Greenhouse gas emissions and chemical and physical soil attributes of off-season agricultural production systems in the Savannah of Maranhão State, Brazil.

Management of agricultural production systems interferes with greenhouse gases (GHG) emissions, thereby altering physical, chemical, and biological attributes of soil; therefore, it is important to understand the relationship between soil attributes and GHG emissions. This study evaluated GHG emissions and their relationship with soil attributes in off- season soybean, maize, brachiaria and eucalyptus production systems. The experiment was carried out in Brejo, Maranhão, Brazil, with soybean (Glycine max), maize (Zea mays), brachiaria (Urochloa ruzizienses), and eucalyptus (Eucalyptus grandis). Fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were evaluated using air samples analyzed by gas chromatography. Soil attributes were ammonium and nitrate contents, total organic carbon, moisture, pH, density, total porosity, and water-filled pore space. N2O flux was 287.1 μg m-2 h -1 for eucalyptus cultivation, while areas cultivated with soybeans, maize and brachiaria had influxes of 46.7, 7.2, and 13.17 μg m-2 h-1, respectively. In the off-season, the highest emissions of N2O and CO2 were measured in eucalyptus areas due to soil moisture and porosity conditions provided by accumulation of litter on the soil surface.