Monday, November 10, 2008

Community Ecology

Today I'm learning about the chemical (carbon, nitrogen, and phosphorus) cycles in the ecosystem. Specifically, that nitrogen in the air (N2) is useless to most organisms until little nitrogen-fixing bacteria can convert it into an organic form (NH3, ammonia, or something like it). Nitrogen-fixation is a rate-limiting process, meaning it's the slowest part of getting plants to grow.

Commercial fertilizers add nitrogen (I assume as ammonia or something like it, the useful kind) to the soil so plants don't have to wait for bacteria to fix the nitrogen, and they can grow faster and bigger. But I wondered about organic fertilizer (derived from poop). Does it contain ammonia-related nitrogen or does it still require the bacteria?

Wikipedia didn't have the answer, and neither did my textbook. But I found the coolest website: and I asked an expert:

Question asked:
I would like to know about the chemical composition of manure used as fertilizer. Does it contain fixed nitrogen, in a form that plants can readily use, or does it contain nitrogen that must be processed by bacteria before plants can use it? Is the same true for phosphorus?

An hour or so later, I got an email:

A question you asked via eXtension's 'Ask an Expert' tool has been answered!

Manure contains both an organic form of nitrogen and ammonical-N fraction. Depending on the livestock it comes from, bedding, storage etc., manures will vary as to how much is organic and how much is in the ammonical-N form. The organic needs to be broken down by mico organisms before it is available to the plants. The ammonical-N is available to both plants and micro organisms. Here is a suggested web cast to some of these questions:
also check here:
This states that 80-100% of the P from manure is considered available to plants.

A manure analysis will indicate the plant available nutrients from individual manure samples.

-Natalie Rector
Michigan State University Extension
Thank you, Natalie Rector, of Michigan State University Extension!

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