Taking a procedure for ICP and adapting it to use with AAS
In short - it depends. For most metals no problem in using the same digestion protocol for ICP (OES or MS) or AAS. Are you using flame or graphite furnace?  If you are using flame AAS -just prepare a blank digest (same ratio of acids but no sample) use that as you blank.  If you are looking to quantify Na, K or Ca there can be significant background issues from soil samples - most trace metals are not a problem - but you need a good blank to qualify.  The LOD (limit of detection) will vary depending upon the matrix S/N (signal to noise).
Hope that helps.  If using graphite AAS you are typically limited as to the amount (volume wise) you can add to  the furnace.  You can try multiple dry downs before atomization.  Again a good plank is paramount.