Oilseed rape cropping systems in NW Europe

Olaf Christen¹⁾, Eric Evans²⁾, Christer Nielsson³⁾ and Christian Haldrup⁴⁾

¹⁾ Institute of Crop Science and Plant Breeding, Christian-Albrechts-University, 24118 Kiel, Germany, ²⁾ University of Newcastle, Newcastle upon Tyne NE1 7RU, United Kingdom
³⁾ Swedish University of Agricultural Sciences, S 230 53 Alnarp, Sweden
⁴⁾ Danish Agricultural Advisory Centre, DK 8200 Aarhus, Denmark

Abstract

Oilseed rape is an important crop in arable farming systems in NW Europe. An EU concerted action (COST-Project AIR3 CT 94-2231 "Adaptation of oilseed crops management to new common agricultural policy") offered a unique opportunity to collect and compare information from different countries on the current husbandry of the crop. This paper describes the trends in the areas and yields of spring and winter oilseed rape in Denmark, Sweden, UK and Germany with special references to the differences in husbandry, i.e. tillage, fertilization, plant protection and rotational considerations. Additional data is included on the main pests, diseases and weeds in the different countries.

Although the environmental conditions in the countries in NW Europe differ only slightly, the husbandry varies considerably. This applies for example to the cropping systems in general but also to husbandry details such as sowing rates and pesticide applications. Additionally, Sweden and Denmark have a strict policy on the use of pesticides, which restricts the options of available chemical plant protection measures. On the other hand, farmers in those countries are increasingly looking for alternative non chemical methods of control.

Keywords: Husbandry, yield, nitrogen fertilization, fungicide application

Introduction

Oilseed rape has a long tradition in the cropping systems in Denmark, Sweden, the UK and Germany. There are, however, fundamental differences with respect to the cropping system and the level of inputs such as nitrogen and agrochemicals in the different regions. The main reasons for these differences are:

a) environmental conditions. The maritime climate in the north contrasts markedly with the more continental climate of southern and south-eastern parts of Europe which results in frequent dry-spells during the growing season.

b) farm size, fundamental differences exist in farm size across and even within each country, e.g. UK and Sweden, and between former East- and former West-Germany. This has an important influence on the workload per hectare, which in turn influences timeliness of fertilizer input and the ability to apply crop protection chemicals at the most appropriate time.

Generally speaking, the highest input, and the shortest rotations with respect to oilseed rape are currently found in the northern part of Germany and the UK with a strong maritime influence and heavy, loam soils. With few exceptions, crop inputs decreases further south within Germany and is lower in Denmark and Sweden.

Yields and areas of Cropping

The yield of oilseed rape in Germany and the UK has increased from around 2 t ha^-1 at the beginning of the sixties to over 3 t ha^-1 in recent years (Fig. 1). In Sweden and Denmark yields have not increased so markedly. On individual fields 5 t ha^-1 is possible. The increase in overall production (Fig. 2) has occurred mainly in Germany and the UK and arises from an increase in both yield and the area of cultivation. In Sweden the area of oilseed rape has decreased after the country joined the EU. Spring oilseed rape is traditionally more important in Denmark and Sweden compared to the other two countries, however, the area of spring rape in Germany and the UK can vary from season to season depending on crop value relative to production costs and on occasions to the level of winter kill.

Fig. 1: Yield (t/ha^-1) of oilseed rape in Denmark, Sweden, the UK and Germany (1991 - 1998)

Fig. 2: Production (Mt) of oilseed rape in Denmark, Sweden, UK and Germany (1991 - 1998)

Growing and crop rotation

In all countries oilseed rape cropping is mainly confined to arable farms without a significant proportion of sugar beet, potatoes, or vegetables. For the highest yields, oilseed rape needs to be preceded by an early harvested crop, such as winter barley. In the more southerly regions of Germany and the UK, or during favourable autumn weather conditions winter wheat may offer an opportunity for winter oilseed rape establishment Oilseed rape is not normally grown in rotation with sugar beet because of the problems of rapeseed volunteers and the risk of nematode infection and therefore rotations will mostly consist of various cereals and rapeseed. The shortest crop rotations are currently practised in the northern part of Germany (Schleswig-Holstein, Mecklenburg-Vorpommern and Niedersachsen), these are normally three-course rotations with oilseed rape - winter wheat - winter barley or even two-course rotations. On some farms barley might be replaced by winter wheat. In the UK oilseed rape is normally grown every four years, frequently the first crop after set-aside. While in Denmark and Sweden rotational breaks tend to be longer compared with the UK and Germany. There are small areas in Schleswig-Holstein as well as in the northern parts of Niedersachsen (Lower Saxonie) with serious rotational problems of oilseed rape due to occurrence of clubroot (Plasmodiophora brassicae). In these parts oilseed rape has been grown for extended periods every second year or continuously for a number of years. Rotational problems are not regarded as a major limit on rapeseed production at the present time.

