organic vs. non-organic fertilizer?

Asked September 22, 2014, 5:11 PM EDT

Hi, I'm a gardener in Steamboat Springs. I subscribe to a few horticultural magazines, and they regularly run articles about organic gardening that assert that chemical fertilizers are bad for microbes in the soil (without specifying how). Then, in the same issue, another article will recommend conventional fertilizer. Can you shed some light? Is there any scientific evidence one way or the other?

Thank you!

Routt County Colorado horticulture soil and fertility issues

2 Responses

"Chemical" or synthetic fertilizers generally (unless they are nitrate-based, water-soluble fertilizers) require microbial activity to "digest" the fertilizer - which makes the N available for plant use. Similarly, natural organic fertilizers require microbial activity to release their stored nitrogen. Thus, BOTH types of fertilizers are dependent upon soil microbial activity to release their stored nitrogen. One benefit of using natural organic fertilizers is that you add a considerable amount of organic matter to the soil when you use them - since the contents of a bag of natural organic fertilizer will contain perhaps 80-90% (by weight) organic matter. Conversely, a bag of synthetic fertilizer contains no organic matter. In the end, the nitrogen molecules that are absorbed by the plant and used for growth are chemically identical - whether they come from a synthetic fertilizer or an organic-based fertilizer. And neither type is toxic to or "bad for" soil microbes.

I would add here that people (and fertilizer companies) on both sides of the natural vs. organic fertilizer debate will do their best to "shade" the truth to make their side look its best - or to sell their respective kind of fertilizer. While both types of fertilizers have their pros and cons, both kinds can be used very effectively to fertilize vegetables, lawns, trees, etc.

I hope that answers your question?

Thank you very much for taking the time to help me out. It's a confusing topic because people get so adamant about their "side." I use compost and manure pretty heavily, but I sneak in a little 20-20-20 once a year, too. You have alleviated my guilt on that score!