Short-term effects of a wildfire on the nitrogen status and its mineralization kinetics in an atlantic forest soil
1993
Prieto-Fernandez, A. | Villar, M.C. | Carballas, M. | Carballas, T.
A Humic Cambisol developed over granite under Pinus pinaster Sol. located in the Atlantic climate zone, which had been affected by a high intensity wildfire, was studied 1 month after burning. The soil had a very rich organic matter A horizon, 30 cm deep. The effects of the fire on the N status and N mineralization capacity were estimated comparing the surface (0-5 cm) and subsurface (5-10 cm) layers from the burnt soil with the corresponding layers from the same unburnt soil. N mineralization kinetics were determined by aerobic incubation at 28 degrees C for 11 weeks. The fire increased the total N content in the surface layer but not in the subsurface. Total inorganic N, which was mainly in the form of NH4(+)-N, increased after the burning in both layers, whereas NO3(-)-N content, which was very low, only increased in the subsurface layer. The fire increased the N mineralization capacity, but did not modify organic N mineralization behaviour. Ammonification largely predominated over nitrification in both the unburnt and the burnt soils. N mineralization kinetics followed the first order equation Nm = N0(1 - e(-Kt)) but the fire affected the kinetic parameters. The potentially-mineralizable N decreased and the kinetic constant increased in the burnt samples showing that the wildfire reduced the mineralizable organic-N reserves and increased the mineralization rate, thus predicting a rapid depletion of the labile organic N. The temporary ability of the burnt soil to supply available N is recommended to be used to grow an early crop to avoid physical soil degradation.
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