Soil nitrogen mineralization and immobilization in response to periodic prescribed fire in a loblolly pine plantation

Abstract

Additions of 15N-labelled ammonium sulfate were used to evaluate the effects of burning at 2- and 4-year intervals during a 24-year period on nitrogen mineralization and immobilization in a loblolly pine (Pinustaeda L.) stand. Net N mineralization in 10-day laboratory incubations of Oe + Oa plus 0–10 cm mineral soil was greatest in the control (210 mg N/m2), intermediate for the 2 year interval burn treatment (87 mg N/m2), and lowest for the 4 year interval burn treatment (78 mg N/m2). Forest floor and mineral soil C/N ratios were greater for the burn treatments than for the control. All samples showed >95% immobilization of added 15N ammonium sulfate, the pattern being 2-year interval >4-year interval control. Both burning regimes appeared to increase N immobilization and decrease N availability on this very N-poor site.