CO2 exchanges and evapotranspiration of a grazed pasture under tropical climate conditions

Abstract

• Evapotranspiration and CO 2 exchange were assessed in grazed pasture. • The seasonality of CO 2 exchange was strongly agreement with rainfall seasonality. • Grazed tropical pasture acted as CO 2 sink taking into account all uncertainties. • Averaged NEE 2 year was -230 ± 22 gC m −2 y −1 . • WUE was similar to the values found in other pastures around the world. Studies concerning the role of livestock farming on the regional budget of CO 2 in Northeast of Brazil are scarce. Thus, our main objective was to evaluate the variability of CO 2 exchange and evapotranspiration (ET) of a cultivated tropical forage C4 grass ( Brachiaria brizantha ) grazed by sheep for meat production. The experiment was conducted during the period from 2015-oct-01 to 2017-sep-30 using an eddy covariance flux tower. The pasture acted as a moderate CO 2 sink, with mean annual net ecosystem exchange of -215 ± 22 g C m −2 y −1 , while the average uncertainty associated with the calculation procedure was 15 g C m −2 ± 7.20% of NEP. The mean annual ET was 967 ± 245 mm. Carbon use efficiency at the ecosystem level was 0.20 ± 0.03, which is more efficient compared to similar experiments in grazed environments around the world. Water use efficiency at the ecosystem level was 1.14 ± 0.01 g C (kg H 2 O) −1 .