Denitrification losses from sandy and sandy loam soils under spring barley fertilized with slurry and ammonium nitrate

The interaction between soil factors and denitrification loss from soil is not well understood. This study was conducted to determine whether soil air-filled porosity (AFP), nitrate concentration and N management could explain some of the large variation found in denitrification studies. Denitrification losses from a coarse sandy soil and a sandy loam soil under spring barley were measured during a three-year period using the acetylene-based static soil core method. The sandy loam soil received 100 and 133 kg inorganic N ha(-1) yr(-1) in pig slurry and inorganic fertilizer, respectively, while the coarse sandy soil received 100 and 120 kg inorganic N ha(-1) yr(-1) in pig slurry and inorganic fertilizer, respectively. In the coarse sandy soil no interaction between soil AFP and soil nitrate concentration in relation to denitrification existed-during the three years investigated, and annual losses arising from denitrification were low (<1 kg N ha(-1)). In this soil type the low denitrification loss from the plot treated with slurry is explained by the inability of the slurry to create hot spots owing to the slurry incorporation technique (harrowing) and to the amount of slurry used (30 Mg). Annual losses arising from denitrification in the sandy loam soil were in the order inorganic fertilized > slurry fertilized > control. In this soil type a linear relationship between log(10) denitrification activity and air-filled porosity could explain 50% of the variation in denitrification activity, but no influence of soil nitrate concentration was found. The regression parameters for the AFP regression varied between unamended and amended soil, with the highest slope in the amended soil regression.