How can i deal with a 1 acre field full of brambles. part 2

yes once the glcophosphate hit the soil it will become inactive. any plant it touches it will effect.

I can attest to the above.My neigbour sprayed her backyard with Roundup.Everything ...even her tree died.We know because if fell directly in the middle of " our" old plum tree.(which by the way died)
Apparently when you spray near a tree the roots get affected.

Very strange Rhodea, the general opinion is that Glyphosate only affects the parts of plants which contain chlorophyllll, ie the green bit. It should not therefore affect the roots of trees unless sprayed on the leaves. We have used it around various trees in our garden without it killing them.
One word of warning, despite the claims Glyphosate is not as environmentally safe as the adverts say. Yes it does eventually break down in the soil, but it does take a while longer than claimed. I would not want to plant vegtables or soft fruit on treated land for a season after spraying.
The triple strength stuff is sprayed on at the same concentration as the ordinary stuff, it is just more concentrated before dilution, so you get more for your money.

Debate aside, you can spray and leave it a week or two. Then you should be able to re-grass the area. However, there are complications as some have hinted to.

One such complication which wasnt mentioned is that you will expose the soil, thus allowing dormant weed seeds to germinate.

If you want to use glyphosate, the best solution in my opinion is to spray, wait a week, remove dead plant material, wait a week, hoe, lay turf....(cross your fingers!)

^.^

Glyphosphate will kill the brambles and weeds on the land but you are still going to have to clear up the rubbish, Fabtabi. The woody stalks of the brambles will still be there. (Actualy, as an afterthought, if Fabtabi has strimmed the brambles down to ankle height, will glyphospate kill the roots if it has no foliage to attach to?).
You will still need to remove the stubble and scarify the ground before you can sow any seed in it.

Well the neighbour sprayed it on eveything.Her yard is brown with weed stalks sticking out.Must be the true wild theme I guess.

Personally I'd get in there and clear out all the rubbish - which you are going to have to get rid of in any case. Then get the whole area ploughed. That way you know there wont be a problem later.

..or if your ambitious you could make a bramble maze(somewhat like a corn maze) , charge a couple of bucks to enter it and you're in business....a way out there suggestion.Lol