Nitrous Oxide and Dinitrogen Emissions from Panicum hemitomon S. Freshwater Marsh Soils Following Addition of N-15 Labelled Ammonium and Nitrate

ABSTRACT

A greenhouse experiment was conducted to assess the denitrifying capacity of Panicum hemitomon Schult. freshwater marsh soils. High rates (100, 200 and 300 kg N ha⁻¹) of N-15 labelled NH₄ ⁺- and NO₃ ⁻-N were applied to the soil surfaces of marsh cores to simulate nutrient loading from anthropogenic sources. Direct gaseous flux of N₂ and N₂O resulting from nitrification-denitrification in the flooded soils were measured over 46 d after N addition. Dinitrogen and N₂O emissions from the soil surface were significantly affected by rate and form of inorganic N applied. Denitrification of added labelled NO₃-N began immediately after addition. The nitrification process resulted in a 9 d lag before any of the added labelled NH₄ ⁺-N was denitrified. Maximum N₂ emissions measured from the marsh cores treated with 100, 200 and 300 kg N ha⁻¹ were <15, 650, and 1, 080 for (NH₄)₂SO₄ and 2,700 3,430 and 4,490 g ha⁻¹ d⁻¹ for the KNO₃ treatments, respectively. Nitrous oxide flux ranged from nondetectable concentrations above control values to 1,980 g ha⁻¹ d⁻¹ for the 300 kg KNO₃-N ha⁻¹ treatment. This study demonstrates that the freshwater marsh soils have the potential to remove large inputs of inorganic N through denitrification.