EFFECT OF PLOWING ON CO2, CO, CH4, N2O, AND NO FLUXES FROM TROPICAL SAVANNA SOILS

Using closed chamber techniques, soil fluxes of CO2, CO, CH4, N2O, and NO were measured in unplowed and plowed savannah soil from May 23 to June 11, 1991. During the measurement period the gravimetric soil moisture ranged from 1% to 10%, with an average of 2.7%. Results did not show any notable change in CO2, CH4, and N2O fluxes between unplowed and plowed soil, whereas a significant change in CO and NO fluxes was produced. For CO, nonperturbed soil switches from being a net source (16 ng m-2 s-1 ) to being a net sink (-5.3 ng M-2 s-1) after plowing, and the case of NO the plowing leads to a dramatic increase (from 12.3 to 67.5 ng NO-N m-2 s-1) in the emissions. The addition of fertilizer (phosphate, ammonium, and potassium) to the plowed soil did not produce any significant effect. The simultaneous study of these five trace gases strongly suggests that in the short term, plowing of this savannah soil does not significantly alter the activity that produces trace gases and that the large changes in CO and NO fluxes arc mainly related to an enhancement of the transport of gases within the soil and to a larger surface area in contact with the atmosphere.