Below is a link that has some useful info on finishing alder. I think the main issue is using a pre-conditioner first to avoid blotchiness.

For the stain itself, you might want to look at MinWax Polyshades:

http://www.minwax.com/products/one_step_stain_and_finishes/polyshades.html#Colors

I've had good luck with this brand over the years and they have a couple of blacks to choose from.

Here is a link that might be useful: Staining alder

The link below explains several techniques. Part of the decision is going to be whether you want a transparent or opaque version of black.

If you have followed some of my posts, I am not a fan of Polyshades.

Here is a link that might be useful: staining black

India ink, black milk paint, and aniline dye can all be used to ebonize wood. Each gives a different look. What you use for a topcoat on these stains will of course render the ultimate finished appearance.
Casey