Janet,
yes I'd be using spoilt hay if I can find it for nearly no cost. The
bale are watered for well over a week and started composting (the
reason for the ammonium nitrate) before you plant. So it perhaps by
the time the roots need to bury themselves the inside of the bale is
looser( who knows) The website was jsut an over view if you want I can
post more links that detail it better (I think).
And I think with the supports in the photo the plants MAY have been
young tomatoes. Potatoes are one of the veggies they say ya cant grow
in a bale.
And as Kate says it is just an experiment as I found it interesting and
thought perhaps then I could do a few things in hard to dig areas. I am
looking for no-dig ways to grow as the ground at the new house has
never been used for a veggie patch and to be honest working full time I
cant really be bothered to dig this year.

Cheers and THANKS...
Julie