The relationship between establishment and yield of autumn-sown oilseed rape
About this project
Oilseed rape is currently a major arable crop in its own right and the main break crop in the UK. In the 1993/94 season, just under half a million hectares of rape was grown, 404,000 ha on the main scheme (winter and spring sown crops for human consumption) and 91,000 ha of industrial rape on set-aside. The current position of oilseed rape within UK agriculture has been largely encouraged by EU support mechanisms; first by yield support and since 1992, the area payment scheme. The introduction of this scheme effectively halved the value of the seed yield and shifted the focus toward minimising production costs whilst maintaining consistent yields. Optimising establishment and understanding the yield potential of a given plant population will help growers to achieve this.
In two separate studies we have examined the effect of specific and combined seedbed characteristics on oilseed rape establishment and investigated the likely effect of low population by studying the physiological link between establishment and final harvest.
The data presented suggest that there are yield benefits from lower populations, but these rely on even plant distribution. At face value a move toward lower plant populations is of benefit to the industry, not only in terms of potential yield benefits but also in terms of production costs. Seed rates could be reduced, a cost saving which may become even more important as more expensive hybrid varieties come on line. Lowering plant populations reduces crop height and produces thick stemmed plants which are less susceptible to lodging and hence pod shatter. Unlodged crops also improve speed and ease of harvesting.
In practical terms achieving uniform and low plant populations present problems with slugs, severe pigeon grazing and weed control being of key concern. The answer to these concerns may lie in focusing on maximising uniform establishment at reasonable populations (20-30 plants per m²) through the winter and then managing the canopy either by physical defoliation or through plant growth regulators in the spring. Success in this instance relies on reliable and uniform establishment. In terms of physical seedbed conditions we have highlighted the need, particularly on heavy soils, to be aware of the condition of the surface tilth in the preceding crop and if present, to maintain it through careful management during harvest time. Cultivation choice should be driven by the condition of the surface tilth and the level of cereal residues, the aim being to create as fine a seedbed as possible while diluting cereal residues; these conditions will minimise the risk of poor establishment.
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