Clover stolon growth within clover-rich patches and on the boundaries of patches with surrounding grass

Carol Marriott¹, G R Bolton¹ and Elizabeth I Duff²

¹Macaulay Land Use Research Institute, and ²scottish Agricultural Statistics Service, Craigiebuckler, Aberdeen AB9 2QJ, Scotland, UK.

Introduction
Materials and methods
Results
Discussion
Conclusion
References

Introduction

Persistence and spread of clover in grazed swards depends largely on vegetative growth of stolon tissue. In grazed swards there is seldom a uniform distribution of clover, with clover-rich and clover-poor areas generated as a result of edaphic factors, grazing defoliation and excretal return. The effect of such patchiness on the ability of clover to extend stolons and petioles within clover-rich areas and in the boundary zones of patches was investigated in this experiment.

Materials and methods

The sward was sown in 1989 with a mixture of four ryegrasses (cvs Condesa, Contender, Magella and Barna) and Kent Wild White clover. Three sizes of patch were used in this experiment: circular patches of diameter 0.5 m or 1.5 m and a square patch of 4 x 4 m. At monthly intervals from May until September replicate stolons were marked in the centre and on the edge of patches; one stolon of each type was selected in each of 10 replicate circular patches and 10 replicate stolons were selected in a single large patch. Initial total stolon length (to a branch or until disappearance into the ground) and length of the marked unit (node 3 to stolon tip) were recorded. Further measurements included petiole length and sward surface height of surrounding grass and clover. Measurements were made at the time of marking and again 1 and 2 weeks later. Different stolons were used for each measurement period. The initial length of stolons was used as a covariate in the analysis. Sheep were excluded from the site during the measurement periods.

Results

Stolon and petiole extension were significantly higher (p<0.001) from May until July than at later measurement dates (Table 1). The position of the stolon and the size of the clover patch both affected stolon extension; meaned over all dates, it was greater on the edge of a patch than in the centre (13.2 cf 5.5 mm/week, sed 0.97) and greater in small and medium patches than in the large (10.9, 10.3 and 6.9 mm/week, sed 1.19).

There was no overall effect of stolon position on petiole extension, but petiole extension was greater at the edge compared with the centre of medium patches (Table 2).

Sward heights of grass were highest in June, while those of clover were highest in July (Figure 1). The vertical height difference between grass and clover was significantly higher (P<0.001) in June than on subsequent dates. The sward heights of both grass and clover were taller in the centre than on the edge of patches (by 1.3-2.5 cm and 1.0-1.9 cm respectively for grass and clover). The vertical height difference between grass and clover was greater in the centre than on the edge of patches (P<0.05 for small and medium patches).

Table 1 Seasonal pattern of stolon and total petiole extension on marked stolons (nun/week).

Measurement periods
	22.5-5.6.92	19.6-3.7.92	16.7-30.7.92	13.8-27.8.92	17.9-1.10.92	sed
Stolen	16.2	14.0	10.3	3.7	2.6	1.54
Petiole	-	48.2	61.0	31.5	27.6	2.20

Table 2 Total petiole extension on marked stolons within and on the edge of different sizes of clover patch (mm/week), sed = 2.70

	Small	Patch size	Large
		Medium
Stolon position
Inside	43.3	38.5	39.2
Edge	47.3	50.5	33.7

Figure 1 Sward surface heights (cm) of grass and clover at the end of measurement periods.

Discussion

The growth of petioles and stolons of clover differed depending on the spatial arrangement of clover in the sward. There was a negative relationship between sward height and stolon extension, with the greatest extension at the edge of patches where absolute sward height (and vertical height difference in small and medium patches) were less than in the patch centre. This may be a response to the perceived R: FR light ratio. In previous measurements we found a higher R: FR ratio at the edge of patches (C. Marriott and G.R. Bolton, unpublished), and Thompson and Harper (1988) found that stolon growth in undefoliated plants grown under greenhouse conditions was reduced by canopy filtered radiation. The values for stolon extension are larger than those measured in sheep-grazed swards where animals were present during the measurement period (Barthram et al., 1992), but may be similar to those found in rotationally grazed swards.

Conclusion

The results indicate that the boundaries of clover-rich zones can change rapidly in early summer as stolons grow into predominantly grassy areas.

References

BARTHRAM, G.T., GRANT, S.A. and ELSTON, D.A. (1992) The effects of sward height and nitrogen fertilizer application on changes in sward composition, white clover growth and the stock carrying capacity of an upland perennial ryegrass/white clover sward grazed by sheep for four years. Grass and Forage Science. 47, 326-41.

THOMPSON, L. and HARPER, J.L. (1988) The efect of grasses on the quality of transmitted radiation and its influence on the growth of white clover. Oecologia, 75, 343-7.