P.Nykänen-Kurki
Agricultural Research Centre, South Savo Research Station, 50600 Mikkeli, Finland
Introduction
Materials and methods
Results
Discussion
Conclusions
References
Some white clover cultivars have proved productive in Finland (Nykänen-Kurki, 1994). However, there is little seed of adapted white clover on the market, and some farmers are interested in seed production on their own farms. The aim of this study was to evaluate the possibilities of white clover seed production under extreme climatic conditions.
The white clover cultivars, Undrom and Sonja from Sweden, Jögeva 4 from Estonia, AberCrest and AberHerald from the United Kingdom and the Finnish ecotype Tammisto, were sown pure without a cover crop at Mikkeli in June 1993. Plots were fertilized in spring the following year with 10, 50 and 90 kg ha-1 of N, P and K, respectively. A split-plot design with four replications was used with three defoliation treatments (no cut, cut before bud emergence (June 9, 1994) and late cut after bud emergence (June 28, 1994)). Plots were treated with 'Reglone' (diquat, 200 g l-1) with 3 1 ha-1 on 18 August except for one replicate left demonstrate harvest without desiccant. The height of leaves and inflorescences was measured with a sward stick. Inflorescence production, pure seed yield, 1000-seed weight and germination were determined. Weather conditions over the harvesting period were recorded. Results of the first harvesting year, 1994, are presented.
Although the growth of white clover started slowly due to low temperatures in spring, all plots were well established before flowering. Effective day degrees (thermic sum above 5°C) were 170°C and 342°C at the first and the second defoliation date, respectively. The average values of the period 1961-1990 were 220°C and 412°C, respectively. Height of leaves and inflorescences differed according to cultivar, but defoliation had no effect (Figure 1).
Figure 1. Height of inflorescences and leaves of white clover, 1994.
The difference between height of inflorescences and leaves was the greatest in Jögeva 4,14 cm, and less than 10 cm in AberCrest and AberHerald. The length of petioles differed less than the height of inflorescences between cultivars. Plots, which were cut on 9 June, started flowering during the first week of July, two days earlier than those not cut. Defoliation on 28 June delayed flowering by nearly one week. Cultivar rather than defoliation affected the number of inflorescences (Figure 2). Tammisto produced significantly more inflorescences than the other cultivars, while AberHerald was the least productive.
Seeds were ripe in late August. Reglone-treated plots were harvested on 25 August. Mean temperature of the month, 14.6°C, was normal, but precipitation was 106 mm (120%). Eleven rainy days in August (Figure 3.) made harvesting difficult. Yields were rather low. Harvesting of Reglone-untreated plots was impossible due to rapid vegetative growth. Pure seed yields ranged from 24 to 130 kg ha-1 according to cultivar. The last defoliation decreased seed production, but differences were significant only between cultivars. Jögeva 4, Tammisto and Sonja produced seed the best, and AberCrest, AberHerald and Undrom were the poorest.
Figure 3. Mean day temperatures and precipitation in August 1994 and 1970-1994.
Purity of seed yield varied from 84.9% to 94.2% (Table), the rest consisting of undeveloped white clover seeds and seeds of Poa species. The overall 1000-seed weight, 0.6 g - 0.7 g, was normal. Germination ranged from 69% in AberHerald to 76% in Jögeva 4 after seven days of germination, which suggested AberHerald to have the highest proportion of hard seeds.
Quality of white clover seed the first harvesting year, 1994.
|
|
Cultivar |
|||||
|
Tammisto |
Jögeva 4 |
Sonja |
AberCrest |
AberHerald |
Undrom |
|
|
Purity, % |
86.5 |
93.7 |
94.2 |
95.0 |
88.7 |
84.9 |
|
1000-seed weight, g |
0.7 |
0.6 |
0.6 |
0.6 |
0.6 |
0.7 |
|
Germination, % |
72 |
76 |
72 |
74 |
69 |
73 |
In the UK, defoliation before inflorescence bud emergence did not stimulate inflorescence production, but defoliation after emergence increased the number of inflorescences (Marshall et al., 1993a). Under Finnish conditions, defoliation before bud emergence had no effect on flowering. At the end of June it was too late to enhance inflorescence production; on the contrary, it decreased flowering. To determine the optimum defoliation date and bud development in different cultivars under northern conditions, it is suggested that bud emergence be recorded carefully together with effective day degrees.
In Mikkeli, cultivar rather than defoliation before or after bud emergence affected the harvestable seed yield as also reported by Marshall et al. (1993b). Although the potential harvestable seed yield should increase with the number of inflorescences, in practice the seed yield is dependent on the harvesting process and especially the climatic conditions then prevailing.
1. Desiccant was needed to harvest seed yield under unfavourable climatic conditions.
2. Optimum defoliation date for stimulation of inflorescence production was not found.
3. Seed production characteristics differed between cultivars.
4. Weather conditions outweighed cultivar characteristics such as inflorescence position.
5. Seed quality was only moderate under extreme harvesting conditions.
MARSHALL, AH., HOLLINGTON, P.A. and HIDES, D.H. (1993a) Spring defoliation of white clover seed crops. 1. Inflorescence production of contrasting white clover cultivars. Grass and Forage Science, 48, 301-309.
MARSHALL, AH., HOLLINGTON, P.A. and HIDES, D.H. (1993b) Spring defoliation of white clover seed crops. 2. Potential harvestable seed yield and seed yield components of contrasting white clover cultivars. Grass and Forage Science, 48, 310-316.
NYKÄNEN-KURKI, P. (1994) Growth of white clover in various grass mixtures. Workshop Proceedings of the 15th General Meeting of the European Grassland Federation, Wageningen, The Netherlands, pp. 31-33.