Oilseed rape itself is considered as an excellent preceding crop for cereals. In most areas of Germany the value of an oilseed rape crop is similar to a preceding legume like peas. Given the current level of external input in wheat cropping, a wheat following rapeseed will, on average, yield 10 % more than a wheat grown continuously. (Christen et al. 1992) This positive effect is due to a break in the disease cycle for a number of cereal pathogens (e.g. Gaeumannomyces graminis) and also the favourable effect of rape on soil structure

In recent years there has been considerable discussion of the merits of oilseed rape in crop rotations in relation to residual nitrogen following the rape harvest, leading to nitrate pollution of the ground and drinking water due to a limited capacity of the following winter wheat to take up this residual nitrogen in the autumn.

Key agronomic factors

Choice of variety

In all countries oilseed rape varieties are selected which combine high yields with good resistance to as many diseases as possible. In Sweden winter hardiness is the first factor for the choice of variety. In recent years hybrid varieties have become more popular as growers have gained experience in their cultivation and are prepared to manage the crops more intensively. In Germany the hybrid varieties are especially used for late sowing dates.

Soil treatment and sowing methods

The standard tillage method for winter oilseed rape consists of ploughing followed by a harrowing, however, the soil treatment and sowing methods differs with respect to the farm size and the need to conserve water These conditions apply to parts of former East-Germany apart from the northern region of Mecklenburg-Vorpommern and on clay soils in the drier areas of southern England. In these areas a number of farms employ minimum tillage treatments for all crops including oilseed rape, although the establishment of oilseed rape with minimum tillage systems present a very different problem to that of cereal establishment due to seed size and the presence of cereal residue. McWilliam et al. (1998) measured the relative importance of the different factors influencing establishment and concluded that more detailed attention should be given to conserving the natural tilth through the use of appropriate cultivation systems. In Sweden and Denmark direct drill has become very popular for winter oilseed rape especially in dry summers.

Establishment

There is little variation in the date of sowing winter oilseed rape in Germany and the UK. The range is from the middle of August in the northern part of Germany and the UK, to the middle of September in the drier eastern regions of southern Germany. Spring rape is normally sown during March and April, as soon as soil conditions become favourable. Traditionally seed rates for winter rape have been higher in the UK than in the other countries at around 6 kg ha, while in Germany they vary between 2.5 and 4.5 kg ha, and slightly higher in Sweden (up to 12 kg/ha) and Denmark. Increasing the seed rate does not compensate for late autumn drilling. Seed rates for the spring sown crop tend to be higher to compensate for the lower degree of branching.

Fertilization

With the introduction of area aid payments the recommended rates of nitrogen for winter oilseed rape have been reduced throughout Europe. The highest amounts of nitrogen currently applied will vary from 150 to 230 kg N ha. Areas of high nitrogen inputs include Schleswig-Holstein and Mecklenburg-Vorpommern regions of Germany and southern England. Nitrogen fertilization to winter oilseed rape tends to be a little bit less in Sweden in Denmark. Nitrogen applications to spring rape will vary from 100 to 150 kg N ha depending on locality and its place in the rotation.

Only limited amounts of nitrogen will be applied in the autumn to the winter sown crop, normally between and 30 and 50 kg N ha. Trial results in the UK have shown little benefit from splitting the spring nitrogen dressing, although in practice the majority of growers will apply half the required amount when growth starts and the remainder between late March and mid April (Chalmers et al. 1992). Which concurs with the situation in Sweden. In Germany spring nitrogen is split, between the beginning of the crop development in spring and stem elongation. In recent years there has been a growing interest in sulphur fertilization, especially for the winter sown crop due to lower sulphur emissions. Most farmers will apply sulphur in one form or another , especially when oilseed rape is grown on light, shallow soils. The annual amounts range between 30 to 60 kg S/ha. Results from field trials in the UK have recorded yield increases of between 15 and 74%, depending on site and seasonal climatic conditions (Withers et al. 1995). In Germany oilseed rape will receive organic manures mainly as slurry, depending on availability. Slurry is applied to winter oilseed rape before ploughing in the autumn or in the spring when growth has recommenced. Despite the considerable uptake of nitrogen in autumn compared with cereals, recovery of this nitrogen in the seed is very low.

