Plant characteristics of two contrasting white clover cultivars under rotational cattle grazing

Mats Höglind and Bodil E. Frankow-Lindberg Swedish University of Agricultural Sciences, Department of Crop Production Science, P.O. Box 7043, S-750 07 Uppsala, Sweden

Introduction
Materials and methods
Results
Conclusions
References

Introduction

The only information available in Sweden today on the productivity and persistence of different white clover (Trifolium repens L.) cultivars has been obtained in 'cutting-only' experiments (Nilsdotter-Linde, 1993). Results obtained from cutting trials, however, cannot uncritically be applied to a situation with grazing animals (Evans et al., 1992), where selective grazing, trampling and depositon of dung and urine are known to influence both dry matter yield and botanical composition of the sward.

This paper reports some preliminary results from an ongoing project in which two Swedish-bred cultivars were evaluated under grazing by cattle. We wanted to know which plant characteristics conferred persistence and high yield to white clover under cattle grazing in the Scandinavian environment.

Materials and methods

The two cultivars under study, both classified as medium-leaved (Caradus, 1986), were Sandra, a selection for improved seed-setting from high-yielding material collected in New Zealand, Wales, Denmark and USA and Undrom, a selection for winter hardiness from Danish Morsö x Swedish Skultuna. Each cultivar (5 kg/ha) was sown in May 1991, in mixtures with 6 kg/ha Phleum pratense L. (cv. Alexander), 10 kg/ha Festuca pratensis Huds. (cv. Sv. Sena) and 4 kg/ha Poa pratensis L. (cv. Sobra) and replicated eight times within a randomized complete block design (plot size 1, 5 x 10 m²) on a heavy clay in the eastern part of central Sweden (lat. 58° 58' N).

During the first experimental year, 1992, the sward was rotationally grazed four times by lactating cows at intervals of 4-5 weeks, between 6 June and 13 September. Immediately following each grazing, which lasted 2-4 days, the sward was trimmed to a residual height of 6-7 cm. No fertilizer N was given to the sward. Before each grazing, two plots per cultivar were cut with a motor scythe, leaving a stubble height of 5 cm, and sub-sampled for determination of dry matter (DM) yield and botanical composition. A rotational scheme was used, so that each plot was cut only once during the season. Harvest dates were 4 June, 1 July, 3 August and 7 September.

Weekly, detailed sward measurements were undertaken during three periods; in spring from the onset of growth until a week before turnout (13 April to 25 May), in summer during the regrowth between the second and third grazings (6 July to 27 July) and in autumn between the last grazing and the end of the growing season (14 September to 20 October). DM yield, botanical composition and the number of clover leaves carrying a visible petiole were estimated from two 10x10 cm² samples per plot cut at ground level and the number of leaves, branches and flowers which appeared and died were recorded on 2-5 marked stolons per plot. In addition, during the summer and autumn measurement periods, the following observations were made on two stolons per plot: lamina area, lamina weight, petiole length and petiole weight of individual leaves, the number of fully-developed living leaves per growing point (i.e. leaves that have reached at least stage 0.6 (Carlson, 1966)), internode length (between the first and second fully-developed leaf counted from the stolen tip) and stolon diameter (by the node of the first leaf). At the beginning and end of each measurement period, the number of growing points and the dry weight of stolons were determined from two 15x15 cm² turves per plot.

Results

The total yield of laminae plus petioles cut at 5 cm was somewhat higher for Sandra than for Undrom; 7590 vs. 7000 kg DM/ha. For both swards, the clover content of the cut herbage was c. 90%. Stolon mass was similar for both cultivars; the amount of live stolons present at the end of season was 1990 and 1930 kg DM/ha for Sandra and Undrom, respectively.

The individual leaves of Sandra were larger than those of Undrom in terms of both lamina area, lamina weight, petiole length and petiole weight (Table 1). Undrom, on the other hand, had more leaves present per unit area than Sandra. Neither specific leaf area (Table 1) nor rate of leaf appearance (Table 2) differed significantly between the varieties.

