Unless you've got really poor soil I wouldn't be too concerned and stick with a balanced, well aged product. If your soil IS poor, you should consider a soil test and look at the micronutrient content results. Some of these, either being deficient or in excess can make a big difference. There's a good article from Oregon State about fertility that (I hope) someone will chime in with~can't find it now. Hoppy Growing!
Never mind: http://extension.oregonstate.edu/cat.../fg/fg79-e.pdf