Grassland legumes

Cropping practice and use in Denmark

White and red clovers (Trifolium repens &T. pratense) are used in Danish agriculture partly in grazing fields in crop rotation, partly on permanent grassland (set-aside areas, highly sensitive agricultural areas, etc.). White clover is the most frequently used clover on grazing fields in crop rotations. The seed production of white clover is considerable, and Denmark is the largest producer of white clover seed in the EU. Since 2002, the conventional clover grazing field area has decreased by approx. 10,000 ha – a trend which is expected to continue.

On organic farms, white and red clovers are also used extensively as green-manure crops and catch crops.

Lucerne (Medicago sativa) is used for silage – in monoculture or in grass mixtures. The lucerne area is quite small, approx. 2800 and 1300 ha in conventional and organic production respectively, but there is growing interest in the use of lucerne. In 2006, there was a small area of lucerne for seed production. All production of clover seed in Denmark is contracted and is carried out according to the Executive order on field seeds¹⁰ and is thus subject to a range of restrictions in the form of separation distances and cropping intervals.

Crop area, Denmark, 2002 and 2006 (Rounded figures)

Year of cultivation 2002 2006

Conventionally cultivated grazing fields 189,000 ha 180,000 ha Conventional white clover seed production 2,852 ha 4,848 ha Conventional red clover seed production 381 ha 174 ha Conventional lucerne forage production 2400 ha 2750 ha Conventional lucerne seed production 6 ha 88 ha Conventional growing in total 194,600 ha 187,600 ha Organically cultivated grazing fields 34,000 ha 50,700 ha Organically cultivated set-aside areas with legumes 34,000 ha 800 ha Organic white clover seed production 554 ha 879 ha Organic red clover seed production 246 ha 258 ha Organic lucerne forage production 800 ha 1263 ha

Organic lucerne seed production 0 ha 5 ha

Organic growing in total 69,600 ha 53,900 ha Forage legumes in total 264,000 ha 242,000 ha Sources: Kristensen, 2007; The Danish Plant Directorate, 2006a.

The areas with grassland legumes constitute approx. 9% of the total crop area, and this area comprises both grazing fields and pastures. A steadily increasing share of the “grazing fields” is used for cutting or for a combination of cutting and grazing. For the major part of the areas, a first or second cut is taken and subsequently the areas are used for grazing for the rest of the growing season. There was a slight decrease of 9% in the area of grassland legumes from 2002 to 2006. The

10 Danish Plant Directorate Executive Order on field seeds, no. 52 of 24 January 2000 with later amendments

organic share of the areas was 22% of the grassland legume area in 2006. Organic farms commonly have both seed production and grazing fields. The white clover seed areas have increased by approx. 70%.

Both white and red clovers are very common on uncultivated areas (field boundaries, road and wood edges, etc.).

Experience with GM legumes in Denmark

There is no experience of growing GM legumes in Denmark.

Experience with GM legumes in foreign countries

There is no experience of growing GM white clover or GM red clover in foreign countries.

In Australia, permission has been granted for trial releases with a virus resistant white clover.

There have been 2 trial releases in the EU in lucerne (changed lignin biosynthesis and virus resistance).

Field trials with GM lucerne (glyphosinate tolerant) were carried out in the USA in the period 1998-2004, and cultivation is now permitted.

Sources of dispersal

White and red clovers as well as lucerne are cross-pollinating, mostly self-incompatible and are insect-pollinated by honeybees, naturally occurring bumblebees (the latter especially in red clover) and leaf-cutting bees (lucerne). Pollen from white and red clovers and lucerne are dispersed by these pollinating insects. Normally, bees will gather nectar and pollen as close to the beehive as possible, but if the supply of food sources is limited, they will forage at greater distances.

Clover seeds can develop into ”hard seeds”, which can survive in the soil for up to 20 years, and the same applies to lucerne. The seeds that are added to the soil seed bank can germinate later and be propagated in the crop rotation.

In addition to pollen and seed dispersal, white clover is dispersed vegetatively by rooting stolons.

New knowledge

Analyses have been made of pollen dispersal via bumblebees between red clover fields through use of a model for gene dispersal in insect-pollinated crops. The gene dispersal was found to be dependent on the number of visiting bee species and the mutual location of the red clover fields. By way of example, the model shows that gene dispersal via bumblebees between square fields with a width/length of 100 m and a mutual distance of 200 m was 0.17% (Damgaard et al., 2007b).

A research project (SEED) was started in 2006, financed under DARCOF III, in which gene dispersal in white clover is studied, including the degree of self-incompatibility and behaviour of pollinating insects. The objective of the project is to contribute results for establishing cropping methods for reduction of gene dispersal in the production of white clover seeds. Risø and DJF are the participants with DJF as the project manager (DARCOF, 2007).

Measures

It will be very difficult to reduce pollen dispersal via pollinating insects and it is impossible to avoid it completely; knowledge of the influence of honeybees and wild bees on gene dispersal in

grassland legumes is limited.

To reduce the number of seeds that are added to the soil seed bank, seed areas should remain untouched after harvest until the end of autumn to destroy as many of the shed seeds as possible.

Volunteers should be effectively controlled in intervening crops.

It is not possible to effectively prevent pollen and gene dispersal by cutting off clover flower heads in road edges and coverts, as the flower heads are normally positioned very low on the plant, and after repeated cutting the flowering stems become shorter.

Need for further knowledge

Due to the wide distribution of white clover in Denmark, more knowledge on factors determining pollination will be necessary for the establishment of separation distances and instructions on using buffer zones in the form of plants attractive to bees and separate harvesting.

There is a need for determining the extent of pollen dispersal between clover grass areas, seed fields and uncultivated areas and for determining the extent of volunteers producing seeds in other crops (false crop rotation).

Grassland legumes survive for a very long time in the soil – especially due to their ability to develop hard seeds. Measures that can prevent/reduce the presence of hard seeds will contribute to reducing the survival time and with that the levels of admixture.

Furthermore, the development of cropping systems for maintaining varietal purity in seed fields will be of major importance to maintaining Denmark’s position as the leading producer of clover seeds in the EU within both conventional and organic seed production.

There is a need for studying the competitiveness of various biological characteristics in clover in order to assess impacts on gene flow and dispersal of a given trait both in and outside the cultivated areas.

Conclusion

Denmark has a prominent position as producer of white clover seeds, and clover is also widespread in grazing fields and in uncultivated areas. The area with grassland legumes constitutes approx. 9%

of the total crop area, and the organic share of the areas was 22% of the grassland legume area in 2006.

So far, we have no practical experience of GM clover.

White and red clovers are insect-cross pollinating species and therefore have a high potential for pollen dispersal. Also seeds can survive for a long time in soil. Thus, clover has a large ability for dispersal and gene flow– both within and outside the cultivated areas in Denmark.

Based on the present basis of knowledge, it is still not possible to propose guidelines to ensure co-existence in Denmark.

There is a large need of more knowledge concerning pollination biology, methods for reduction of seed dispersal and the competitive ability of GM characteristics both within and outside the cultivated areas.