I'd welcome either folks' received wisdom or scientific evidence that this is any better than sowing in close V-shaped drills.
Well as I see it each pea seed potentially produces a plant and most plants require a bit of space to grow in!
That said;spreading them out thinly in a flat-bottomed trench tends to create this space whereas with a "V" trench you would have to space the seeds out individually along the trench to give the spacing, which can be a rather laborious.
Add to that with the flat trench you effectively have a number of rows creating a situation where the plants tend to support each other, whereas the "V" trench method will only give you a single row.
Personally I do a combination of the two by producing " plug plants" as seen here;
http://www.thegardenersalmanac.co.uk/Content/P/Peas/Peas.htmSo to sum up I don't think any one of these methods is better than the other.
Pros & Cons;
Flat trench: Potentially uses most seeds!
V trench: will usually uses fewer seeds subject to the length of the row!
Plug plants: In terms of seed usage somewhere in-between both of the above.
The reason I use the plug plant method is I can get off to an early start, less chance of vermin eating the seeds and I find I get better continuity in so far as I set up a second row of seeds when I plant out the first row, and depending upon the weather I have been known to sow another batch to be ready for replacing the first batch after harvesting!
So in conclusion: Not very scientific but effective!