Ah,
this is hard to say. It gets technical here. You test your soil or get it tested and look at the ppm counts of Fe and Mn.
You adjust from there and remember that you move the Mn up in steps to just about match the Fe (or both as needed)
Here's a pic of Tweeter's soil report - post adjustments. This is your goal zone = 100ppm of each, his overage is OK.
Here's a link to understanding soil test reports - it gives amounts in lbs per acre to use.....
It's been said that you might consider raising Mn levels in soil my only 20ppm at a time....... I get the idea so it's not over done..
One might try adding 1/4 tsp to a gallon of water (that you have a ppm value to) and test the ppm of that for the change. Use it to wet a cft of soil and retest the soil. You now have the knowing of how much it effects the soil ppm. That is now your key to how much to use in that water to effect the proper adjustment in the soil.
Keep in mind that Your local USDA field office should offer cheap soil testing.....Otherwise ask your local college (helps to know folks in the AG dept.) Otherwise a quick net search should list some close to you....
That help?