Nitric oxide emissions from a southern African savanna

NO fluxes from soils of a periodically flooded tropical savanna in southern Africa were investigated and modeled. In the laboratory, NO production rat es, NO consumption rate constants, NO mixing ratios, relationships between NO emissions and soil temperature and moisture were determined for nutrient -poor, nutrient-rich savanna soils and a floodplain soil. The NO production rate and consumption rate constants of the floodplain soil (1.96 ng N s(-1 ) per kilogram of soil and 2.04 x 10(-5) m(3) s(-1) per kilogram of soil, r espectively) were significantly higher than those of the savanna soils (ave rage of 1.28 ng N s(-1) per kilogram of soil and 1.47 x 10(-5) m(3) s(-1) p er kilogram of soil, respectively), but there were no significant differenc e between the nutrient-rich and nutrient-poor soils. NO flux rates increase d exponentially with soil temperature. NO flux rates increased with soil mo isture reaching a maximum near the field capacity (7.5 - 10% and 31.2% grav imetric water content for savanna and floodplain soils, respectively), afte r which the NO flux rate declined. These laboratory data were used in a mod el to estimate field NO flux rates, which were compared with actual field N O emission measurements. The NO model was modified to incorporate NO "pulsi ng" after the first rains of the season. Correlation between the modeled an d field NO fluxes from the nutrient-poor savanna, nutrient-rich savanna, an d the floodplain soils showed tau(2) values of 0.91, 0.82, and 0.74, respec tively. The NO model was linked with a soil moisture and temperature model to predict annual NO emission estimates from savannas. Annual NO flux from the nutrient-poor and nutrient-rich savannas was estimated to be 0.16 x 10( -3) and 0.14 x 10(-3) kg N m(-2) yr(-1), respectively, which agree well wit h estimates from other savanna studies.