IMMEDIATE EFFECTS OF PRESCRIBED BURNING ON MINERAL SOIL NITROGEN IN PONDEROSA PINE OF NEW MEXICO

Abstract

Three 0.1-ha ponderosa pine (Pinus ponderosa Dougl. ex Laws) sites were burned in the fall of 1981. The burn was mainly a groundfire. Burn intensity was 980, 1760, and 2280 kJ s-1 m-1 on sites 1, 2, and 3, respectively. We analyzed the mineral soils on each of these sites for total N, NO2-+NO3--N and NH4+-N prior to prescribed burning, 1 d postburn, and 30 d postburn. On the most intense burn, NH4+- N levels increased threefold from preburn (10 ppm) to 1 d postburn (32 ppm), but declined somewhat 30 d following the burn (24 ppm). Concentrations of NO2-+NO3--N on site 3 rose from 1 ppm preburn and 1 d postburn to 5 ppm 30 d postburn. There were no significant differences in soil total N after burning. Immediate postburn inorganic N values for ponderosa pine mineral soils have not been previously reported in the literature. It is important to investigate burned soils immediately after burning to better understand sequential processes involved in postfire inorganic N dynamics.