Effects of prolonged flooding on the cycling of dissolved inorganic carbon in Plinthosols

Cultivation of flooded rice has developed in wetlands of the Cerrado Biome as a result of the expansion of the Brazilian agricultural frontier. Changes in soil moisture content due to agricultural practices associated with flood irrigation may induce geochemical transformations in the soil. The present study aimed at investigating the effect of flood irrigation on inorganic carbon cycling through the determination of dissolved inorganic carbon (DIC) concentrations. Incubation experiments under anoxic and reducing conditions were carried out in laboratory with samples of horizons A, AB, Bf1 and Bf2 of Plinthosols profiles from areas under 20 and 30 year of flood irrigation and natural area of the Irrigation Project Luiz Alves do Araguaia, GO, Brazil. Soil samples under flooding were incubated for 1, 7, 15, 30, 60 and 120 days to simulate the effect of prolonged flooding and after incubation the liquid fraction was analyzed for DIC. Higher concentrations of DIC were found in the A horizon (up to 37.2 mg/L) from soil profiles under cultivation, which may be associated with liming or desorption processes of carbon species. DIC correlated with soil electrical conductivity and Eh. It is concluded that solubilization of inorganic carbon is favored by flood irrigation, especially in Plinthosols that have received liming, as well as by the reducing state of the soil and higher concentrations of ions in solution.