OVERWINTERING AND SPRING GROWTH OF FOUR WHITE CLOVER CULTIVARS - S. Puzio, A. Kornher and F. Taube

Department of Grass and Forage Science, Christian-Albrechts-University, 24098 Kiel, Germany

SUMMARY

A field trial of four white clover cultivars grown in binary mixtures with two perennial ryegrass cultivars was established in May 1994. Detailed morphological measurements were carried out on clover leaves, buds, stolons and roots from late autumn to spring in 1994-1997, and changes in the total non-structural carbohydrate content (TNC) of the stolons were recorded. Severe frosts in 1995/96 caused very large dry matter losses. As a result of the extremely cold winter cv. Huia developed the lowest significant leaf and bud weight. From the beginning of the winter until spring this cultivar showed a decrease in stolon length of 68 percent, whereas other cultivars had losses of only 39 percent. Also, the accumulation of TNC in autumn was found to be about 10 percent less in Huia than in the other cultivars. Variation in spring yield in 1996 was explained to 55 percent by stolon weight and to 61 percent by carbohydrate reserves in winter. With weak development of stolons, buds, leaves, and low TNC content, in winter 1996, cv. Huia gave in spring 1996 its lowest yield. In spring 1997, no significant differences in morphological development were observed. As the previous year, cv. Huia showed the lowest stolon weight and carbohydrate content, but attained a similar level of yield in spring compared to the cvs. Aberherald and Gigant.

Keywords: overwintering, spring growth, Trifolium repens L., white clover.

INTRODUCTION

White clover is the most important forage legume currently grown in cool, temperate environments. Due to its high nutritional quality and digestibility, white clover enhances the nutritive value of a grass/clover sward. To profit from the advantages of this legume a proportion of about 30 percent of the annual dry matter yield is required (Rhodes et al., 1993). However, fluctuations in clover yield, both from year to year and within the season makes it difficult to manage the clover content and especially in spring the clover yield is very low. This may be due to a limited winter hardiness and the inferior growth at low temperatures compared to the companion grass. The present study investigates the relationship between overwintering and clover yield in spring with regard to different white clover cultivars.

MATERIALS AND METHODS

The experiment was established near Kiel in May 1994. The experimental site was located in the east of Schleswig-Holstein in a hilly landscape with sandy loamy Cambisol (pH 6.7), average yearly precipitation of 716 mm and an average yearly temperature of 7.8°C. The design of the experiment was a randomized block with three replicates.

The trial consisted of four white clover cvs.; Aberherald, Huia, Milkanova and N.F.G.Gigant. These were sown in mixture with two perennial ryegrass cvs.; Preference (medium-late-heading) and Vigor (late-heading), at seeding rates of 2 kg ha^-1 clover seed and 23 kg ha^-1 grass seed. The plots received 30 kg ha^-1 N at the beginning of the vegetation period. Samples were taken five times in the period from November until April.

RESULTS AND DISCUSSION

The development of white clover in spring was mainly determined by sward age and weather conditions during the winter period. In winter 1996 the extremely cold weather caused very large dry matter losses, mainly in leaf and stolon weight (Figure 1). From autumn until spring stolon weight decreased by 59 percent compared to the other years with losses of about 36 percent. As a result of the long frost period white clover developed very slowly in spring 1996 and the leaf weight of 5 g m^-2 in April was only a tenth of the leaf mass of the following year. Differences between the clover cultivars were especially distinct in spring 1996. Cultivar Huia showed significantly the significantly lowest leaf, bud and stolon weight at this time and also the accumulation of TNC in autumn was found to be about 10 percent less in Huia than in the other cultivars. The cvs. were Aberherald and Milkanova distinguished from other cultivars by a strong leaf and bud development. This superiority indicates that a high leaf dry matter yield in spring is achieved by the formation of numerous large leaves. The leaf size alone is not decisive as shown by the cv. Gigant. Variation in spring yield 1996 was explained to 55 percent by stolon weight and to 61 percent by the amount of TNC in winter. In spring these relationships differed between the years. There was a big positive influence of leaf weight on the development of white clover in spring 1996, whereas in the following year no significant influence could be noticed. Differences between the cultivars with respect to the morphological parameters were visible in a similar manner in spring yield. In agreement with the weak development in winter 1996 cv. Huia significantly gave the lowest yield in spring 1996 compared to the other cultivars (Table 1). Differences in stolon development in winter 1997 had no impact on the subsequent spring yield. Only cv. Milkanova showed a significantly higher yield compared to cv. Huia. Rhodes (1991) pointed out that, after mild winters where stolon losses are small, differences in yield between cultivars may be due to other characters than stolon amount.

Figure 1. Development of leaf and stolon weight with regard to sum of temperature (°C > 0 °C), November (N) until April/May (A/M) 1995 - 1997 (mean of two grass cvs.).

Table 1. Clover dry matter yield (t ha^-1), primary growth 1995 - 1997 (LSD: Least square difference at P = 0.05).

REFERENCES

Rhodes, I. 1991. Progress in white clover breeding. In: White clover development in Europe. REUR Technical Series 19, FAO Rome, 1-9.

Rhodes, I. & Webb, J. 1993. Improvement of white clover. Outlook on Agriculture, 22, 189-194.