Great discussion, everyone!
I spoke with EarthTools again, and they seem to get nervous about anyone trying to use their tractors on much more than 1/2 acre. I told them I'd hire out the plowing with a 4 wheel tractor and use the 2 wheeler for everything else, but even with 1 acre they said that's a "mega-farm" for a 2 wheeler. I know of people (and not just Jean-Martin) using BCS on an acre or more, so I know it's doable. But according to Earthtools at least, that's people who have no problem with working crazy hours. For a 4 wheel tractor, an acre can be plowed/cultivated in a matter of hours. For 2 wheels, 1 acre means dawn to dusk plowing (or harrowing or whatever) for 2 whole days. Presumably this is precisely what Jean-Martin does. So the question here becomes "Is it worth it?"
That's where we get back into the discussion of bed spacing. Many vegetable growers appreciate being able to straddle rows or jump over rows easily, which has led to the popularity of the 30" bed. The minimum tread spacing on most 4 wheel tractors is 48", which is slightly too wide to straddle (I'm 6'4" so I'm able to do it just barely, but there's nothing wrong with staying on one side of the path, harvesting down the row, then coming back up the other side to harvest the other half). On the other hand, many growers working with 4 wheel tractors plow rows "on the flat" or use some kind of bed shaper to make narrow single rows. It's not really a permanent bed system, but the plowing is more efficient so that doesn't matter so much. However, this tends to leave more open bare soil, which gets weedy and can erode away on the wind if kept well-weeded. This can be mitigated with mulch (whether plastic or organic matter).
There is the question of row-feet per acre. The land I'm working with is about 540' x 150', which is just shy of 2 acres. With 60" strips (4 wheel tractor spacing) and 100' beds, I get 30 rows of beds with 5 beds per row (10 feet head on the end of each bed for turnaround). That's 150 beds and 15,000 row feet. If I use 42" strips (2 wheel tractor spacing), I get 43 rows, but still 5 beds per row. You don't magically get more beds per row if you don't need 10 feet of turnaround, because the beds are still 100 feet long. If the width was 100' instead of 150', I could easily rearrange so that some beds on the end run perpendicular, but in this case there's simply going to be wasted space no matter what. Anyway, that gives 215 beds total, which means 21,500 row feet. Now, on the surface, it looks like "more row feet = more vegetables = more money per acre", right? Well, the devil is in the details. With 48" beds, I can plant more rows of carrots and beets and spinach and all the small vegetables. Then, for large vegetables, like say tomatoes... so tomatoes are going to be trellised up, and the leaves below the lowest fruits will be removed, creating light and space for small vegetables like more carrots to be interplanted directly beneath the tomatoes. With 30" beds I'd worry about root competition and available light, with 48" I'm not as worried. Then there's the bed hogs like melons and squash. If you do 30" beds, you're sacrificing a lot of beds to let them sprawl. With 48" beds (plus paths), you're only sacrificing one adjacent bed for sprawl.
And then we get to the heart of it all: is it truly feasible to use BCS/Grillo on the whole 2 acres? Those machines force you to stay small, because if you try to do too much with them you get burnout. In all likelihood I wouldn't cultivate more than 1 acre with the 2 wheel, which would be something closer to 11,000 row feet. Certainly you can still make a living off of that. But I happen to have extra land.
Of course there are more considerations. Commercial grade rowcovers and landscape fabrics are more common in 4 foot widths than 30". High tunnels are usually 14 feet wide, which is just enough for 3 4' beds plus two paths. (Granted, it's also the right size for 4 30" beds plus paths). And then there's the issue of breakdowns and repairs, which was one of my main concerns about using an old 4 wheeler. I'm not sure that I have an answer, except to say that because (used) implement prices are so much cheaper for 4 wheel tractors, I can buy 2 tractors and still come out ahead of buying all new gear for 2 wheelers (I can't wait for years scouring classified ads in a 500 mile radius for a used BCS). I'm not yet convinced that I need a 48" version of the Rinaldi power harrow when a disc can do almost as good a job for a fraction of the price. I acknowledge that repair bills for 4 wheel tractors could be hefty. In the "Organic Farmer's Business Handbook", Wiswall estimates (from experience) that the average annual repair bill for a Ford 4000 is $300.
So, all in all, I think I'm finally convinced to go the 4 wheel tractor route. Maybe in 2 years I'll look back at this post and think "Ha! What a fool!" Oh well, that's life.
I bookmarked an article in I think Yesterday's Tractors about "What to look for in a used tractor" which went over some of the mechanical stuff to look at. Does anyone have any other resources like that?
