Keep feeding the tree from early spring right on into summer. In mid to late June you will candle this tree. Visually group the candles into three sizes, large, medium, and small. Cut only the largest exterior candles right at the base. The cut should be perpendicular to the growth, no angle. This will force the meristematic growth back along the branch and pop buds from some of the needle pairs. So this young branch will have only one candle removed unless it has more than one excessively large candle.
Don't confuse this with bud pinching. Allow the candle to grow as long as it wants. Sometimes with healthy black pines, they can get several feet long! Cut this about the third week of June for your area. Then remove the fertilizer. You will see new buds forming in a matter of days. You will have a number of them forming at the base of the cut you made, and probably some others popping back along the branch as well.
If you have more than two at the tip, choose two of similar size (small ones if you have to hold back the growth, large ones if you have a weak branch and want to encourage it.) The first time you do this to a branch, the candles should be arranged horizontally, but sometimes in later pinchings you will want vertical buds.
The second flush of growth will be less vigorous, and when it stops extending, you can begin feeding at half strength again until fall. In fall, do any light pruning you need to do and put the tree away for the winter.
This differs from what you have read some places in a few key areas. Many will say to cut back this tree hard in the fall, not summer. It may work as well except that you don't get a second growth surge until next spring. With this method you get twice the ramification in one year. In another year or two you will begin working on balancing the growth of this branch.
This also differs from the candling method used for developed trees, in that all but the smallest candles are cut, starting with the weakest so they have longer to develop and get stronger. This is an energy balancing technique that not only should shorten your needles, it should make all your needles about the same length. Save this technique for a more advanced tree.
All this being said, I wish you had a better tree to work on. You can use all the proper technique in the world with this one, but it will never be even a moderately nice tree. The roots look bad, the trunk is straight and thin, and you have swelling from a whorl of branches about halfway up. I hope you didn't pay too much for this tree. Good luck with it, work with it, and learn from it how these trees grow so you can feel confident to buy better material.
