『Abstract
Natural and prescribed fires (including site preparation burning)
are common in pine and mixed-pine forests in the southeastern
USA. The present high fuel load condition of many forests has
renewed concerns about the effects of hot fires on soil nutrients
and on nonpoint sources of pollution [i.e. sediments and phosphorus
(P)]. Variation in temperature and velocity of fire due to unequal
fuel loading and soil moisture can affect the extent of soil nutrient
alterations including transformation of organic forms of P (Po)
to inorganic forms (Pi). This variation in fire severity is difficult
to capture systematically in the field, thus laboratory experiments
simulating fire have been utilized. Most of these studies have
used long duration treatments (＞1 h) that do not reflect field
conditions where soils may be heated for only minutes. The objective
of this study was to investigate soil P changes in relation to
short-duration soil heating. Soil samples were collected before
and after a prescribed burn in a 40-yr-old loblolly pine forest.
Pre-burn soil samples were also subjected to temperature (100,
200, 300, 500, and 1000℃) by heating duration (2.5, 5, 15, 30,
and 45 min) treatments in the laboratory. In all cases, a partial
sequential P extraction was performed. We hypothesized that pyromineralization
of O horizon would increase water extractable soil P in the A
horizon along with Po transformation to Pi within the A horizon.
In the field, the NaHCO3 inorganic P fraction
increased in 0-5 cm by 0.8 kg P ha-1 one week after
the burn: this increase was likely due to ash addition. In the
laboratory, all 0-5 cm soil P pools responded to heating with
Po converting to Pi and total P declining at the highest temperatures
and durations. The combination of temperature*duration
determined the extent of change with a high temperature-short
duration (e.g., 1000℃*2.5 min) burn having the same
impact on soil P as a medium temperature-longer duration burn
(e.g., 300℃*45 min). Increasing forest fuel loads may
be sufficient to alter the fire severity of future prescribed
fires such that an increase in A horizon Po transformations to
Pi could prove to be significant for P mobility in soils and plant
growth.
Keywords: P fractionation; Organic matter combustion; Fire severity;
Fuel loads』
1. Introduction
2. Materials and methods
2.1. Prescribed burn field study
2.1.1. Site description
2.1.2. Experimental and sampling design
2.1.3. Soil P fractionation
2.2. Laboratory heating study
2.2.1. Experimental design
2.2.2. Statistical analysis
3. Results
3.1. Prescribed burn field study
3.2. Laboratory heating study
4. Discussion
5. Conclusion
References