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Name: Patrick
Status: Student
Age: 9-12
Location: Massachusetts 
Country: United States
Date: January 29, 2005


Question:
My group and I are in participating in a group 4 project required for IB Science. Our question that was given to us asked: Does forest fires effect the nitrate levels in the soil?
To answer this question we took several samples, some being of burnt soil, and others being of a control group of unburnt soil in the same environment. Our hypothesis was that nitrate levels would be higher in burnt soil than in unburnt soil. However we found the opposite.
Why would this be?



Replies:
At high temperature, like might be encountered in a forest fire or prairie fire, nitrate that is formed by the reaction of ammonia with oxygen, could further react by oxidizing organic matter, to produce carbon dioxide and nitrogen gas (among many other possible reactions). Possibly the critical parameter is the temperature of the ground. It is a pretty complex system, so it is hard to predict all the possible outcomes that might occur.

Vince Calder


Patrick,

Most forest soils have only 10% to 20% organic material, and forest fires usually stay in the forest canopy. Sometimes the litter on the ground will burn also, but the soil usually does not burn much unless it is very dry.

At any rate, if you burn the organic material in the soil you will release nitrogen from the soil either as nitrate aerosol or nitrogen oxides gas. So, your finding of less nitrate may not be a surprise if soil did burn and the forest material was burned off without depositing much ash on the soil.

David R. Cook
Atmospheric Physics and Chemistry Section
Environmental Research Division
Argonne National Laboratory



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