N2o and ch4 efflux from loblolly and slash pine plantations: response to throughfall exclusion by fertilizer manipulation, and thinning, fertilization and herbicide, planting density, cultural treatments

Nitrous oxide (N2O) and methane (CH4) are greenhouse gases that might be released or consumed in response to planting density, fertilization, vegetation control, or thinning of southern pine plantations. In a throughfall exclusion x fertilization manipulation, over two years, fertilization increased N2O but not CH4 efflux. Efflux of CH4 was significantly decreased (increased consumption) in response to throughfall exclusion. A test of N fertilizers (urea, ammonium nitrate, or diammonium phosphate) also found significantly increased N2O efflux from all forms. N2O and CH4 efflux were also measured over one year in three sites of a Lower Coastal Plain Culture x Density (CD) study and three sites of a Mid-Rotation Treatment (MRT) study. In CD there was no main effect of Culture or Density on N2O or CH4 efflux. In the MRT, where N fertilization had recently occurred, there was an effect of thin, herb, and fert on N2O but not on CH4.