What’s better for the environment, synthetic fertilizer or manure?

Question: What’s better for the environment, fertilizing with synthetic fertilizer or with animal manure? Are they both the same once you put them on the soil?

Answer: This question is difficult to answer in a short space. Both types of fertilizers can be beneficial to the environment and both can damage the environment. It depends on how they are managed.


A manure spreader. Texas A&M AgriLife Research photo by Kay Ledbetter

The term “synthetic fertilizer” is a misnomer because all the inorganic compounds found in commercial fertilizers are also found in nature. It happens that animal manure contains the same nutrients, too, only they’re in organic forms. Before the nutrients in manure can be used by plants, however, the manure must undergo microbial decomposition, which releases the nutrients into the soil in forms that plants can absorb.

The nutrient forms released during microbial decomposition are inorganic ions that are identical to the ions supplied by commercial fertilizers. For example, nitrogen in animal manure is in organic forms such as proteins, urea, and amino acids. When the microbes decompose these organic forms, they release the ion, ammonium (NH4+). Further microbial activity eventually converts ammonium to the ion, nitrate (NO3).

The ammonium and nitrate ions released during the decomposition of manure are the very same ones that are supplied by an ammonium nitrate fertilizer. Also, a common commercial source of nitrogen is urea, which is an organic compound found in animal manure.

Over-application or improperly timed applications of both types of fertilizer can damage the environment. So, again it’s not really a question of “synthetic fertilizer” versus “animal manure.” It’s a question of how they are used.

–Answered by Gary “Pete” Peterson, Colorado State University

Have a question for Soils Matter? Post it as a comment below, or email us at soils-matter@soils.org

One response to “What’s better for the environment, synthetic fertilizer or manure?

  1. The only thing you’re missing is transportation costs. How about an comparative analysis of the transportation costs (and, by extension, the carbon footprint) of synthetic fertilizers versus manure?

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