GenEERA IV – Modelling for the dispersal behaviour of oilseed rape on a landscape scale – North-East Germany regional study

(2001 - 2004) Leibniz-Centre for Agricultural Landscape Research (ZALF), Müncheberg

Topic

The project is part of the GenEERA joint research project (generic analysis and extrapolation of oilseed rape dispersal). The aim of the research project was to evaluate the dispersal and persistence of genetically modified oilseed rape (Brassica napus) for North-East Germany as part of a regional study.

Model construction was based on an evaluation of existing data, case studies with real usage data and expert interviews. In close collaboration with the associated part-projects focusing on North-West Germany (Lower Saxony and Schleswig-Holstein), sensitive regions were identified for North-East Germany that are particularly relevant for future monitoring of the cultivation of genetically modified oilseed rape varieties.

Summary

In the regional distribution of rape cultivation in Northern Germany there were obvious regional centres, in which rape cultivation reached average cultivation concentrations of 15–25 per cent of the total arable area. Rape cultivation returned to the same fields in at least 80 per cent of cases after a two- to three-year cultivation gap, leading to the establishment of area-wide, permanent wild rape populations. As well as self-sown rape, charlock, flixweed and in places wild radish were among the most common potential outcross partners for GM rape in the agricultural area. These species occurred on 25-30 per cent of all arable fields.

The spatiotemporal density of cultivation is decisive for the spread of genome material via seeds in the soil. Because of the ability of rape seeds to remain viable in the soil for many years, it can be assumed that the cultivation of genetically modified rape varieties will lead to a continual increase in their proportion of the soil seed bank. The accumulation trend can also be accelerated by a rapid succession of rape crops on the same plot.

Experiment description

In order to be able to predict the dispersal behaviour of rape for large areas, the dispersal paths and scale of the dispersal of transgenic oilseed rape were analysed for Northern Germany.

The Centre for Agricultural Landscape Research (ZALF) investigated the variance of cultivation factors over large areas that are relevant for the dispersal of oilseed rape.

The sub-areas investigated to identify the influence and control possibilities of agricultural management on the dispersal of oilseed rape genome material include:

the spatial and temporal distribution of oilseed rape cultivation,
the occurrence of self-sown oilseed rape and other potential crossing partners on the arable fields and in the accompanying structures,
the regional differences in oilseed rape cultivation and their impacts on e.g. genome dispersal via seeds.

Results

Spatiotemporal density

Germany is Europe’s largest producer of oilseed rape. In 2001 at least 38 per cent of total European rape cultivation took place in Germany. Because of the relative economic attractiveness of oilseed rape, cultivation in Germany is rising steeply.

In the regional distribution of rape cultivation in Northern Germany there is a clear regional concentration in east Schleswig-Holstein, north-east Brandenburg, the whole of Mecklenburg-Western Pomerania and in southern Lower Saxony. In these centres, rape cultivation reaches average cultivation concentrations of 15–25 per cent of the total arable land. This means a high average spatial density (nearly every fourth arable field per year) and temporal density (nearly every fourth year on the same field) for the cultivation of oilseed rape.

Diag.1: Return of oilseed rape cultivation to the same field in years. Results of the evaluation of real usage data from a sub-area of Uckermark in north-east Brandenburg (N= 506 arable fields on 17 farms, 1999-2003)

Photo 1: Incidence of flowering self-sown rape in Triticale in Uckermark (north-east Brandenburg 2003)

Diag. 2: Model results for rape seed content in the soil in the 10th modelling year, adjusted for rape cultivation density in Mecklenburg-Western Pomerania and Brandenburg

In the cultivation centres, a further increase in rape cultivation leads to the cropping intervals for oilseed rape being reduced to less than the ideal agronomic term, i.e. to less than three years. This is already the case to a significant extent (10-15 per cent), as studies of typical real usage data show (Diag. 1).

Incidence of self-sown rape outside the cultivation area

The high spatial density and the short- to medium-term return of rape cultivation on the same area leads to the establishment of area-wide, permanent wild rape populations. These wild rape populations can be regulated by agricultural management, but cannot be totally destroyed or prevented. In sample surveys in one research area, self-sown rape was seen to reach the flowering stage on 10-11 per cent of arable fields not cultivated with rape (Photo 1).

Weak points for the regulation of wild rape in the cultivation system are primarily dicotyledonous crops (e.g. sugar beet, sunflowers) and the staggered or delayed germination of self-sown rape. With rape cultivation densities of between 15 and 20 per cent, and a return of cultivation to the same field within four to five years, the permanent establishment and reproduction of self-sown rape populations on arable fields and in associated structures appears unavoidable. As well as self-sown rape, charlock, flixweed and in places wild radish, were among the most commonly found potential outcross partners for GM oilseed rape in the agricultural zone. These species are found on almost 25-30 per cent of all arable fields, as well as less frequently on fallow land and in associated biotopes.

Model results for the accumulation of seeds in the soil

The results of the individual-based modelling for the states of Brandenburg and Mecklenburg-Western Pomerania were applied to the regions. The key factor in determining the dispersal of genome material via seeds in the soil is the spatiotemporal cultivation density of genetically modified oilseed rape. Because of the rape seeds’ ability to survive for many years in the soil, it can be assumed that the cultivation of genetically modified rape varieties on today’s scale will lead to a continual increase in their proportion of the seed bank. The accumulation trend can also be accelerated by a rapid succession of rape crops on the same plot. For this reason, in areas with high cultivation concentrations of oilseed rape, the formation of higher soil seed bank levels of GM oilseed rape is likely across the area, than in regions with less oilseed rape cultivation. The regional concentration of oilseed rape cultivation in Brandenburg and Mecklenburg-Western Pomerania has consequences for the monitoring of potential seed-borne genome dispersal of oilseed rape and for potential control mechanisms (e.g. coexistence conditions). They suggest special consideration of individual cultivation regions (Uckermark, Prignitz, Fläming) for Brandenburg, and an area-wide approach for Mecklenburg-Western Pomerania (Diag. 2).