Optimising establishment of winter oilseed rape on clays

Summary

Establishment of oilseed rape is particularly difficult on clay soils, especially when straw is incorporated. This represents a significant problem to the industry as most oilseed rape (70%) is grown on clay soils. This document reviews the factors which influence the establishment of oilseed rape on clay soils. This is achieved by first detailing the physical and chemical requirements of a rape seed for germination and also the factors which may act to inhibit germination and impede the development of the young seedling.

The ability of clay soils to provide a suitable environment for the germination and subsequent establishment of a rape plant are examined. The important factors for this process are; the underlying soil structure and its ability to produce a natural seedbed, previous cropping, moisture supply, pests and diseases. This work indicates that it is impossible to define the seedbed and population of rape which will establish purely on the basis of the type of cultivation machinery used. It is concluded that there is no single engineering solution or simple prescription for obtaining an idea seedbed.

The interactions between soil type, previous crop, moisture supply and cultivation are examined, both in the context of producing a suitable seedbed and in terms of post-cultivation effects on pests, diseases and the physical environment of the seedling.

These analyses are synthesised into a number of 'Decision Trees' which plot the likely progress of given options on different soil types under a standard set of conditions (dry, wet, normal, plus straw, without straw) and thus suggest the best strategies for successful establishment under these different scenarios.

The review concludes with a number of R&D recommendations, the principal one being a pressing need to establish a 'testbed' system where all biotic and abiotic factors can be monitored in order to determine the precise effects of different seasonal conditions and cultivation techniques on oilseed rape performance, and thereby to validate the decision trees.

Whilst oilseed rape is grown predominantly as a break crop on clay soils in the east of England , approximately 30% is grown on lighter, better-structured soils. A better understanding of the seed establishment process could allow a) earlier sowing of seed in these soils, and b) precision drilling, which enables reduced seed rates to be used, a particularly important point given the extra cost of new hybrid rape varieties.