Evaluation of factors affecting yield improvement in oilseed rape

Abstract

Oilseed rape has shown little increase in average commercial yields from 1980 onwards, whereas there has been some progress in improving yields through breeding.  The project aimed to identify and evaluate the likely causes of the failure of the commercial crop yields to improve compared to the yield of Recommended List (RL) trials. 

Statistical analysis confirmed that yield of oilseed rape from RL trials has increased at approximately 0.033t/ha/year since 1987, whereas there has not been an increase in yield of commercial crops over this time.  This has been confirmed even when the RL trial yields are adjusted to represent a similar varietal composition to the national crop in any given year.  The difference between the trial and commercial yields increased in the early 1990s, thereafter returning to pre-1990 levels before increasing again. 

An increase in disease levels, particularly light leaf spot, is a major factor in accounting for this yield differential.  Another important factor is that of sulphur availability.  Atmospheric sulphur deposition has declined markedly and, although it is not possible to quantify national yield effect, much of the UK crop is now at high risk of sulphur deficiency.  Variation in the proportion of spring rape grown from year to year has made a smaller contribution to the failure of the commercial crop to increase yield.  Nitrogen fertiliser is applied at a lower rate now than in the 1980s, but this is only likely to be responsible for a small effect on yield. 

Recommendations from this work and others offer the farmer opportunities for implementing disease control strategies and avoidance of sulphur deficiency.  In order to achieve closer to the practically attainable oilseed rape yield, as demonstrated by RL trials and to develop an upward trend in national commercial yield, it is necessary to ensure that the messages from this and associated research projects are delivered to farmers, and acted upon.