EFFECTS OF VEGETATION REGIME ON DENITRIFICATION POTENTIAL IN 2 TROPICAL VOLCANIC SOILS

Effects of vegetation and nutrient availability on potentail denitrifi cation rates were studied in two volcanic, alluvial-terrace soils in l owland Costa Rica that differ greatly in weathering stage and thus in availability of P and base cations. Potential denitrification rates we re significantly higher in plots where vegetation had been left undist urbed than in plots where all vegetation had been removed continuously , and were higher on the less fertile of the two soils. The potential denitrification rates were correlated strongly with respiration rates, levels of mineralizable N, microbial biomass, and moisture content, a nd moderately well with concentrations of extractable NH4+, Kjeldahl N , and total C. In all plots, denitrification rates were stimulated by the removal of O2 and by the addition of glucose but not by the additi on of water or NO3-.