A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Effects of different pasture management in emissions of soil trace gases (N 2 O, NO andCO 2 )Alexandre Pinto1, Mercedes Bustamante1, Richard Zepp2, Roger Burke2, Keith Kisselle2,Laura Viana1, Catarina Garofalo1, Marirosa Molina21) Universidade de Brasília, Brazil (aspinto@unb.br)2) United States Environmental Protection Agency, Athens, Georgia, USAIn the central savanna region of Brazil, the “Cerrado”, it is estimated that there areapproximately 50 million hectares of planted pasture, mainly Brachiaria spp., almost allutilized for beef production. Our objective was to assess the effects of active pasturemanagement on the exchange of trace gases (N 2 O, NO and CO 2 ) between soil and theatmosphere. Using chamber techniques, trace gases have been measured monthly on a farmin Planaltina – GO, Brazil (15 o 13’ S, 47 o 42’W) since November 2001. Three areas ofcerrado stricto sensu were converted to pasture (Brachiaria brizantha) in 1991 and havebeen managed since 1999 as follow: 1) N and P fertilized plot (N = 60 kg ha -1 , P = 12 kgha -1 ), 2) Brachiaria associated with a legume (Stylosanthes guianensis) with addition of P(12 kg ha -1 ), and 3) a control plot without management. A fourth area of cerradão (densecerrado) was converted to pasture in 1999 and was left without management. All treatmentsshowed high variability of soil N gases emissions. The plot converted in 1999 showed thehighest NO fluxes (0.05 – 0.2 ng N cm -2 h -1 ) except during November 2001, when thehighest average NO flux (3.6 ng N cm -2 h -1 ) was observed in the control treatment. The plotassociated with legumes showed higher emissions of N 2 O (0.6 – 2.0 ng N cm -2 h -1 ) in thebeginning of the wet season, but in March 2002 the highest average N 2 O emission wasobserved in the control plot (6.7 ng N cm -2 h -1 ). Despite some peaks, the total emissions ofNO and N 2 O could be considered low. The CO 2 fluxes were larger in the managed pastures(fertilized and legume treatments, highest average flux = 9.9 µmol m-2 s-1) than in thecontrol plot early in the rainy season. The variability of CO 2 fluxes decreased withintreatments and between treatments at the end of the wet season (April 2002).Address first author: Universidade de BrasíliaCampus Universitário Darcy Ribeiro, Asa NorteDepartamento de EcologiaCEP 70919-970, Brasília - DF