thanks every one for your input, I'm still in two minds though....
the bit I don't get is: if no residue is left in the soil, what about when
the roots of the weeds start to break down wont they release chemicals,
which will be then taken up by whats ever growing?
the trouble is I've got about 450 square meters to clear and its taken about
an hour to do one properly
and now I'm dreaming of roots
thanks
Paul