Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Factors Affecting Mineral Nitrogen Transformations by Soil Heating: A Laboratory Simulated Fire Study.

Authors
item Glass, Dallas - UNIV. OF NEVADA RENO
item Johnson, Dale - UNIV. OF NEVADA RENO
item Blank, Robert
item Miller, Watkins - UNIV. OF NEVADA RENO

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 2008
Publication Date: June 15, 2008
Citation: Glass, D.W., Johnson, D.W., Blank, R.R., Miller, W.W. 2008. Factors Affecting Mineral Nitrogen Transformations by Soil Heating: A Laboratory Simulated Fire Study. Soil Science. 173:387-400.

Interpretive Summary: Considerable uncertainty exists regarding the interactive effect of forest fire intensity and moisture content on nitrogen and carbon transformation in soil. We conducted a laboratory muffle furnace experiment to quantify the effect of temperature, length of elevated temperature, and moisture content on nitrogen and carbon transformations on two forest soil types typical of the Sierra Nevada Mountain of California. Ammonium and mineral N generally increased with greater durations and temperatures, sometimes declining at the highest combinations. Nitrate values peaked at low temperatures followed by declines at greater temperatures and durations. Little or no change was seen in total N, total C, and C:N ratio except at high temperatures and durations where C and N declined along with NH4+ and mineral N. These data will prove valuable in future prescription burns.

Technical Abstract: Two forest soils from the Sierra Nevada Mountains of California were brought into the laboratory and subjected to simulated burning in a muffle furnace at several durations, oven temperatures, and water contents. Soils were analyzed for NO3-, NH4+, mineral N, total N, total C, and C:N responses to the treatments. Ammonium and mineral N generally increased with greater durations and temperatures, sometimes declining at the highest combinations. Nitrate values peaked at low temperatures followed by declines at greater temperatures and durations. Little or no change was seen in total N, total C, and C:N ratio except at high temperatures and durations where C and N declined along with NH4+ and mineral N. Soil internal temperatures were monitored immediately following burning. Soil internal temperatures increased to near 100 degree C with greater applied furnace temperatures and durations, leveled off for periods depending on initial water content, and then increased to 300 to 400 degree C at higher temperatures and durations. Plotted against final soil internal temperature, NH4+ increased up to different critical temperatures (depending on water content) then decreased. This experiment suggests that fire severity (indicated by a combination of burn duration and temperature) has the greatest influence on inorganic N and causes increases in mineral N after fire up to threshold values, after which it decreases. Management implications including burn season, fire prescriptions, and burning across different soil types are discussed.

Last Modified: 4/19/2014
Footer Content Back to Top of Page