I've used permies.com's internal search and Google but I haven't found a satisfying answer to this, so:
I've worked on a conventional organic farm for about 22 months. We grew vegetables. The weeds were a nightmare. In total, thousands of hours went into hand weeding. I hated that work. So, when I accidentally heard of steam weeding I became enthusiastic. A team of researchers (http://www.darcof.dk/enews/sep04/steam.html) found that with 70°C (158°F) hot steam that goes down 20cm (8 inches) deep into the soil you can practically kill the entire seed bank so that weed numbers will be a stunning 99% lower.
I know that practically all soil life gets destroyed this way. Also the useful stuff. I also know that what is often considered a "weed" can be a good indicator of the state of your soil. And yes, many weeds are edible and even healthy. Furthermore I'm aware that the creation of the steam takes a lot of energy.
But after all, I'm still tempted by steam weeding because it may free the farmer and his employees of a lot of unpleasant work.
And Sepp Holzer said that soil life can immigrate over a radius of two meters (6ft 7in). So that problem is not so bad if you make your field only four meters (13ft 1in) wide or leave some "islands" of covered ground in the field like I've seen them on pictures of Holzers old farm Krameterhof.
So here are my questions: What do you permaculture people think about steam weeding?
Can anybody imagine creating and supplying hot water for steam with a solar collector (not photovoltaic, just collectors that heat up water) or another sustainable source?
I've also written an e-mail to the Krameterhof. I'm excited what their perspective is.
I have so much time and effort to establish a strong community of beneficial soil microbes, that I could not bring myself to even consider steam sterilizing my soil. I can tell you from experience that it can take years for Mother Nature to re-establish soil life. I stupidly killed a quarter acre of soil life by scalping the meadow grass then letting the ground dry out for several months. Very little grew there for two years while I tried to make it into a garden. Oh yes, young weeds sprouted, but they grew poorly because the soil couldn't maintain moisture nor breakdown the soil contents into plant available nutrients. My garden veggies did poorly too. The soil visually looked dead for about two years. It took a lot of work, time, compost,manure, and water to reclaim it.
Perhaps steaming the upper inch of soil would not be so disastrous.....much like using a flamer in new seedling weeds. A flamer, properly used, does little damage to soil life.
It's never too late to start! I retired to homestead on the slopes of Mauna Loa, an active volcano. I relate snippets of my endeavor on my blog : www.kaufarmer.blogspot.com