Apparent Nitrogen Fixation in Soil Influenced by Prescribed Burning
1971
Jorgensen, J. R. | Wells, C. G.
Nitrogen increases of 23 kg/ha/year were associated with annually burned loblolly pine (Pinus taeda L.) in the lower Coastal Plain of South Carolina. Unburned areas showed no increase of N. Nitrogen fixation in cores from the forest floor and at depths of 0–1 and 3–4 cm was assayed using the acetylene-ethylene technique, with the ethylene produced related to N fixation. In the 0–4 cm of mineral soil on burned plots more than 4 g/ha of N were fixed in 24 hours, but only 0.2 g/ha were fixed on unburned areas. Up to 61 g/ha of N were fixed in 24 hours in individual samples from burned areas. Most fixation in the burned areas took place in 14% of the samples; half the samples fixed no N or an insignificant amount, regardless of burning treatment. Fixation rate increased as moisture content increased from below to above field capacity and as temperature increased from 25 to 35C. However, the rate of increase related to temperature and moisture was usually associated with samples which had fixed N under less favorable conditions, rather than with the initiation of fixation in more samples.
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