D.A. Davies and M. FothergillAFRC Institute of Grassland and Environmental Research Plas Gogerddan, Aberystwyth, Dyfed SY23 3EB, UK
Introduction
Methods and materials
Results
Discussion
Acknowledgement
References
White clover (Trifolium repens) varieties are evaluated for the UK National List under two cutting managements when grown with perennial ryegrass (Lolium perenne). Productivity is assessed by cutting 4-6 times annually at 3-4 cm height. Persistency is determined from ground cover measurements in the autumn of the third harvest year on swards that have been cut every 10-15 days at 2-3 cm height. Concern has, however, been expressed about the validity of this information in relation to performance under actual grazing, particularly in intensive sheep systems (Swift et al, 1992).
Research was carried out at Aberystwyth over 3 years (1989-91) to study the productivity and survival of white clover under continuous stocking by sheep compared to those under cutting. A range of cutting heights and frequencies was used which included the two regimes in the official tests.
The investigation was carried out at Plas Gogerddan (52°26'N, 04°01'W), 30 m above sea level with mean annual rainfall of 1030 mm and screen temperature of 9.7°C. Three white clover varieties were used in the experiment: small-leaved Aberystwyth S184; small-leaved AberEndura, a prostrate selection from Turkish material; medium-leaved Grasslands Huia from New Zealand. Each variety was sown, during summer 1988, at a seed rate of 3.5 kg/ha with 18 kg/ha of Talbot intermediate-flowering perennial ryegrass. Individual plot size was 5x2 m for the cutting treatments and 0.3 ha for the grazed treatment. All treatments were replicated three times.
During the 3 harvest years (1989-91) the following treatments were imposed on the cut plots:
T1 cut every 10 d at 2-3 cm, 120 kg N/ha (NL yield regime);
T2 cut every 21 d at 3-4 cm, 160 kg N/ha (intermediate treatment);
T3 cut every 42 d at 3-4 cm, 200 kg N/ha (NL persistence regime).
The differential N applications were imposed to account for the N removed in the herbage. Harvest was by means of a reciprocating-blade mower.
In each of the 3 years, the grazed plots (CS), which received no fertilizer N, were continuously stocked with ewes and lambs from early spring (mean date 23 March) until weaning (mean date 18 June), maintaining a sward surface height of 4-5 cm by regular adjustment of animal number on individual plots. After weaning, the pastures were stocked with lambs, maintaining a sward height of 5-6 cm before grazing down to 3 cm by termination of grazing in late autumn (mean date 6 November). Herbage production was monitored by ground-level sampling every 21 d with electric sheep shears, inside and outside 2 x 1 m exclosure cages.
A sample of the harvested herbage was separated by hand to assess clover contribution. Core samples were lifted in spring and autumn to monitor grass tiller and clover growing point numbers and clover stolon length per unit area of ground.
In this paper, the results are presented as the mean value of the three varieties averaged over the 3 years (1989-91). Total herbage dry matter (DM) production was highest on CS and lowest on T1 (Table 1). Clover DM production was also very poor on T1. The contribution of clover to total herbage production was similar on all four treatments.
Table 1 Herbage production and clover contribution under cutting and grazing, mean 1989-91
|
Treatment |
Total production t DM/ha |
Clover production t DM/ha |
Clover contribution % of DM |
|
T1 |
3.39 |
0.86 |
24.9 |
|
T2 |
6.73 |
1.83 |
28.0 |
|
T3 |
8.60 |
2.15 |
26.0 |
|
CS |
10.91 |
2.36 |
21.7 |
|
SE |
0.446 |
0.142 |
2.27 |
|
Significance |
P< 0.001 |
P< 0.001 |
NS |
Survival of white clover and perennial ryegrass was very poor on T1 (Table 2). Plant population of the two sown species was much higher under grazing than under all cutting treatments. The ingress of Poa, mainly Poa annua, was severe on T1 and minimal on T3.
Table 2 Grass tiller and clover growing point number and clover stolen length under cutting and grazing, autumn 1991
|
Treatment |
Perennial ryegrass |
Poa spp. |
Clover |
Clover stolon |
|
|
No/m2 × 103
|
m/m2
|
||||
|
T1 |
2.25 |
15.51 |
0.50 |
9 |
|
|
T2 |
4.40 |
6.91 |
2.34 |
62 |
|
|
T3 |
4.78 |
0.40 |
1.57 |
45 |
|
|
CS |
11.34 |
9.67 |
4.91 |
62 |
|
|
SE |
0.719 |
1.379 |
0.581 |
9.2 |
|
|
Significance |
P<0.01 |
P< 0.001 |
P<0.01 |
P< 0.001 |
|
The production, survival and morphology of white clover and perennial ryegrass under the cutting heights and frequencies imposed in the study were different to those in the continuously stocked pasture. Of particular concern was the poor performance of both species in T1, the National List management for assessing clover persistence. This result is in contrast to the experience of Swift et al. (1992) who found the treatment too lenient towards medium- and large-leaved varieties relative to their persistence under sheep grazing.
In a previous paper from this research, Davies and Fothergill (1993) compared the relative performance of the three white clover varieties. They concluded that none of the three cutting regimes adequately reflected the relative difference between the varieties in lamb production. Herbage measurements on the grazed pastures were also deficient in this respect, highlighting the limitations of the cage technique for assessing production under grazing.
The work presented was commissioned by the Ministry of Agriculture, Fisheries and Food.
DAVIES D.A. and FOTHERGILL M. (1993) Relative productivity and persistence of white clover cultivars under cutting or continuous stocking by sheep. Proceedings of XVII International Grassland Congress. Palmerston North. New Zealand (in press)
SWIFT G., MORRISON M.W., CLELAND A.T., SMITH-TAYLOR C.A.B. and DICKSON J.M. (1992) Comparison of white clover varieties under cutting and grazing. Grass and Forage Science. 47, 8-13.
