[jambop]

I think I may have asked this question in the past but I don't think there was a definitive answer so will ask again.
I have seen lots of comments about onions being grown on ground that has had manure added to it. The jist seems to be that for some reason manured ground causes onions to rot ? Is this myth or fact? I can understand how manured soil could cause a lot of green growth but why would there be rot issues? I have often read that it is difficult to over fertilise onions so would question this addition of adding manure having any effect fertilisation wise as cow manure is not a particularly high source of nitrogen and the suggested rate of application is about 5kg per square metre. So does anybody actually know the answer to this question?

[mumofstig]

I think the RHS knows what it is talking about 
https://www.rhs.org.uk/advice/profile?PID=680

Choose an open, sunny site and well-drained soil. High humidity around the foliage and wet soils make the crop more prone to disease attack. Onions do not thrive on acid soils (below pH 6.5). Reduce acidity by applying lime in autumn and winter.
Onions have a limited root system therefore improving the soil with plentiful organic matter is invaluable. Apply two bucketfuls of well-rotted manure or other organic matter such as garden compost every square metre (yard). This will help add nutrients, improve the soil structure and hold moisture. Avoid using fresh manure.
Little fertiliser is required at planting, apply 35g per sq m (1oz per sq yd) of Growmore or twice as much organic fertiliser such as dried poultry manure pellets. If you cannot apply organic matter – use more fertiliser, up to twice as much if the soil is poor.

my bold, I thought that point was important.

[jambop]

So the message is add manure to improve the soil but be careful not to add if too fresh! I like the idea of manure for my garden as I can get plentiful supplies free from the farmer. I am working on building up some raised beds and am applying plenty of manure to them, mainly to improve the structure of the soil which is great when at just the right moisture content but really hard when dry.