Daily and seasonal patterns of CO₂ fluxes and evapotranspiration in maize-grass intercropping

Variação diária e sazonal dos fluxos de CO₂ e evapotranspiração no consórcio milho-pastagem

ABSTRACT

Studies that investigate the relationships between CO₂ fluxes and evapotranspiration (ET) are important for predicting how agricultural ecosystems will respond to climate changes. However, none was made on the maize-grass intercropping system in Brazil. The aim of this study was to determine the ET and CO₂ fluxes in a signal grass pasture intercropped with maize, in São João, Pernambuco, Brazil, in a drought year. Furthermore, the soil water storage (SWS) and leaf area index (LAI) were determined. The latent heat flux was the main consumer of the available energy and the daily and seasonal ET and CO₂ variations were mainly controlled by rainfall, through the changes in soil water content and consequently in SWS. The agroecosystem acted as an atmospheric carbon source, during drier periods and lower LAI, and as an atmospheric carbon sink, during wetter periods and higher LAI values. In a dry year, the intercropping sequestered 2.9 t C ha^-1, which was equivalent to 8.0 kg C ha^-1 d^-1. This study showed strong seasonal fluctuations in maize-grass intercropping CO₂ fluxes, due to seasonality of rainfall, and that this agroecosystem is vulnerable to low SWS, with significant reduction in CO₂ uptake during these periods.

Key words:
eddy covariance; carbon; climate change