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Survey of current harvesting, drying and storage practices with oilseed rape


HGCA PROJECT REPORT 371

Survey of current harvesting, drying and storage practices with oilseed rape


by
D M Armitage1, A J Prickett1, K. Norman2 and K B Wildey3


1 Central Science Laboratory, Sand Hutton York YO41 1NZ
2Velcourt Ltd., The Annex, NIAB, Huntingdon Road, Cambridge, CB3 0LE
3Technology For Growth, Rectory Barn, Terrington, York YO60 6PU

September 2005

Abstract

Telephone interviews with crushers preceded a survey of 101 producers which comprised a face-to-face questionnaire of harvesting, drying and storage practices with a parallel sampling exercise to inform HGCA of the changes of on-farm management and storage practices and future research requirements.  On-site sampling was run in parallel to support the results of the questionnaires and to enable assessments of mite infestation, and rapeseed moisture content.

Two-thirds of farmers need to dry rapeseed and most harvest at above 12% which is the critical moisture content threshold for the production of ochratoxin A (OTA).  A survey of OTA levels in rapeseed is therefore recommended. Moisture measurement is most commonly relied upon for hot-air dryer settings, yet less than half of the farmers calibrate the meters properly by returning them to the manufacturers. Therefore the importance of proper calibration should be publicised.

Only one-quarter of farmers accepted that 7.5% was the safe mc for long-term storage, although this proportion is almost double the response 10 years ago. This recommendation still needs emphasizing. One third of farmers using floor-dryers took over a month to dry the seed. In view of the threat from mycotoxin production; associated advice and improvement to floor drying might well be required. There is no clear consensus on safe drying temperatures for rapeseed when hot-air drying. Clearer advice, resulting from research associating safe drying temperatures with rancidity (FFA levels), is required. About 20% of farmers had difficulties in cooling. 

The variability in fan running time and the complications of operating ambient air drying systems to cool the grain all indicate the benefit of adapting engineering cooling models to develop faster cooling strategies for rapeseed.  Half the farmers used the on-floor drying system to additionally cool the seed. This is the first clear indication we have had of this practice and greater experimental experience as a basis for advice on this practice is clearly needed. 

Most rejections were for admixture, which can be best remedied by improvements in weed control and cleaning practice. One-fifth of farmers experienced seed heating which causes rancidity and therefore affects market quality, yet there is no clear indication in the literature of the cause. More than a quarter of farmers had problems with mites; 43 had infestations in excess of 10,000/kg at the surface but only 10 had similar populations beneath, indicating it was a superficial problem. Mites were not a great concern of the crushers and there were few rejections citing mites as a cause. 

Nevertheless, they clearly cause farmers great concern and a great deal of expense and energy is expended on their behalf.  It is therefore recommended that a study be carried out to define market thresholds of mites with regard to effect on FFA and allergen levels. Available remedial treatments for mites are few and one-fifth of farmers expressed discontent with available treatment options.

The only other option is fumigation and information on its efficacy against mites is equally limited. Research on these treatment options would also therefore be beneficial. Perhaps because of the limited pesticide options to treat the grain, fabric treatments have doubled since 1995 although there is no indication of their effectiveness in limiting mite numbers.  This is another area where objective scientific research would help minimise unnecessary pesticide use and expenditure.
 

 

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