ADAH probably gave you the best information they have. ADAH doesn't have the National Archive microfilm, so they couldn't provide anything from that source.

Under antebellum Alabama law, the state militia was organized into divisions, brigades, regiments and companies, mainly based on counties and county subdivisions. Citizens elected militia officers just like we elect members of our county commission or school board today. ADAH has that information. By law citizens eligible for militia duty were expected to report for company, battalion and regimental drill every so often, or pay a small fine.

When the Harpers Ferry attack took place in October 1859, people realized that if something like this took place in Alabama, the militia could do little to surpress or repel it. In February 1860 the legislature created the Alabama Volunteer Corps to address emergencies. By the time Alabama left the Union, 110 AVC companies had been organized. Unlike the regular militia, these men were equipped with modern firearms purchased by the state. They were uniformed, equipped and drilled regularly, ready on call from the Governor of Alabama. ADAH has that information.

The regular militia included units like the 89th that you asked about. In early March 1862 most Confederate troops at Mobile, New Orleans and Pensacola were sent to reenforce Albert Sidney Johnston's army. When they left the Governor of Alabama called the state militia for home defense. By law the militia could be called into service for a short period, usually 90 days, so the payment receipt on file represents
that term. The men weren't away from home long, and were never too far from home, either.

In August 1863 the state legislature abolished all previous militia laws and set up a system of 1st and 2nd Class Reserves. This system was in use in most Alabama counties during the final year of the war. ADAH has that information, too.

Here's an old post about ADAH holdings for militia:
http://www.history-sites.com/cgi-bin/bbs62x/alcwmb/arch_config.pl?md=read;id=7429