Dig deep to get the taproot. On year-old seedlings, it's about four times as long as the above-ground shoot.

Resin

You did dig and transplant while they were still dormant, right?
I've rarely had problems with transplanting dormant bareroot 1-yr seedling nut trees, even when I've provided them with no appreciable aftercare beyond their initial watering-in, but they certainly benefit from mulching and supplemental watering, as needed, during the first year.
I wouldn't be surprised with a 10-20% failure rate, but 70% is awfully high.
As Resin indicated, try to preserve as much taproot and lateral roots as possible - they're reserve energy storage receptacles, providing the 'food' these seedlings need to re-establish root mass lost in transplanting and pushing new growth in the ensuing growing season. Generally, I recommend against any amendments in the planting hole - just crumble and replace the native soil that you initially removed; your seedlings' roots eventually have to grow in that native soil, so they'd just as well get on with it from the outset.

I did (try) to get all the tap root but.....I did it while they were active - not dormant.

I'll try dormant however, is ALL the tap root necessary? What about that little inch you just can't get?

or try planting the nuts where you want the tree ....

in my zone 5 .... trees are transplanted in fall after leaf fall ... min 60 days prior to ground freeze .... aka dormant

or in spring... as soon as the ground thaws .. while dormant .... 60 to 90 days before the heat of summer.. and at least 30 to 40 days before the leaves come out ..

frankly ... z4 is no different than my 5 .. and these times.. for us.. is when you should do all transplanting of all types of stock ... in case you wanted to know ...

as long as the ground is thawed.. theoretically there can be root growth [depending on soil temps]... transplanting in fall.. gives you two cool seasons to grow roots... before the heat of the summer ...

good luck

ken

"is ALL the tap root necessary? What about that little inch you just can't get? "

No, but remember the taproot is likely to be over a metre long!

Resin

All of the above pertains, and clearly, the reason for your lack of success was doing the transplanting while trees were leafed out.

I've come to be pretty much a black walnut hater, what with all the volunteers-usually with a squirrel assist-coming up in all the shrub and perennial/annual beds I must manage at my day job. If you don't get 'em weeded out while they're still very young, and right after a soaking rain, they can be real b*stards to yank out! Often times, all I can do is somehow bend them to the ground and away from the other vegetation, and hit 'em with a shot of Roundup.

But oh yeah, you're trying to grow them! Best of luck.

+oM

Wisconsitom.....thank you very much concerning transplanting leafed out trees. I know the walnut sends out many volunteers and that's what I want. I'm planting these trees in an 8 acre field. I want it to be wooded in the future. Thus, the more the merrier.

Thank you all for your wonderful advice. I have learned much.

Kay

Kay,
There's nothing 'magical' about a taproot, despite some folks' reverence for them - it is primarily an energy storage vessel, an evolutionary development allowing young seedlings to recover and re-sprout rapidly after being browsed off by deer/rabbits or burned back by fast-moving grass fires. I always try to preserve as much taproot as is possible when digging bareroot transplants, but don't despair if I cut it 12-16"(or less) below the soil surface.
While most nut trees are pretty strongly taprooted, black walnut seems to lose that trait early on, and they tend to have a more lateralized root system than most oaks, hickories, pecans, etc., even within the first growing season.
Moving those seedlings after they had broken dormancy is probably the culprit behind their poor survival rate. I usually try to move them in late Feb/early March here in southern KY.

I think Kens suggestion of planting nuts in the spot you want them to grow is very good idea.Why go threw all that work of transplanting.

I would include collecting the seed nuts from the trees with the straightest and best form.Avoid nuts from trees that have many side branches.Plant more trees per /acre than you'll need,you can always thin the poorly formed trees.
Also plant fast growing trees to give the walnuts competition this will give you straighter trunks with fewer side branches.
Check out Wisconsin Walnut Council http://www.wiscwalnutcouncil.org/Contact_Us.htm

lp

lp........thanks for the website. I never would have guessed there was such an organization.