Table 1. Leaf characteristics

Harvest date	Cultivar	Lamina area (cm2)	Lamina weight(mg)	Specific leaf area(cm2g-1)	Petiole length (mm)	Petiole weight (mg)
23 July	Undrom	8,5	26	326	175	23
	Sandra	11,1	34	332	206	37
s.e.m. and sign. of difference		0,3*	1**	10ns	8*	2***
20 Oct.	Undrom	5,0	16	311	68	11
	Sandra	8,0	26	308	94	20
s.e.m. and sign. of difference		1,0*	3*	13ns	7*	3*

Table 2. Rate of leaf appearance (new leaves stolon^-1 week ^-1) and branching (new branches stolen'! week ^-1)

	13 April-25 May		6 July-27 July		14 September-20 October
	Leaf app.	Branching	Leaf app.	Branching	Leaf app.	Branching
Undrom	0,53	0	1,33	0,23	0,44	0,13
Sandra	0,57	0	0,35	0,35	0,45	0,10
s.e.m. and sign. of difference	0,02ns		0,07ns	0,03*	0,03ns	0,02*

In summer, Sandra had a somewhat higher branching rate than Undrom, while in autumn the reverse was the case (Table 2). Sandra had thicker stolons than Undrom (Table 3), while neither internode length nor number of leaves per growing point differed consistently between the cultivars.

Table 3. Stolon characteristics

Harvest date	Cultivar	Stolon diameter (mm)	Internode length (mm)	No. of leaves per growing point
27 July	Undrom	2,2	12,0	3, 2
	Sandra	2,3	15,3	3,4
s.e.m. and sign. of difference		0,1ns	1,6ns	0,1ns
20 October	Undrom	2,9	3,3	2, 1
	Sandra	3,3	3,3	2,2
s.e.m. and sign. of difference		0, 1*	0,5ns	0,1ns

Undrom had more growing points per unit area than Sandra at all exept the first sampling date in summer (Figure la), although the difference was never significant. Sandra always had the highest stolon dry weight per growing point (Figure 1b). For both cultivars, the lowest values for number of growing points were recorded in late spring, and the highest in autumn. Sandra allocated a larger proportion of dry matter into petioles than Undrom in summer and autumn (Table 4) and a smaller proportion into laminae in summer. Data also indicate that Undrom allocated a slightly, but not significant, larger proportion of dry matter into stolons than Sandra in autumn.

Table 4. Dry matter partitioning (dry weight of different plant parts in percentage of total aboveground dry weight)

Harvest date	Cultivar	Laminae	Petioles	Stolons
27 July	Undrom	37,2	31,2	31,6
	Sandra	31,1	35,4	33,5
s.e.m. and sign. of difference		1,6*	1,1*	2,2ns
20 October	Undrom	17,8	11,6	70,6
	Sandra	18,8	16,1	65,1
s.e.m. and sign. of difference		1,9ns	1,2*	2,2ns

Figure 1. Number of growing points per m² (a) and stolen dry weight per growing point (b). = Undrom = Sandra

Conclusions

The results presented are preliminary. However, data so far collected indicate that:

1. Sandra has larger leaves than Undrom.

2. Undrom has more leaves and growing points present per unit area than Sandra.

3. Stolen dry weight seems not to differ very much between the varieties.

4. Sandra allocates proportionally more dry matter into petioles and, at least in summer, less into laminae than Undrom, while Undrom allocates more of its dry matter into stolons than Sandra during autumn.

Continued experimentation will show whether the cultivar differences so far found will stand also after several years of grazing. The question which plant characteristics are best correlated with persistence and productivity under grazing could then be better answered.

References

CARADUS, J. R. World checklist of white clover varieties. New Zealand Journal of Experimental Agriculture. 14. 119-164.

CARLSON, G. E. 1966. Growth of clover leaves - developmental morphology and parameters at ten stages. Crop Science. 6, 293-294.

EVANS, D. R., WILLIAMS, T. A. and EVANS, S. A. 1992 Evaluation of white clover varieties under grazing and their role in farm systems. Grass and Forage Science. 47, 342-352.

NILSDOTTER-LINDE, N. 1993. Vallväxter. Sorter till slåtter, bete och grönfoder för södra och mellersta Sverige 1993. Sveriges lantbruksuniversitet. Speciella skrifter 50.