Nitrogen release in organic matter?

Question

Here is the question...

I have a soil that is 4% organic matter. Calculate the pounds of nitrogen that in will be relased from the OM in one year. Please help. I know I had this in my notes at one time but think that the kids ate them. It is finals week and would appreciate any help you can give me!

Answer 1

While organic matter on decomposition does release nitogen nutrients it is not possible to answer the question as stated.

New organic matter will yield far more nitrogen than very old matter. Given a soil temperture profile one can evaluate the ratio of new to old humus. But there are significant differences based on soil temperature.  Canadian Prarie soils have far more carbon and less nitrogen, while a soil that is in Tennessee would have much less carbon to nitrogen ratio. Tropical soils of course have almost no carbon content but not nearly zero nitrogen, as they benefit from recent decomposition of fresh vegetation.

Answer 2

Increased tillage increases the decomposition rate of organic matter which therefore increases the amount of nitrogen released.  Intensive tillage also burns up the OM which reduces tilth.  The cotton soils of Alabama, Mississippi and Georgia are good examples.  Back in the 30's, many of those soils had less than 1% OM and is why they set up like concrete in dry weather.

Answer 3

They estimate  roughly that soil with a 5% organic matter content  will release 65 pounds of Nitrogen per year. In your case that would be 4/5 of that or 52 pounds of Nitrogen.  There are a lot of variables influencing that like temperature, rainfall, etc.