Well rotted manure

It depends on what you want to grow-some crops do well on freshly manured soil -some don't like it

However this time of year- unless you intend to sow/plant anything immediately- I would spread the whole lot over the area -lightly fork it in -and let the worms and the weather do the rest

What are you fellow plot-holders doing?

Good advice from Geoff. Carrots and parsnips resent freshly-manured soil. Yours will be good for them both next season.

I spread manure over all my veg garden and rotovate it in in spring, or I leave it in piles and put antiweed fabric on the rest in autumn then spread the manure and rotovate in spring, but I don't grow carrots (soil not light enough and too stony, despite removing loads). It usually does pretty well and parsnips don't seem to mind the manure - but it is well rotted. Potatoes seem to be happy with the manure.

An inch doesn't sound like an awful lot to be honest-you don't have to be that precise

Just get barrow-loads spread it about and dig it in-you will soon get an idea of quantities

Carrots and parsnips dont like manure ,it will cause them to fork.Received wisdom says they should only be planted in ground manured for a previous crop.You should not manure the section where you will be planting carrotrs and parsnips.almost everything else will be fine with manure that has been dug in,or spread over the plot the previous autumn.A covering 2 to3 inches deep is recomended.Some vegetables are happy in freshly manured ground,eg potatoes,peas,beans,brasicas.In order to avoid having to manure virtually your entire plot every year,it is usual practise to manure one third of a plot as part of rotational growing.This means the entire plot is manured every 3 years.Much easier on the back.  Good luck.   C.G.