Vertical changes in denitrification activity and denitrifying bacterial populations in Kuroboku upland soil with slurry application

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The vertical changes in the denitrification activity and de nitrifying bacterial populations were investigated in a Kuroboku upland soil with slurry application, where the nitrogen balance had been determined (Niimi and Nishida 1999: Estimation of denitrification by using δ15N values in upland field applied with a large amount of slurry barnyard manure. In 10th Nitrogen Workshop Program and s, IV, p. 41). Averaged cell density of the denitrifying bacterial populations significantly increased in relation to the level of slurry application, 0, 60, 150, and 300 fresh-wt. Mg ha−1. The denitrifying bacterial populations showed a higher correlation with the potential denitrification activity than with the fresh denitrification activity. Averaged contribution of the potential denitrification activity in three soil layers (approximately 5–20, 20–45, and 45–80 cm) to the total activity was 90, 9.5, and 0.4%, respectively. Annual nitrogen loss associated with the denitrification activity in the 0, 60, 150, and 300 Mg ha−1 plots was found to amount to 15.6, 20.0, 41.5, and 94.7 kg-N ha−1 y−1 based on the data from the fresh denitrification activity and to 38.6, 39.1, 163.8, and 611.8 kg-N ha−1 y−1 based on the data from the potential denitrification activity. The above results indicate that by only conducting a surface soil survey, it was possible to obtain a rough estimation of the nitrogen loss associated with the potential denitrification activity in a Kuroboku upland soil with slurry application.