Nitrification Potential and Inorganic Nitrogen Dynamics in a Soil Applied with Anaerobic Digestion Effluents.

Nitrogen (N) chemical fertilizers have been applied to soils excessively over prolonged time causing environmental problems in the past. Therefore, organic forms of N fertilizer have received much attention in recent years as alternative N source for plants. Anaerobic digestion effluents (ADEs) among other organic fertilizers contain appreciable amounts of N, mostly as ammonium-nitrogen (NH₄⁺-N). However, ADEs still need to be well evaluated for their effectiveness to supply the plant nutrient being compared with other organic fertilizers. Therefore, the objective of this study was to evaluate through incubation experiments potential of ADEs as organic fertilizer in comparison with other organic fertilizers in terms of nitrification potential and inorganic nitrogen dynamics when applied to soils. A soil used in this study was an Andisol in Tokyo, Japan and oven-dried, and sieved by 2 mm. An ADE used in this study was derived from cow manure. ADE application rates were 0, 250, 500, 750, and 1000 mg NH₄⁺-N kg^–1 soil (0N, 250N, 500N, 750N, and 1000N, respectively). Soils with ADEs were incubated at 30˚C with 60% of water holding capacity for 1, 3, 7, 15, 30, and 60 d. At each sampling date, NH₄⁺-N, nitrate-nitrogen (NO₃^–-N), pH, and nitrification activity of the soil were analyzed. Nitrification potential of the soil was calculated by differences in NO₃^–-N concentrations between the first and last sampling dates. While NH₄⁺-N increased, NO₃^–-N and pH decreased from 3 or 7 d through 30 d in all experimental treatments. Nitrification activity became comparable among the treatments on 30 d. Nitrification potential of ADE increased 2.66 times more than other organic fertilizers on 30 d because ADE might have enhanced nitrification bacteria activity. Although 60 d samples are yet to be analyzed, ADE might have a more fertilizer effect particularly for N than other organic fertilizers because of greater nitrification potential.