I often use organic fertilizers.

They are much better.

Organic fertilizers are naturally-occurring fertilizers (e.g. peat moss or green manure), or naturally occurring mineral deposits (e.g. saltpeter).

Naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed, humic acid, brassin and guano. Sewage sludge use in organic agricultural operations in the U.S. has been extremely limited and rare due to USDA prohibition of the practice (due to toxic metal accumulation, among other factors)
Organic fertilizers also re-emphasize the role of humus and other organic components of soil, which are believed to play several important roles:

* Mobilizing existing soil nutrients, so that good growth is achieved with lower nutrient densities while wasting less
* Releasing nutrients at a slower, more consistent rate, helping to avoid a boom-and-bust pattern
* Helping to retain soil moisture, reducing the stress due to temporary moisture stress
* Improving the soil structure
* Helping to prevent topsoil erosion (responsible for desertfication and the Dust bowl

Organic fertilizers also have the advantage of avoiding certain problems associated with the regular heavy use of artificial fertilizers:

* The necessity of reapplying artificial fertilizers regularly (and perhaps in increasing quantities) to maintain fertility
* Extensive runoff of soluble nitrogen and phosphorus, leading to eutrophication of bodies of water (which causes fish kills)
* Costs are lower for if fertilizer is locally available