The dimensions you gave equals 1.8 acres. I could get hundreds of trees on that. Perhaps that's not the cleared area but the total picture.

The orchard would look nice with rows following the contour. But air drainage would be better up and down the hill, basically NS. I'd recommend dwarf trees planted about 6ft by 12ft. Those can be kept to 8-10ft tall. A wider spacing is certainly possible but it's hard to keep widely spaced trees short.

Thanks fruitnut.

It's a big field. We have 40 acres (mostly wooded) and this is the smallest of the cleared fields. One thing I probably wasn't that clear about in the original post was that I'm definitely not trying to fill up the whole field with trees. I just can't take care of that many. So only a portion of the field will be for the fruit trees.

I've read that you should avoid planting in the lowest points of fields if you can, so I was looking at the uphill side (roughly green area in new pic). Just wasn't sure how to orient the rows or whether it mattered. My idea was to make the rows run E-W so that they get more southern exposure (assuming the rows are spaced further than the trees within a row). The air drainage thing you mention is interesting.

Also, I have most of the apple trees already in a planting bed (I grafted them this year). They're on semi-dwarf rootstock.

Thanks again for the response. I'll think on it some more. The big question mark will be getting water to them (there's a small creek running along the southeast side of the field, which seems tempting to try to draw from somehow, but I suspect I'll be carting in water).

Sam:

If the trees are pretty widely spaced, row direction won't affect light interception. But it is usually recommended that rows run NS so that sun shines on each side of the rows for half the day.

Lets say you allow your trees to grow about 12ft tall by 12ft wide. Spacing the trees out 20ft by 20ft or wider would offer the advantage of good air flow and sunlight on all sides of the tree. This not only helps with production because of good light but reduces disease pressure. The trees and fruit dry off more quickly in the morning. Keeping the branches thinned out helps here also. I like to be able to see the fruit in the center of the tree. If you can't see it, the tree is too dense.