Effects of water-addition on N oxides and CO2 fluxes from soils in pastures of Central Brazil
Alexandre
de Siqueira
Pinto, University of Brasilia, alexandrep@ftb.br
(Presenting)
Mercedes
Maria Cunha
Bustamante, University of Brasilia, mercedes@unb.br
Laura
Tillman
Viana, University of Brasilia, lviana@unb.br
Keith
Kisselle, USEPA, kisselle.keith@epa.gov
Roger
A.
Burke, USEPA, burke.roger@epa.gov
Richard
Zepp, USEPA, zepp.richard@epa.gov
Planted pastures, mainly Brachiaria spp, represent the main land use type in the Cerrado region (savannas of Central Brazil) with an area of approximately 50 million ha. In the Cerrado, ca. 90% of the precipitation falls during the rainy season and this seasonality has marked effects on the trace gas dynamics from soils to the atmosphere. In order to assess the effects of the first rains (transition dry-wet season) on N soil dynamics (available inorganic N, NO and N2O fluxes) and soil respiration in pastures we performed an artificial water addition experiment (simulating 5 mm rain) in September 2002 (end of dry season). The experiment was carried out in a farm in Planaltina-GO, Brazil (15o 13’ S, 47o 42’W). Three areas of cerrado were converted to pasture (Brachiaria brizantha) in 1991 and after 10 years these areas showed traits of degradation. The pastures have been managed since 1999 to recover productivity as follow: (1) fertilization with N and P (fertilized plot) or (2) association of Brachiaria with the N-fixing legume Stylosanthes guianensis (legume-grass plot). A third plot was left without management (traditional plot) and a fourth area of cerrado was converted to pasture in 1999 (young pasture). Trace gas measurements were done 30 min, 24 h and 48 h after water addition. Soil N2O fluxes were below detection limit in all the plots even after the water addition. A reduction of N-inorganic availability was observed along the experiment only in traditional plot (72.3 to 35.8 mg kg-1). The young and fertilized pastures showed higher increase of soil NO fluxes after water addition (6.8 ng N cm-2 h-1 and 4.2 ng N cm-2 h-1 against 1.0 ng N cm-2 h-1 and 0.1 ng N cm-2 h-1, respectively, in the dry plots). All pulses were short-lived except in young pasture, where NO flux 48 h after the water addition was three-fold higher than in dry plots (3.0 ng N cm-2 h-1). Soil respiration in the grass-legume pasture showed the highest increase after water addition (three-fold reaching 8.3 µmol m-2 s-1). The results indicated that the transition of dry-wet season could be an important period for NO and CO2 soil emissions in pastures of the Cerrado region.
Submetido por Alexandre de Siqueira Pinto em 24-MAR-2004