or perhaps "ridger". I would say these terms were synonymous. Huitenga's agricultural dictionary has aanaardwerktuig (ridger, ridging implement).

Support found for bed former:
http://www.baselier.com/en/prod_rgv_overzicht.shtml
(which has a photo of a rugvormer)

http://www.ento.csiro.au/research/pestmgmt/biofumigation/Ima...
A deeper cultivation is then carried out with a chisel plough. In preparation for planting potatoes, a four-row bed former is then used to form the hills, and the annual cycle resumes.

Ridger:
http://www.abbeygardensales.co.uk/subprod/mini-tillers-00010... (suggests ridger does seem to be a smaller implement)
http://www.indiaagronet.com/indiaagronet/Crop_Husbandry/crop...


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Note added at 56 mins (2005-12-14 07:57:35 GMT)
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So we're talking about potatoes (context helps!). It seems that the bedvormer is perhaps just one implement in the overall aanaardsysteem. I'd suggest "potato ridger" for rugvormer (plenty of Google support) (or just ridger) and "ridging system" for aanaardsysteem. My "Potato Terms" dictionary (FR/DE/EN only) has "ridger" (Häufler/butteuse) and also "bedder" (Beetformer/billonneuse), which could be your "bedmachine". Hard to say without further context. That makes three queries in one question ;-))

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Note added at 1 hr 29 mins (2005-12-14 08:30:49 GMT)
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sorry, I meant the *rugvormer* was part of the overall aanaardsysteem.