[Graeme Park]

Hi chaps. I’d like some advice on how to deal with my raised bed soil. Should I buy some new top soil?
Last year I built three 1m² raised beds and filled them with compost from the local dump.
I planted a host of things: tomtoms, pumpkins, peppers, etc. I had an explosion of foliage but little or no flowers or fruit.
I believe the culprit was too much nitrogen in the soil as I was recently told that the dump compost is famously nitrogen-rich and experienced gardeners use it sparingly. 
A bit of reading this year leads me to believe that the nitrogen has probably washed away. However, the beds could benefit for a few more inches of soil this year. I’d like to top them up.

So, some questions:
Should I test the old compost before topping up the beds or is it safe to assume the nitrogen level will have dropped sufficiently?
Would a good quality top soil be a good bet to top up?
Should I mix this through the existing medium or simply lay on the beds?
Hoping to have a more fruitful year this year!
Thanks

[mumofstig]

Welcome to the forum:)
Soil would be the best bet, but 'good quality' topsoil sold in bags often has fertilisers already added.
Try to find some without any, or you'll just lake things worse IMO. Perhaps find some on freecycle - just have a look at it before you collect it - you don't want clay subsoil 

I'd mix it all together and give it a good soak, to settle it, before you sow or plant anything in it. Good luck!

[Goosegirl]

The soil on my raised beds does settle down over time and needs topping-up but they didn't originally have as much nitrogen as yours has now. Some of it will have washed away over Winter but I don't know how much is still in there. Get one of those paper strip jobbies that either aquarium people use to test nitrogen levels as they're quite cheap or a similar product (see this link from eBay: https://www.ebay.co.uk/i/332235399206?chn=ps). The source of topsoil can vary as to what type of soil it is and where it came from, but adding brown stuff such as straw, shredded papers and old leaves will help to reduce the level as they use it when they decompose.

[Dev]

Get yourself a copy of Charles Dowding's Vegetable Course. Not only is it very informative and a good gardening read, it will explain that you don't need to dig compost in - you can simply put a layer on top and plant into it. If you need a lot try CPA for mushroom/farmyard compost. If a small amount use a couple of bags of B & Q compost (or Wilko's if you have a local branch).

[Graeme Park]

Thank you guys!
I’ll get myself a few bags of top soil and chuff it through before giving it a test in a few weeks.
Good to hear about adding the brown - I piled shredded leaves over the beds in autumn, I’ll work them through too and hope for the best!