Weed Control Measures

Currently the main chemical for weed control in Germany and the UK for winter oilseed rape is Metazachlor, alone, or in a mixture with Quinmerac with approximately 80 to 90 % of the area sprayed with this herbicide in Germany. Volunteer cereals and grass weeds require additional treatment with chemicals such as Fluazifob or Cycloxydim. In some areas of Germany the cropping of oilseed rape is virtually restricted by the increasing occurrence of hedge mustard (Sisymbrium officinale), while Capsella bursa pastoris and Viola arvensis are becoming increasingly troublesome due to the absence of effective herbicides. Only a few herbicides are approved for use in Denmark for oilseed rape, however in Sweden weeds are normally not as important as in the other countries. To control dicotyledonus weeds Napropamid, Clopyralid and Propyzamid are available. For grasses and volunteer control, Fluazifob, Propaquinzafop or Haloxyfop are used. There is an increasing interest in Denmark to grow oilseed rape with a 50 cm row spacing in order to allow for a mechanical weed control.

Pests and Diseases

Several diseases can infect winter oilseed rape and frequently result in yield losses in the four countries, on the other hand, disease is rarely a problem in the spring crop. The main problems arise from infection with Pyrenopeziza brassicae, Sclerotinia sclerotiorum, Phoma lingam and Alternaria. In the UK Peronospora parasitica can be troublesome during wet periods in the autumn, while in some areas Verticillium dhaliae has become an important fungal disease. The input level of fungicides varies within the four countries, although widespread fungicide use has become less cost effective in recent years.

In northern Germany as well as the UK Tebuconazol or a mixture of Carbendazim and Flusilazole may be applied in the autumn to control foliar and stem diseases and to increase winter hardiness. Such an autumn application is only seldom applied in other parts of Germany. Plant growth regulators are not widely applied. The other important application date for fungicides is post flowering to combat Sclerotinia and Alternaria during periods of wet weather. In drier regions Sclerotinia will not have a major effect on yield in most years. Treatments against pests are routinely applied in most areas in Germany depending on the incidence of the pest, while in the UK more reliance is now based on threshold values to predict pesticide needs. Slugs have become a major problem of winter sown rape, especially after wet summers and , where reduced tillage has been followed to establish the crop. Other important pests are thrips (Thrips angusticeps) and flea beetles (Phyllotreta spp.). During spring the most important pest is the blossom beetle (Meligethes aeneus).

Harvest

Winter oilseed rape in Germany is predominately harvested by direct threshing, while in the UK swathing has become the most common harvesting method, although direct combining is practiced in southerrn England under favourable conditions. In Germany swathing is restricted to a few areas along the west-coast of Schleswig-Holstein where the high risk of severe winds immediately before harvest can result in considerable loss of seed. In Denmark the situation is quite different with most field swathed before threshing.

The described husbandry applies to all oilseed rape production in the four countries regardless if it’s end use.

References

Chalmers, A.G., R.J., Darby, E.J. Evans, A.H. Sinclair, and P.J.A. Withers, 1992: Crop nutrition and fertiliser requirements for the double low oilseed rape crop. H.G.C.A Report No OS5 156 pp.

Christen, O., K. Sieling and  H. Hanus, H., 1992: The effect of different preceding crops on the development, growth and yield of winter wheat. European Journal of Agronomy, 1 (1), 21-28

McWilliam, S.C., D.T. Stokes and R.K. Scott, 1998: Establishment of oilseed rape: the influence of physical characteristics of seedbeds and weather on germination, emergence and seedling survival. H.G.C.A. Project Report No OS31 99p.

Withers, P.J.A., E.J. Evans, P.E. Bilsborrow, G.F.J. Milford, S.P. McGrath, F. Zhao, and K.C. Walker, 1995: Development and prediction of sulphur deficiency in winter oilseed rape. H.G.C.A. Project Report No OS11 22 pp.