Increase magnesium over one acre

I've had some trouble finding a good answer for this one...
I have about an acre I am converting for vine and fruit trees. The Mg is low in relation to the C for my sandy loam soil, and I'd like to increase the Mg.

The base saturation of Mg is 1.6%.   VS    33.4% Ca.

The ph is OK, it had been limed with calcitic, so liming with dolomitic doesn't seem like a good option.

Epsom salts are too intensive or expensive for such a size?

Thanks for your input!

The sandy soil bit might be key. I'd be afraid that anything you were to add, would simply leach out.

Did you find this article?  https://www.growerssecret.com/blog/ferti-facts-magnesium0
"Today, magnesium can be extracted from dolomite (CaCO3·MgCO3), or carnallite (KCl·MgCl2·6H2O), but is most often obtained from seawater."

Have you considered a different approach - biochar, carbon and microbes? Making biochar from whatever woody material you can easily acquire, inoculating it with microbes from decent compost, and mixing it into your soil. Yes, some people make a big deal about temperature and size of "perfect" biochar, but if the issue is sandy soil and you can make the biochar yourself out of local, free material (think heat-treated pallets if that's what's free), perfect isn't necessary.

Here's a link to permies biochar forum if you want to take a look: https://permies.com/f/190/biochar

Hi Dave,
Welcome to Permies!

I was going to say the same thing as Jay :) Compost and biochar. I can't think of any cheap methods to increase magnesium specifically. However, there is often plenty of a mineral in the soil, but it is unavailable to the plants. Increasing soil health by increasing the micro-organisms will increase the availability of all the nutrients in the soil. And would help hold nutrients that are added later.

I have the opposite dynamic with too much Mag to Ca. In your case I would look into foliar sprays, ideally mixing in contextually suitable rock dusts and kelp into compost teas. Foliar uptake is much higher in efficiency per amount of input material. Jon Kempf of Advanced Eco Agriculture (with a great wonky podcast on the topic) is a good resource to look into.

Thanks all!  Am looking into biochar production (I did just clear out a ton of an invasive buckthorn I could split betwen biochar and hugelkultur).

It looks like the Mg changes will otherwise be more local and gradual for this.  
(And for sure there will be soil-building activities on-top as a rule once things are in the ground, and the fungal network wil help regulate availability, I've got a lot of organic matter to work with already.)