86 |
145 |
48 |
29.9 |
18 |
22 |
170 |
37.0 |
|
P value |
NS |
NS |
NS |
0.016 |
NS |
NS |
NS |
NS |
|
SED (4 dfs) |
45.8 |
49.9 |
74.7 |
9.52 |
19.8 |
37.2 |
130.8 |
24.05 |
Although the herbage mass of the three white clover cvs. in March 1992 was very similar, clear differences in lamb liveweight gain were established in favour of the control sward (cv. Menna) in the period from turn-out to shearing in June (Table 1). Given that swards were being grazed to the same height, this can be interpreted as a greater ability on the part of the cv. Menna sward to extend its foliage into the grazed horizon. During the rest of 1992 and in 1993 clover yields fluctuated and neither lamb liveweight gain or carrying capacity showed significant differences. The high error terms for the clover yields (Table 2) are probably a reflection of the small number of quadrats that could be cut and processed on each occasion. The significantly superior stolon density for cv. AberCrest in October 1993 supports the greater DM yields for this cultivar reported by Rhodes et al. (1994).
Table 3. Mean maximum and minimum air temperature (°C), number of air frosts (< 0°C) and total rainfall (mm) for 4-month periods 1991-1993.
|
|
1991/2 |
1992/3 |
1993 |
|||||
|
B |
C |
A |
B |
C |
A |
B |
||
|
Air T (°C) |
Min |
10.4 |
2.8 |
6.5 |
9.6 |
3.7 |
6.6 |
8.7 |
|
|
Max |
18.3 |
8.4 |
15.0 |
16.4 |
9.1 |
13.8 |
15.8 |
|
No. of air frosts |
Nil |
28 |
2 |
1 |
15 |
6 |
Nil |
|
|
Rainfall (mm) |
254 |
245 |
218 |
346 |
466 |
342 |
396 |
|
|
A |
= |
first half grazing season, March-June |
|
B |
= |
second half grazing season, July-October |
|
C |
= |
winter, November-February. |
Although the 1992-3 winter was milder than the preceding one (Table 3), clover yields in March 1993 were lower than in 1992, possibly adversely affected by the high rainfall. In both years, March - June and July-October temperatures were broadly similar. However, the higher rainfall in the first half of 1993 may have allowed greater trampling damage to the clover in that year and contributed to the poor mid-season clover yields recorded. Clover DM yields were generally depressed, possibly on account of the fertility of the site and the continuous sheep grazing management imposed (Newton and Davies, 1986).
In conclusion, no sustained differences were found between the three white clover cultivars under the conditions of this experiment, in terms of sheep performance, sward carrying capacity, content of white clover DM, or clover stolon density.
We acknowledge financial support from MAFF and the BBSRC for the execution of these studies.
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NEWTON, J.E. and DAVIES, D.A. (1986) White clover and sheep production. Occasional Symposium No. 21, British Grassland Society, pp. 79-87.
NIAB (1994) Recommended list of grasses and herbage legumes 1994/95. National Institute of Agricultural Botany, Cambridge, pp. 44.
PASCAL, J.A. and SHEPPARD, B.W. (1985) The development of a strip-seeder for sward improvement. Research and Development in Agriculture 2, 125-134.
RHODES, I., COLLINS, R.P. and EVANS, D.R. (1994) Breeding white clover for tolerance to low temperature and grazing stress. Euphytica 77, 239-242.
SAC (1994) Recommended list of herbage varieties, 1994/95. Scottish Agricultural College, Edinburgh.
SHELDRICK, R.D., LAVENDER, R.H. and MARTYN, T.M. (1993) A field evaluation of two white clover cultivars selected for winter hardiness. In: White clover in Europe: State of the Art. FAO, Rome. REUR Technical Series 29, 91-93.
WOLEDGE, J., TEWSON, V. and DAVIDSON, I.A. (1990) Growth of grass/clover mixtures during winter. Grass and Forage Science 45, 191-202.
