CO ₂ Flux In a wheat/soybean succession in subtropical Brazil: A carbon sink

The subtropical region of Brazil is home to 33% of the soybean growing area and 90% of the wheat growing area of this country, being a soybean/wheat succession with fallow between crops used in about 11% of the cultivated area. No study has quantified CO2 fluxes in annual soybean/wheat succession in this region. Hence, this study analyzed the seasonality of CO2 exchange (net ecosystem exchange; NEE) in a 2015/2016 wheat/soybean succession in a commercial farm located in Carazinho, Rio Grande do Sul State, Brazil. The eddy covariance (EC) technique was used to estimate the annual carbon balance of this system. The NEE was partitioned between gross primary productivity and ecosystem respiration to understand the dynamics of these fluxes during a year of wheat/soybean succession. Considering the net ecosystem balance between photosynthesis and respiration during the growing season, both soybean and wheat absorbed CO2 from the atmosphere (NEE wheat: -347 ± 4 g C m-2 ; NEE soybean: -242 ± 3 g C m-2 ). The fallow periods between growing seasons, however, acted as a source of 156 ± 2 g C m-2 , reducing the C absorbed by the crops by 27%. For one year, the net biome productivity was -50 g C m-2 yr-1 . The results obtained here demonstrate that the wheat/soybean succession was a net carbon sink under these specific climatic conditions and field management practices and the long fallow period between crops limited the agroecosystem from becoming a more efficient CO2 sink. This article is protected by copyright. All rights reserved.